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VFD voltage

ivak245

Jun 11, 2021
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Jun 11, 2021
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I have a VFD driving a 3 phase motor (220V). The setup works fine, but I decided I need to run a small 24volt transformer to operate the switchgear. I thought I may be able to connect the primary of the transformer across 1 phase of the VFD output, but when measuring the AC voltage across 1 phase (delta connection), it was all over the place, going up to 1000VAC and going down to 200volts, not stable at all (Digital multimeter). Thinking it was something to do with the waveform that the VFD outputs, I connected the primary across one phase anyway, and then measured the output. This was around 65 volts, too high for me, so I disconnected it. The VFD output is fixed at supply frequency, i.e. 50 Hz. Is this wild voltage swing I am measuring across any 1 phase because the VFD puts out a not-so-sine wave?
 

Tha fios agaibh

Aug 11, 2014
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Aug 11, 2014
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2,241
Yes, the VFD output is a pulsing waveform that digitally simulates a sine wave.
Even if it worked, I wouldn't chance hooking it up like that.
See if the drive has an auxiliary output that you can use to connect your controls.
 

Minder

Apr 24, 2015
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Apr 24, 2015
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You are also potentially damaging your VFD by placing odd loads on it.
It is not designed for that.
 

ivak245

Jun 11, 2021
59
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Jun 11, 2021
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Why not put it on the input side?
Physical distance. The VFD is driving an overhead hoist, and the original transformer is mounted in the hoist itself, and was originally a 2 X 220v primary unit, connected to 1 phase of a 440 volt 3phase supply. I ended up running a separate 230V single phase supply to the transformer. The VFD is mounted on the wall so I can control the speed .
 

Bluejets

Oct 5, 2014
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I ended up running a separate 230V single phase supply to the transformer.
So where is the 24v transformer now?
Your reasoning doesn't make any sense.
If the vfd is on the wall with a mains supply , put the 24v transformer there.
 
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