Using caps to balance 440V RPC

I read a lot of write ups on using capacitors to balance the 3PH out of a
idler motor.
But, I can't find anything on using them with a 440V system.
Brief description of my set-up: (what I'm trying to run is a 5HP 440V lathe
motor 2 speed, reversible)
I have a 110V 1PH 1.5HP pony motor, belted to a 230V 3PH 7.5HP idler motor.
Feeding the idler motor with 220V 1PH on A & C leg, wild leg on B. A B & C
feed into a 440/208 auto transformer 'backwards' to boost the voltage.
I'm having a hell-uv-a time dialing in my 440V. I have multi taps on the
transformer, but try as I might. I just can't get 3 legs of 440. I can get
two, but as soon as I try to dial in the wild leg, (using the taps) one of
the other legs goes high or low.
Any help appreciated
Reply to
Milo
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How does voltage look on the 230v side?
i
Reply to
Ignoramus31514
All 3 legs are +/- 230V
Peace Milo
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Reply to
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.
Reply to
Proctologically Violated©®
There are no caps in the system at this time.
Peace Milo
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Reply to
Milo
Add two caps, one on legs 1-3 and one on 2-3, start with 140 uF.
Reply to
Ignoramus23604
Add them after the transformer?
Peace Milo
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Reply to
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.
i
Reply to
Ignoramus23604
Thanks for your help, I start looking for caps.
Peace Milo
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Reply to
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
Reply to
Joseph Gwinn
This is not professional, but should be helpful. I don't know if pics are allowed here. So here is a link.
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Peace Milo
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Reply to
Milo
Heh!! an unconventional way of drawing it but perfectly clear.
With the pony motor you don't need to worry about starting. Just put a run cap from each 220 leg to the wild leg. Iggy had some values for the caps, good place to start.
Here's a good place to start for the necessary caps.
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Milo wrote:
Reply to
RoyJ
Thanks for the help. I'll post back here as soon as get some caps.
Peace Milo
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Reply to
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.
Reply to
Proctologically Violated©®
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.
Reply to
Milo
Should be A-C and B-C, assuming A and B are "line in" and C is the generated leg.
Could you clarify.
i
Reply to
Ignoramus23604
Sorry my typo. The caps are hooked A-C & B-C
Peace Milo
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Reply to
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.
i
Reply to
Ignoramus23604
Ask and or ; both noted surplus outlets.
Reply to
David Lesher
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.
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Now the voltage reading with idler running, not hooked to transformer:
Leg 1 = 256V
Leg 2 = 241V
Leg 3 = 268V
Peace Milo
Reply to
Milo

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