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3 phase converter help


Sep 28, 2022
Hello All,

I’m having issues setting up a 3 phase converter. I have a 20 hp motor I’m using for the idler. I bought a converter self wire kit off eBay that came with schematics. Got everything wired up to my 220 panel and the idler came on and ran fine. Tried to turn on a machine to test it and it wouldn’t start, the motor just hums. It was late so I called it a day. The next morning I had a thought that the motor was wired for 440 not 220. Well it was, I rewired for 220 and now when I power the converter on it only gets up to about half speed. When it was wired for 440 I caked the output and T1 to ground was right around 120, T2 to ground was 120 as well. T3 to ground was reading 440v. Checked the incoming and L1 to ground was 120 L2 the same. L3 which has nothing connected is reading 440. I’m at a loss. Any info or help is greatly appreciated. Thanks


Jan 31, 2011
BFE Nevada/San Marcos Tx
My thoughts, #1 double or triple check your wiring, #2 call person/co that sold you the kit, #3 give us a link to what you bought. The generated leg usually runs a little high, especially unloaded, throw a load on it and see where voltage goes, 440v sounds too high, but I'm no expert.


Oct 29, 2017
Assuming it is a capacitor start phase converter, it uses the third leg for starting. Sounds like that leg is still wired for 440 which prevents it from getting up to full speed and causes it to generate way too much voltage.

BT Fabrication

Nov 3, 2019
Ontario Canada
everyone has no idea what you are even working on exactly. could be good, could be complete junk. thats why you spend the $500 and get one pre made by someone knowing what exactly it needs.


Cast Iron
May 25, 2020
Rural S.W. Indiana
When it was wired for 440 I caked the output and T1 to ground was right around 120, T2 to ground was 120 as well. T3 to ground was reading 440v.
It sounds like the idler, while wired for 440V, indeed generated 440V, and caused problems (destroyed) other components in the RPC or other equipment that was connected to it. Beyond that, it is very difficult to say without schematics and some testing with a voltmeter.

This would be better posted in the VFD/RPC/Transformer board of this forum.
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Jun 16, 2001
St Louis
Don't measure to ground. Measure from line-to-line. That is the voltage you want.

The idler, even if wired for 440, would not have generated 440, it would have generated something similar to what is coming in. Only if the incoming lines were connected for 230V, but the "generated leg" was still wired 440 would it have produced a higher voltage output by itself.

However, it is quite possible to produce a high voltage if there are "balance" capacitors connected to the generated leg output. Try first disconnecting those,Check the resulting voltages.

The low speed may be due to the start capacitor being still connected when it should have been disconnected. There are other possible causes also.

Some kits use standard electrolytic start capacitors, which have black plastic cases. Those would not tolerate a failure to disconnect for very long.

Others use the same metal cased "run" type capacitors for both the start and balance capacitors. Those will stand staying connected (but may fail if the voltage is too high). If that is what you have, it can be difficult to determine which set is for "start" and which for "balancing". The "start" set will have a larger total capacitance (sum of the ratings of the individual capacitors) than the balance set.

If you can identify the start capacitors, and determine if they are being disconnected, that may help. They should be connected to a contactor (relay) so that they can be disconnected after starting.

A good close-up picture of the innards of your unit would help determine what you are dealing with.
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