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Subject: Re: Microwave oven from 110V to 220V
References: <3DA42F7E.C83136F3@nf.sympatico.ca> <3DA43808.60C7A155@webaccess.net>
Date: Wed, 09 Oct 2002 14:29:34 -0230
NNTP-Posting-Date: Wed, 09 Oct 2002 13:01:31 EDT
Organization: Bell Sympatico
Chuck Simmons wrote:
> Terry wrote:
> > Ahmdsamir wrote:
> > >
> > > Hi there
> > > is it ok to use a transformer to run a microwave oven originaly for
> > > 110V/60Hz , with a 220/[50Hz]?? i.e. does the mains frequency has any effect
> > > on the operation of the microwave???
> > >
> > > thanks
> > > ahmdsamir
> > Possibly OK; although the internal transformer will be less
> > efficient at 50 Hz. and so may get hotter especially with
> > prolonged use. I don't think it will affect the control functions
> > (push buttons/display etc.) if yours has that feature. What size
> > and type is yours?
> > But more to the point microwaves take a lot of power for brief
> > periods so a pretty big separate transformer, or something, will
> > be required to step down the 220 to 110!
> > If you use a single winding auto transformer it will have to
> > carry the total power required which can be anywhere from 600 to
> > 1200 watts.
> > If you use a 'bucking' transformer arrangement the secondary
> > winding feeding the microwave and opposing the 220 volts so that
> > it is 'stepped down' to 110, will have to be wound with
> > sufficiently heavy wire to carry the total current required by
> > the microwave; even though in this configuration the transformer
> > will only have to handle half of the total power required by the
> > microwave. Transformers of this size are not necessarily small or
> > cheap!
> 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
> ... The times have been,
> That, when the brains were out,
> the man would die. ... Macbeth
> Chuck Simmons email@example.com
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.
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