[R-390] Isolation Transformer update

Thu, 06 Nov 2003 20:14:07 +0100

Hi Barry, 

didn't you mention before that the transformer is rated 9A or was this
per winding and doubles if used in parallel? Anyhow you have either a
1kVA or even a 2kVA transformer and for something like this about 30W to
50W iron loss is quite good. You will get some cooper loss too at
maximum current but this is well within specs. 

73
Heinz DH2FA, KM5VT

Roy Morgan wrote:
> 
> 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!
> 7130 Panorama Drive, Derwood MD 20855
> Home: 301-330-8828 Work: Voice: 301-975-3254,  Fax: 301-948-6213
> [email protected] --
> 
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