[Boatanchors] output xfmr measurement

[Ron]

Simple numerical example: Say you apply 1VAC to the secondary 
and measure 25VAC across the primary, 

Turns Ratio (Primary turns/Secondary turns): 25VAC / 1VAC = 25.
Also, if draw from the source driving the secondary is, say, 1A, 
current provided by the primary must be 1A / 25 = 0.04A. 

The impedance ratio (primary impedance / secondary impedance) 
is: 25^2 = 625. In this example, the source driving the secondary 
'sees' a load of  1VAC / 1A = 1 Ohm and the primary load must 
then be 25VAC / 0.04A = 625 Ohm.

Power delivered to the primary (25VAC * 0.04A = 1W) is 
exactly the same as power drawn by the secondary load 
(1VAC * 1A = 1W), since the transformer in this example is 
lossless.

Also note that I followed your nomenclature: the driven coil is
called 'secondary' and the loaded coil is called primary. Usually, 
this is the other way around.

-- Ron





________________________________
From: Dick KF4NS <kf4nsradio at verizon.net>
To: boatanchors at mailman.qth.net
Sent: Tue, February 16, 2010 6:27:08 PM
Subject: [Boatanchors] output xfmr measurement

Some time ago a friend (now SK) sent to me a brief test method for 'Z' 
of output xmfrs.

It is a bit vague but maybe someone can decipher it. He said:

"Apply 60hz at 1 volt on the secondary and measuring the primary will 
give you the turns ratio. The 'Z' ratio would be the square root of 
the turns ratio".

Can someone give me a mathamatical example of his test? Measuring what 
in the primary and how do you compute the square root of a ratio? 
Guess my math knowledge is a bit hazy.

thanks and 73, Dick KF4NS
St Petersburg, FL 33714 USA
Keep The Glow! 

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