Re: Tranformer efficency VS Frequency

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

Original poster: "davep by way of Terry Fritz <twftesla-at-qwest-dot-net>" <davep-at-quik-dot-com>

Tesla list wrote:
 
> 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,

	I'll assume a smiley face is implied here... 8)>>

> the manufacturer of a transformer tends to optimize its design for the
> intended frequency.

	Indeed, or frequency range.  Wider range or higher efficiency
	costs money.

> 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.

	Serious HF work used ferrite or as noted, trick laminations.
	(and not all ferrite is created equal...)

> 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.

	Or for special alloys... unless needed...

> ----- 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

	If staying in EE, more will be done, going into more
	detail..  entire books, indeed entire shelves of books
	have been writ on power transformer design and optimization.
	Many 'lab experiments' and accompanying materials skip
	over details.

>> 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

	This is VA, rather than power.

>> using ordinary multimeters (not true rms ones)

	Good catch.

>> frequency was varied from 2Hz to 2Khz.

>> Heres the rub, i was expecting to see an increase in effiency as
>> frequency increased,

	Why?

>> bearing in mind the way switched mode power supplies work,

	Was the transformer designed for switched mode supply?
	If testing such, the results might have been different.
	(also:  the phrase switched mode supply covers a range
	of different supply types...)

	Switch mode supplies use transformers carefully optimized,
	in choice of core material and lamination thickness, and
	as noted, sometimes type of wire.
>> what we actually found was that effiency peaked sharply at almost
>>exactly 50Hz and dropped off sharply either side - which puzzled me.

	Assuming this was a 50 Hz (as opposed to 60 Hz or whatever)
	transformer, makes perfect sense.

>> My theories are - transformers really do this,

	Some do.  cf above.

>> maybe it is somehting to do with the thickness of the laminations
>>and induced eddy currents

	That's part of it.  Also 'steels' come in a huge, evergrowing
	range.  In general, a steel suitable for HF work will be more
	expensive than needed for 50 Hz.

> > OR our meters are at fault

	Unlikely.
	Tho it is not possible to measure power with voltmeters and
	ammeters.  (Its semi OK with resistive loads.)

> - DOES ANYONE HAVE A BETTER EXPLAINATION?

	cf that shelf full of reference books i mentioned.

> > This does have a relevance to tesla coils - wouldn't it be great
>>not tohave to lug a great hunk of iron and copper when you want to
>>run your coil - maybe we can harness the SMPSU's out of the newer
>>breed of microwaves - maybe this will be the 'next big thing' in
>>coiling.
	Maybe.
	If full of semiconductors, these PSUs will need careful
	watching to see that surges, stray RF, etc, do not eat them alive.

	best
	dwp