Re: Some transformer theory

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

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

Actually, if you measure the DC resistance of each winding, then measure the
apparent L, with the other winding both open and shorted you can measure all
the transformer parameters... (I'm too lazy to figure out all the algebra,
so it's "left as an exercise for the reader").. You could even measure the
leakage C between windings.

The real question would be how much the series R will throw off the
measurement of L (not knowing, off hand, how the meter measures L).

Your basic flyback transformer is a normal transformer, probably some
significant leakage inductance.  All the usual transformer math should work.


----- Original Message -----
From: "Tesla list" <tesla-at-pupman-dot-com>
To: <tesla-at-pupman-dot-com>
Sent: Sunday, February 02, 2003 10:12 AM
Subject: Some transformer theory


 > Original poster: "Matthew Smith by way of Terry Fritz
<teslalist-at-qwest-dot-net>" <matt-at-kbc-dot-net.au>
 >
 > Hi All
 >
 > Since MOT's came into vogue on this list, there have been various
proposals
 > for checking the secondary voltage in absence of an HV probe.  I did my
 > calculations of the turns ratio by feeding the various transformers that I
 > had lying around with 24V - 1/10th of the normal line voltage.
 >
 > Do we really need to energise them at all?  We should be able to derive
the
 > turns ration from:
 >
 > Square root (Zs / Zp)
 >
 > I did this for a couple and found that I was within less than a percent of
 > the value determined by the 24V energisation (I did the tests some time
 > ago, but had been thoughful enough to write the ratios on the transformer
 > bodies).  Measurement of resistance and inductance was by means of my
 > faithful Wavetek 27XP which, I suppose, was energising the windings ;-)
 >
 > I re-did the calculations and found that, with the numbers we are dealing
 > with, you can actually get to less than half of a percent of the result
 > above simply by taking:
 >
 > Square root (Ls / Lp)
 >
 > The greatest inaccuracy in my tests was some 14V out of over 2000V - not
 > something that I'm going to lose sleep over!
 >
 > Now for my questions:
 >
 > I have seen comments that MOT's get hot when energised and under no
 > load;  using V*V / Zp for one of the units gave me a whopping 600W+ - am I
 > working this out right or are they really that inefficient?
 >
 > Next question:
 >
 > Can the root of the impedance ratio also be applied to flyback
transformers
 > - are they "classical" transformers, or are they in the TC bracket, where
 > turns ratios cease to be entirely relevant?  I didn't have one with a
known
 > turns ratio to test, but measured one and the ratio *looked* sensible.
 >
 > Cheers
 >
 > M
 >
 > --
 > Matthew Smith
 > IT Consultant - KBC, South Australia
 > http://www.kbc-dot-net.au
 >
 >
 >