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From: John Woodgate
Subject: Re: Doubling wallwart power rating
Date: Mon, 7 Oct 2002 11:28:19 +0100
Organization: JMWA Electronics Consultancy
Reply-To: John Woodgate
NNTP-Posting-Date: Mon, 7 Oct 2002 12:12:40 +0000 (UTC)
X-Newsreader: Turnpike (32) Version 4.01 <5Z8C9wtxbnpWyFnyfFzqmVF739>
I read in sci.electronics.design that Nico Coesel
wrote (in <email@example.com>)
about 'Doubling wallwart power rating', on Mon, 7 Oct 2002:
>firstname.lastname@example.org (N. Thornton) wrote:
>>Wall warts come in plastic cases, which must be very poor heat
>>dissipators. If vent holes are added top and bottom, I wonder what
>>sort of power out increase one could get.
>>More TF cooling = more i flow acceptable.
>>More diode cooling = more i flow acceptable also.
>>Anyone have an idea what sort of gains we might be looking at?
>I don't think this will work. The core of the transformer will
>saturate at higher current. Most wall warts have little to no reserve
>on their core size. Getting more power from a wall wart is not going
No, the induction in the core **decreases** at higher output currents,
It increases at higher input voltages. The extra heat generated by
higher output current is due to the copper loss - the resistances of the
windings. In a wall-wart, the copper loss under normal conditions is
much larger than the iron loss due to hysteresis and eddy currents in
The fact remains that it is difficult to cool a small transformer. To
get good ventilation, you need a tall box (chimney effect) with quite
large ventilation holes (low viscous drag). Not very practicable for a
Regards, John Woodgate, OOO - Own Opinions Only. http://www.jmwa.demon.co.uk
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