Do you know that a VFD can effect DC drives ?

D. Thomas · Jul 7, 2002

I was running a Hardinge lathe today, using a VFD as phase converter for the drive motor, but with the 90 volt DC feed motor drive wired direct to 115 Volt single phase input it required. The DC drive was acting really weird in that it would surge at random. This was most curious, as I tested the lathe extensively when I first bought it and the DC drive worked perfectly. I finally figured out that it didn't surge at all when just the DC was running and the VFD was turned off. So, the VFD was effecting the current for the whole shop somehow, as the 115 volt single phase input was on a seperate circuit. Any of you electrical folks got an explaination for this ?

Forrest Addy · Jul 8, 2002

N-n-n-nope! Try shilding the control leads of the DC drive. Next the motor leads from the VFD.

After that, punt

J Tiers · Jul 29, 2002

What Forrest said, but before punting, put in the input filtering that the VFD folks reccommend.
Or if you don't want to pay $300 for $50 worth of stuff, you can do your own with some "forrest" inductors with or without any capacitors.

Electronic surplus places often have line filters which are good for at least 240VAC, less often 3phase. But even three separate single wire ones may help. If you put it on the DC drive, it will be more effective for that unit alone.

I think the high frequency stuff was confusing the DC drive control sircuits. They are noisy to begin with, but the extra uncorrelated noise might do bad things, especially if you had a remote pot.

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Do you know that a VFD can effect DC drives ?

D. Thomas

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Forrest Addy

Diamond

J Tiers

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