# 1 primary 2 secondarys

#### wes

Joined Aug 24, 2007
242
Hi, i have a question about what would happen if you took a normal 1 primary and 2 secondary transformer and hooked it up so that the 2 secondarys are now the primary and the primary is now the secondary. if one of the primarys is 300V and 1A and the other is 12 V and 20A. would this combine in the secondary of the transformer. btw the frequency is 60Hz and it's single phase power. thanks for any feedback

#### bloguetronica

Joined Apr 27, 2007
1,540
If you connect the "secondaries" in series and supply 24V AC to the secondaries, then you will get 300V AC on the "primary". A step-down transformer can be used as a step-up one. You can connect the secondaries in parallel and supply 12V AC to both secondaries, but you will need twice the current.

#### recca02

Joined Apr 2, 2007
1,212
do not know the wiring of a transformer with two secondary but if they are independent
without tapping which seems to be the case.then even powering any one of the secondary with rated voltage will give the voltage at the primary as well as other secondary that equals the rated voltages.
if both are powered at the same time then u must take care that the phase angle and frequencies of both sources match else expect unexpected results .

#### techroomt

Joined May 19, 2004
198
you can only connect the secondary's (now primary's) in parallel if the two windings are exactly the same number of turns. and, you must observe the polarity's of the windings as well. otherwise you must observe the maximum amp capacity of each winding in use.

#### thingmaker3

Joined May 16, 2005
5,083
Wes, you only gave ratings for two of the three windings. Can you provide more data? Tell us what the ratings xformer was designed for, and I can provide some combinations for you to experiment with.

#### wes

Joined Aug 24, 2007
242
well the ratings of the transformer I dont really know but what I am really trying to ask is it possible to combine the two primarys (originaly secondary) so that the secondary (originaly primary) is the combination of the 2 primarys . example, P1 = 300v/1A P2 = 12v/20A so the secondarys would be S1 = 312V or 288V idk? / 10.5A or more or less ?.

#### recca02

Joined Apr 2, 2007
1,212
as already stated in earlier posts application of rated voltage on any of the secondary will give rated voltage on other two windings. if both secondaries are connected to supply no change will occur just the power will be shared by them. However the two sources of 12 and 300 v in that case must match in phase and frequency.
BTW the power ratings of two secondary dont seem to match.

#### thingmaker3

Joined May 16, 2005
5,083
I'm not able to decipher your examples. You speak of two windings on one side and one winding on the other, but you only list a total of two voltage/current ratings. You should be listing three.

#### bloguetronica

Joined Apr 27, 2007
1,540
...then even powering any one of the secondary with rated voltage will give the voltage at the primary as well as other secondary that equals the rated voltages...
Indeed, but not with full current.

#### recca02

Joined Apr 2, 2007
1,212
yup,
the power will be shared by the windings and even at full current of secondary other windings will not be at full current--but that becomes only a concern if u are going to power a larger load.

btw i think the OP is more concerned about polarity markings.