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#170712 - 11/09/07 12:20 PM wrong way Transformer
MMK Offline
Member

Registered: 11/02/07
Posts: 20
Loc: Ireland
Has anyone any ideas on using a Transformer (1kVA) the wrong way round. The transformer has a 230VAC primary and a 110VAC secondary. Would it be OK to use the secondary as the input(110VAC) and put the load on the primary - a 230VAC motor. Only need about 250Watts.
Will it work?
Michael.

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#170713 - 11/09/07 03:10 PM Re: wrong way Transformer [Re: MMK]
electure Offline

Member

Registered: 12/24/00
Posts: 4225
Loc: Fullerton, CA USA
Sure it will. \:\)

The secondary just becomes the primary, and the primary the secondary.

I'm not sure about the overcurrent protection required in your part of the World, but it will work properly

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#170714 - 11/09/07 03:42 PM Re: wrong way Transformer [Re: electure]
JValdes Offline
Member

Registered: 06/03/07
Posts: 308
Loc: South Carolina
Normally I would say yes, if it were 240/480 volt. But I am not sure with 120 volt. You only have one CCC and a neutral. But I think you are okay. Protect XFMR on line side as current is less.
I have never back fed a 120/240 volt XFMR, so I am not sure about the neutral.

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#170715 - 11/09/07 04:30 PM Re: wrong way Transformer [Re: JValdes]
electure Offline

Member

Registered: 12/24/00
Posts: 4225
Loc: Fullerton, CA USA
J Valdez:
At "110" Volts you will have 2 current carrying conductors...both the ungrounded conductor and the grounded conductor are current carrying.

The current on the line side will be MORE than the current on the load side.
The OP never said this is a 120/240 transformer, rather a 230 to 110 transformer.



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#170734 - 11/10/07 08:16 AM Re: wrong way Transformer [Re: electure]
gfretwell Offline

Member

Registered: 07/20/04
Posts: 9012
Loc: Estero,Fl,usa
We used a "backward" transformer in our shop for many years. I had a 240v blower motor out of a tape drive we used for shop air on the 120v they supplied us using a convenience outlet transformer, usually providing 120 out of the 240 in the computer room.
_________________________
Greg Fretwell

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#170736 - 11/10/07 08:51 AM Re: wrong way Transformer [Re: gfretwell]
JValdes Offline
Member

Registered: 06/03/07
Posts: 308
Loc: South Carolina
electure....Thanks for the clarification. I should have counted the nuetral as a CCC.....John

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#170739 - 11/10/07 11:16 AM Re: wrong way Transformer [Re: MMK]
Redsy Offline
Member

Registered: 03/28/01
Posts: 2138
Loc: Bucks County PA
Wouldn't you need to ground one of the secondary (230-volt)conductors?

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#170741 - 11/10/07 12:57 PM Re: wrong way Transformer [Re: Redsy]
Alan Nadon Offline
Member

Registered: 03/10/05
Posts: 398
Loc: Elkhart, IN. USA
No. Use a seperate BONDING conductor to "ground" the secondary enclosure.
Note that the 120 primary will draw 2+ the amps of the secondary load.
Ohms Law.....Obey it. God doesn't give tickets.
_________________________
Alan--
If it was easy, anyone could do it.

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#170748 - 11/10/07 02:24 PM Re: wrong way Transformer [Re: MMK]
Redsy Offline
Member

Registered: 03/28/01
Posts: 2138
Loc: Bucks County PA
You would be permitted to ground one of the conductors.
Would it be advisable to ground one or not?
Opinions, please?

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#170749 - 11/10/07 02:54 PM Re: wrong way Transformer [Re: Redsy]
gfretwell Offline

Member

Registered: 07/20/04
Posts: 9012
Loc: Estero,Fl,usa
We discussed this before. If the transformer is part of the building wiring you need to ground the secondary, with few exceptions. If it is a cord and plug connected appliance you don't. (that was where I went wronmg the last time it was discussed) It is very common that a lab work bench supply is flaoting but this is a cord and plug cionnected appliance, not building wiring. We had the same situation with our compressor at the shop. The whole assembly was behind a 5-15 plug.
_________________________
Greg Fretwell

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