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From: "Graham Holloway"
Subject: Re: Microwave oven from 110V to 220V
Date: Wed, 9 Oct 2002 18:36:02 +0100
References: <3DA42F7E.C83136F3@nf.sympatico.ca> <3DA43808.60C7A155@webaccess.net> <3DA46076.D91BDAB2@nf.sympatico.ca>
NNTP-Posting-Date: Wed, 9 Oct 2002 17:40:16 +0000 (UTC)
X-Newsreader: Microsoft Outlook Express 5.50.4522.1200
"Terry" wrote in message
> > By what enormously strange method of calculation do you get the result
> > that the ordinary transformer "will only have to handle half of the
> > total power?" Did someone change the laws of the universe while I was
> > sleeping?
> > Chuck
> > --
> > ... The times have been,
> > That, when the brains were out,
> > the man would die. ... Macbeth
> > Chuck Simmons firstname.lastname@example.org
> Not an 'ordinary transformer'. But one used in what is commonly
> referred to as a 'voltage bucking' arrangement' With voltage
> bucking the input to a a two winding 2 to 1 transformer is the
> 220 volt mains; the output is 110 volts. Instead of using this
> 110 volts to power the microwave directly; that is the entire
> load being transformed from 220 to 110 through the transformer
> the 110 volt transformer output is wired so as to oppose (or go
> against) the same 220 volts being presented to the input. Thus we
> have 220 minus 110 volts = 110.
> So, if you think about it, half of the power load of the
> microwave is supplied directly (as it were) from the 220 volts
> and the other half via the voltage opposing transformer. The
> proviso as mentioned is that a) the transformer secondary winding
> must be able to carry the total amount of current, in amps, that
> flows through it.
> What makes this a bit easier to understand is that we are, in
> this theoretical case, dealing with exactly half the voltage. But
> the idea of buck or boost applies to situations where one needs
> to only slightly reduce or increase voltages etc. e.g. one can
> boost up or buck down a mains supply by a few volts in order to
> get a piece of equipment to operate correctly or to test that it
> will continue to operate at reduced or increased voltage. Also
> the insulation of the transfomer secondary must also be able to
> withstand the maximum voltage impressed on it, namely 220 volts.
> Have fun?
The buck/boost technique is useful for small changes in voltage. However,
with an output of half the input, the total power "through" the transformer
is the same as the total output power. It really is equivalent to a
centre-tapped autotransformer, which has the advantage of less insulation.
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