I have a transformer recovered from a previous project. My intention is to wire it up in a case and rectify and filter it's output for testing linear power supply circuits. The transformer is 2 x115 Volts primary, and 2 x 15 Volts secondary, at a power of 300 VA. In its previous use it powered a linear power supply circuit with 4 x series pass transistors.
The issue I have is the power supply it came from dropped at least 1.4 Volts under heavy loads 10 Amps plus. The capacitance of the filtered input was 28000 uf 35 Volt electrolytic capacitors, which I thought would handle the ripple current easily. The capacitors where through hole radial, but not high ripple snap in type can electrolytic capacitors.
I have built a MOT power supply in the past with a rewound secondary winding of 14.70 Volts, that circuit uses 90000 uf of capacitance, a low dropout regulator and only dips 0.2 Volts at 10 Amps. So as I'm going to be using this reclaimed transformer for a testing device, I could do with out to much dropping under load tests. I'm not sure why it dipped in voltage in it's previous application, but it did. Anything I test with it I'm shooting for just over 20 Volts rectified and filtered. The only difference in the two power supplys MOT, and linear series pass units where the transistors. In the MOT they where MJ11015 pnp, and in the unit I reclaimed the transformer from they where MJ4502 pnp transistors.
So I've got just over 15 Volts AC with this transformer that's reclaimed, I didn't want to go silly on the rectified capacitance filtering, but think I need about 50000 uf of high ripple snap in capacitance. So I figured the transformers maximum rating is 10 Amps for each secondary winding in parallel. A total of 20 Amps, it's a good quality toroidal transformer made by Vigortronix. Is it possible the previous application circuit it was in caused the voltage drop ? All wiring was rated at 20 Amps for cable in it's previous use. I'm just at a loss as to why it dropped that 1.4 Volts under a 10 Amp load.
I know there is probably no definitive answer, but looking for help on possible probabilities to this issue.
Thank you for reading, any ideas appreciated.