H & R 500ua 5kv transformer
From: Alfred C. Erpel [SMTP:aerpel-at-op-dot-net]
Sent: Sunday, February 01, 1998 10:34 AM
To: Tesla List
Subject: H & R 500ua 5kv transformer
I bought the Herbach and Rademan 5kv 500ua transformer TM90XFR1341,
+ACQ-4.50 US. This has a nice painted steel box that can be opened by drilling
out 4 rivets. There is a nice removable (not potted) 2600 ohm wound resistor
inside in series with the primary that limits the current to 500ua together
with the primary's resistance/reactance. There are two nice .06 x 1 x 2.5
inch mica insulators.
I unpotted this at 275 degrees F in my oven (my first try at this).
There was very little odor, and it dissipated quickly. This is the kind of
thing you could do 38 times without your wife knowing about it and
everything would be just fine, and then the 39th time she comes home and
flames out. Explaining the 38 previous times would not matter. (I am not
here advocating sneaking around on your wife).
I cleaned it in hot kerosene (got this idea from a recent poster on this
list, forget who) and rinsed it in mineral oil. Next time I will just clean
in hot mineral oil (don't like kerosene smell although hot mineral oil is
much more likely to flash when lid is opened). Regardless, IMHO this is very
safe. I had the hotplate on a concrete floor away from stuff with fire
extinguisher handy. If you lift lid and it flashes, don't freak and knock
over pot, just close lid and extinguish.
The core is a rectangle 2 x 4 x 1.1 thick laminations interleaved, 4
screws, the opening is 1 x 2 centered, primary and secondary on same side of
rectangle. The primary is 207 ohms and the secondary is 34,000 ohms. The
primary appears to resonate with a 1 uF capacitor in series (at 60hz US),
this gives a Q of around 1.8 and the voltage on the primary reads around
200v, so I can get close to the rated 5kv output with 113v (my measured)
voltage. With 4.4 uF on primary and .22 uF on secondary, I get a much hotter
spark. The secondary appears to have over 200 H inductance. I have gotten
weird results with different combination of capacitance on the primary and
secondary like consistent sparks for 10 seconds at least .4 inches long. But
I can't repeat later. Probably unusual resonances in secondary. There might
be a sweet spot that puts out 10kv constantly, but I have not found it.
There will also be the issue of whether the secondary coil will flash over
at this high voltage. The output of this transformer is in the 40 watt range
and might be useful for a very small desktop unit.