MagneQuest/Peerless Forum

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perhaps... and you make a good point....

Posted by mqracing on May 16, 2004 at 12:42:09:
Hi Paul:
Within minutes of hitting the send button... I was already thinking of writing an addendum pointing toward the consideration you mention above re: leakage inductances, cacpacitances,and etc.
I had thought of pointing out that ratio'ing down... though much more preferable (i.e., not as harmful as ratio'ing up in most cases)... still... none-the-less is not a substitute for the proper part for the job....
so... that... say a 2.5K "Friar Tuck" trans... built along the same performance profile as the 5K Robin Hood... would look quite different electrically and be moreso optimized for 2.5K as opposed to a ratio'ed down RH. I agree.
the 2.5K trans would have fewer turns, thinner pads btwn windings, and the net leakage inductance would be half of the RH at 5K. And since the AC voltage gradients are different... the insulation package would be different and optimized for the 2.5K impedance.
So... yep.... "universals" aren't optimized fully for each condition and that is an argument I've made for years and basically why I still prefer to recommend that folks use transformers at their design centers.... i.e., use them where they have been optimized.
now...imagine a 5K three way universal.... rig it for 2.5K, 5K and 10K... and then study it's performance... do FR tests at each impedance, calculate insertion losses, do square waves to see how each tap will behave differently, do low frequency power response plots for each.... and you would find that the unit behaves best at it's nominal design center.
"Universals" (one size fits the skinny, medium and fat man) are great for manufacturer's because they can offer or cover three or more different applications from one transformer... but... does each of these "impedances" have equal performance for each tap or operating point? Nope.
In the case of ratio'ing down (as the poster orig inquiried about)... far less harm is generally imposed on the performance.... not ideal by any means... because your moving away (by defintion) the ideal (optimized) point of operation.... by less harm than ratio'ing up...
and after studying the original posters idea... I was a bit surprised, that the RH actually moved perhaps less off of "ideal" than I might have suspected... hence, my willingness, to provisionally back off of my *dire* warnings.
if the Robin Hood series goes well perhaps we should follow it up with a Friar Tuck series for 2.5K or 3K. For there still remains no equal substitute for using a properly designed part at it's design center for the job you need to do...
MSL