[R-390] Isolation Transformer update

[Roy Morgan]

At 08:46 AM 11/6/03 -0600, you wrote:
>I did some experimentation last night.  With no load and the primaries
>connected in parallel at the 120V tap, the primary drew about 350mA.  At the
>110V tap, it drew almost 500mA.
>
>I then connected the series 75W light bulb.  The 120V tap caused a dull glow
>while the 110V tap produced about twice that brightness (although still
>quite dull).

The change in brightness with current is very dramatic and non linear at 
the point where it's glowing dull-ly.  so "twice the brightness" may be 
only 10 % more current.

>I didn't attempt the primary at the 104V tap.

With the light bulb in series, you can't hurt anything.. If the transformer 
is a dead short the bulb will turn on to normal bright ness and pass only 
half an amp.

And, measure the voltage at the transformer.. For low bulb brightness, it 
will be close to line (applied) voltage. At higher brightness, it will drop 
substantially -- you may have had only 90 volts on the transformer.

Your current measurement may be fooling you. the thing is VERY reactive at 
no load, so that 500 ma may be well out of phase with the applied voltage. 
You certainly should not expect to multiply the 500 ma by the transformer 
input terminal voltage to get the dissipated power.  A one ohm resistor in 
series and a dual trace scope to watch voltage and current is very 
instructive here.

Roy



- Roy Morgan, K1LKY since 1959 - Keep 'em Glowing!
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