# [EVDL] 240 volt relay at 120 volts



## EVDL List (Jul 27, 2007)

What would happen if a 240 volt relay saw 120 volts on it's coil? Would 
it just sit there for days? Overheat? Close intermittently?

The reason is I am wiring up a 240-208 buck transformer for my Prizm so 
I can charge on 240v (it gets upset at 240, it likes 208). However I 
also like to charge at 120v, and I would like it to cut out the 
transformer on 120 but not on 240.

I should be able to do this with a simple SPDT relay that would be wired 
across the input and if closed would open a short across the buck 
windings on the transformer. Thus if one sees 120 on the input the relay 
is open, and the transformer's buck is shorted. If it sees 240, the 
relay closes and the transformer comes into action.

Will this work?

Chris

_______________________________________________
| Moratorium on drag racing discussion is in effect.
| Please take those discussions elsewhere. Thanks.
|
| REPLYING: address your message to [email protected] only.
| Multiple-address or CCed messages may be rejected.
| UNSUBSCRIBE: http://www.evdl.org/help/index.html#usub
| OTHER HELP: http://evdl.org/help/
| CONFIGURE: http://lists.sjsu.edu/mailman/listinfo/ev


----------



## EVDL List (Jul 27, 2007)

Hello Chris,

If the primary of the transformer is a duel voltage input for 120/240 volts, 
it should have four leads mark 1,2,3 and 4. The 1 and 2 leads are one 120 
volt winding and the 3 and 4 is the other 120 volt winding.

240 volt input:

Connect one of the 240 power line to transformer lead 1
Connect the other 240 power line to transformer lead 4
The transformer leads 2 and 3 are connected to thus
connected both 120 volt windings in series.

120 volt input:



Using the full KVA rating of the transformer by paralleling
the two transformer 120 leads together:

Connect one of the 120 power lines to the transformer leads
1 and 3
Connect the other 120 neutral power line to the transformer
to leads 2 and 4.

This type of connections from 240 to 120 volts is normally done by a motor 
manual switch which you can get at some motor shops. They are a selector 
switch design for induction loads come in 2, 3 and 4 pole two or three 
position. You will need a 4 pole three position to do this switch over.

Some times these switches are also known as A/C switches or Drum Selector 
Switches. These type of switches have double spacing between the contactors 
which have a Make-Break-Break-Make contact mechanism instead of a simple 
Make-Make type.

Do not use a relay on this circuit. Relays are only use for control 
circuits, not power circuits. Contactors are use for power circuits.
You would need something like a four pole reversing contactor for this 
circuit.

My old battery charger had this type of transformer which I can either 
select 120-208-240 volts with a GE Switchboard type of switch that had 
multiple contacts.

Roland











----- Original Message ----- 
From: "Chris Zach" <[email protected]>
To: <[email protected]>
Sent: Saturday, August 13, 2011 3:36 PM
Subject: [EVDL] 240 volt relay at 120 volts


> What would happen if a 240 volt relay saw 120 volts on it's coil? Would
> it just sit there for days? Overheat? Close intermittently?
>
> The reason is I am wiring up a 240-208 buck transformer for my Prizm so
> I can charge on 240v (it gets upset at 240, it likes 208). However I
> also like to charge at 120v, and I would like it to cut out the
> transformer on 120 but not on 240.
>
> I should be able to do this with a simple SPDT relay that would be wired
> across the input and if closed would open a short across the buck
> windings on the transformer. Thus if one sees 120 on the input the relay
> is open, and the transformer's buck is shorted. If it sees 240, the
> relay closes and the transformer comes into action.
>
> Will this work?
>
> Chris
>
> _______________________________________________
> | Moratorium on drag racing discussion is in effect.
> | Please take those discussions elsewhere. Thanks.
> |
> | REPLYING: address your message to [email protected] only.
> | Multiple-address or CCed messages may be rejected.
> | UNSUBSCRIBE: http://www.evdl.org/help/index.html#usub
> | OTHER HELP: http://evdl.org/help/
> | CONFIGURE: http://lists.sjsu.edu/mailman/listinfo/ev
> 

_______________________________________________
| Moratorium on drag racing discussion is in effect.
| Please take those discussions elsewhere. Thanks.
|
| REPLYING: address your message to [email protected] only.
| Multiple-address or CCed messages may be rejected.
| UNSUBSCRIBE: http://www.evdl.org/help/index.html#usub
| OTHER HELP: http://evdl.org/help/
| CONFIGURE: http://lists.sjsu.edu/mailman/listinfo/ev


----------



## EVDL List (Jul 27, 2007)

If you are switching between 120 and 240V anyway
then you can also see if you can set it up to
change the voltage reduction at 240 (to 208V)
into a voltage boost at 120V (to 136 or 152V
depending if the trafo has a 120V tap to
maintain the 32V secondary) 


Cor van de Water
Chief Scientist
Proxim Wireless Corporation http://www.proxim.com
Email: [email protected] Private: http://www.cvandewater.com
Skype: cor_van_de_water XoIP: +31877841130
Tel: +1 408 383 7626 Tel: +91 (040)23117400 x203 

-----Original Message-----
From: [email protected] [mailto:[email protected]] On
Behalf Of Chris Zach
Sent: Saturday, August 13, 2011 2:36 PM
To: [email protected]
Subject: [EVDL] 240 volt relay at 120 volts

What would happen if a 240 volt relay saw 120 volts on it's coil? Would
it just sit there for days? Overheat? Close intermittently?

The reason is I am wiring up a 240-208 buck transformer for my Prizm so
I can charge on 240v (it gets upset at 240, it likes 208). However I
also like to charge at 120v, and I would like it to cut out the
transformer on 120 but not on 240.

I should be able to do this with a simple SPDT relay that would be wired
across the input and if closed would open a short across the buck
windings on the transformer. Thus if one sees 120 on the input the relay
is open, and the transformer's buck is shorted. If it sees 240, the
relay closes and the transformer comes into action.

Will this work?

Chris

_______________________________________________
| Moratorium on drag racing discussion is in effect.
| Please take those discussions elsewhere. Thanks.
|
| REPLYING: address your message to [email protected] only.
| Multiple-address or CCed messages may be rejected.
| UNSUBSCRIBE: http://www.evdl.org/help/index.html#usub
| OTHER HELP: http://evdl.org/help/
| CONFIGURE: http://lists.sjsu.edu/mailman/listinfo/ev

_______________________________________________
| Moratorium on drag racing discussion is in effect.
| Please take those discussions elsewhere. Thanks.
|
| REPLYING: address your message to [email protected] only.
| Multiple-address or CCed messages may be rejected.
| UNSUBSCRIBE: http://www.evdl.org/help/index.html#usub
| OTHER HELP: http://evdl.org/help/
| CONFIGURE: http://lists.sjsu.edu/mailman/listinfo/ev


----------

