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Re: Tranformer efficency VS Frequency



Original poster: "Jim Lux by way of Terry Fritz <twftesla-at-qwest-dot-net>" <jimlux-at-earthlink-dot-net>

You want to watch out for inductance and non unity power factor.  I assume
you were operating into a resistive load?  Oddly, the manufacturer of a
transformer tends to optimize its design for the intended frequency. As the
frequency goes up, core losses due to things like eddy currents goes up:
laminations that are thin for 50/60 Hz might not be thin for 400 Hz.
Mechanical vibrations that are negligible at 50/60 Hz might be significant
at higher frequencies (either due to loose laminations or magnetostriction).
skin effect definitely gets worse as the frequency goes up (hence the
popularity of Litz wire in very high frequency switching power supplies).

Everything is a tradeoff... and you can be sure that the mfr doesn't spend
any extra money on iron or copper than they need to.

----- Original Message -----
From: "Tesla list" <tesla-at-pupman-dot-com>
To: <tesla-at-pupman-dot-com>
Sent: Saturday, March 09, 2002 2:29 PM
Subject: Tranformer efficency VS Frequency


> Original poster: "Alexander Rice by way of Terry Fritz
<twftesla-at-qwest-dot-net>" <alex-at-rices.myip-dot-org>
>
> Hi All
> We did an eperiment in physics today which investigated the effects of
> operating frequency on the efficiency of an ordinary laminated core
> transformer.
> Using a power sign gen we input current at varying frequency into the
> transformer, power in and power out was calculated from the product of
> Current and
> Voltage at each side using ordinary multimeters (not true rms ones)
> frquency was
> varied from 2Hz to 2Khz.
>
> Heres the rub, i was expecting to see an increase in effiency as frequency
> increased, bearing in mind the way switched mode power supplies work, what
> we actually
> found was that effiency peaked sharply at almost exactly 50Hz and dropped
> off sharply
> either side - which puzzled me. My theories are - transformers really do
> this, maybee
> it is somehting to do with the thickness of the laminations and induced
> eddy currents
> OR our meters are at fault - DOES ANYONE HAVE A BETTER EXPLAINATION?
>
> This does have a relevance to tesla coils - wouldnt it be great not to
have
> to lug a
> great hunk of iron and copper when you want to run your coil - maybee we
> can harness
> the SMPSU's out of the newer breed of microwaves - maybeee this will be
the
> 'next big
> thing' in coiling
>
> a mildly confused
>
> Alex
>
>
>
>