Need help! Balance voltage rotary converter motor 7.5 hp

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After I start the 10 hp

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T-T3 = 230
T1-T2 = 233
T2-T3 = 252 volts

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That seems about right when idling unloaded. Adding the load should bring it in pretty close.

It really looks like your line voltage is sagging quite a bit when running, 243 down to 233. I would expect more like a 2 or 3 volt drop, that would indicate that the wiring is too small.

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Originally Posted by Jim Dawson

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That seems about right when idling unloaded. Adding the load should bring it in pretty close.

It really looks like your line voltage is sagging quite a bit when running, 243 down to 233. I would expect more like a 2 or 3 volt drop, that would indicate that the wiring is too small.

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I just notice that the incoming voltage varies between 233 to 245 here.
I’m having a hard time trying to balance the voltage in load. There is one thing for sure, the extra 74 uf I added on the capacitor starter makes a big difference. The 10 hp has no problem to start and the breaker does not open at all.
I’m lost a bit with the voltage balance.
Before I start the 10 hp, L1-L2 is 240 volts
After I start the 10 hp, T1-T2 is 238, T1-T3 248 and T2-T3 262 volts.
Where should I add or remove capacitors?

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Originally Posted by jfroux_1

Before I start the 10 hp, L1-L2 is 240 volts
After I start the 10 hp, T1-T2 is 238, T1-T3 248 and T2-T3 262 volts.
Where should I had or remove capacitors?

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I'm not exactly sure. But more importantly, what do the voltages look like with a load on it? You will always have a high leg when running unloaded. I think my high leg is about 10V above L1-L2 with no load, but loaded all are very close to L1-L2 +/- 2 volts.

Also what is the L1-L2 voltage when running?

EDIT: Try this, pull the belt off of the 5 HP compressor motor and start it with the RPC, then see what the voltages are.

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Originally Posted by Jim Dawson

I'm not exactly sure. But more importantly, what do the voltages look like with a load on it? You will always have a high leg when running unloaded. I think my high leg is about 10V above L1-L2 with no load, but loaded all are very close to L1-L2 +/- 2 volts.

Also what is the L1-L2 voltage when running?

EDIT: Try this, pull the belt off of the 5 HP compressor motor and start it with the RPC, then see what the voltages are.

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Hi Jim, the number I put were with the 10 hp running the T30. I gave up on the 5 hp this morning. When I'll find a cheap smaller pulley I may try again just to see. But with the 74 uf I added on the starter capacitor the breaker doesn't open even when the air compressor works hard and the motor start and stop often.

I'd like to balance the voltage a bit more before I consider the project done. I'm just not sure where I should add or remove run capacitors.

You have to measure the voltages when the system has a load on it. With no load on the RPC, the numbers are meaningless. Try connecting the 5HP with the belts off. That way you are putting a load on the RPC, your voltages will be different when you do this and the should come close to what you want.

I gave up on the RP this morning and I put back the 10 hp with the smaller pulley and it drives my T30 with very good results since I increased the cp starter by 74 uf. The breaker doesn't open anymore even when it works hard. I also fix my 50 amp plug wires connection. Now before I start my air compressor the L1-L2 is 238 and after I start it, T1-T2 goes to 234, T1-T3 = 235 and T2-T3 = 245. I live with that voltage balance, the motor doesn't heat and the breaker doesn't open. Thanks for all your advice Jim.