# Basic Transformer Question

Discussion in 'Electronic Basics' started by [email protected], Nov 15, 2005.

1. ### Guest

I have a transformer with a 120V primary and a center tapped secondary,
each side producing 51V. I can see 4 wires comming out of the
secondary A, B, C, D where B & C are tied together forming the center
tap. I want to get more current at 51V than each individual side can
provide. Is there anything wrong with breaking the connection between
B & C and connecting A&C together and B&D together to make the
transformer into esentially a 120V primary, 51V secondary? I know I
could just do it and see what happens, but this is a heavy duty
transformer and I don't want to mess it up. Any advice would be
greatly appreciated. Thanks

2. ### John PopelishGuest

Conceptually, there is nothing wrong with paralleling two similar
windings to get a single output with a higher current capability.
But, if one winding has any difference in turns count than the other,
the slight difference in voltage will cause current to circulate
through the two windings, heating them up.

I would connect one pair of ends together and measure the voltage
between the remaining pair of ends, to make sure that this voltage is
essentially zero, before connecting those ends together.

3. ### Pooh BearGuest

Yes, you can do that.

As John says though., you need to be sure that both windings are of exactly
equal voltage ( i.e. the same number of turns ).

Graham

4. ### Guest

I tried it and it seems to be working ok. There is a small voltage
difference of around .020V or 20mv. It doesn't seem to be causing any
overheating or other problems.

5. ### Pooh BearGuest

That's fine. In practice the 2 windings won't be *exactly* the same
voltage down to the millivolt level.

Graham

6. ### Jasen BettsGuest

the safe way:

disconnect B and C , measure the resistance between A and C (it should be
infinite), if it isn't stop. connect A and C power it up and measure the voltage
between B and D, it should be 0, if it is it's safe to connect them.

Bye.
Jasen

7. ### Guest

I hooked up a 7 amp load to the transformer last night and it is not
even begining to show any signs of strain. I was using a DVOM with the
10 amp AC setting. The DVOM was rated to function to 10A but the test
leads that came with it were certainly not. Before I reallized what
was happing, one of the test leads burt up. I don't think it hurt the
DVOM though.