# Dual primary / dual secondary transformer heat up

I've built this 220v DC motor controller. I use a 2x110v - 2x15v transformer to power up the stator.

The transformer is a Myrra 45064 with the primary windings connected as follows: pins 1 and 9 connected to the mains, pins 4 and 6 in short.

On the secondary windings, i've connected pin 12 and 19 to a rectifier, and 14 and 17 in short.

When I plug it in at 220v AC, the transformer heats up very fast and outputs ~12V out of the expected 30V. Didn't keep it powered more then 6 seconds.

I thought that this pin configuration should connect the 2 halves of the transformer in series and output 15+15V.

Am I connecting them wrong, or there could be another cause for the high current through the transformer?

P.S.: The schematic on github shows a 3 port primary winding, however, the board is built with the connections done as explained above.

• Try open secondary first and see that you have ~30V, then connect a few hundred ohms to it and see if it behaves as it should. If yes, then check the bridge, the capacitor, the wires, more than that I cannot help, this is a "blind answer" for my part. – Vlad Sep 10 '12 at 13:43
• Have you tried it with the load disconnected? It sounds like you're simply overloading the transformer. – Dave Tweed Sep 10 '12 at 13:44
• I've totally isolated the transformer, ran 220 through the extreme pins in the primary, short the middle primary pins. I've also separated the 2 secondaries. Voltage/secondary ~6V instead of 15. The trafo is new. No idea what's going on. – Valer Sep 10 '12 at 14:52

Primary Pin Connections        |    Secondary Pin Connections