Tapping a Fadal transformer for RPC

[Hobby Shop]

Hi guys. I added a late 1900’s Fadal VMC15 to the shop and I have a couple questions about the transformer taps and RPC.

The service manual says the Fadal should get 190-240v max.
My incoming voltage is 242v and my RPC manufactured leg is 236v unloaded. When I turn on the P&W lathe with a 7.5hp motor, my RPC voltage drops to 215v. The voltage at the lathe is consistent at 215v idling or with the spindle turning at 800rpm. I haven’t checked the voltage drop while making a cut yet.


The Fadal transformer has the ability to tap all three incoming lines for multiple voltages.

1) Should I turn the lathe on when running the Fadal and tap the transformer for 215V?
2) Should I tap L1& L3 for 240v and tap L2 (manufactured leg) for 230v and leave the lathe off?

200amp single phase service
20hp RPC on 100amp breaker.

Thanks,
Andy

 

[BT Fabrication]

id be saying one of your generated leg caps area dead..... more you add, the higher the gen leg makes, but that pulls down the other legs much lower. keep within 5% of each other if possible.

 

[Red James]

It is important to measure your voltages LEG-TO-LEG, not to ground!

 

[Hobby Shop]

id be saying one of your generated leg caps area dead..... more you add, the higher the gen leg makes, but that pulls down the other legs much lower. keep within 5% of each other if possible.

Sorry about that, Its been a few days since I checked the thread. What makes you think one of the caps is dead, the voltage drops to low? I’ll double check everything in the morning.

When I run a motor 7.5hp and under, the manufactured leg is 215v or higher but never above 236v. If all is good, do you think I should install an additional cap? How can you balance within 5% with a range of motors between 1-15hp?

Thanks,
Andy

 

[Hobby Shop]

It is important to measure your voltages LEG-TO-LEG, not to ground!

Sorry for the delay. If I don’t check the wild leg to ground, how do I know what the actual voltage is doing? Does everything balance out after it gets to the motor? My biggest concern is sending to much voltage to the computer and drives.

Thanks,
Andy