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Re: Testing H&R Transformers
Subject:
Re: Testing H&R Transformers
Date:
Fri, 14 Mar 1997 19:14:25 -0500
From:
"Thomas McGahee" <tom_mcgahee-at-sigmais-dot-com>
To:
"Tesla List" <tesla-at-pupman-dot-com>
Fellow Coilers,
Had a few hours yesterday and today to do some experimenting with the
two
H&R
transformers that I have. At the moment I have only one Tesla Coil set
up
in my shop. All the others are in various states of disarray as I am
attempting some other experiments with various component parts of the
systems.
The working Tesla coil was being used with a 7,500 volt -at- 60 ma
transformer. Not your standard transformer, but that's par for the
course
around here, where most everything is scrounged rather than bought.
Anyway,
I disconnected the regular transformer and connected up *two* of the H&R
transformers with their primaries in parallel and their secondaries in
series. I did *not* connect up the resonant capacitor that was supplied.
Spark gap used was a single variable static gap (because I wanted to
test
the transformers at the extreme by opening the gap all the way out to
where
the spark gap stopped firing. For all these tests I removed all chokes,
as
I wanted to see if the transformer was prone to failure).
The results are: the secondary coil produced a spark that was twice as
long
and much
hotter than with the original transformer. I attribute this to the extra
current capability of the H&R transformers. Please note that I was *not*
using the transformer in its resonant mode. In its resonant mode it
produces 5KV per transformer, but without the resonant mode it acts as a
2,600 volt 300 ma straight transformer as far as I can tell. That means
that together the two transformers were producing about 5,200 volts at
300
ma.
While I am disappointed that the 5KV rating per transformer could not be
attained in straight transformer mode at 120 AC input, I am still happy
with my purchase. I ran the poor thing for 15 minutes continuously as a
sort of torture test. The transformers were just barely warm at the end
of
the test. In fact, they were almost cold.
I am interested in seeing what these transformers will do when driving a
decent multiple static gap. By the way, quenching becomes even more
important as you increase the *current* supplied by the transformer. If
the
arc is not blasted with air the spark gap spark can begin to flame. My
single static spark gap looks more like a Jacob's ladder or flamethrower
when I turn off the blower. If the gap is allowed to become too hot,
then
it flames and secondary spark activity decreases accordingly. This is
not
due to any defect in the transformers being tested... it is just what
happens naturally with higher input currents. Make sure you have a spark
gap setup that can handle the increased currents! Otherwise you will get
disappointing results.
I tried running *one* of these puppies with 220 volts on the
primary in straight transformer mode. The core must have been
saturating,
because the quality of the spark at the spark gap changed drastically.
The
primary warmed up considerably, so I terminated this part of the
experiment
after only about 4 minutes of testing. I definitely do not recommend
running these things too much above the rated primary voltage. Looks
like
you can push them to 150 VAC with little problem, however, so you can
crank
up your variacs on these! At 220 VAC there was no permanent damage done
to
the transformer, but it did heat up, and the output became very
flame-like
at the spark gap.
By the way, I have been informed that H&R is supplying several
variations
on this transformer. One of them uses quick connect terminals and is
very
clean looking, and the other model has insulated wires for all the
inputs
and outputs. This second model is the same internally, but does not look
as
"spiffy" as the first model. They work identically and have the same
ratings.
I am sorry that these transformers are not exactly as great as I at
first
thought they were going to be. However, it turns out that they are still
quite useable. My tests indicate that it should be possible to run at
least
three and possibly even four of these with the secondaries in series.
Remember that the insulation is designed for 5KV operation per
transformer,
and that without the resonating
capacitor the voltage out is about half that. Exercise prudent caution
with
these transformers. The raw arcs really flame up! If you are concerned
about the level of high voltage when putting these in series, you can
opt
to connect the secondary center tap of the two-transformer pair to a
Good
RF Ground.
There is no need to remove the resonating winding... just don't connect
anything up to it.
Several people asked about using these transformers for Jacob's ladders.
Two of them in series make a pretty good Jacob's ladder. You might want
to
try playing around with using the resonant winding and its associated
capacitor in this application. There are several possible combinations
that
can be tried. Be aware that the arc is quite HOT, and it will melt metal
electrodes quite readily if the arc is allowed to stay in one place for
more than a fraction of a second. Mine chewed up a chunk of #12 solid
copper wire and spit out little metal balls. So your metal electrodes
need
to be something that can take the heat. I only ran a quick test for
Jacob's
ladder operation. Enough to show me that the arc produced is very nice.
I
did not run an extended test to see if the transformers got warm or
anything. I'll leave that to someone who has nothing better to do with
their transformers. I'm putting *my* two transformers into permanent
service on my present coil. And I hope to maybe add another transformer
in
the near future to raise the voltage level up a bit higher.
Someone asked about putting these units in oil. It looks like they would
operate well in such an environment. If you do this, you might want to
carefully perforate the outer protective covering on the HV winding so
that
air bubbles can be more readily removed. I will be running my two
transformers as-is for now, and if I experience any future difficulties
I
will report them to the Tesla list.
It is evident that the increased current capability over that of a neon
is
very desireable. I will continue to look for other high current
transformers that can be used in Tesla coil applications.
Fr. Tom McGahee