[polyal]

i have two identical transformers 240v / 21v sec
can they be configured to give me 21-0-21
regards
polyal

 

[davelectronic]

Transformer in series

Hi polyal.
I am not 100% sure as ive not done it before, i did read some where if there in phase it will work, i am not sure putting them in series and using a meter to see, then maybe reconfigure if not, try that, personally i dont see the point, ok for series connection or parallel. Somethings telling me its no, but i might be wrong, iam a hobbyist, ive used single series and parallel but not tried what your asking. Dave.

 

[Resqueline]

Sure, it can be done. Being identical their phasing should be the same. Primaries in parallel and secondaries in series.

 

[davelectronic]

transformers in series

Hi Resqueline.
So the center of the series connection can be used at 0 volts AC for a center tap rectification, if yes that answers my own not completely being sure. Dave.

 

[daddles]

Cut the top of the transformers off (in your mind, of course ), extend the central core (I'm assuming an E core) and drop the windings of the other transformer on the core. Then replace the top you cut off. Excluding saturation issues, the two cores should now behave like a center-tapped transformer, as long as the windings' phases are the same. At least that's my mental model...

 

[Resqueline]

Yes, you wire them just like you would DC supplies, and you get twice the VA rating of each. Of course you also need to pay attention to the primary polarity.

 

[davelectronic]

Centre tap transformer

That answers the op for me, and handy to know, ive a couple of low VA transformers in the cupboard, it adds more options, thanks to you both for your input. Dave.

 

[polyal]

thanks for the replies.....i suppose if the primaries were wired in series
it would become a 10.5v - 0 - 10.5v since there would be 120v across
each primary ( and a combined VA )

polyal

 

[Resqueline]

Yep, that's right (and the total VA rating would be the same as for one - since the voltage is halved but the allowable current stays the same).

 

[duke37]

Two transformers instead of one has the disadvantage that if they are to feed a diode rectifier, there will be a net DC current in the transformer giving the possibility of core saturation.
If you want a +/- DC supply you might be better using a bridge rectifier on each transformer and then putting these in series.