#garfield Logs

Dec 01 2022

12:20 AM rue_mohr: WormFood, what do you think of the gear counter?
04:38 AM Tom_L: nice one
04:38 AM Tom_L: on the motor & encoder counter :)
04:42 AM rue_mohr: so
04:43 AM rue_mohr: why, when I go to sleep a little early,
04:43 AM rue_mohr: do I wake up at 2am
04:43 AM rue_mohr: heh, it doesn't count encoders all that good tho
04:44 AM rue_mohr: I'm going to a site to help a guy at 10am
04:44 AM rue_mohr: its almost 3am and I'm awake
04:44 AM rue_mohr: this is not helpful
04:44 AM rue_mohr: did I even get sleep?
04:44 AM Tom_L: go back to sleep a while
04:45 AM Tom_L: i am ;)
04:45 AM rue_mohr: I cant, I'm awake
04:45 AM Tom_L: you can
04:46 AM Tom_L: just need to retrain your brain & body a bit
04:46 AM rue_mohr: no, I can hardly sleep when I am tired
04:46 AM rue_mohr: and I'm freaking awake
04:56 AM rue_mohr: -
07:09 AM Tom_L: .
11:04 AM aandrew: "modified vacuum cleaner motor" ?
11:11 AM rue_mohr: a bridge rectifier across the armature so that its directional
11:12 AM rue_mohr: otherwise a universal motor will only go one way
11:13 AM aandrew: interesting
11:13 AM aandrew: you always have all these interesting tricks up your sleeve
11:13 AM rue_mohr: I wonder if I can find a 3 phase VFD to turn into a tripple axis DC driver
11:14 AM rue_mohr: I completely overlooked the fact that the induction from the motors would kick up the supply voltage
11:14 AM rue_mohr: and those PC power supplies have no margin for that
11:15 AM rue_mohr: the 10w clamp resistors I was using?
11:15 AM rue_mohr: they died a horrid death
11:15 AM rue_mohr: the second one just disintegrated when I took the clamp off
11:15 AM aandrew: they're pretty cheap now, and I even found this on ali not too long ago: https://www.aliexpress.com/item/4000859985694.html
11:15 AM aandrew: basically add your own mosfets or possibly even igbts
11:15 AM rue_mohr: I can use broken ones
11:16 AM rue_mohr: I'm shooting for a 10hp-100hp VFD
11:16 AM rue_mohr: these are 120V motors, so I'm running on +-175V at 6A ea
11:16 AM aandrew: you might have good luck on ebay for that stuff
11:17 AM rue_mohr: was looking, no
11:17 AM aandrew: you can also do single phase in, 3 phase out with them if you either derate them ~60% or buy ones specifically for single-to-three phase operation which usually have more caps to compensate
11:17 AM rue_mohr: there are some descent deals, but I need like $0-$40
11:17 AM rue_mohr: its a DC motor
11:17 AM rue_mohr: not 3 phase
11:17 AM aandrew: oh yeah you own't find 100hp for $40
11:18 AM rue_mohr: not even broken
11:18 AM rue_mohr: the broken ones are $100usd
11:18 AM rue_mohr: http://ruemohr.org/~ircjunk/tempimage/p1260956.jpg
11:19 AM rue_mohr: this is the idea with the 3 phase VFD
11:19 AM rue_mohr: I rewire it from the fet drivers up
11:19 AM rue_mohr: or down, or whatever...
11:20 AM rue_mohr: it occurs to me now, that I could take the existing circuit, and instead of routing the flyback to the power rails, route it directly to resistors
11:20 AM rue_mohr: but a 600V VFD would be ok with the voltages even after the flyback
11:22 AM aandrew: broken VFDs are usually blown IGBTs or caps, maybe the rectifier front end if they've been abused
11:22 AM rue_mohr: thats ok
11:22 AM * aandrew spent 13y designing these things
11:22 AM rue_mohr: I can take 2/3 of a blown input rectifier and I'm still ok
11:23 AM rue_mohr: and if I can replace the igbt's then I'm ok (not a monolythic module)
11:23 AM rue_mohr: :]
11:23 AM rue_mohr: all the fet/igbt drivers float eh?
11:23 AM aandrew: yep and that's exactly what the single-to-three phase configuration is, just have to mind the ripple current on the caps and the peak currents on the rectifiers since they're usually designed fairly close to their service lifetime
11:24 AM rue_mohr: it quite spooked me when running that motor pushed the supply votlage up enough to blow the mov
11:24 AM rue_mohr: and that only one of the two caps has that overvoltage protection
11:24 AM aandrew: well the monolithic ones aren't even that scary, they're more or less standardized unless you were doing what we were doing and getting either custom-labelling semikron or IR IGBTs or doing what TB Woods was doing and actually doing COB in-house for their smaller units
11:25 AM rue_mohr: :)
11:25 AM rue_mohr: am I right to think that overvoltage protection is usually a seperate circuit across the bus?
11:26 AM rue_mohr: aka, rectifier->bus, protection->bus, half driver->bus x3
11:34 AM rue_mohr: no, new take on the gear counting
11:34 AM rue_mohr: not sure how completely to implement it yet
11:35 AM rue_mohr: fft based, but not threshold image based
11:42 AM aandrew: rue_mohr: at least on our VFDs there was MOV protection but honestly that's a one-shot kind of protection. THe real protection was the bus overvoltage detection. the first level would warn the software to speed up the motor (if configured to do so) or engage the DC braking resistor. The second level would force the resistor on and possibly fault out
11:43 AM aandrew: optional line reactor --> bridge --> caps --> igbts --> optional load reactor --> motor
11:43 AM aandrew: hanging off caps was another igbt and resistor
11:44 AM aandrew: the regenerative drives replaced teh bridge with igbts of course, and there was sometimes a huge honking DC choke between the bridge and caps
11:44 AM aandrew: you could also do "soft start" drives which replaced the bridge with three diodes and three SCRs so you could phase them back and not draw so much power to charge up the caps
11:45 AM aandrew: woo my tiny 120VAC transformers arrived
11:48 AM aandrew: just little 5W things
11:48 AM aandrew: oh wait
11:48 AM aandrew: these might not be good to put across 50Hz
11:48 AM aandrew: https://www.mouser.ca/ProductDetail/710-750310787
11:48 AM aandrew: I just noticed 100kHz
11:48 AM aandrew: they seemed too good to be true
11:49 AM aandrew: back to using the larger EI laminated ones I guess
11:50 AM Tom_itx is now known as Tom_L
12:24 PM WormFood: <rue_mohr> WormFood, what do you think of the gear counter? <-- I'm not sure what to think. What exactly is a "gear counter". My gear counter is at 42. That is, I have 42 pieces of gear. ;)
04:17 PM Tom_L: WormFood, just tell him you like it alot since he put so much work in on it :)
04:27 PM WormFood: I didn't go back too far in the channel history, but I saw some interesting things, but not enough context to form an opinion. He's one of the smartest guys I know, and always impresses me with is projects, so I have no doubt whatever he's doing is cool, especially if he asks me about it. ;)