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IndustryArena Forum > CNC Electronics > Phase Converters > Need help! Balance voltage rotary converter motor 7.5 hp
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  1. #61

    Re: Need help! Balance voltage rotary converter motor 7.5 hp

    After I start the 10 hp
    T-T3 = 230
    T1-T2 = 233
    T2-T3 = 252 volts


    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.
    Jim Dawson
    Sandy, Oregon, USA

  2. #62
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    Re: Need help! Balance voltage rotary converter motor 7.5 hp

    Quote Originally Posted by Jim Dawson View Post
    [COLOR=#000000]

    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.
    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?

  3. #63

    Re: Need help! Balance voltage rotary converter motor 7.5 hp

    Quote Originally Posted by jfroux_1 View Post
    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?
    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.
    Jim Dawson
    Sandy, Oregon, USA

  4. #64
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    Re: Need help! Balance voltage rotary converter motor 7.5 hp

    Quote Originally Posted by Jim Dawson View Post
    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.
    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.

  5. #65

    Re: Need help! Balance voltage rotary converter motor 7.5 hp

    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.
    Jim Dawson
    Sandy, Oregon, USA

  6. #66
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    Re: Need help! Balance voltage rotary converter motor 7.5 hp

    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.

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