Buck and Boost Transformers

[Mr. Technical]

Hello everyone,

I'd like to know if buck and boost transformers could be causing me to blow my X axis transistors (see my 'X axis transistor failed again' string) I have 2 Square D catalog # 500SV43F buck and boost transformers that may be pushing the voltage and currents too high mounted to the side of my BP Series I Boss 6. In the following link: http://stevenengineering.com/Tech_Su...Fs/45SPSAT.pdf mine are wired as shown in diagram 6. I think that table 9 of the linked document applies to my setup.

I think that they must have been necessary at one time, but in my shop may be causing problems. I have a Ronk Roto-Con Mark II RPC, (10 KVA, 10 total HP, FLA single phase of 53) with (2) 50 Mfd run caps wired in parallel. My output voltage from the RPC is as follows:
A-B=250 (A is the wild leg, not a line in)
A-C=228
B-C=244

Do I need these transformers??

On the output size of these buck and boost transrformers I have:
A-B=252 (again, A is the wild leg, not a line in)
A-C=275
B-C=270

Both sets of numbers are not under load. Would I hurt anything by bypassing both of these transformers, and going straight from the RPC to the contactor on the mill? Thanks for any and all help!!

Ian

[Al_The_Man]

It appears you are using it in the boost mode? and I would think you are using diagram 6, not 9.
The measured voltage input to the BB Txr seems to be is closer to your required voltage i.e. lower, then go direct from the primary (input) side. If it solves the problem, then disconnect the transformer completely.
Al.

[Mr. Technical]

Yes, diagram 6 refers to my setup. I'll remove the transformers and see what happens. Thanks!

Ian

[Mr. Technical]

Success!!

Cutting the transformers out of the system puts my voltages at the correct levels, and more importantly, does not blow transistors any more! Life is good.

Ian