16 kg inductance.
A friend discarded a large old industrial 230 / 110 V step-down transformer because it got very hot even with the secondary open-circuit. He thought it was rated at 3 KVA. The secondary winding is 2.6 mm diameter wire, so I thought it might be a nice large inductance of low resistance. I am disappointed and puzzled. I tried it as an inductance to smooth the output from a simple mains charger with a bridge rectifier, giving 13 V dc at 10 amps. I measured dc and ac current with a clamp meter, before and after I wired the inductance in series between the charger and a large good 12 V battery:
Before, with no inductance:- 11 amp dc, 12 amp ac.
With inductance in series:- 1.9 amp dc, 0.4 amp ac; and the voltages across the inductance were then 0.55 V dc and 6.5 V ac.
If I assume the equivalent frequency from the full-wave rectifier is 2 x 50 Hz, then these measurements give a dc resistance of 0.29 ohm, and (I think) an ac impedance of 16.3 ohm and an inductance of only 0.026 henry.
The 0.29 ohm seems a bit high for 2.6 mm diameter wire. But the 0.026 henry seems strangely low for such a massive transformer. I do not understand transformers – even if they are ‘perfect’. But as this massive 16 kg transformer was discarded because it got too hot, I presume there are shorted turns in primary and/or secondary. How could these cause a high dc resistance combined with such a low inductance - even at this relatively small dc current? I am disappointed! But I would appreciate enlightenment please. AlanW
Anyone have any ideas ??
I'm really rusty on inductance
ChrisB
