Bad VFD, or Bad motor?
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- Опубликовано: 11 фев 2025
- Hey Guys, working on a Taiwanese Bridgeport clone. The motor is acting strange. This is a quick video of what it's doing on the VFD. I've tested it on mains, and didn't have any issues, but of course, it ramped up pretty quick. If anyone has any thoughts, let me know. I'm going to try it on a known good VFD this weekend.
If it was me, I would first use a volt meter to trouble shoot it. Ideally a good quality fast acting one, but most any should work. When the motor is running measure the voltage fluctuation of each leg. The bad leg should behave differently. Reading/bouncing more than the good legs. Then swap the phases around. If the problem leg moves, it is the VFD. A o-scope would be better, but not always available. Plus a lot of users don't know how to use one.
I'd think about hooking it up to an Oscope, rather than a meter. Definitely something funky going on with your pixies
It's either the VFD or incorrect wiring. If it's the VFD, one of the phase generator circuits probably pooped out. Simple diagnostic is to monitor each leg using an oscilloscope to ensure the correct voltage, phase and frequency. If one of them is bad, open up the VFD and trace the lead through the circuit checking for the defective part. Sometimes a visual scan will reveal something obvious like a burnt out diode or IGBT. It could also be a simple wiring issue where it's wired as delta instead of Wye where the motor isn't supplied with enough causing it to have a lower stalling torque at lower speeds. Since the direct mains runs at full speed, you won't notice the hiccups.
The wiring is correct. (6 wires from the motor + 3 for the mains, can be 220/440) I went in and double checked it and wired it all back together. I can throw the scope on it this weekend or try another VFD.
Hi! Have you tried using another VFD? I'd like to hear the result. Thank you.
It was a bad VFD. Ended up being 1/2 of one of the phases.. So probably a bad cap or SCR. Works perfectly fine with new VFD. I probably should pull this video down.
@@KnoxMachiningthan byou so much. Having the same problem but unfortunately i don't have spare Vfd to try on.
@basictechnolo-g5578 Using a vote meter, ohm out each phase on the motor. They should all be very close to the same value. (Disconnect all 3 wires and check between each one).
Hmmm…..I am lucky cuz if this was me…I just call my buddy Carl as know nothing electrical…best of luck
Ha Ha Chuck, I don't have a Carl! :)
you have to check the parameters of the VFD. What type of VFD do you have on this machine??
Yes. Where some that we tweaked, but in the end, it's a very simply VFD with very few documented features. I've since checked the motor on another VFD and it ran fine. Looks like one of the IGBT transistors has died causing it to be only 2-1/2 phases.
Good odds it’s the VFD, I’ve found a few with one IGBT failed and would still run. So your running on 2.5 phase not 3 phase. Easy check at 50% / 30 hz speed. Measure the AC voltage at the motor power connections (motor connected) leaving the drive. T1 to T2, T1 to T3, T2 to T3. They should all be quiet close in value, if one reading is say 20 volts lower, its the drive. Note the voltage will probably be less than the motor nameplate at the lower speed. Be carful it’s dangerous voltage and I’ve had a few drives explode while testing one that was suspicious. PPE required !!
Dean, I think this is the best explanation thus far. I hadn't though about just loosing 1/2 of a phase. I was wondering how it could be running good at higher speeds. This makes perfect sense. I'll try and test it with the volt meter while running at 30hz and see what the voltage is.
I know exactly what's wrong. Something is broke.
Ha.. Yup.
imbalance? Bearings? ...... or yea you might take your DMM and look at each leg of the magnet wire
Bearings sounded fine.. runs good at speed, so, It's not that. It's the VFD dropping or a leg or something, or maybe something wrong with one of the coils. But, I ohmed them out and they all matched.
If the motor runs on the correct 3 phase voltage and you can vary the torque with some restraining method then it's probably the inverter. You should use a scope which is digital and view each phase for possible problem while varying the torque. More than likely will need to R/R inverter. Probably not a bad idea to have a spare which works on hand. Good luck! Enjoyed watching.
I'm pretty sure at this point that it's the VFD. I'm not really wanting to do a component repair on it. It's a real low end unit. The one I installed on the Bridgeport was a low end, but had more options and better documentation. I'm thinking I'll pick up another one. If we where a production shop, then yea, having a spare on hand would be good.. but since this is just a Maker Space, I don't think it's a big deal.
@@KnoxMachining I wish you could send it to me. I will gladly repair a VFD and put some oomph in my bandsaw.