Using caps to balance 440V RPC

How does voltage look on the 230v side?

All 3 legs are +/- 230V

Peace Milo

So you're saying you have the rpc balanced with caps, before you add the transformers?

What values have you used?

Also, I don't know that you need a pony motor, as I think you need caps from A to B *and* from B to C. To start the idler, just disconnect the B to C caps, start the idler with A to B caps, and then switch in B to C caps.

But, either way, if you have the rpc balanced before adding the transformer, mebbe just experiment with add'l caps after adding the transformer -- with the same taps for all three phases.

There are no caps in the system at this time.

Peace Milo

Add two caps, one on legs 1-3 and one on 2-3, start with 140 uF.

Add them after the transformer?

Peace Milo

Add them onto the motor, before transformer.

My phase converter has this configuration, capacitors on each leg, and it works well, both under load as well as without. I redid my math, and in proportion to your idler's HP, you would need 80 uF, if you were to use the same uF per HP as I do.

Thanks for your help, I start looking for caps.

Peace Milo

If I understand the description, the autotransformer is three phase. If so, one can the treat autotransformer and motor as a unit, and apply the balancing capacitors to the idler motor as if it were connected to a 220 volt 3 phase motor. Varying the taps on the autotransformer doesn't sound right.

A wiring diagram would be useful.

Joe Gwinn

This is not professional, but should be helpful. I don't know if pics are allowed here. So here is a link.

Heh!! an unconventional way of drawing it but perfectly clear.

With the p>> >>

Thanks for the help. I'll post back here as soon as get some caps.

Peace Milo

Not a bad site, but not super bargains.

Graingers actually has better prices and a better selection, in their "closeouts" -- which appear at the end of a selected category, which could be after quite a few pages. I got quite a supply of caps for a bit cheaper from them. Their regular prices are of course not so good.

Funny that a dyed-in-the-wool traditional non-discount supplier like Graingers can beat so-called "surplus houses" on the internet, when they want to. Of course, they don't often want to, but it sez lots about these surplus places -- they have our informational number, dats f'sure.

OK, here are the results of connecting 104uF caps between legs A-B & B-C on the output of the idler motor.

At the motor A-C = 238V A-B = 255V B-C = 218V (B is the 'wild" leg

At the transformer output H-1-H-2 = 493V H-1-H-3 = 501V H-2-H-3 = 517V The taps on the transformer are set as low as they go.

Should be A-C and B-C, assuming A and B are "line in" and C is the generated leg.

Could you clarify.

Sorry my typo. The caps are hooked A-C & B-C

Peace Milo

The voltages that you posted, are suggestive that you were correct in stating how you connected the caps (improperly). Try to connect them properly and see if voltages normalize.

Try without the transformer connected, first.

Ask and or ; both noted surplus outlets.

Ok here are the connections and readings before the transformer:

Idler motor 9 leads, leg 1 = 3&9, leg 2 = 2&8, leg 3 = 1&7 leads 4*5*6 joined.

Now the caps (they were wired correctly, however I should add that the caps consist of 4- 26uF caps in parallel). So leg1 to cap,(and wire to transformer) cap to leg 2. leg 3 to other cap,(and wire to transformer) cap to leg 2. Sorry I can't explain in proper terms. I will add to my drawing and post a link.

Leg 1 = 256V

Leg 2 = 241V

Leg 3 = 268V

Peace Milo