Re: transformer measured L, etc.

["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>

I was thinking about power transformers in the scrap yard.. the 1kHz test
frequency of the average L meter in a DMM isn't likely to excite any
resonances, but your point is well taken.
----- Original Message -----
From: "Tesla list" <tesla-at-pupman-dot-com>
To: <tesla-at-pupman-dot-com>
Sent: Tuesday, February 04, 2003 6:34 AM
Subject: Re: transformer measured L, etc.


 > Original poster: "Malcolm Watts by way of Terry Fritz
<teslalist-at-qwest-dot-net>" <m.j.watts-at-massey.ac.nz>
 >
 > Hi Jim,
 >
 > On 3 Feb 2003, at 18:33, Tesla list wrote:
 >
 >  > Original poster: "Jim Lux by way of Terry Fritz <teslalist-at-qwest-dot-net>"
 > <jimlux-at-earthlink-dot-net>
 >  >
 >  > It occurs to me that for an idealized transformer, you can measure just
the
 >  > open circuit inductances to get the turns ratio.  Both windings have
 >  > essentially the same core, and in most power transformers, the windings
are
 >  > reasonably compact, so the inductance will be proportional to the
square of
 >  > the number of turns.
 >  >
 >  > Therefore: N2/N1 = sqrt(L2/L1)
 >
 > For ideal, yes. But none are ideal in practice. The test frequency
 > must be well below any self-resonant frequencies present and from
 > experience, I advise placing a signal voltage source across the
 > winding with the higest inductance to de-Q the transformer as much as
 > possible.
 >
 > Regards,
 > Malcolm
 >
 >