Folowing on from thread lower down. I just tried this to see what sort of
results you get simulating such a multi-secondary transformer using a known
good one but not using the primary.
I used a variac supply near the bottom of its range at 18volts and a 25 ohm,
20W dropper to feed 50Hz (UK)ac into a secondary. Assuming you have a
reasonable idea of the voltage of one 'unknown' secondary.
The transformer I used was 240V (UK) with marked 2 separate secondaries of
6.3V, 0.6A and a 150-0-150 at 25mA.
With 3.43V ac on one '6.3V' secondary there was open circuit 3.40 on the
other isolated '6.3' and 161.4V end-to-end on the '150-0-150' and incidently
116.4 on the primary.
Then loading with different resistors
100K, 161.4 drops to 159.1

5.8K on 161.4 drops to 55.8, 3.43 input drops to 1.64
swapping to 5.8K on 3.4 , no change

1K on 161.4 to 12.1 and 3.43 to 0.771
swap to 1K on 3.4 , drops to 3.39

270 ohm , 161.4 to 3.34V
270 on 3.40, drops to 3.37

56 ohm on 161.4 to .704 and 3.43 to .54V
56 on 3.4 , drops to 3.28 and 3.43 to 3.42

8.2 ohm on 3.4 , drops to 2.55 and 3.4 drops to 2.99V


The size of the transformer gives an idea of the overal sum of Volt x amps
as well as repeating the above with load resistors on each secondary should
give an idea of voltages and currents per secondary, without powering the
primary.
Anyone care to make an empirical formula from the above loading data and
give an idea of its applicability to the general case ?

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