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From: Tony Williams
Subject: Re: Doubling wallwart power rating
Date: Tue, 08 Oct 2002 15:32:46 +0100
References: <email@example.com> <firstname.lastname@example.org> <8e+6RgBNico9EwL3@jmwa.demon.co.uk>
NNTP-Posting-Date: Tue, 8 Oct 2002 15:04:32 +0000 (UTC)
User-Agent: Pluto/1.14i (RISC-OS/3.60)
In article ,
Phil Allison wrote:
> ** I can view the primary current wavefrom
> - pure magnetising current.
Interested question Phil. Was the no load current
purely in quadrature, or was there a significant
inphase component.... indicating large iron losses?
> > If you design a transformer so that the core is deep into saturation at
> > nominal mains voltage (which is what is implied by the input current
> > being the same on no-load as on full load), it WILL overheat under
> > safety testing at high mains voltage (+6% or +10% depending on the
> > standard; one even requires +15%!).
>** Well, plug paks tend to get 24 hour, 365 day
> usage and often with low or no loads.
Best efficiency is when iron losses = copper
losses, but never possible at 50Hz. Or is it?
I do believe that this method of designing/using
transformers is an attempt to get the no load
iron losses near to the full load copper losses.
After all who says that a transformer should only
run hot at full load..... if it runs as hot at no
load, then this must be a condition of minimum
iron in the design.
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