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Lets do some HBT (was new HBT info for Doug)
Hi Doug,
Original Poster: Doug Brunner <dabrunner-at-earthlink-dot-net>
How big an inductor will I need? Also, do you think using a combination of
resistive and inductive load is a good idea? I've seen that advocated in some
places. I'd probably use a low-saturation salt water resistive load (heat
buffer, and a lot less expensive).
About getting wire from the old xfmrs--they're actually low-voltage
transformers, and I'm pulling it off the 120-volt primary. The insulation
*should* hold.
If I can, I'll use all new wire, but I might run out. As for the VA rating,
I'm building about 6 kVA in, and about 2-4 kVA out (hysteresis/eddy/etc.
loss).
One other thing-what does HBT stand for? I've seen NST and MOT, but HBT?
Okay lets go:
I will assume you are looking for an VA rating of 6kVA. This means your
inductive ballast will need to have a rating of 6kVA, so that it can supply
your wanted 6kVA.
That way you can run your inductor at full power w/o having to worry about
your HBT (BTW: HBT means Home Brew Transformer. I use the abreviation because
Iīm too lazy to always write what HBT stands for) going up in smoke. An old
welding transformer (short out the secondary) would be perfect. If you go one
step further and make some low resistance, high amperage shunts for the
secondary of the welding xformer, you can make a stepped inductor. Depending
on the load you place on the secondary of the limiting inductor you can adjust
the current that will flow thru your HBT. If you find a welding xformer with a
variable current control (of the magnetic shunt type) you are off even better.
This lets you leave out the variac for now (saving some money). A resistor in
series with your inductor will smooth the output of your HBT. The large
variation in magnetic flux going thru your limiter (as your spark gap fires
and stops firing) makes the output of your HBT jump around (If you are near
the HBT or the inductor you will feel this as a thump. A resistor canīt follow
this jumping, so it effectively dampens the output, which results in smoother
operation. You could use your salt water resistor, but I think an oven element
or other high power resistor would be less maintainence prone. Oven elements
arenīt that expensive (on my last post I was talking of using only a
resisitive load.. this isnīt the way to go. The combo is perfect).
So the best bet (altho most expensive, too) would be a variac, a resistive
load and a limiting inductor in series with your HBTīs primary.
I think your input/output wishes can be easily met, as a matter of fact, you
wonīt have such huge losses as you are assuming. 6 kVA in // 4 KVA out is a
loss factor of almost 40% and at 2kVA out its a 70% loss. I think even the
worst xformer design will do better than that.
Assuming 6KVA
Output: 15kV-at-400mA
Input: 240V-at-60Hz
Input current: ~25Amps
TPV=0.47683
Primary:114 turns of AWG 14
Secondary: 7207turns of AWG 25
CSA = 2.5876 sq in.
Put in an oil bath this HBT will run day and night.
If you can get a defective welding (or other kind of low voltage/high current)
transformer rated at 6kVA and are able to dismantle the core, you are on your
way to make a cheapy HBT power pig.
"Brewer" greets from germany,
Reinhard