Transformer output voltage Vs turns ratio: HELP!

hobbs125

I just built a transformer to the specs of the original.

The transformer has a turns ratio of 1:16. Input to primary is 12V.
The problem I am having is a very low voltage at the secondary side. The no load voltage was the highest (40V) that I have got out of it so far.

The primary coil has a 200 Ohm resistor in series. I removed that to get more current to the primary but got the same results?

Anyone here have any suggestions as to why I'm not getting the full secondary voltage?

sophiecentaur

If it gets hot then you could have a shorted turn.
How much current does the primary take when the secondary is open circuited.
Is it possible that you have an enormous gap in the core?
How does it perform with the primary and secondary reversed (using a low voltage source to feed the secondary).

Why is there a 200 Ohm resistor in series with the primary?

hobbs125

Noe of the coils get hot, except the primary when I remove the resistor, then it gets too hot.

Primary current with secondary open is 45mA.
There is a very small gap in the core (probably about .005"-.01")
With the primary and secondary reversed (there are 3 secondary coils so I only connected to one) turns ratio is 5.4:1. I applied 12V to the secondary and with the primary open I get 400mV. When I short circuit the primary I get .5mA.

Carl Pugh

Are you using film insulated wire?
Try using a signal generator or function generator. Vary the frequency and see what you get.
Are you using the same core material as the origional?
Is there insulation over the core?
Are you testing the transformer at the frequency the transformer was designed for?

NascentOxygen

Is the primary a centre-tapped winding?

sophiecentaur

If the primary gets hot without a shorted turn or a secondary load, its self inductance is not high enough. Where did you get the design from? It needs sufficient turns on it; the turns ratio is another issue.