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From: "Phil Allison"
References: <3E1CD631.7F015840@rica.net> <3E1E6684.3BEF12AA@rica.net>
Subject: Re: PSU's: Exceeding transformer rated current
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Date: Thu, 9 Jan 2003 17:54:07 +1100
NNTP-Posting-Date: Thu, 09 Jan 2003 17:43:42 EST
Organization: Telstra BigPond Internet Services (http://www.bigpond.com)
"John Popelish" wrote in message
> 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
> > switching the half wave load on and off.
> > The current in the primary built up to its final value in just
> > 1 second, it took a very similar time to return to the oroginal value
> > the load was removed.
> > I guess that means it took about 50 "steps" to walk the core into
> > 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.
** I placed a 6.8 volt, 3 watt zener in series with the primary. This
creates a DC component in the supply and did appear to compensate for the
effect of the half wave secondary load.
I tried the same set up with a 160 VA 36 volt toroidal and got
text book results in terms of waveforms.
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