Question for the transformer experts. I have an old C core transformer that I rewound for a different output voltage (120v), each leg of the core has a bobbin and windings on it , I wanted to end up with a 120v primary winding and a 60v secondary on each bobbin, connected in series they would be 240v primary and 110v secondary. The primary was already there so I left this as it was, I finished winding one half and though I'd see how close I had got with the turns so I assembled it with only one bobbin, both halves of the C core held together with a g clamp. As there was only one primary winding I ran it from a variac at half voltage.
I always run setups like this initially through a series lamp limiter incase I've fouled up the connections, the lamp lights up alerting me and also protects against blown fuses or worse. The lamp did come on but only dimly (60w globe) I though nothing of it. I expected to measure 60v at the secondary but found about 48v, I reached for the variac control thinking I had set it incorrectly and saw it was set at 120v (half my local mains voltage). Measuring the mains voltage across the primary I found 98v. Increasing the variac voltage, the lamp just got brighter and the voltage across the primary stayed at 98v. Very confusing, it appeared that the core had saturated.
I carried on and completed the winding job, reassembled this time with both bobbins and found that I had exactly 60v at each secondary, 240v across the primary and not even a glimmer from the lamp limiter, I could run the variac up to 260v at which point I had a faint glimmer from the lamp.
I can't figure out why it appeared that the core had saturated well before the designed input voltage had been reached with only one bobbin in place. Does anyone have an answer ?
I always run setups like this initially through a series lamp limiter incase I've fouled up the connections, the lamp lights up alerting me and also protects against blown fuses or worse. The lamp did come on but only dimly (60w globe) I though nothing of it. I expected to measure 60v at the secondary but found about 48v, I reached for the variac control thinking I had set it incorrectly and saw it was set at 120v (half my local mains voltage). Measuring the mains voltage across the primary I found 98v. Increasing the variac voltage, the lamp just got brighter and the voltage across the primary stayed at 98v. Very confusing, it appeared that the core had saturated.
I carried on and completed the winding job, reassembled this time with both bobbins and found that I had exactly 60v at each secondary, 240v across the primary and not even a glimmer from the lamp limiter, I could run the variac up to 260v at which point I had a faint glimmer from the lamp.
I can't figure out why it appeared that the core had saturated well before the designed input voltage had been reached with only one bobbin in place. Does anyone have an answer ?
