control and balance

[ILCML]

I have a 3 hp @ 208/230v 3P nameplate motor with a control circuit with various items in it.
For much of the control circuit, 120v is needed, so he (the previous eng.)was using one leg of the 3 phase to neutral. However, after some investigation, the control circuit is consuming nearly the current of the motor. So, I thought I'd balance the load out as best I could. My problem now, is that there is no way to determine whether the customer will have a 3phase/neutral wye supply or one with a high delta leg. I need to make it so that either is acceptable.....without using another transformer or anything remotely costly or realestate greedy. Any suggestions? I am unable to tell the customer beforehand that he should use a supply with a WYE configuration.....

 

[itsmoked]

Can you just use an omnivorous switcher instead of any transformers? They take in like 90-250V and output your control voltage. Then you can avoid caring about how the customer power is supplied.

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[ILCML]

I'm not familiar with those....got a link?

 

[Skogsgurra]

May be a problem if it is AC 120 you need.

Gunnar Englund

http://www.gke.org

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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

 

[ILCML]

It is.

 

[ccjersey]

That's a robust control circuit! How can it consume close to the same amperage as the 3 hp motor?

What about making the control/auxillary circuits all line-line loads and balance it across the 3 phases as much as possible. If that's not possible, leave it all on one leg, mark that clearly and document it in all literature for the installer.

 

[HCBFlash]

Wye is not necessary. A leg with 120v potential to the grounded conductor (neutral) is all. Open delta used to be commonplace, and had 2 legs on a centertapped winding, with the tap grounded. Not that those details matter.

Everything has its cost. Specifying a neutral and the voltage of L1 to neutral is not problematic. The fact that a 3phase power source of 208 - 230 VAC 60Hz is required and specified better not be a problem!

Wye is easier for (some) people to deal with when it comes to single phase loads. It is not better than wye for 3-phase loads, and not necessarily better than wye for single phase loads either.

It sounds as though you fully realize that bringing in a separate neutral conductor and not using a control xfmr is,,, well,,, kinda cheesy. I did it too a time or two, before I knew any better. At least use a control circuit fuse (or circuit breaker).

Please let us all know how this works out for you! and don't forget faq731-376