# Transformer question

#### Do you have a question? Post it now! No Registration Necessary

Translate This Thread From English to

•  Subject
• Author
• Posted on

I have a 14V centre tap transformer which was connected to an
amplifier board in parallel. I connected the two AC outputs together
so I could use it with another project but I couldn't get a reading on
the multimeter. Do these only work in parallel? Why would it only give
me a reading when measuring the two AC outs seperate?

I am also thinking about getting a 9-0-9V toroidal from Altronics but
want to use it was a single voltage supply. Can I join the two 9V
outputs together to make 18V?

Thank you.

Re: Transformer question

"Matthew"

**  Bet there were a couple of diodes involves in that example.

**  That is just what happens.

**  Because the two AC voltages have opposite polarity.

At each point in time, the voltage on one terminal is of the opposite sign
to the other.

**  You do NOT do that   -  the two 9 volt wires will measure 18 volts from
one to the other.

The situation is no more complicated than with a couple of  1.5 volt cells
in a torch handle  -  the transformer centre tap is similar to the spot
where the top of one cell touches the base of the other.

..............    Phil

Re: Transformer question

On Sun, 20 Mar 2005 20:46:53 +1100, "Phil Allison"

Ok. What if I first pass both AC outputs through diodes so it it then
DC, and then connect the two DC outputs together. That would be OK
wouldn't it?

Thanks.

Re: Transformer question

If you want to get 18v from a 9-0-9 transformer then connect one of
the 9 v leads to ground and the other 9v lead will be actually 18v
(and the 0v lead/centre tap will be at 9v).

You can also put a bridge rectifer across the two 9v leads (take one ~
or AC terminal of the bridge to one of the 9v leads and take the other
~ or AC terminal to the other 9v lead - ignore and insulate the 0v

Alan

--
++++++++++++++++++++++++++++++++++++++++++
Jenal Communications
We've slightly trimmed the long signature. Click to see the full one.
Re: Transformer question

The outputs of a centre tapped transformer cannot normally be connected
together - there is usually only one seconday winding on the transformer,
with a connection to the center of this winding (called the center tap), not
two separate secondary windings.  So essentially, in your case (assuming
from your description), the transformer has a 28V secondary winding with a
tap in the middle (at 14 V).  Connecting two transformer outputs in parallel
could be a good way of stuffing it.  From your description you sound like
you're connecting the outputs of some interposing circuitry - what's
probably happening is some protective circuitry is killing the output to
protect against the dead short on the outputs (hence no volts when connected
together, but volts when separate).

If its a center tap (which it seems to be) you don't need to connect the two
9V outputs - just use the +9 & -9 V ends as they are the two ends of the 18V
secondary.

Ciao

Kevin