#linuxcnc Logs

Oct 16 2018

#linuxcnc Calendar

12:05 AM XXCoder: ugh
12:09 AM XXCoder: home early because back pain got out of hand
12:37 AM jesseg: hey guys I blew up my 2.2KW chinesium VFD experimenting to see how many times I could reverse my mill motor at full speed using the mill reverse switch. The answer was several times.
12:38 AM jesseg: Anyway, they are cheap and I wanted to know.. LOL.. but decided to try and not do that (and maybe I'll add a breaking resistor)
12:38 AM jesseg: anyway, getting as a replacement this one: https://www.ebay.com/itm/272864331363
12:38 AM jesseg: What I did find was OK was starting and stopping the mill using the mill controls as long as I let it come to a full stop before reversing directions.
12:39 AM XXCoder: man
12:39 AM XXCoder: cheap is such a fluid meaning
12:39 AM XXCoder: 2.2kw vfd isnt cheap to me ;)
12:39 AM jesseg: so I'm hoping to use this 7.5kw unit as a sort of local 3 phase power for both the mill and lathe
12:40 AM XXCoder: is m5 a blocking call?
12:40 AM jesseg: XXCoder, yeah $75 isn't cheap for me either. But compared to the $1800 I paid for a thrashed worn out mill, and the $1160 of new bearings/parts it needed (which I did a year later...), or the $3000 I spent on a 1965 lathe..... $75 is kind of cheap.
12:43 AM jesseg: and compared to the cost of an allen bradley VFD, $75 is cheapish.
12:43 AM XXCoder: I guess so
12:44 AM jesseg: mind you I wish I hadn't blown it up... I really should have installed a breaking resistor..
12:45 AM XXCoder: i bet yeah
12:45 AM jesseg: however, I was hoping the engineers had been half with it and made some provisions for protecting itself..
12:45 AM XXCoder: chineseium and sane design?
12:45 AM jesseg: All they'd have to do is write the firmware to monitor the capacitor bank voltage and stop breaking if the voltage got out of bounds
12:45 AM jesseg: lol good point. but the thing did work amazingly well.
12:46 AM jesseg: in fact a lot better then I thought it would before I bought it
12:53 AM rmu: jesseg: accelerating a motor just because the dc link voltage goes up can lead to very unsafe conditions IMHO
12:54 AM jesseg: rmu, I don't know what "dc link voltage" means in this case
12:54 AM jesseg: can you please explain?
12:55 AM jesseg: and I also don't know what you mean by accelerating a motor
12:56 AM jesseg: and what unsafe conditions did you have in mind?
12:56 AM jesseg: oh, do you mean it's not safe to run a 3 phase motor on 3 phase line power from the power co without a VFD?
12:57 AM rmu: if i want the motor to stop it usually needs to stop, so you can't (as a VFD) just decide to do something else
12:57 AM rmu: unsafe condition is spinning motor that should have stopped seconds ago
12:58 AM jesseg: oh, are you saying that relying on the motor to take its time to coast to a stop upon power loss is what's not safe?
12:59 AM rmu: in extreme cases the motor could coast for a very long time and even then you have no guarantee that voltage doesnt get too high
12:59 AM jesseg: what voltage where?
12:59 AM rmu: DC-voltage in the VFD
12:59 AM jesseg: what would make it get so high? energy from the mains, or energy from the coasting motor?
01:00 AM rmu: imagine lathe spindle with large mass in the chuck rotating at high speed
01:00 AM jesseg: oh, are you just saying that using motor breaking via the VFD without a breaking resistor is a bad idea?
01:00 AM jesseg: I confirmed that you are correct on that point :D :D
01:01 AM rmu: the rotational energy has to go somewhere, motor works as generator and feeds energy back into the VFD, which usually can't feed it back to mains
01:01 AM XXCoder: spinning thing is one of ponental schemes of energy storage
01:01 AM XXCoder: so not surpised
01:02 AM rmu: i think we had this discussion a few days ago with DC servo as lathe spindle drive and dying gecko G320s
01:03 AM jesseg: rmu, yeah if the VFD tries to perform motor braking it recaptures some of that energy and stores it in the filter capacitors, thus raising their voltage level. But if it just lets the motor free-wheel and doesn't try to brake the motor, then there's no boost above normal operating voltage level on the filter caps
01:03 AM rmu: jesseg: exactly. if you don't tell the VFD to try to break the motor it won't do it.
01:03 AM rmu: brake
01:04 AM rmu: freewheeling a lathe spindle could take minutes to stop ;)
01:04 AM jesseg: yeah so I should be fine switching off the mill / lathe motor with the OEM motor switch, as long as I wait for the motor to stop before reversing directions with the OEM motor control switch
01:05 AM jesseg: yeah I may put on a halogen bulb motor break
01:05 AM rmu: using a contactor or switch between VFD and Motor may be a bad idea, but that depends
01:06 AM jesseg: or a DC motor break -- put 12 volts DC across one of the windings when the motor is free wheeling and disconnected from the VFD to provide eddy breaking
01:06 AM jesseg: I did a lot of testing switching the motor on and off with a manual switch between the motor and the VFD.
01:06 AM jesseg: As long as I didn't reverse directions with the motor still spinning, it seemed quite fine. And should, since the VFD does monitor its output current in an effort of self preservation.
01:06 AM rmu: that can generate voltage spikes that the VFD doesn't particularly like
01:07 AM jesseg: Are you saying it generates spikes on the motor side of the manual switch, or the VFD side of the manual switch?
01:08 AM rmu: if you want the motor to stop quickly i think you can just short all 3 windings, but that probably dumps most of the rotational energy into the windings (heating them up)
01:08 AM jesseg: rmu, yeah that's why I was thinking some 500W halogen bulbs
01:08 AM jesseg: 6 of them since they are 120v each
01:08 AM jesseg: that would provide a pretty quick stop but not so fast that it just heated the motor windings.
01:08 AM XXCoder: those lights would glow only on feedback?
01:09 AM jesseg: XXCoder, only during braking
01:09 AM XXCoder: ahh
01:09 AM jesseg: from the generated energy
01:10 AM rmu: jesseg: if you switch off your motor the switch will make a spark and while the spark is sparking your circuit is still closed, but may develop a very high voltage
01:11 AM jesseg: rmu, according to the laws of inductance (which are what produce the spark) the current through the spark are constant current essentially. The voltage spikes, but that's on the motor side. The VFD should not see that high voltage because the bulk of the inductance in this circuit is in the windings of the motor.
01:12 AM XXCoder: to bad cant feed it back into battery
01:12 AM XXCoder: then use battery to spin up
01:12 AM rmu: the voltage develops over the switch
01:12 AM jesseg: And in fact, the VFD, during normal operation, is *constantly* subject to hammering by the inductive kickback of the motor's windings because every time it switches off a coil, the inductive kickback slams the diodes built into the IGBTs. So the VFD is made to handle that constant inductive repetitive kickback.
01:13 AM rmu: so one side of the switch is connected to VFD directly, the other one through motor winding
01:13 AM jesseg: yes, the voltage is developed in the motor, across the switch, but the VFD sees it as a constant current.
01:14 AM jesseg: When you open the circuit in an inductive circuit, the current begins decreasing, not increasing.
01:15 AM jesseg: And the VFD only sees the current going through the motor, not the voltage that's being developed by the motor but lost across an open switch.
01:15 AM rmu: jesseg: in a sense, the VFD doesn't switch off the current, it recirculates it either via body diodes or via synchronous rectification, so this inductive kickback will not raise voltage
01:16 AM flyback: that's one of the benefits of igbt
01:16 AM jesseg: it most definitely can raise the voltage during PWM motor braking.
01:16 AM flyback: noty good reverse protection cause they need a diode for that
01:16 AM jesseg: that's the whole idea of regenerative braking.
01:16 AM flyback: but in general they can be abused a lot longer than a mosfet
01:17 AM flyback: neat little trannies
01:18 AM rmu: flyback: i think that just comes from some details from construction of IGBTs and MOSFETS, IGBTs also have drawbacks
01:18 AM jesseg: rmu, and that's why a VFD needs a breaking resistor is to dissipate the raised voltage on the filter caps during motor braking
01:19 AM jesseg: blah braking resistor, I don't think I'll ever be able to keep the spelling correct on those :P sorry guys
01:20 AM jesseg: anyway, the only way the system can raise the voltage on the filter caps above the mains voltage during braking is because of the inductive kickback during braking.
01:20 AM flyback: RMU YEAH at lower voltages mosfets are better
01:20 AM flyback: 200v and down
01:21 AM jesseg: Don't IGBT's have a couple volts of drop even when turned fully on, which increases power loss at lower voltages/higher currents?
01:22 AM rmu: with a mosfet there is a tradeoff between max voltage and resitance when fully turned on, so higher permissible voltages implies higher resistance
01:23 AM rmu: there is a point where IGBTs with their inherent diode-drop become more efficient that MOSFETs
01:23 AM jesseg: yeah
01:23 AM flyback: rmu yeah 200v up
01:23 AM flyback: or high currents
01:23 AM jesseg: and it seems it's a lot easier to make a 1600v IGBT than it is a mosfet :P
01:24 AM rmu: switching speed
01:24 AM flyback: switching speed is not that much of a concern for mains shit
01:24 AM flyback: even for motor control etc
01:24 AM flyback: you can only do a few hundred hz before the power starts bouncing off the motor windings
01:24 AM rmu: it is for very efficient power converters
01:24 AM jesseg: I think my new 7.5kw says it only switches at 16khz
01:24 AM rmu: thing electric cars, battery chargers, etc...
01:24 AM rmu: think
01:24 AM jesseg: and the old one switched at a khz or something
01:25 AM flyback: even high efficient smps are mabye a few mhz
01:25 AM flyback: mosyt aren't even mhz
01:25 AM rmu: you can't drive IGBTs with MHz
01:25 AM rmu: 10s of kHz at best
01:34 AM flyback: stuff is all neat
01:34 AM flyback: even the early stuff gto
01:34 AM flyback: was so much better than direct mains driving train motors
01:38 AM rmu: jesseg: https://www.schneider-electric.ca/en/faqs/FA173243/
01:39 AM rmu: and https://www.eng-tips.com/viewthread.cfm?qid=221338
01:45 AM jesseg: rmu, thanks
01:46 AM jesseg: but.... Much of that information stems from popular opinion from people who are not SMPS design engineers.
01:46 AM jesseg: and who don't really understand the dynamics
01:48 AM jesseg: and granted, if I was on the board to advise on the construction a megawatt department of defence factory VFD setup, I'd generally not recomend using the VFDs outside of their manufacturers rules, for the simple reason that if something goes wrong (even if it was entirely unrelated) and violation of rules would be blamed.
01:48 AM jesseg: But in my home shop, I think I'll try it as an experiment.
01:49 AM jesseg: I know the VFDs have output current transformers and are supposed to limit their output current to safe levels
01:50 AM jesseg: so they should be safe from motor slamming from a standstill.
01:50 AM jesseg: However, they obviously do not protect from pumping up the filter caps too much -- at least not without a breaking resistor :D
01:53 AM sync: flyback: modern fets are way better than most igbts at mains voltages
01:54 AM sync: jesseg: were you driving the motor above its nominal frequency?
01:54 AM jesseg: sync, no, but at full frequency - 60hz, USA.
01:55 AM sync: then the vfd sucks
01:55 AM sync: because it should just freewheel above a certain voltage
01:55 AM jesseg: hey it was a cheapo chinesium. And I repeatedly reversed reversed the motor with the switch.
01:55 AM jesseg: sync, but I agree, if it had been engineered right it should handle it fine. But that's why they cost $75, and not $750 :D
01:56 AM sync: they don't cost $750 in 2.2kW
01:56 AM sync: but yes
01:56 AM Deejay: moin
01:56 AM jesseg: lol ok but a nice 2k2w allen bradley that takes 220v single phase is more than $75 :D
01:57 AM sync: idk, I only buy siemens or yaskawa/omron
01:58 AM jesseg: here's a yaskawa 2k2 for $575 + $20 shipping
01:59 AM jesseg: I did experiment with a 1.5kw allen bradley, but it refuses to start the motor if you connect the motor after spooling up the VFD. You have to have the motor connected at the time you enable the VFD output
02:01 AM jesseg: Mornin' Deejay
02:01 AM Deejay: hey :)
02:01 AM jesseg: Omron fro $345 delivered, so yeah not as bad as I thought, but a lot more than $75.
02:02 AM sync: "a lot" yeah, well
02:02 AM sync: they work tho
02:02 AM sync: I usually snag them off ebay
02:02 AM jesseg: yeah that's where I'm looking
02:03 AM jesseg: sync, hey do you know if they support post-VFD start/stop switches?
02:03 AM sync: don't do that
02:04 AM sync: that is not what they were made to do
02:04 AM jesseg: Basically I just want 3 phase but I don't want to buy it from the local power co.. I just want to use my machine switches :P
02:04 AM sync: just put a vfd in every machine
02:09 AM rmu: jesseg: switching on the load side doesn't destroy the immediately (usually), but it stresses it, it leaves permanent physical damage in the IGBTs
02:09 AM rmu: destroy the VFD
02:10 AM jesseg: rmu, I don't understand why it would on a correctly engineered VFD. According to the rules of inductance, the current does not start instantly but rather it ramps up essentially at a rate of L/V
02:11 AM jesseg: sure, it starts out in a motor stalled condition, but that's just like overloading the motor -- a condition which the VFD should be designed to deal with no problem.
02:11 AM jesseg: and in fact that's why these have current sensors on 2 of the 3 output legs so they can limit current in case of motor stall
02:12 AM rmu: reality doesn't care if anybody understands it
02:14 AM jesseg: Fair enough :D
02:15 AM rmu: even without motor inductance opening a circuit with significant current creates a voltage spike (because wires also do have inductance), and IGBTs generally don't like that
02:15 AM rmu: voltage spike
02:16 AM jesseg: Q: And where is that voltage spike present? A: Across the freshly opened contact point. Not across the IGBTs.
02:16 AM jesseg: so why would they care?
02:16 AM rmu: in case of schneider electric, vfd manufacturer specifies that this kind of damage is not covered under warranty, so it seems they engineer their drives to not be subjected to this treatment
02:17 AM rmu: jesseg: because both ends of the contact point are connected to your VFD
02:17 AM rmu: (probably with motor windings in between)
02:17 AM jesseg: yeah of course they gotta cover their behind. Whether they find every possible excuse to get out of a warranty claim.
02:17 AM rmu: i don't say you couldn't engineer a VFD for that use-case, i say usually they are not
02:17 AM rmu: same with stepper drives
02:18 AM rmu: try disconnecting a running stepper motor between motor and drive, may result in instant death of output-mosfets
02:18 AM jesseg: I see no reason for that. They are fully diode snubbed/clamped.
02:19 AM jesseg: Disconnecting the wires cannot produce any currents higher than is normal during operation.
02:20 AM rmu: it produces very high voltages
02:22 AM jesseg: yeah but they are produced across the freshly opened contact area -- not the mosfets..
02:23 AM rmu: the mosfets see this voltage
02:23 AM jesseg: as long as the voltage & current *across* the *pins* of the *mosfets* is within spec they will not be damaged
02:23 AM jesseg: they dont' *see* it because it's common mode.
02:23 AM rmu: no
02:24 AM rmu: in theory this voltage could even damage your windings
02:24 AM jesseg: you mean the 2kv produced at the opening of the contact creates a 2kv differential voltage across the drain and source of the mosfet?
02:24 AM jesseg: rmu, in theory yeah it could.. but... in practice (lol) people have been switching off 3 phase motors on 3 phase mains power for decades. and the windings have to deal with it.
02:26 AM rmu: yes, because mechanical switches are "slow"
02:26 AM jesseg: In practice, as the switch opens, a glorious spark is produced which produces a little plasma field, which clamps the inductive kickback surprisingly at a few hundred volts (plasma has pretty low resistance compared to air) and this allows the inductive energy to dissipate without particularly high voltage being developed.
02:28 AM rmu: you can argue that as long as you want, even only a few hundred volts is plenty for IGBTs and too much for typical stepper driver mosfets
02:28 AM sync: you only have about 200V headroom in typical applications
02:29 AM jesseg: well remember the voltage developed across the freshly opened switch does not end up across the D/S on the fet.
02:29 AM sync: which will be easily be blazed through when the cable fall off
02:29 AM sync: of course it does
02:29 AM jesseg: ok well consult with a SMPS design engineer you trust and get back to me on that.
02:29 AM jesseg: :D
02:29 AM sync: I think I'm qualified enough to say that it does
02:30 AM rmu: hehe
02:30 AM jesseg: sync, please explain :D
02:30 AM rmu: assertion by authority doesn't work in here ;)
02:30 AM sync: well, jesseg is trying to do the same
02:31 AM sync: jesseg: I have developed a servo drive and I am an EE by trade
02:31 AM jesseg: sync, me too
02:32 AM sync: well then you must understand why you will see the voltage at the fet side
02:32 AM jesseg: I worked ~15 years at a company that designed up to 4kw audio amplifiers which involve switching large quantities of power in highly inductive environments
02:33 AM jesseg: you can't get 4kw out of a 4 ohm speaker at 12v so you have to have a powerful DC-DC converter to boost the voltage up to a hundred or two
02:33 AM jesseg: let me sketch on shared whiteboard
02:34 AM rmu: jesseg: try disconnecting the mosfet driving your DC-DC transformer while under current a few times and look what happens
02:34 AM sync: I do know how car amps work
02:36 AM sync: do a quick analysis of a lumped model
02:36 AM sync: with reasonable values
02:37 AM jesseg: https://awwapp.com/b/u5tg1irot/
02:38 AM * rmu fetching popcorn
02:38 AM jesseg: ok so when the switch opens, explain to me how the voltage that's developed across the open switch from the inductance dumping can create high voltage across the fet?
02:39 AM jesseg: If the voltage tries to go below ground, the body diode catches it. If it tries to go above g+100v bus, the other diode catches it.
02:39 AM rmu: jesseg: both ends of your motor are connected directly (via switch) to high rail
02:40 AM rmu: (or coil)
02:40 AM sync: that is not how the output of a vfd looks
02:40 AM sync: yeah
02:40 AM jesseg: rmu, well, in the case of a 3 phase motor, all 3 ends of your motor are connected to the centers on 3 half bridges.
02:40 AM rmu: surely you have something mixed up
02:40 AM jesseg: look guys I could draw 6 half bridges and their body diodes.
02:40 AM sync: two are enough
02:40 AM jesseg: But at an instant, a single coil will have current going in only one direction.. so the circuit is essentially as I draw.
02:41 AM rmu: red is me
02:41 AM jesseg: hahahaha oh I was in a hurry and drew the motor on the wrong side of the snubber diode
02:42 AM jesseg: that was just a mistake
02:42 AM jesseg: hit contrl Z a few times to undo your red and I'll fix the black
02:42 AM rmu: voila
02:42 AM jesseg: thanks
02:42 AM jesseg: that's what I meant
02:42 AM jesseg: so continue with your red please :D
02:44 AM jesseg: Draw in the voltages across the fet, the coil, and the switch. They need to balance eachother.
02:44 AM jesseg: you've drawn the current path
02:44 AM rmu: so you have current flowing and open the switch, it develops a voltage, and mosfets sees this voltage
02:45 AM jesseg: ok great pencil in please the voltages across the fet, the coil, and the switch at the moment the switch opens
02:45 AM jesseg: it doesn't have to be exact - just make up a value for the switch.
02:45 AM rmu: i tried writing 1kv there
02:45 AM jesseg: I really appreciate this by the way guys -- I'm about to learn something that I have been unable to grasp in 40 years :D
02:46 AM jesseg: cool I see the 1kv
02:46 AM jesseg: ok now fill in the voltages across the coil and the fet
02:46 AM jesseg: hint: They need to add up to 1kv.
02:47 AM jesseg: with bias for the 100v of course as needed
02:47 AM sync: they need to add up to the dI/dt
02:47 AM sync: *L
02:47 AM jesseg: at any instant, the voltages can be represented without consideration of time or current.
02:48 AM jesseg: or inductance.
02:48 AM rmu: so if ground is = per definition and other end of coil is at 100V per definition that leaves the mosfet at the difference to 1kv whichever sign that would be
02:48 AM jesseg: We already know there's 1000v across the switch at this instant.
02:48 AM rmu: s/=/0/
02:49 AM jesseg: rmu, so there's 1kv across the mosfet's D and S?
02:51 AM sync: well, if you idealize your circuit then the coil disappears and is just a straight connection
02:51 AM jesseg: Oh, don't forget to write in a voltage for the coil also
02:51 AM rmu: in the static case replacing the switch with a voltage source it would be a voltage divider between whatever resistance a dead mosfet has and the winding
02:51 AM jesseg: well remember, the coil had current in it, and now the switch is open, so the coil has some inductive kickback voltage across its terminals, right?
02:52 AM sync: no, as you want a static case
02:52 AM sync: there is no kickback
02:52 AM sync: as nothing changes
02:52 AM jesseg: wait, if there's no kickback voltage then where does that 1kv across the switch come from?
02:52 AM sync: you need to look at the diff-q
02:52 AM jesseg: flyback, you know about these things, right? what is flyback voltage?
02:52 AM sync: because this is transient
02:53 AM sync: but even so
02:53 AM sync: if you do what rmu said
02:53 AM sync: and put in a voltage source
02:54 AM jesseg: we need to figure out whether an inductor produces a high voltage flyback pulse when you drop the current from large to zero
02:54 AM rmu: voltage proportional dot current
02:54 AM jesseg: if we can't agree on that we're in trouble :D
02:54 AM sync: dI/dt*L
02:54 AM sync: = Ul
02:54 AM sync: that is how it works
02:55 AM rmu: the larger the current change per time the larger the voltage
02:55 AM jesseg: All the old cars and motorcycles relied on inductive kickback -- when the current suddenly drops to zero, the voltage suddenly shoots towards the roof
02:55 AM jesseg: so in our diagram, there was current and the switch has just opened, and there's 1kv across the switch...
02:55 AM sync: .... which is dI/dt * l = Ul
02:56 AM jesseg: And you're saying there's no voltage across the terminals of the inductor?
02:56 AM sync: do you understand differential equations?
02:57 AM rmu: yeah probably it is kind of wrong to say the voltage develops over the switch
02:57 AM jesseg: let's talk about differential equations tomorrow. I'd just love to keep on topic here. We've already established that the time it took the switch to open is significantly short compared to the inductance and stored energy.
02:58 AM jesseg: rmu, if there's no voltage across the switch then why do they draw out such a nice arc if you don't open them quickly?
02:58 AM jesseg: or if you don't use a magnetic blowout?
02:58 AM sync: dude, diff-eqs are how all of this works
02:58 AM rmu: the voltage is generated by the inductance to counteract change of current
02:58 AM jesseg: sync, I know but we're not dealing with a change in current that is subtle compared to the inductance.
02:58 AM sync: yes we are
02:58 AM rmu: the switch drops whatever the plasma needs to keep current flowing
02:58 AM jesseg: For our purpose we can consider that dt is zero.
02:58 AM sync: that is how it works
02:59 AM sync: if dI is zero the voltage is zero
02:59 AM rmu: the mosfet sees the rest of that voltage
02:59 AM jesseg: no the voltage is infinite
02:59 AM jesseg: oh sorry I read dt :P
02:59 AM jesseg: no dI is also huge in this case
02:59 AM sync: that is not what you just said
02:59 AM jesseg: we go from something significant to zero -- until the plasma kicks in
03:00 AM jesseg: oh, I'm sorry, did I forget to mention that the coil has a bunch of normal operating current in it and the switch has JUST opened.
03:00 AM jesseg: There's a brightly glowing plasma which we've established to be 1kv for the sake of argument.
03:01 AM sync: if the switch has juuust opened the dI/dt is infinity
03:01 AM jesseg: We're looking at an instant in time. We are looking at dt=0.
03:01 AM sync: thus the voltage is infinity
03:01 AM jesseg: exactly
03:01 AM jesseg: but we've picked a number of 1kv
03:01 AM jesseg: due to the plasma which we've assumed has just kicked in.
03:02 AM jesseg: and I think 1kv is a perfectly acceptable range for the sake of discussion.
03:02 AM jesseg: hey our plasma vanished
03:02 AM jesseg: who blew out the plasma :P
03:03 AM rmu: the plasma vanishes when your inductive energy is dissipated
03:03 AM jesseg: I really want to understand this guys. I know when you have current in an inductor and you open a switch in series with said inductor, high voltage is produced by the coil and jumps between the contacts of the switch.
03:04 AM jesseg: Wouldn't you agree that in general that is true?
03:04 AM rmu: yes
03:04 AM rmu: probably called "self inductance" in englisch
03:04 AM jesseg: great, I'll write 1kv back at the switch
03:05 AM jesseg: or inductive kickback, right? or flyback? because the voltage developed is in the opposite polarity (when looking at the coil terminals) as the voltage which produced the current to begin with, right?
03:05 AM rmu: jesseg: the inductor develops a voltage that is proportional to the change in current flowing in your circuit
03:06 AM rmu: jesseg: the switch tries to interrupt the current relatively quickly, so a proportionally high voltage develops accross the inductor, the plasma more or less shorts this to the mosfet side
03:06 AM jesseg: rmu, we've just established that the current has dropped to zero because the switch has mechanically opened, and that the voltage has shot towards infinity until the plasma arced at 1kv
03:07 AM rmu: no the current does not immediately drop to zero
03:07 AM jesseg: rmu, it looks to me like the plasma shorts this to the other contact in the switch, providing a gentle letdown of current through the fet
03:07 AM rmu: it takes some ms
03:07 AM jesseg: rmu, well, once the contacts are no longer touching there is no current until the air breaks down into plasma.
03:08 AM jesseg: But look the point is that we're looking at the instant in time when there's 1kv across the switch, right?
03:08 AM rmu: so for the sake of argument take 1A of current through a 1H inductance, dropping this current to 0 in 1ms will result/need a voltage of 1kV
03:09 AM jesseg: great. so we've further established that we had 1H, 1A, and the resistance of the switch opening has created a drop to 0 in 1MS, during which time there was a 1kv voltage across the switch, right? (Assuming your math is correct I did not check it.)
03:10 AM jesseg: So during that 1mS, we've established that there is 1kv across the switch. Right?
03:10 AM rmu: no voltage is accross the inductor. voltage accross the switch will depend on plasma
03:10 AM jesseg: OK so write 0V across the inductor
03:10 AM rmu: 1kV
03:10 AM jesseg: I beg to differ, but I'm trying to learn from you.
03:11 AM jesseg: huh?
03:11 AM jesseg: 1kv across the inductor? That's what I'd say, or 900 or 1100 but not zero
03:11 AM jesseg: anyway, write it in please if you might be so kind :D
03:11 AM jesseg: whatever you say it is
03:11 AM rmu: can you clear the board
03:12 AM jesseg: sure
03:12 AM jesseg: here is clear board: https://awwapp.com/b/ui2p1y56z/
03:13 AM jesseg: hey who's erasing my work of fart?
03:13 AM jesseg: :P
03:16 AM rmu: hehe
03:17 AM jesseg: oh cool we can set the battery to 1uv and the inductor to 1 micro ohm to make calculations easier
03:18 AM jesseg: your artwork is prettier than mine, that's for sure :D
03:18 AM rmu: that doesn't change anything
03:19 AM jesseg: oh cool, you doing the half bridge there sync?
03:19 AM jesseg: oh better yet a full h-bridge :D
03:20 AM jesseg: sync, don't forget your body diodes and your large size vbus+ filter cap
03:20 AM rmu: look at the other board. see why it is a problem if you introduce a switch between H and mosfet?
03:21 AM jesseg: rmu, which other board? the H bridge or the LBS (Inductor, Battery, Switch) loop?
03:21 AM rmu: H bridge
03:21 AM jesseg: yeah looking at it, don't see a problem yet
03:21 AM jesseg: can I draw in the body diodes and the vbus filter cap?
03:22 AM jesseg: umm, the formula you gave is for an *inductor* -- but you have a switch in series with it.
03:23 AM rmu: the body diodes need some time to react and also don't withstand arbitrary voltages
03:23 AM rmu: yes draw them in
03:23 AM rmu: the switch causes the dt
03:23 AM jesseg: they may need some time which is perhaps why they often have RC snubbers too
03:23 AM rmu: yeah, but those are not large enough to accomodate load-side switching
03:24 AM jesseg: but during normal operation, the motor winding kickback is constantly hammering the snubber / body diodes
03:24 AM jesseg: no, the RC snubbers just keep things under control while the diodes kick in
03:25 AM jesseg: you seriously cannot say V=L*(dI/dT) for a switch in series with an inductor. That's the voltage across the *inductor* by itself.
03:25 AM rmu: the switch is causing a change in current
03:25 AM jesseg: The switch has its own voltage which is a function of the current and the plasma characteristics
03:26 AM rmu: yeah, and the voltage drop over the switch while it is arcing is low
03:26 AM jesseg: sure the switch causes the change in current but the inductor voltage must be referenced to the terminals of the inductor
03:26 AM rmu: the mistake in the earliest picture was the other leg of the voltage meter was on the wrong end of the coil
03:27 AM jesseg: which other picture? the one I drew?
03:27 AM rmu: so in colors are usual current paths while switching, what kind of recirculation is used depends
03:27 AM jesseg: oh your Battery Inductor Switch loop -- no you had that one correct. Seriously :D
03:27 AM rmu: this here is correct under the assumption that the switch has zero resistance while arcing
03:27 AM rmu: https://awwapp.com/b/ui2p1y56z/
03:27 AM jesseg: LOL you cannot have zero resistance while arcing.
03:27 AM rmu: the very first picture
03:27 AM jesseg: it would still be closed.
03:28 AM rmu: yeah so take a could of ohms and calculate your voltage drop
03:29 AM rmu: voltage accross (switch in series to coil) will be high enough to damage the transistors
03:29 AM jesseg: is a could of ohms like a can of ohms? P
03:29 AM rmu: or your ultra-fast clamp diodes
03:29 AM rmu: couple sorry
03:29 AM jesseg: no gents we have a serious problem here if we can't apply the formula for an inductor without first putting a switch in series with it
03:30 AM jesseg: Adding the switch into the measured voltage totally complicates things and it's no longer just V=L*(dI/dT)
03:30 AM jesseg: Look at their diagram here: https://www.allaboutcircuits.com/textbook/direct-current/chpt-15/inductors-and-calculus/
03:30 AM jesseg: or find your own if you don't trust them
03:30 AM jesseg: I'm really not making this up :D
03:31 AM jesseg: The voltage across the inductor *itself* is V=L*(dI/dT).
03:31 AM jesseg: Not the voltage across an inductor in series with anything else.
03:31 AM rmu: better
03:34 AM rmu: modulo phase couldn draw that better
03:34 AM jesseg: btw we were talking about snubbers and the time it takes the body diodes to react. One trick we'd do is limit the slew rate of the mosfets (usually by adding some capacitance between gate and drain) which would produce more heat in the fets naturally but it'd also slow the turnoff time which would allow the body diodes more time to activate
03:35 AM jesseg: rmu, not sure I follow. BUt see how they show the volt meter for V=L*(dI/dT) across the inductor only -- not the switch, not the battery, just the inductor?
03:35 AM rmu: hehe
03:36 AM rmu: inductance law only describes inductance, the switch is very very complex with it's plasma, but it determines the amount of current change per time
03:36 AM jesseg: True.
03:37 AM rmu: typical contacters to turn motors on or off will have a time characteristic that will generate voltages in the kVs
03:37 AM rmu: go measure
03:38 AM rmu: and the mechanism is as illustrated, current changes abruptly, inductor answers with high voltage
03:38 AM rmu: both terminals of inductor are connected to legs of H bridge, either directly, or via low-impedance-plasma
03:38 AM rmu: so H bridge sees high voltage
03:38 AM jesseg: But the inductor goes by the rule V=L*(dI/dT). Who cares what is *causing* the dI, it could be a switch, a transistor, a photocell, another motor, who cares -- the inductor responds according to V=L*(dI/dT) and you must place the volt meter just across the inductor.
03:39 AM jesseg: rmu, so how much voltage will be across the inductor while there's 1kv across the switch?
03:39 AM rmu: you are going in circles
03:40 AM jesseg: because you're saying that there's 1kv across the switch, zero volts across the inductor, and 1kv across the fets. But I'm sorry neither the fets nor the switch have the capability to produce 1kv.
03:40 AM jesseg: The only thing i the circuit that has the ability to produce 1kv is the inductor and you're saying there's no voltage across it.
03:41 AM jesseg: "the only thing *in* that circuit..."
03:41 AM rmu: no i said half an hour ago that was a mistake to draw the voltage over the switch, the voltage is over the coil and per extension of low impedance plasma over switch in series with coil for a short moment
03:41 AM rmu: like in picture
03:41 AM jesseg: oh, so 1kv across the switch, and 1kv across the coil?
03:42 AM rmu: blue line in the h-bridge board
03:43 AM jesseg: Can't tell me there's no high voltage across the switch. I've seen the arcs, I've felt the shocks when a 12v inductive load is disconnected and my fingers are across the switch.
03:43 AM jesseg: and I know 12vdc doesn't feel that way all by itself :P
03:45 AM rmu: in that case your finger was the mosfet
03:45 AM jesseg: No in that case my finger was the plasma.
03:45 AM rmu: arc doesn't say much, welding uses high current and low voltage
03:45 AM jesseg: that's why I threw in the bit about the finger
03:46 AM jesseg: However, I also know that switching off an inductive load draws a much longer arc than a purely resistive load. Which, by the way my good friend, is why welders have huge inductors in them in series with the output voltage.
03:47 AM rmu: no, the reason is to keep current stable in light of AC input
03:47 AM jesseg: lol I was working on a 4kw Generac propane generator the other day and I have 20VDC feeding into the field winding (which is around 14 ohms and has massive inductance.) When I drew apart the wires, it drew out a lovely silent arc about 3/8"
03:47 AM rmu: without using capacitors with huge permissible ripple currents
03:48 AM jesseg: LOL.. The series inductor definitely evens out the current, but don't you think that it also causes some inductive kickback causing a voltage spike if you lift the rod, helping sustain the arc?
03:48 AM rmu: whatever, nowadays welders are nothing more than large SMPSes and potentially H-bridge output
03:49 AM jesseg: lol they have some heavy duty inductors in them too, but they just operate at much higher frequencies :P
03:50 AM jesseg: Regarding our theoretical circuit we draw on the whiteboards -- The reason I ask if there's also 1kv across the coil as well as across the switch is because if so, then there has to be either 2kv or ~0v across the fets. Which is probably why you won't answer as to whether there's 1kv across the coil.
03:51 AM rmu: if you can read the board and the graphs you see what voltage i say is over the coil and over the switch
03:51 AM jesseg: oh did you update it?
03:51 AM jesseg: oh cool I didn't know you moved the volt meter to the other side of the switch.. Thanks !
03:51 AM rmu: i put in a second one
03:51 AM jesseg: cool yeah that's god
03:52 AM jesseg: good I mean :P
03:52 AM jesseg: so at the moment that there is 1kv across the switch, how much is across the inductor?
03:52 AM jesseg: My math is telling me 1kv if both bottom side fets are on.
03:52 AM rmu: the thing is you can also put the voltmeter back because for the short time of the transient the switch will have small resistance and hence low voltage drop that is very small compared to voltage over inductor
03:53 AM rmu: so imagine a rubber band, stretched, under tension
03:53 AM rmu: a mosfet on each end
03:53 AM rmu: then you cut it somewhere
03:53 AM jesseg: Well, we've been looking at that place in time when the voltage is at 1kv on the switch. Would you prefer to look at the scenario much earlier when there is 200v on the switch?
03:54 AM rmu: look at the graph
03:55 AM rmu: if you need more exact graphs you are welcome to draw this circuit in your favourite SPICE and simulate it
03:55 AM rmu: place voltmeters whereever you want
03:55 AM jesseg: If I do, and it agrees with me, will you say my spice is wrong?
03:55 AM jesseg: :P
03:55 AM rmu: probably
03:56 AM jesseg: so what if I draw it in your favorite spice?
03:56 AM rmu: i'm not sure what you are saying
03:56 AM jesseg: I'm saying that at any instant the voltage across the fets will be essentially the voltage across the inductor minus the voltage across the switch.
03:56 AM jesseg: And that as a result, the opening of the switch does not induce high voltage across the fets.
03:56 AM rmu: so if the inductor develops 1kV and the switch is essentially closed, the FETs will see 1kv
03:57 AM jesseg: Now turning off the fets produces high voltage across the fets, but that is how a SMPS works.
03:57 AM jesseg: The inductor won't develop 1kv if the switch is essentially closed.
03:57 AM jesseg: Because there will be no change in current and no change in voltage.
03:57 AM rmu: if the switch causes the current to drop it will
03:58 AM jesseg: well it essentially can't cause the current to drop if it's essentially closed
03:58 AM jesseg: Remember, opening the switch -- to whatever degree you open it -- does not increase the current. Period.
03:59 AM rmu: i don't have an accurate model of a switch and the plasma at these timescales
03:59 AM rmu: but
03:59 AM rmu: the switch resists the current
04:00 AM rmu: the assumption that the inductive voltage drops over the resistance of the plasma is wrong
04:00 AM rmu: empirically that is trivially demonstrated
04:00 AM jesseg: There's no voltage drop over plasma?
04:00 AM rmu: there is, but not sufficient to protect your switches, that is the whole point
04:01 AM jesseg: I agree it's much less than the breakdown voltage of air but there is still some voltage drop or there wouldn't be any power dissipated and no light or heat.
04:01 AM jesseg: The reason a plasma arc produces heat is because power is converted and you need current and voltage drop for power to be converted from electrical to heat.
04:02 AM jesseg: Plasma does exhibit negative resistance -- but not at zero volts :P
04:05 AM jesseg: rmu, Well my friend, I am asking a very simple question. I thank you for your effort and I really enjoyed this discussion, but I hope you can understand how your reluctance to answer that simple question causes me to be skeptical of your understanding of the issue. Maybe you're right but can't figure out how to put it in words. I'll keep trying to understand it. But I suspect we aren't progressing too much more tonight and it's 2AM in my timezone.
04:05 AM rmu: what is your simple question
04:06 AM rmu: quick, i' running out of popcorn
04:06 AM jesseg: At the point that the voltage is 1kv across the switch, what is the voltage across the inductor?
04:06 AM rmu: why is there 1kv accross the switch
04:07 AM jesseg: because it just opened and there's currently current flowing through it which the inductor is producing
04:07 AM jesseg: Remember, the current does not increase when the switch opens, it begins decreasing
04:07 AM rmu: the voltage accross the inductor is whatever develops because of L dot i
04:08 AM jesseg: it is what it is, huh :D
04:09 AM rmu: no, it depends on current change the switch and its plasma causes
04:09 AM rmu: but not on the voltage the switch drops
04:09 AM jesseg: Can we agree that at this instant in time, both bottom side fets are switched on and are 1 milliohm fest?
04:10 AM rmu: fest?
04:10 AM jesseg: fets
04:10 AM rmu: and?
04:10 AM jesseg: hey it's 2AM here :P
04:10 AM jesseg: so both fets bottom side fets are on. There is 1 amp flowing. The switch opens. Does the current through the inductor go up or down?
04:10 AM rmu: so you put 1kV accross 2 milliohm
04:11 AM jesseg: You can answer your question by answering mine :D
04:11 AM rmu: current decays
04:11 AM jesseg: roger on that
04:11 AM jesseg: so what will the voltage drop across the fets be?
04:12 AM jesseg: Initially 1mv each, right?
04:12 AM jesseg: and decaying, right?
04:12 AM rmu: if it decys in 1ms and your inductor has 1H the mosfets see 1kV minus voltage drop of arc plasma
04:13 AM rmu: the mosfest is not "on" for this voltage
04:13 AM jesseg: work where me here please. If the current never exceeds 1A, ohms law tells us V=IR, and R=0.001, V also must be 0.001, right?
04:13 AM rmu: mosfet is not an ohmic resistance
04:13 AM jesseg: How can you possibly exert 1kv across a 0.001 resistor with only 1a to work with?
04:14 AM rmu: much less so an IGBT or a diode
04:14 AM jesseg: well, they rate them in ohms and they are sort of ohmic although I agree not super linear
04:14 AM jesseg: they being fets
04:15 AM jesseg: but we've been drawing fets and they simplify the problem, so unless you're telling me that fets don't suffer from the problem we've been discussion, please lets stick with fets.
04:15 AM rmu: what happens with n-type mosfet if gate voltage << drain voltage
04:16 AM rmu: jesseg: ?
04:16 AM jesseg: you never did answer my question about how you could get 1kv across a turned on rds=1mohm mosfet with only 1 amp.
04:16 AM rmu: the n-type mosfet is not 1mohm if you apply 1kV
04:16 AM jesseg: going off to the topic of a fets driver not working correctly is another issue
04:16 AM jesseg: hmm you have a serious confusion about cause and effect.
04:17 AM rmu: no, you think the mosfet can dissipate all the energy before significant voltage can develop
04:17 AM jesseg: 1A into 0.001 ohms is not that much energy.
04:17 AM jesseg: And you already agreed that when the switch open the current decays, not rises.
04:18 AM jesseg: hey can we simplify this -- and replace the mosfet with a plain 0.001 ohm resistor?
04:18 AM jesseg: So the inductor has 1amp flowing in it by some means not present in this circuit. The switch is opened. The switch has 1kv across it. There's somewhat less than an amp flowing.
04:18 AM jesseg: How in the world is less than an amp going to produce 1kv across a 1milliohm resistor?
04:19 AM rmu: hehe. ask the inductor. that was the precondition of the excercise
04:20 AM jesseg: Well Sir, were not gaining ground. Perhaps you could discuss it with an EE friend of yours that you trust. Or read some books. Anyway, I've done my best to explain and that is insufficient. If you would enjoy more discussion on the topic, so would I, but I'll let you bring it up if you so choose. Thank you very much for the effort. And good night for today :D
04:21 AM rmu: have fun destroying VFDs ;)
04:21 AM jesseg: yeah it's a blast. Sounded like a 22 shot going off :D
04:21 AM rmu: "because i can"
04:22 AM jesseg: nah I hope to not blow up any more. but it sure went with a bang when it went.
04:23 AM jesseg: I suspect it was trying to brake the motor and it pumped up the filter cap bank above the voltage rating for the fets till they umm avalanched with flame
04:23 AM rmu: i can recommend "Tietze Schenk", there should be englisch translations
04:27 AM jesseg: Ahh, do they write "Electronic Circuits" type books?
04:28 AM jesseg: If I get the book from inter library loan and it agrees with me, will you just say they are wrong? :P
04:28 AM jesseg: Like this one? https://books.google.com/books?id=CLQvCwAAQBAJ&source=gbs_similarbooks
04:30 AM rmu: i could make a parrot irc script for you, then rmu will say whatever you want
04:34 AM jesseg: hmm that book doesn't have a chapter on inductors, although it has one one switchmode power supplies
04:34 AM jesseg: but it looks pretty high level, although google preview doesn't show all the pages lol
04:35 AM jesseg: oh well, good night
04:35 AM rmu: good night
04:36 AM rmu: and don't switch off your motor while the mosfets are not in fast decay mdoe
04:39 AM jesseg: I think I'll see how I get along just making sure I don't turn back on a motor in the opposite direction while it's still spinning full speed in the previous direction.
04:40 AM jesseg: if that bytes me too then I'll know. Or by then maybe I'll have built myself a VFD that is made for full speed hardware switch reversals.
04:42 AM rmu: jesseg: look for stmbl
04:56 AM jesseg: As in the servo drive ?
04:57 AM jesseg: oh ok cool yeah
04:58 AM jesseg: but I was thinking of actually taking one of these chinese VFDs and replacing the logic board with my own
04:58 AM jesseg: they have one board that's all the high power stuff with optically isolated gate drivers for the IGBTs, then they have another board that is the logic board with the CPU and all that
04:58 AM jesseg: anyway.. I'm off for the night. Catch you later :D
05:12 AM Tom_L: 32░F Hi 59
05:13 AM jthornton: morning
05:13 AM Tom_L: morning
05:13 AM Tom_L: summer sure left quick
05:14 AM XXCoder: really? summer felt very long
05:14 AM jthornton: 42┬░F high 55┬░F... just turned the heater on this monring
05:14 AM XXCoder: heh for a change here is warmer at peak of 61f
05:15 AM jthornton: looks like a fall to me here
05:15 AM XXCoder: i had to leave work earlier than planned though
05:16 AM XXCoder: back pain was pretty damn bad
05:16 AM XXCoder: still is but carefully not moving back its ok
05:24 AM jthornton: bad disk?
05:24 AM XXCoder: maybe dunno I have had arthitis since I was 27, but its rather sudden and at upper back so dunno
05:30 AM jthornton: wife gets back pain from time to time and it just knocks her down
05:32 AM XXCoder: only sometimes?
05:32 AM XXCoder: it never stops for me, im just used to it. upper is new though
05:32 AM jthornton: yea something she does just triggers it but she has no clue what it is
05:35 AM jthornton: well crap I got the 160 x 128 digole oled to work on the i2c buss but can't find a driver for it
05:39 AM XXCoder: thats odd. I wonder if its diet changes, sleath disk slip, etc
05:45 AM jthornton: pain can be such a strange thing to diagnose
05:48 AM XXCoder: yep
05:48 AM XXCoder: "owie" isnt very detailed
05:49 AM XXCoder: I bet you that in future we would have nanomachines attached to all nerves so we can detailed pain map, as well as can cut off
05:49 AM jthornton: that might be a ways off
05:50 AM jthornton: yea I think I found the ST7735 driver and I think it's the one I need
05:50 AM XXCoder: prerty cool https://www.youtube.com/watch?v=is-rSK5y6EQ too bad its useless for me
05:51 AM jthornton: "It turns out I bought a very expensive tray." HAHAHAHAHAHAHAH´╗┐
05:52 AM XXCoder: yep lol
05:53 AM jthornton: I wonder if I got another broken egg laid from the roost this morning...
05:53 AM XXCoder: for a sec I thought yo meant rooster. kinda confusing
05:55 AM jthornton: naw, I have one hen confused about time and she lays and egg before dawn and of course it breaks when it falls from that height
05:58 AM XXCoder: from roost sitting rods or something
05:59 AM XXCoder: lol https://www.youtube.com/watch?v=1lRI35gKSPA
06:00 AM jthornton: in nature chickens roost on tree limbs in my roost area they roost on 2x3 with the narrow side up
06:00 AM XXCoder: I had forgotten about it. theres even xkcd jobe about that
06:00 AM jthornton: and yes hens stand up when they lay the egg
06:00 AM XXCoder: oh its amazon kindle not wikireader
06:01 AM XXCoder: https://imgs.xkcd.com/comics/kindle.png
06:05 AM XXCoder: lol apparently can buy 10 for 10 bucks
06:05 AM XXCoder: all of em is not functional due to missing special sdcard
06:05 AM XXCoder: https://www.ebay.com/itm/LOT-of-10-WikiReader-Pandigital-Wikipedia-Pan-Reader-01-NO-SD-Card-FOR-PARTS/202467314899?hash=item2f23fe0cd3:g:ZCIAAOSwkQBbtpnQ:rk:7:pf:0
06:05 AM XXCoder: I wonder if its any use for hackers
06:36 AM jthornton: 10 more minutes and the light comes on and the door opens... no egg yet from sidekick
06:52 AM jthornton: hmm the damn light did not come on again this morning
06:59 AM gloops: hmm wheres the motor experts
07:00 AM gloops: old bandsaw motor testing - motor turns, but i can stop the pulley easily by hand, it stays quivering a few seconds, then goes again, sometimes the opposite direction
07:01 AM gloops: cap looks pretty old and battered
07:05 AM jthornton: if it is a start cap once the motor is up to speed it's not used
07:07 AM gloops: hmm thats what i thought, i dont know if it is just start or run capacitor
07:07 AM gloops: could just stick another one on
07:09 AM jthornton: a start capacitor will measure between 70 and 120 micro Farads
07:09 AM jthornton: any markings on it?
07:09 AM gloops: lol, its fixed
07:10 AM gloops: rook cover off to get to cap connections, wiggled a few wires, tried again - boom
07:10 AM gloops: i think ill take the connectors off and clean them up a bit it will be fine
07:10 AM gloops: hopefully
07:12 AM gloops: hmm, no, still starts different direction every time, power is there now though
07:15 AM gloops: ill try another cap, reckon it is sortable
07:20 AM gloops: nah its working with old cap fine, i think these old caps sometimes take some filling when theyve been discharged a long time
09:31 AM CaptHindsight: gloops: http://www.capacitorguide.com/motor-starting-capacitor/
09:32 AM CaptHindsight: http://www.capacitorformotor.com/starting_capacitor.html
09:34 AM gloops: hmm, this one is a metal case
09:34 AM gloops: it does some to be working ok now, motor kicks when it starts and seems to have full power
09:34 AM gloops: initially no kick and no power
10:56 AM jesseg: Good Morning/Evening/As Appropriate in your timezone :D (Morning for me)
10:59 AM pink_vampire: hi jesseg
11:00 AM jesseg: hey pink_vampire how's it going?
11:01 AM pink_vampire: I just got acrylic cement!
11:01 AM pink_vampire: the smell is just mmmm
11:01 AM jesseg: excellent! How is it?
11:01 AM jesseg: lol oh stinks does it?
11:02 AM jesseg: oh is it glue for chemically welding acrylic pieces together?
11:02 AM pink_vampire: yeah, it is sooo amazing!
11:02 AM pink_vampire: you need to get some
11:02 AM jesseg: cool, what kind did you get?
11:02 AM jesseg: I need to get some acrylic too :P
11:04 AM pink_vampire: I want to try making a stand with it
11:25 AM fragalot: hey
11:25 AM pink_vampire: hi fragalot
11:43 AM pcw_home: Jesseg, switching the motor side of a VFD _will_ kill it eventually unless you have specific protection to avoid arcing or protect against the steep wavefronts that arcing creates
11:44 AM pcw_home: showering arcs can generate kilovolt steps with picosecond rise times, these generate significant voltages across even ground planes
11:44 AM Tom_L: pcw_home, are http://store.mesanet.com/index.php?route=product/product&path=83_89&product_id=127 and https://mesaus.com/index.php?route=product/product&path=65&product_id=65https://mesaus.com/index.php?route=product/product&path=65&product_id=65 the same?
11:46 AM pcw_home: 10V full scale and 300V full scale (just different input resistors)
11:47 AM Tom_L: ok
11:54 AM miss0r|office: fragalot hello
11:54 AM miss0r|office: Today I picked up a Super nintendo entertainment system "nintendo classic mini" with 21 games on it :) for around 60eur
11:55 AM miss0r|office: I just couldn't help myself
11:55 AM fragalot: I still have my original SNES :D
11:56 AM miss0r|office: I borrowed mine to a friend of mine many years ago. He had a gunnie pig, who ate the cables and took a shit in the cartridge bay
11:56 AM Tom_L: skunkworks, do you have a link to your plasma torch height control video?
11:56 AM fragalot: so.. that's going into your new maho control panel right?
11:56 AM miss0r|office: fragalot: Realy nowhere else to put this thing
11:56 AM fragalot: :D
11:56 AM miss0r|office: long 3D run - supar mario world
11:56 AM miss0r|office: slow slotting - zelda
11:57 AM fragalot: :D
11:57 AM miss0r|office: broke an endmill - street fighter
11:57 AM fragalot: don't forget about kirbey
11:57 AM fragalot: kirby? how do you spell that again
11:57 AM fragalot: kirby's adventure
11:57 AM miss0r|office: Indeed. I have all the kirby games on this thing
11:57 AM fragalot: took me 12 years to complete that one
11:57 AM miss0r|office: "kirby super star - 8 games in one"
11:57 AM miss0r|office: :)
11:57 AM fragalot: fancy
11:58 AM miss0r|office: it also has MEGA MAN X !
11:58 AM miss0r|office: :D
11:59 AM miss0r|office: I don't know this "starfox" game. but apparently this comes with "starfox II - never before released" then it MUST be good :]
12:01 PM fragalot: never heard of it
12:01 PM miss0r|office: it has "never before released!**" but I can't see where the two start referres to...
12:01 PM fragalot: lol
12:01 PM miss0r|office: I still have my commodore 64.. But all my tapes are bad
12:01 PM miss0r|office: I have an old scumbag armada laptop, that emulates a tapedrive, though :) Its a hassle to use, so I don't get around to it much
12:01 PM fragalot: so many mosquitoes trying to get in through the window atm
12:02 PM miss0r|office: so your mosquitos recovered? I've only seen perhaps.. two or three mosquitos since early july
12:02 PM miss0r|office: And we have a serious mosquito problem normally
12:04 PM fragalot: they haven't even left yet
12:05 PM miss0r|office: lol
12:05 PM fragalot: I heard on the radio that they are expecting them to cause hell all the way up to christmas
12:05 PM miss0r|office: lucky you
12:05 PM miss0r|office: :D
12:12 PM jelly-home is now known as jelly
01:58 PM yooosunshine: Can ethercat slaves demand the master to have distributed clocks on?
01:58 PM yooosunshine: so hard to find info on this stuff
01:59 PM fragalot: isn't that something for the master to decide, rather than the slave?
01:59 PM pink_vampire: https://www.youtube.com/watch?v=IOXXiPK1L4s
02:01 PM fragalot: I've considered CBN wheels, but at the same time i've got a stack of white & greens to plow through first :P
02:01 PM fragalot: (white would be replaced by CBN, green would need diamond)
02:02 PM pink_vampire: you can't use them on carbide?
02:03 PM fragalot: diamond is much better
02:04 PM fragalot: CBN cutting carbide will wear pretty quick
02:05 PM pink_vampire: one day.. i will get a grinder.. one day
02:08 PM fragalot: they can be cheap, messy things
02:08 PM fragalot: or expensive, messy things.. depending on your requirements
02:09 PM pink_vampire: i'm not sure i need one..
02:09 PM fragalot: mine's paid itself back in carbide i've saved several times already
02:11 PM SpeedEvil: jthornton: https://i.imgur.com/MtdRUF5.jpg
02:12 PM pink_vampire: fragalot: what do you mean?
02:13 PM fragalot: pink_vampire: I hate throwing out an entire insert just because a tiny corner broke off, so I regrind it..
02:13 PM fragalot: pink_vampire: and custom HSS cutters save the day a lot
02:14 PM fragalot: pink_vampire: plus I regrind the ends of my endmills
02:17 PM syyl_: cheap!
02:19 PM fragalot: syyl_: you're one to talk :D
02:19 PM syyl_: :D
02:19 PM FinboySlick: schaublin owners have their cheapskate cards revoked, fragalot
02:19 PM fragalot: I wouldn't mind an air bearing setup on the deckel clone
02:19 PM syyl_: haha
02:20 PM syyl_: next he buys a mercedes
02:20 PM fragalot: audi!
02:20 PM fragalot: :D
02:20 PM pink_vampire: let me see
02:20 PM syyl_: and wears fancy pants
02:20 PM fragalot: no pants.
02:20 PM syyl_: uh
02:20 PM fragalot: it's hot today
02:20 PM syyl_: uhm
02:20 PM syyl_: :D
02:20 PM FinboySlick: Oh he's already Mr Fancy Pants to me.
02:21 PM syyl_: speaking of fancy
02:21 PM syyl_: get cbn for hss!
02:21 PM fragalot: I use CBN on the tool grinder, standard white & green combo setup on the bench grinder
02:21 PM FinboySlick: It's just good on hardened steel though, no?
02:21 PM fragalot: well, or diamond
02:22 PM syyl_: yes, cbn only for hardened steel
02:22 PM syyl_: nothing else
02:30 PM fragalot: man that inconel part edge precision has been showing on YT just tears through carbide
02:31 PM fragalot: single cut.. index, single cut.. index.
02:32 PM syyl_: i love when he shows the pile of used inserts and endmills during a job :D
02:32 PM fragalot: I'd be happy to buy 'm for scrap value from him :D
02:34 PM fragalot: I have to say though I love the style of machine he's using
02:34 PM gregcnc: integrex of some flavor?
02:35 PM fragalot: indeed
02:35 PM gregcnc: i wonder if that
02:35 PM gregcnc: is all he has
02:35 PM FinboySlick: fragalot: Link us poor Schaublin-deficient plebs.
02:35 PM FinboySlick: I want to see.
02:36 PM fragalot: gregcnc: far from, the shop overview videos show a HUGE shop
02:36 PM fragalot: he's even got his own cnc cutter grinder
02:36 PM gregcnc: ok, i have seen that
02:36 PM gregcnc: haven't
02:36 PM fragalot: FinboySlick: https://www.youtube.com/watch?v=lI-59aZgY_M <= last video he's uploaded
02:36 PM fragalot: the carbide indexing is shown better in the previous videos
02:37 PM fragalot: and are well worth watching because that part is insanely complicated to make :D
02:39 PM gregcnc: man, the quote on that part
02:39 PM fragalot: lol yea
02:43 PM FinboySlick: The machine reminds me of a CTX Gamma or somesuch.
02:47 PM FinboySlick: Though his method of setting the cutter 'height' with a gage pin seems odd to me.
02:47 PM Tom_L: how so?
02:47 PM FinboySlick: Is that precise enough?
02:47 PM fragalot: very
02:48 PM fragalot: the pin has a very well known diameter, and it's a go/no go style of measurement similar to gauge blocks
02:48 PM fragalot: either it fits under, or it doesn't
02:48 PM Tom_L: JT sets his with a dowel pin
02:48 PM fragalot: so if you manually step the cutter away in 0.001mm increments, you know that you are within 0.001mm with the height
02:49 PM Tom_L: i have sometimes
02:49 PM Tom_L: he probably has the part geometry offset the pin thickness
02:49 PM Tom_L: or sets it when he does the length offset
02:49 PM fragalot: either way works
02:49 PM Tom_L: yeah
02:50 PM Tom_L: just personal preference
02:50 PM fragalot: or a shop agreement :P
02:50 PM fragalot: nothing worse than a bunch of CNC operators that don't agree on work methods that need to fill in for the other when he falls ill
02:50 PM Tom_L: 11:10 reminds me of a dentist
02:52 PM gregcnc: probably work lined up for him waits until he's back
02:52 PM fragalot: gregcnc: depends on the shop & the deadlines and/or customer
02:57 PM jthornton: SpeedEvil: mine are like that when you don't have any mealworms for them to munch on
03:00 PM gregcnc: he has his own machines in rented space in a bigger shop as is basically a contractor, now that sounds convenient
03:00 PM fragalot: gregcnc: sounds like fraud :P
03:00 PM fragalot: in dutch it's called a "schijnzelfstandige"
03:03 PM gregcnc: maybe over there, I don't think that's a problem here
03:04 PM syyl_: fragalot, that scheinselbstst├Ąndig here
03:04 PM syyl_: sounds almost the same
03:04 PM syyl_: :D
03:06 PM syyl_: absolutely like the edge precision videos
03:07 PM syyl_: he is so calm
03:07 PM syyl_: :D
03:07 PM cpresser: syyl_: are you running this youtube-channel? https://www.youtube.com/user/syyl/videos
03:07 PM fragalot: syyl_: Yeah :D very skilled operator too
03:07 PM FinboySlick: The guy has a heck of a chin/jaw.
03:07 PM syyl_: yes, cpresser
03:08 PM FinboySlick: fragalot: reminds me of a line from Tango and Cash.
03:08 PM cpresser: syyl_: +1 for the videos.. i learned a lot
03:08 PM syyl_: thanks :)
03:08 PM FinboySlick: syyl_: I'm a total fan too.
03:08 PM * syyl_ gets red
03:09 PM * fragalot gives syyl_ a thumb down to even things out a bit
03:09 PM syyl_: thanks
03:09 PM syyl_: gets me back on ground level
03:09 PM fragalot: any time :-)
03:09 PM gregcnc: is instafollower
03:09 PM syyl_: or i will just a video from robrenz ;)
03:10 PM fragalot: I do find it weird that almost every video ever uploaded has that groupie clicking the thumb down in the first few seconds after it's published
03:10 PM FinboySlick: fragalot: We all know it's you.
03:11 PM fragalot: nah :P
03:11 PM FinboySlick: The other suspect would be Pete because he's jealous of people with functional lathes.
03:12 PM fragalot: lol
03:14 PM syyl_: pete?
03:15 PM fragalot: Mr Pete, I assume
03:15 PM syyl_: oh
03:15 PM syyl_: hasnt he like 15 lathes?
03:15 PM FinboySlick: beachbumpete, formerly PeteFromTn
03:15 PM gregcnc: pete in FL
03:15 PM fragalot: never mind :D
03:15 PM syyl_: ah
03:16 PM FinboySlick: We haven't seen pete in a while, btw. I hope the hurricanes spared him.
03:20 PM FinboySlick: Which reminds me of this little gem: http://www.myconfinedspace.com/wp-content/uploads/2018/10/keep-sending-them-hurricanes.jpg
03:33 PM gloops: this is a hurricane https://upload.wikimedia.org/wikipedia/commons/thumb/2/28/Hurricane_mk1_r4118_fairford_arp.jpg/1200px-Hurricane_mk1_r4118_fairford_arp.jpg
03:34 PM FinboySlick: gloops: Pete can't get these though, they require a functional lathe to make.
03:35 PM gloops: yes the Brits certainly had those...
03:35 PM gregcnc: yes a proper hurricane
03:35 PM gloops: speaking of..
03:38 PM fragalot: gloops: well the brits did have to make up for the shitty pilots somehow..
03:38 PM * fragalot runs
03:39 PM gloops: remember churchills words fragalot
03:39 PM gloops: never in the field of human conflict, was so much owed, by so many, to so few
03:40 PM fragalot: war does indeed line the pockets of the few
03:40 PM FinboySlick: gloops: I'm pretty sure he was referring to the money he borrowed from the US ;)
03:40 PM gloops: they were only a handful of kids, but they turned the war around
03:41 PM gloops: FinboySlick ahh yes the yanks, never saw one for 5 years
03:41 PM fragalot: gloops: the trick is to let everyone wear themselves out first.. thin the herd
03:42 PM fragalot: and THEN come to the rescue
03:42 PM FinboySlick: Irony is that Prescott Bush was actually financing the reich at the same time. There were congressional hearings but I he manage to squirm his way out of that one and sired two US presidents.
03:42 PM fragalot: FinboySlick: isn't that the USA way?
03:43 PM gloops: the yanks thought hitler would keep the commies from moving west
03:44 PM FinboySlick: The history they don't make movies about really should have movies made about it. 'American Made' being a good exception.
03:44 PM FinboySlick: gloops: Hope you saw that one, good plane action in it.
03:45 PM gloops: dont think ive seen it
03:45 PM gloops: anyway time to become horizontal
03:45 PM FinboySlick: Not warplanes, sadly.
03:45 PM fragalot: FinboySlick: part of the issue may be that "ye who winneth the war, writheth history"
03:45 PM fragalot: because both sides did atrocious things, yet the winning party gets to try to hide theirs
03:50 PM FinboySlick: My favorite bit of history to share lately with the rise of young communists is this: When Marx thew his tantrum at his bosses at the New York Daily Tribune because they wouldn't grant him an expense account. He left and found a patron to help him write his manifesto: J.P. Morgan.
03:51 PM FinboySlick: I find it delightful to point out that Marx was financed by one of the world's biggest 'evil capitalist'.
03:52 PM fragalot: the issue is always in the extremes, regardless of "which way you swing"
03:56 PM FinboySlick: Wait, pete was here?
03:56 PM FinboySlick: And I was all worried for him.
03:57 PM Deejay: gn8
04:01 PM jthornton: Digole Digital solutions you will find it's so easy to use and fun... actually it's impossible to use and very frustrating but it does have a nice splash screen
05:56 PM CaptHindsight: if they can't spam the channel do they now just make and break connections every 2 minutes for an hour or two?
05:58 PM * JT-Shop never sees join part messages
05:59 PM JT-Shop: CaptHindsight: I've had poor connections before that caused a ton of join parts
06:00 PM JT-Shop: goodnight
07:07 PM SpeedEvil is now known as Guest30245
07:11 PM BitEvil is now known as SpeedEvil
08:56 PM gregcnc: IS
08:56 PM gregcnc: is youtube completely crashed?
08:56 PM SpeedEvil: yes
08:57 PM SpeedEvil: Well, I've not seen anyone saying it works, globally.
08:57 PM Tom_L: somebody else was complaining about it so probably
08:57 PM gregcnc: is the end near?
08:58 PM Tom_L: you have been isolated from humanity
08:58 PM gregcnc: I had to change a lathe program from an iscar multi function drill/boringbar to sparate tools
08:59 PM gregcnc: I don't know how I didn't break the drill because I forgot to change the line for the first drill from X4. to X0.
09:00 PM gregcnc: it was in 6061 and the cutting edge was lined up such that it was essentially boring
09:00 PM gregcnc: 2mm off center on the drill
09:00 PM gregcnc: made good parts after I fixed that
09:01 PM gregcnc: dumb Emco fauxnuc doesn't cancel canned cycles properly and broke the iscar tool in the first place
09:02 PM * SpeedEvil ponders geometry of drill as boring bar.
09:19 PM Jymmm: SpeedEvil: better than rebar ;)
09:19 PM * SpeedEvil is again annoyed that 'steel' is pretty much adequate to determine stiffness.