How to get 41amps from RPC

[Danny Barber]

I bought a transformer to run my 440v lathe. The transformer is Sola Hevi Duty, 15kva. http://www.clrwtr.com/PDF/Sola-Hevi-...ansformers.pdf Thats what the tech suggested. Now I need to come up with 41 amps from my RPC to run the transformer. My current RPC is a 3hp, 3ph motor powered by 220 1ph. It only puts out about 8amps. I'm sure I can come up with a bigger motor for the RPC but I don't know what size to get. Is there a way to up the amps whithout changing RPC motor size.

Any help here would be appreciated.

[David L Morse]

The kVA rating of the transformer is the maximum you can pass through it to the load. With no load the transformer will draw only a small fraction of that. The kVA usage of the lathe will determine how much current your RPC needs to supply.

So, for example, if you have a 5HP 480V motor on the high voltage side then the load on the 240V side of the transformer looks just like a 5HP 240V motor plus some small power loss in the transformer.

Also, where did you get the 41A number? 15kVA at 240V is 36A.

[Jason Roehl]

What is the HP rating of your lathe (or the Full Load Amps--FLA--at the rated voltages)? That's your only real concern. If your lathe is 2HP or less, your RPC is probably sufficient. You only need a little more HP in your RPC than the rating of your lathe to account for the heat losses in the RPC and the transformer.

A transformer doesn't "run" per se, it steps an incoming voltage up (or down), with a proportionate loss (or gain) in amperage--it's a passive device. So a 15kVA transformer with a 208V input and 480V output will see approximately 72A max on the input, and output 31A max. But if you only have a 5HP/480V load on the output side (about 4000W), the input side will only draw about the same 4000W, which is about 19A at 208V.

What are the nameplate ratings on your RPC? (Volts, amps, HP, etc.)