25 May
2011
25 May
'11
5:27 p.m.
From:?h.j.stegeman at hccnet.nl
Date:?Tue, 24 May 2011 17:08:31 +0200
I am restoring an old IBM terminal with a ferro resonance transformer.
I slowly increase the prim voltage with a variac.
At the same time I measure the sec voltages.
The normal voltage at the prim site is 240V
At +/- 130V (prim) I have already normal voltage at the sec site.
(+5V , -18V etc)
The sec side is loaded and contains no regulators.
Anyone any idea why at 130v everything is normal.
I don't dear to go to 220V
Thanks for all your replies.
Henk--
I just repaired two DEC ferroresonant power supplies that are 115VAC
input. From 45VAC to 115VAC input the +10/-15VDC output is at the
normal voltage. What you are seeing is the ferroresonant circuit at
work.
Our power supplies lasted just a few hours before the AC capacitor
failed. I was able to find replacement "run" capacitors on eBay. You
can't use "start" capacitors because they are not designed for a 100%
duty cycle.
Michael Thompson