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Re: 10KV RMS -at- 300MA for less than $100
Subject:
Re: 10KV RMS -at- 300MA for less than $100
Date:
Sun, 23 Mar 1997 09:38:40 -0500
From:
"Thomas McGahee" <tom_mcgahee-at-sigmais-dot-com>
To:
<tesla-at-pupman-dot-com>
The original reply got chopped off, so I am re-posting this
> Subject: Re: 10KV RMS -at- 300MA for less than $100
> Date: Saturday, March 22, 1997 2:23 PM
>
> > 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