VFD Issue

[sdmuleman]

Trying to get a cheap chinese POS VFD to work on my bridgeport - the VFD is new and I just installed it an wired it in but I'm getting strange results. The VFD seems to think it's working properly and does not show any error codes but I'm only getting ~5 VAC between each of the output legs. I have ~140 VAC between each leg and ground. The VFD is a 2.2 KW 'HY' unit, running off 220 single phase. Mill is a BP series 1 2HP. I have measured the VFD output with the motor connected and disconnected and get the same result. The motor turns freely and was working when I tested it with a rotary phase converter, though this was before putting the head back together and not using the current wiring so there's slim chance there's something wrong there.

Thoughts? My guess is something wrong with the VFD, but I want to make sure it's not something I messed up first.

Thanks,
~John

 

[JimDawson]

Check your setup in the VFD parameters. Make sure the max output current matches the motor data plate current. Normally these are set a bit low from the factory. It sounds like the VFD is current limiting.

 

[sdmuleman]

Would it still do this with the motor disconnected though? I get the same results with the motor connect or not - same voltage phase to phase and phase to ground. That's the part that gets me - if there was a motor or wiring issue I would expect to see different results with the motor disconnected.

The motor voltage and current parameters match the motor.

 

[JimDawson]

Would it still do this with the motor disconnected though? I get the same results with the motor connect or not - same voltage phase to phase and phase to ground. That's the part that gets me - if there was a motor or wiring issue I would expect to see different results with the motor disconnected.

The motor voltage and current parameters match the motor.

VFDs don't like to be disconnected from the motor. I don't know what you would see in that condition. But I am surprised that you get that much voltage leg to ground, on the other hand, I have never checked one that way.

Another thing to check is that the max speed isn't set for 1Hz or something. Normally the VFDs I get are set for 10 or 20 Hz from the factory with a long acceleration ramp set.

This one is a bit puzzling, if all of the parameters are set correctly, then I would say that you may have gotten a bad unit, assuming the motor is correctly wired. Pretty hard to fowl that one up, you only have 3 wires to worry about. Since the motor was running before the change, I think that pretty much eliminates that as a problem.

Unless you are measuring the voltages with a good, true RMS meter (like a Fluke 87-V), you may not be reading the voltage correctly. The wave form coming out of the VFD is pretty strange. It really takes a good meter, that is designed for industrial electronics to read a VFD output.

At this point I would go back through the parameter setting again.

 

[sdmuleman]

It could very well be the meter, it's certainly not a good quality meter... though it does give me an accurate reading on the 220V input.

I have it set for 50 Hz currently - seemed like a good starting point.

I've got another motor I'll try hooking up to it, and try running the spindle motor with a RFC to make sure that part works.

 

[John Hasler]

VFDs don't like to be disconnected from the motor. I don't know what you would see in that condition. But I am surprised that you get that much voltage leg to ground, on the other hand, I have never checked one that way.

Another thing to check is that the max speed isn't set for 1Hz or something. Normally the VFDs I get are set for 10 or 20 Hz from the factory with a long acceleration ramp set.

This one is a bit puzzling, if all of the parameters are set correctly, then I would say that you may have gotten a bad unit, assuming the motor is correctly wired. Pretty hard to fowl that one up, you only have 3 wires to worry about. Since the motor was running before the change, I think that pretty much eliminates that as a problem.

Unless you are measuring the voltages with a good, true RMS meter (like a Fluke 87-V), you may not be reading the voltage correctly. The wave form coming out of the VFD is pretty strange. It really takes a good meter, that is designed for industrial electronics to read a VFD output.

At this point I would go back through the parameter setting again.

That's the voltage I would expect to see phase to neutral if the VFD was putting out 240 phase to phase. While there is no external neutral in this circuit I would expec that the virtual one would be close to ground. It's hard to see how you get 140 phase to ground on all phases and yet little or no phase to phase voltage, though. While a cheapie meter might not give the correct RMS voltage for the VFD output I would expect it to be within 20% or so.

[Edit] Check for DC on the VFD outputs.

 

[JimDawson]

That's the voltage I would expect to see phase to neutral if the VFD was putting out 240 phase to phase. While there is no external neutral in this circuit I would expec that the virtual one would be close to ground. It's hard to see how you get 140 phase to ground on all phases and yet little or no phase to phase voltage, though. While a cheapie meter might not give the correct RMS voltage for the VFD output I would expect it to be within 20% or so.

[Edit] Check for DC on the VFD outputs.

I just checked the voltages on my mill, I'm getting 155.2VAC leg to ground and at 6Hz 111.3VAC leg to leg, at 50Hz I'm getting 244.5VAC leg to leg, measured with a Fluke 87-V. At least this gives you a target.

 

[sdmuleman]

Found it. Base frequency was set to 400 instead of 60. That, and my meter is a cheap POS.... Now I just have to figure out why the head I just put back together rattles....

 

[JimDawson]

Found it. Base frequency was set to 400 instead of 60. That, and my meter is a cheap POS.... Now I just have to figure out why the head I just put back together rattles....

Happy you found it. And the head thing really sucks.

Best of luck.