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Runing a 3-Phase Motor VFD from Single Phase
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EHT:
Hi All,

I have a machine with a large 600W AC motor which contains its own variable frequency drive (VFD) which allows the motor to run at a range of speeds. It has a 3-phase input but I need to run it from single-phase. It seems to me that I can do this very simply and without an external converter. The VFD circuit rectifies the incoming line AC to DC and then has a digitally controlled variable frequency driver circuit which runs the motor from that. i.e. as simply depicted here.

The AC input goes into a PCB which is a set of filters (X caps, MOVs and a choke) which then go into a panel mounted bridge rectifier, from there into the main PCB (see pics). These particular models are usually sold as single-phase; mine is unusual. It is rated “200-440V AC 3 Phase”, allowing it to run in US or Europe. I’m in UK so 240V single phase (440V 3-phase if I had it). I suspect that the main PCB is the same between the single phase input and 3-phase input units, with the difference being the line filter and the bridge rectifier. I attach a picture of the filter PCB, the bridge and the main VFD PCB.

So, I think I can simply disconnect one of the 3 line inputs (or maybe tie two of the 3 together) and run it on single phase 240V AC. My thinking is that the bridge rectifier is rated for the higher current that would be needed for 3-phase in the USA and it will just rectify the single phase “as normal”.

I wonder:
-   Is that correct?
-   If so, does it matter if I leave the spare live input floating or connect two of the 3 together?
-   am I missing anything?


Thanks!
ogden:

--- Quote from: EHT on December 02, 2018, 08:12:16 pm ---It is rated “200-440V AC 3 Phase”

--- End quote ---

Modern 3-phase devices shall have phase fault detection so it either will not mind 1 phase and just work or (most likely) will not. Definitely not self-destruct.
Benta:
Connect all three phases together and run it from a single phase. No problem at all. You may need to use a thicker wire for neutral, but 600 W is not a lot.

langwadt:
the biggest issue with 3 vs. 1 phase is that 3 phase needs much less capacitance after the rectifier, if it was made for single phase that should taken care of
Benta:
@Langwadt: good point, I'd forgotten about that. Don't think it's an issue here, though.
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