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#170712 - 11/09/07 04:20 PM wrong way Transformer  
MMK  Offline
Member
Joined: Nov 2007
Posts: 20
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.


Work Gear for Electricians and the Trades

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


Member
Joined: Dec 2000
Posts: 4,262
Fullerton, CA USA
Sure it will. smile

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


#170714 - 11/09/07 07:42 PM Re: wrong way Transformer [Re: electure]  
JValdes  Offline
Member
Joined: Jun 2007
Posts: 301
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.


#170715 - 11/09/07 08:30 PM Re: wrong way Transformer [Re: JValdes]  
electure  Offline


Member
Joined: Dec 2000
Posts: 4,262
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.




#170734 - 11/10/07 12:16 PM Re: wrong way Transformer [Re: electure]  
gfretwell  Offline


Member
Joined: Jul 2004
Posts: 9,123
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

#170736 - 11/10/07 12:51 PM Re: wrong way Transformer [Re: gfretwell]  
JValdes  Offline
Member
Joined: Jun 2007
Posts: 301
South Carolina
electure....Thanks for the clarification. I should have counted the nuetral as a CCC.....John


#170739 - 11/10/07 03:16 PM Re: wrong way Transformer [Re: MMK]  
Redsy  Offline
Member
Joined: Mar 2001
Posts: 2,056
Bucks County PA
Wouldn't you need to ground one of the secondary (230-volt)conductors?


#170741 - 11/10/07 04:57 PM Re: wrong way Transformer [Re: Redsy]  
Alan Nadon  Offline
Member
Joined: Mar 2005
Posts: 399
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.

#170748 - 11/10/07 06:24 PM Re: wrong way Transformer [Re: MMK]  
Redsy  Offline
Member
Joined: Mar 2001
Posts: 2,056
Bucks County PA
You would be permitted to ground one of the conductors.
Would it be advisable to ground one or not?
Opinions, please?


#170749 - 11/10/07 06:54 PM Re: wrong way Transformer [Re: Redsy]  
gfretwell  Offline


Member
Joined: Jul 2004
Posts: 9,123
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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