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Re: 10KV RMS -at- 300MA for less than $100
Subject:
Re: 10KV RMS -at- 300MA for less than $100
Date:
Sat, 22 Mar 1997 14:23:24 -0500
From:
"Thomas McGahee" <tom_mcgahee-at-sigmais-dot-com>
To:
"Tesla List" <tesla-at-pupman-dot-com>
CC:
"Robert W. Stephens" <rwstephens-at-headwaters-dot-com>, "Steve Date"
<sdate-at-gte-dot-net>,
"Harle, Stanley P." <sharle-at-mailgate.46tg.af.mil>, "Tesla-2"
<tesla-2-at-emachine-dot-com>, <sgreiner-at-wwnet-dot-com>,
"huffman" <huffman-at-FNAL.GOV>, "Bob Schumann"
<tesla-at-america-dot-com>,
<Benson_Barry%PAX5-at-mr.nawcad.navy.mil>, "Mike Hammer"
<mhammer-at-misslink-dot-net>
> Tue, 18 Mar 1997 14:12:17 -0800
> Skip Greiner <sgreiner-at-wwnet-dot-com>
> To: Tesla List <tesla-at-pupman-dot-com>
***SNIP***
>
> Hi Fr. McGahee and All
>
>
> Today I received 2 of the infamous trannies from H&R. They appear to
> have arrived in good shape. They do have the wire leads which is
> apparently a plus. Good. They arrived without a wiring diagram. Can you
> help? The terminals are marked 1 thru 7. 6 and 7 should be the HV leads
> since they have the HV connector on them. 1 and 2 go to what I assume is
> the resonator winding which is totally separate from the second winding
> which contains the HV winding. 3, 4 and 5 I assume are the primary
> 115vac inputs. If all of the above is true, do you know how 3,4 and 5
> are to be connected?
*** INCORRECT! PLEASE SEE BELOW! ***
>
> Before I blow one of these up, there is one thing in the discussion so
> far which I do not understand. What is the problem with running these
> things in a TC application *with* the resonator cap connected? I'd
> really appreciate some inputs on this.
>
> Thanks in advance
>
> Skip
Skip, Huffman, and others interested in the H&R transformers,
At the end of this post I have appended the relevant portions of Barry
Benson's latest response to my queries concerning his successful use of
the
H&R transformer. Please read it in its entirety.
In the meantime I will attempt an appropriate response to Skip's
questions,
and a few other questions that have been raised.
Different versions of this transformer have the wires *numbered somewhat
differently*. For this reason I will refrain from talking about them by
number, as that might lead to someone misunderstanding and assuming that
the same numbers apply to their particular transformer. However, it is
easy
in practice to figure out what each wire or terminal is, so that is what
we
will do!
It appears that the C&H transformer is for all intents and purposes the
same transformer as the H&R transformer (but the C&H costs a few bucks
more).
1) The High Voltage Secondary is the largest winding on the transformer.
It
has two connections. If you have the wire-lead style transformer, then
you
will find two Black High Voltage Silicone wires that have a breakdown
rating of 20KV marked on them. If you have the quick-connect style
transformer, then the terminals are mounted about 1.5" apart. (This
close
spacing is the real weak point of the H&R transformers. The ones with
wire
leads are less prone to arc-over in Tesla coil use).
Examination of the wire used in the secondary shows it to be #28 gauge,
which is excellent. HV insulation is impregnated paper between winding
layers, and cloth tape that has been heavily varnished as a protective
outer covering. This appears to be more than adequate. The weak spot, as
already noted, is the spacing between the inner and outer HV leads in
the
case of the quick-connect variety. If you have the quick-connect variety
you can modify it *without* disassembling the whole transformer.
2) The secondary is physically wound over the Resonating Winding. This
winding is center-tapped. In the wire-lead style transformer, these
wires
are red. In the quick-connect style the three terminals are located on
the
side of the transformer opposite the HV connections.
Barry mentions that he does *NOT* use the Resonating Windings at all. I
have experimented with using them, and have come to the conclusion that
it
is best NOT to use them. When used, the *open circuit* voltage increases
from 2,700 volts to 5,000 volts. But in Tesla coil use this leads to an
undesireable charging pattern that shows itself as a sort of thumping
noise
(the noise is generated in my system by the vibrations of the capacitor
plates. The noise is merely an indicator of the uneven charging
pattern). I
agree with Barry that we do well to just leave the Resonating Windings
alone.
Yeah, well, OK, but for the curious among you, The open circuit voltage
produced (according to *my* meter) is 2,700 volts with *NO* capacitance
used. Applying the supplied 12 MFD -at- 600 VAC oil-filled cap to the two
outside Resonating Winding Terminals resulted in a reading of 5,200
volts.
Using the center-tap and either outside lead resulted in an output of
3,300
volts. The wire used for the Resonating Winding is positively wimpy
compared to the actual primary. Do *NOT* attempt to run the transformer
using the Resonating Winding(s) as the primary! The current drawn
through
the Resonating Winding would exceed the current carrying capacity of the
wire!
PLEASE, don't go trying to run this thing in resonant mode on your Tesla
coil. Not only would it be a bumpy ride, but you may destroy the
transformer.
3) The Primary is the totally separate winding that looks like a
pancake.
It is wound with heavy-duty wire and held together with varnish. On the
quick-connect version you can see the wire. It is quite robust!
Between the primary and the secondary there are two current-limiting
shunts. Removal of these shunts is not adviseable, as then you would
have
to provide external current limiting.
Some people have remarked that they tried to use these things for tube
Tesla coils and found them unsatisfactory. If using the resonant
windings,
I am *sure* they were lousey! They probably jumped all over the place
voltage-wise! If used without the resonant windings then they should be
OK.
By the way, if I were to use these to run tube Tesla coils, I would
probably want to remove the shunts.
***** Some additional comments *****
Safety gaps across *each* transformer are a must. If you have the
quick-connect style transformer, please modify it, or it may not
survive.
Properly modified and protected, the transformers are excellent.
Yes, at 2.7KV RMS the voltage is a bit on the low side. However, the
current capacity is large, and I have found that two of these delivering
5.4KV at 300 ma can do an excellent job in Tesla coil service. I had to
change to a .05 mfd capacitor to get everything matched, and I am going
to
have to fabricate a new spark gap for this sucker, but it is already
producing better output than I used to get with a 15KV 60 ma
transformer.
As a consolation prize, we all get to use capacitors with lower voltage
ratings if we want to.
*** Barry Benson's Latest Reply ***
Fellow coilers,
I finally got a second reply from Barry Benson on Chip's Tesla list
regarding some of the questions about using the H&R transformers. I am
reposting it to the Tesla-2 list since some Tesla-2 members may not be
Tesla list members. For the sake of brevity I have cut out all but the
relevant response material. Hope this proves useful.
Fr. Tom McGahee
> Fri, 21 Mar 1997 12:04:00 -0500 (EST)
> From:
> Benson_Barry%PAX5-at-mr.nawcad.navy.mil
>
> Benson_Barry%PAX5-at-mr.nawcad.navy.mil
>
*** Barry replied as follows: ***
> 1) Do you use the resonating winding at all? The capacitor?
>
> Never used it. Never found a need. I figured that since the
> transformer had enough voltage from TC kickback to arc over
> itself that it might be dangerous to try.
>
> 2) Did you make *any* modifications at all to the transformer itself,
> such
> as removing the shunts? If so, could you explain what you did and how
> you
> did it? What were the practical results? Any "gotchas"?
>
> Never touched it except for repositioning and putting some teflon
> spaghetti tubing on the HV leadout wire. I mentioned this mod
> a while back on the list. If past posts could be organized for
> encyclopaedic perusal it would save a lot of people from the
> past mistakes of others such as myself.
> The transformers that I purchased 10 years ago had an E core with
> a flat plate on the E. No shunts.
> I wouldn't remove the shunts on the new ones without external current
> limiting. It might make it more efficient but at the expense of the
> wire melting from the huge current these things put out.
>
> 3) You mentioned repairing one of the transformers. What is the quality
> of
> their original construction in your opinion? Do you remember
> approximately
> what size wire was used for the secondary? Can they really handle the
> rated
> 300 ma continuously in your opinion?
>
> It appears to have (polyurethane?) impregnated paper between the
> windings. It burns very fast. Not the best insulation. Mine are still
> good
> though after 10 years of use.
>
> 4) Of the failure modes you have experienced, what were they, and how
> can
> they be reduced?
>
> Arc over incinerates the insulation. I protect mine with 1/8" needle
> sharp
> tungsten points set to break over at about 9 kV. Every couple of hours
> they have to be resharpened because of the current. I have thought of
> using a horn gap for future tests because of the high currents. Maybe
> someone can try that out.
>
> 5) Have you added any auxiliary stuff such as external current limiting?
> If
> so, be as explicit as you can as to what you have added, and why.
>
> I originally tried the two variac method. One variac to adjust voltage
> and one in series to adjust the current. The current limiting variac
> didn't because it didn't have the slice out of it as Richard Hull
> pointed out in one of his earlier tapes. As soon as the core saturated
> the breaker poped. I just run the system above that point.
> I also have MOVS across the primary of both transformers.
> One between hot and neutral, one between hot and ground, and one
> between neutral and ground.
>
*** Note: the newer transformers have built-in current limiting at 300
ma
and do not require any external current limiting ***
> 6) The common mode choke you mentioned: is this homemade, or can we buy
> one
> somewhere? Details?
> Noise.
> Homemade. Use an old transformer core with about 1" square cross
> section. My core isn't gapped. Strip the braid off of a couple hundred
> feet of RG58 solid polyethylene (A/U maybe) cable (fun!). Wind about 50
> to 100 turns around each transformer core leg. One winding is connected
> in series with the output lead of one H&R transformer. The other
> winding
> is connected in series with the output lead from the other H&R
> transformer.
> The ends of these windings go to the Tesla coil rotary gap. The sense
> of the winding connections is such that the current flow through one
> winding
> cancels the current flow through the other i.e. "common mode".
> The whole choke is floated electrically by placing it on a 1/8" sheet
> of plexiglas with 3" margins.
> Any current surge that tries to feed into both high voltage leads
> in the same direction at the same time creates magnetic fields that
> add. This makes the common mode choke appear as a very high reactive
> impedance to Tesla coil noise "common" in phase to each line.
> That is how an electrical engineer friend of mine explained it to me.
> He said that the same kind of common mode choke is used in switching
> converters for light weight power supplies to filter niose out of the DC
> output.
>
*** Since the purpose of this choke is to remove noise, it appears to be
purely optional ***
> Current limiting.
> He also said that if the windings were in the same direction then the
> current from the transformers could be limited depending upon the
> number of turns and size of the core (> saturation). He said that the
> much smaller current out of the high voltage side of the transformers
> would be a lot easier to limit this way than with variacs and arc
> welders
> on the multiampere primary side. I've always been intrigued by this but
> never tried it. I will try it on my 10 kw next system.
>
> Cleaning.
> I would recommend dusting off your transformer coils before a run to
> prevent an accident from arc over due to invertebrates and dust.
>
*** Yes, Dead Bug Removal is a must when using open frame transformers
that
are not in any protective enclosures. By the way, what some coilers
thought
were "burn marks" on their transformers simply turned out to be very
black
sooty dust that had been attracted to the transformers when they were
being
used in the electrostatic copiers they were designed for. I use a paint
brush and a little compressed air to clean up such dust. The paint brush
helps to break the stuff loose if it is held on by oil or moisture.
> One more thing.
> The safety gap settings are for dry weather or indoors with cool
> temperatures. High humidity or temperatures (inadvisable) will
> drastically change this.
> Barry
>
My thanks to Barry for taking the time to share with us his knowledge
about
these transformers.
Fr. Tom McGahee