Re: Tranformer efficency VS Frequency

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Malcolm Watts by way of Terry Fritz <twftesla-at-qwest-dot-net>" <m.j.watts-at-massey.ac.nz>

Hi Alex,

On 9 Mar 2002, at 15:29, Tesla list wrote:

> 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?

At frequencies below 50Hz, core losses are increasing as the core 
approaches saturation. Above 50Hz, eddy currents in the laminations 
are increasing as are hysteresis losses. At frequencies considerably 
greater than 50Hz, skin and proximity effects in the windings will be 
influencing results as well. Limitations on the operating frequency 
of switchers are primarily due to the properties of the core material 
which are vastly different from silicon steel. 

Regards,
Malcolm

> 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
> 
> 
> 
> 
>