calculate transformer output?

[Monte]

can you calculate the output for a given input of a transformer by measuring the resistance of the windings? I have a couple transformers from a power supply I took apart, but I don't remember their output. One side has 3 wires, the other has 2 blade connectors, which would be the input/output side?

Can transformers be hooked up in series? I think that's the way these were used before.

Thanks,
Monte

[nophead00]

No you can't calculate the output from the resistance. The output is determined by the ratio of secondary to primary turns, but the primary of a step down transformer will use much thinner wire so the ratio of resistances will be much higher than the turns ratio.

Assuming they are step down transformers then the highest resistance will be the primary.

You can wire the secondaries in series to add the voltages if you get the polarity right.

[Monte]

Originally Posted by nophead00 You can wire the secondaries in series to add the voltages if you get the polarity right.

I lucked out and found a catalog that lists the transformers, so I know which the primary's are.

As far as getting the polarity right for the series hookup on the secondaries, would the physical location of the blade connections be good enough? There's an upper and a lower blade, I'm thinking

t1 upper blade and t2 lower blade = ac series connected secondary out = (2x single transformer voltage)

t1 lower blade > t2 upper blade = series winding connection between the transformers.

What would happen if I got the "polarity" wrong? And I guess at the same time, is there a way I can verify the "polarity"?

Thanks,
Monte

[nophead00]

Monte,
Yes your connection scheme looks right.

It is not easy to see the polarity of AC without an oscilloscope other than connecting them and seeing if the voltages add or subtract on an AC voltmeter.

If you get it wrong the two voltages will cancel out and you will get close to 0 volts.

Chris

[Al_The_Man]

With series connection, as mentioned the output will be 0 or double the voltage of one secondary, there is no risk of damage or short circuit with series, if connecting in parallel then you must phase them first, otherwise overcurrent can occur, there is several previous posts on paralleling.
Al.