From: John Popelish
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Subject: Re: PSU's: Exceeding transformer rated current
Date: Thu, 09 Jan 2003 06:20:01 GMT
NNTP-Posting-Date: Thu, 09 Jan 2003 01:20:01 EST
Phil Allison wrote:
> ** I took a 15 VA E-Core and added a diode and 22 ohms resistor in
> series across the 15 volt secondary. Running it at 200 volts AC (to
> minimise the magnetising current) I monitored the primary waveform while
> switching the half wave load on and off.
> The current in the primary built up to its final value in just under
> 1 second, it took a very similar time to return to the oroginal value when
> the load was removed.
> I guess that means it took about 50 "steps" to walk the core into and
> out of saturation.
Phil, if your experimental setup is still handy, could you try a
modification for me?
I am interested in the result when you add a half cycle voltage
corrector to the primary, consisting of a series diode that carries
the 'on' half cycle current, paralleled with two or more diodes in
inverse parallel that carry the 'off' half cycle current, but lower
the voltage a bit extra, to compensate for the absence of IR drop in
the primary for that half cycle. If the secondary current is not
involved in the saturation, except for the primary IR drop effect on
integrated voltage, some small number of diodes should prevent
saturation when the secondary load is connected, but produce the same
effect when it is open circuited.