# Vfd Voltage Problem. Chinese 'askpower A131'



## oldplanecollector (Jul 4, 2016)

Askpower VFD looks like a chinese knockoff of a chinese huanyang VFD from the outside but the setup parameters are different so any info I found on the Huanyang doesn't help. I think unit may be defective but wanted to ask here in case I'm missing something. There aren't that many variables that can be changed on these units so it SHOULD be pretty straight forward.

Unit is a 2.2kw 240v single phase in to 240 3 phase out.   Verified 240v single phase input, but I'm not getting the 240 3 phase output. At 60hz output on VFD I'm only getting 20v between any pair of 3 phase outputs. I played with max frequency setting and remeasured output voltage. 
40hz=10 volts
60hz=20 volts
120hz=53 volts
240hz=117 volts
400hz=190 volts

I have: Pn02 (initial startup freq) set to 60hz; Pn10 (max runtime freq) set to 60hz; Pn11 (min runtime freq) set to 1.5hz; Pn12 (motor rating) set to 60hz

When max runtime frequency is set to 60hz, I know voltage goes down when frequency is decreased, but when run at the max setting (60hz) I should be seeing 240v.
Anyone have experience with these units and think it sounds like I have something setup wrong. Or does it sound more like a defective unit?


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## mksj (Jul 4, 2016)

You cannot usually measure the VFD AC output voltage using a standard AC voltmeter because the signal is chopped into little DC segments that approximates a sign wave (PWM). If you try to us a standard AC voltmeter the voltage read will also drop off as the frequency is increased. So the AC voltage reading is not reliable, either low or high. There are specific voltmeters and scopes that can be used to look at the VFD output, but the best thing at this point is to connect a 3 phase motor and see if it works.
http://www.fluke.com/fluke/uses/com...motors-drives-pumps-compressors/measuringasds


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## JimDawson (Jul 4, 2016)

Try setting Pn10 to 60, and set the base frequency (Pn12) 60.

Also is the max output current set to the motor nameplate amps?


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## oldplanecollector (Jul 4, 2016)

JimDawson said:


> Try setting Pn10 to 60, and set the base frequency (Pn12) 60.
> 
> Also is the max output current set to the motor nameplate amps?


I already set Pn10 & 12 to 60 hz. No settings for output amps or voltage.


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## JimDawson (Jul 4, 2016)

Maybe this will help

https://en.industryarena.com/forum/vfd-askpower-a131nbc-2022-setup--300736.html


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## oldplanecollector (Jul 4, 2016)

mksj said:


> You cannot usually measure the VFD AC output voltage using a standard AC voltmeter because the signal is chopped into little DC segments that approximates a sign wave (PWM). If you try to us a standard AC voltmeter the voltage read will also drop off as the frequency is increased. So the AC voltage reading is not reliable, either low or high. There are specific voltmeters and scopes that can be used to look at the VFD output, but the best thing at this point is to connect a 3 phase motor and see if it works.
> http://www.fluke.com/fluke/uses/com...motors-drives-pumps-compressors/measuringasds



I was hesitant to hook up the motor if I thought something may not be right for fear of damaging motor.  I had seen that page from Fluke before that you referenced and it confused me because I also have a Leeson (Ac Tech) VFD on my mill and I used a standard meter and measured 240v at 60 hz. The voltage on that unit goes down with lowering frequency.


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## JimDawson (Jul 4, 2016)

The VFD will get really confused if it's not connected to a motor.  I think you're safe connecting it.


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## oldplanecollector (Jul 4, 2016)

JimDawson said:


> The VFD will get really confused if it's not connected to a motor.  I think you're safe connecting it.



yea, I appreciate everyones input, I guess that's what I'll do tomorrow and give it a try. The motor on my surface grinder was modified by the previous owner to replace the original and I was hesitant in case of damage since it would not be an easy replacement.  I understand the reasoning for why a regular DMM won't accurtately measure the voltage from a VFD but I got it in my head that since my Leeson drive seems to show 240 volts this drive should be the same.  I'll plug her in tomorrow and hope for the best.


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## strantor (Jul 5, 2016)

Your problem is likely a combination of the two problems mentioned:


mksj said:


> You cannot usually measure the VFD AC output voltage using a standard AC voltmeter because the signal is chopped into little DC segments that approximates a sign wave (PWM).





JimDawson said:


> The VFD will get really confused if it's not connected to a motor.  I think you're safe connecting it.



Most VFDs take readings of the motor current (and some VFDs take many more readings than just current) while in operation to regulate output voltage. With no motor connected and no current feedback, the VFD will "get really confused" and the output will be something between garbage and white noise. Your DMM has enough trouble trying to measure PWM'd AC, and add to that measuring garbage PWM'd AC, it's not happening. 


FWIW the better instrument for measuring VFD output voltage is an old school analog (needle movement) voltmeter like a Simpson:


Although there are some DMMs made to measure VFD output with an internal low pass filter like the Fluke 289 or 87V.


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## oldplanecollector (Jul 6, 2016)

Just to update and close out this string, all is working.  Hooked up the surface grinder and it fired up and all is well.


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