Modified Transformers

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dabbler
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Modified Transformers

Post by dabbler »

I'm thinking it might be worthwhile to buy two scrapped out plate
transformer and re-winding them. Rewind the first to step-up from
120V to 1200 V and the next one to step up from 1200V to 12KV. The
idea being to wire the secondary of the first transformer to the primary
of the second transformer.

What makes me think it might be doable are these two links.

This link leads to a bookseller who carries a book on making hand
operated winding machines.

http://www.okdpm.com/catalog/category_3 ... age_1.html

This leads to a site owned by a fellow who has custome wound
several transformers.

http://members.tripod.com/~schematics/x ... ormer1.htm

I mentioned re-working plate transformers because they are big
bruisers and I remember my first stepfather, a HAM, using one in his
rig. He used for B+ current on a pair of 833A's as I recall. I might
have the use of this thing mixed up. Anyway, I remember that he was
playing around one day and burned up his plate transformer.
Overmodulation? Anyway, we took it all apart and fixed it.

Here's the thing though, the amperage will have to stay real low, I'm
thinking 2.5 ma at the most.

Comments?

dabbler.
DaveC
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Re: Modified Transformers

Post by DaveC »

Rewinding the plate transformers is itself a good exercise, and possibly useful in the end. You will need to have some insulating varnish and papers, wire of course, and a fair amount of patience,

The one real rough spot may be in getting the laminations apart without damaging them. They are usually varnished along with the windings.. and may present some difficulties.

Connecting the transformers as you have in mind, will be problematic, to say the least. The low voltage one will be straight forward other than the issues mentioned above. But....
the second transformer will not be so easy. Here's why.

The primary of the second transformer will have to be a duplicate of your first transformer's secondary. The secondary of your 2nd transformer, will have to carefully wound, with good interlayer insulation, and 10 times the number of turns as the primary winding. But since the 2nd transformer's primary is exactly like the 1st transformer's secondary (not getting confused I hope)...the secondary of your 2nd transformer will be many many turns.

A nominal value for power line frequency transformers (50/60 Hz) is about 1/7 volt per turn. The exact value depends on the core. Using this value for sake of discussion, the primary needs about 120 /(1/7) turns or about 840 turns. The first secondary needs 10 times that..or 8400 turns. and the 2nd transformer's secondary will need 10 times that or 84000 turns.

If you think it through, you should probably just wind one transformer.. to go from 120 to 12000 volts directly. The large onumber of secondary windings, will require a fairly large core opening.. or window. The plate transformers may not have enough space for all that wire.

Don't want to discourage you, in any way... but there are a few realities to consider, and it is better to do that early on, rather than half way through.

Dave Cooper
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Re: Modified Transformers

Post by dabbler »

Thanks, Dave. I appreciate your taking the time to look at my
proposal. The reason I posted the idea was to get this kind of
feedback.

Here is what I am trying to accomplish. If I do this, I want a reliable
power supply capable of carrying the load for prolonged periods. I
don't want one that is going to overheat and fail after a minute or so of
operation or force me to shut everything down after just a few
seconds.

We've got a dilemma with these small fusors. I don't think they are
large enough to do what we want. How big is the largest one built to
date? I'll bet it's a foot or less in inside diameter. I don't know that its
possible to put 200kv across a vessel that size without a new set of
problems arising. More importantly, I think the plasma needs more
room to dance than what we are providing in these small bottles.

I think what we are looking for is going to happen somewhere above
200kv, maybe not until we reach something over 300kv. The only way
to get there on a amateur budget is to keep the current down. That
means using small quantities of gas.

I guess what I need to do first is to dope out how large the power
supply transformer needs to be and then go looking for a scrapped of
about the right size. Some of those old plate transformer were pretty
big I might find one that would work. It's unlikely that I'll be able to get
my hands on a scrapped distribution transformer because they
invariably repair those jewels and put 'em back into service. This is a
matter of making do with what I can get my hands on.

Is there another transformer design that could be resurrected from
salvage in this way?

dabbler.
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Richard Hull
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Re: Modified Transformers

Post by Richard Hull »

X-ray transformers are our only hope, for the most part. Distribution and potential transformers are nice, but a bit over the top. Regardless, if one seeks to go much above 100kv a multiplier circuit of some sort is a must. (transformers don't go that high.)

We have talked and talked about the nearly ideal, low stored energy IGBT designs where 25-30khz switch frequencies are used to get virtually any voltage, via a multiplier, up to 1megavolt. Not one person has the dollars/ guts/know-how/intiative or combination of these to obtain the special core for the transformer or to develop the asscoiated electronics. All of this is doable now, but not movement.

The reality at the raw amateur level is a wall operated 60hz x-ray unit, some simple HV electrical dabbling and re-tanking. Some custom metering is also required. One must them wrestle with the descision whether to add a smoothing capcitor with its associated lethal and dangerous stored energy or just run full wave rectified with ripple.

The largest spherical fusor body ever constructed by anyone on this list is 8", to my knowledge. The reason why you just can't go beyond this are simple and obvious and have been discussed extensively over the last 6 years here. (mean free path issues vs. gas density.

Making a bigger fusor just makes a bigger fusor. Just like making a bigger tokamak only makes a bigger tokamak. If it won't work in the small, it won't work in the big. Wrong ideas made bigger are just a display of bad ideas on the large.

Richard Hull
Progress may have been a good thing once, but it just went on too long. - Yogi Berra
Fusion is the energy of the future....and it always will be
The more complex the idea put forward by the poor amateur, the more likely it will never see embodiment
dabbler
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Re: Modified Transformers

Post by dabbler »

Richard Hull wrote:
> X-ray transformers are our only hope, for the most part.
Distribution and potential transformers are nice, but a bit over the top.
Regardless, if one seeks to go much above 100kv a multiplier circuit
of some sort is a must. (transformers don't go that high.)

Line voltages on the big transmission lines are 400kv and that is done
with step-up transformers for the most part. It's only been in the last
couple of years that we could make generators produce voltages that
high.

So here's the 64 bit question. Can smaller transformers capable of
voltages in the 100kv-200kv range be made provided the currents are
kept low?
>
> We have talked and talked about the nearly ideal, low stored energy
IGBT designs where 25-30khz switch frequencies are used to get
virtually any voltage, via a multiplier, up to 1megavolt. Not one
person has the dollars/ guts/know-how/intiative or combination of
these to obtain the special core for the transformer or to develop the
asscoiated electronics. All of this is doable now, but not movement.

I'll do some more reading on the subject. What, though, is IGBT? As
for me, I've got the hair and I can probably develop the mechanical
skills I need to do it. What I need is guidance.

>
> The largest spherical fusor body ever constructed by anyone on
this list is 8", to my knowledge. The reason why you just can't go
beyond this are simple and obvious and have been discussed
extensively over the last 6 years here. (mean free path issues vs.
gas density.
>
> Making a bigger fusor just makes a bigger fusor. Just like making a
bigger tokamak only makes a bigger tokamak. If it won't work in the
small, it won't work in the big. Wrong ideas made bigger are just a
display of bad ideas on the large.

I don't know that this is true for two reasons. One, is the recovery of
the energy in the alpha particles, the other is the idea of pumping
200kv through an eight inch space strikes me as being unlikely, even
with vacuum as the insulator.

Not that your point about a bad idea made large isn't well-taken. I do
understand that. But then I have to ask myself if this really is a bad
idea.

dabbler.
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Re: Modified Transformers

Post by dabbler »

Pardon the double post, Richard. Here is something you wrote in
another part of the forum:

The ideal would be a custom wound 1kw high frequency core and
drive electronics with about 20 kv output which could then be voltage
doubled via conventional means. Such a transformer device would
be very expensive indeed. The capacitor requirements would be
greatly reduced and the supply much more efficient.

Is there a transformer type that can be rewound to meet your needs
here? If there is, I'll tackle it. All this time I've been thinking that the
smart thing to do would be to keep the total power down below 2kw,
perferably something close to 1kw. I suspect the FCC imposes a 2kw
power limit HAMs for more than one reason.

I live near enough to a major airport that Tesla and Oudin coils are not
a reasonable or safe option.

dabbler.
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Carl Willis
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Re: Modified Transformers

Post by Carl Willis »

Hi Dabbler,

The IGBT (insulated gate bipolar transistor) combines the best features of the FET with the low voltage drop characteristics of bipolar transistors. Actually there's been quite a bit of progress in the solid-state Tesla coil field recently with IGBTs, particularly the success of doubly-resonant (meaning that there is a resonant capacitor in the PRIMARY of this solid-state system) off-line circuits that can produce potentials as high as conventional disruptive coils and at considerably better efficiency. The IGBT primary circuit, usually a full H-bridge, can be fired at the appropriate time through the use of feedback from the secondary circuit, reducing the chances of blown IGBTs.

This technology can be applied to accelerator power supplies, with two constraints. First, the switching frequency must be low enough so that HV diodes can rectify the output without excessive losses (~50 kHz or lower). Second, the secondary circuit--which in a Tesla coil is a large L / small C circuit, should instead be composed of a number of magnetically-coupled secondary coils with relatively low number of turns to keep the voltage down. Each secondary feeds a filter / storage capacitor through a HV rectifier. Then the secondary circuits are stacked in series to produce HV DC. If done carefully, I think a low-frequency apparatus could be realized without having to look for exotic ferrite cores. Getting 75 kV at up to 20 mA with low ripple could probably be managed with 5-10 individual secondary systems immersed in oil in a plastic pail, with the primary coil around the outside of this pail.

-Carl
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Re: Modified Transformers

Post by Richard Hull »

Carl is right, but again who here is going to tackle this issue?

I hope to dabble with a simple IGBT driver for an extant ferrite core I have associated with a Hi-Volt stack that is rated at 120kv @60ma. Of course, I would never work the voltage to that level nor the current, in my simple design.

Regarding voltage hold off in vacuuo.........the Jefferson National Labs accelerator facility about 80 miles from me stands off 8million volts across a super conducting niobium waveguide of only a 2" gap. So vacuums can have huge voltages in tiny spaces provided the vacuum is high enough.

The problem is for fusion that putting 500,000 volts in an 8" fusor can be done, but at 10e-12 vacuum which means that would be the D2 pressure and thus zero fusion density. The pressure could be raised in a much bigger chamber, but the mean free path would still demand 10e-6 pressures which is still no fusion density of real value. The simple fusor has 1000 times this denisty. Nature conspires constantly to not let casual power producing fusion occur in the universe.

Again, if simple conditions in space at any pressure, and at any voltage or current level within plasmas could do fusion, then all the hydrogen in the universe would have long ago been burned up. The only place we see it working is in stars and then damned inefficiently. Stars slowly plod through their supply of hydrogen so that even the blue dwarfs (fastest burning-shortest lived) take a billion years to grind through there stash.

Richard Hull
Progress may have been a good thing once, but it just went on too long. - Yogi Berra
Fusion is the energy of the future....and it always will be
The more complex the idea put forward by the poor amateur, the more likely it will never see embodiment
Alex Aitken
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Re: Modified Transformers

Post by Alex Aitken »

"Just like making a bigger tokamak only makes a bigger tokamak. If it won't work in the small, it won't work in the big. "

Something of a fundamental point for fusion physics that this isnt true.

If you are trying to do plasma fusion, ie fusion at thermal equilibrium you heat up the plasma and confine it. By virtue of it being a hot plasma some fusion will happen and this will give out energy into keeping the plasma hot. If the energy obtained in fusion exeeds the energy lost, fusion can be maintained and heat extracted and you have a power plant.

Heres the thing with scale. The amount of energy produced by the plasma depends on its temperature, and is proportional to the volume of plasma (Fairly obviosly).

The energy lost by the plasma depends on its temperature, and is proportional to the surface area of the plasma.

So at any given temperature, giving a certain density of fusions/sec as you scale up the device, power loss increases as x^2, power production increases as x^3. So however poor your containment is, you only have to scale up enough and eventually you breakeven.

What bothers me most about fusors, is there is no exponential scale up as you increase power or size, so a fusor that is x orders of magnetude below breakeven would still be however large it was built.
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Re: Modified Transformers

Post by dabbler »

Besides, if it was easy, the Big Labs(tm) would have already solved
the problem, right?

With a bigger fusor, you can increase the depth of the potential well
without arc over, grid transparencies improve and best of all, the
particles have further to fall thus their energies are higher simply
because they have had more time to acclerate.

The trick is finding a size that you can build and run on your budget. I
could, conceivably, build a really large tank. I've done that before. The
trouble with a big tank is that all the other stuff that would need to go
with it would also have to be much larger and therefore much more
expensive. Bussard mentions 100kw to start up a two-meter diameter
reactor and I'll give you long odds that he did not take everything into
account, like running the vacuum pumps for ten days or better just to
evacuate the vessel. Did I mention shielding or foundations? No?
Well, they get into your pocket real bad as well.

I've been thinking about something on the order of eighteen inches,
but even that may turn out to be too big to handle.

dabbler.
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Re: Modified Transformers

Post by dabbler »

Thanks for the input, Carl. What about RF noise absent a spark gap.
Is it eliminated?

dabbler.
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Re: Modified Transformers

Post by dabbler »

What about acceleration?
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Carl Willis
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Re: Modified Transformers

Post by Carl Willis »

The argument for making our fusors SMALLER is the issue of low-energy ion-neutral gas collisions. That just generates heat from input power in the Hirsch-type fusors with self-sustaining discharges. And this has been discussed. For a given cathode potential and gas pressure, closing the vessel / anode in closer around the cathode and thus making a smaller fusor reduces the number of neutral gas atoms in an ion's path to the center, which are a major loss mechanism.

Vacuum arcing isn't a smallness-limiting problem: a good high vacuum can insulate a megavolt across 10 cm. What prevents us from running a tiny 1 cm fusor is the breakdown of the solid dielectric in the power feedthrough that is necessary. This is the one practical limitation that prevents us from getting even smaller fusors.

In a bigger fusor, particles do not have farther to fall in the potential well unless the cathode potential is also made larger. Potential means: if the particle comes from the fusor wall and ends up at a certain cathode potential, it has just gained that much kinetic energy. Making it travel a longer distance means it will just accelerate slower, but will end up at the same energy.

Of course you mentioned the budget concern. An 18" chamber is likely to cost you at least 5 times as much as an 8" chamber, which itself might be twice the cost of a 6" chamber. Of course, you'll pay a lot more for pumps for that big chamber: it's got a lot more surface area, bigger gaskets, more gas volume. I just don't see where the rewards are!

-Carl
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Re: Modified Transformers

Post by Carl Willis »

Hi Dabbler,

Some radiation of RF is inevitable with a switching power supply like I described. But practically, it is not a problem at a distance since these systems are poor radiators.

The stacked multi-coil supply I described has been a reality for some time, commercially. I recently visited with Richard Adler at North Star Research (www.northstar-research.com), who builds small self-contained electron accelerators that use exactly this approach, but on a larger scale than we'd need to run a fusor (hence the special insulation problems that North Star solved with its "nested high voltage" concept). The commercial circuits are proprietary and so we amateurs don't know the little details that go into their design. However, I was pointing out that the amateur tesla coilers have come up with their own designs, such as Chris Hill (www.easternvoltageresearch.com).

I wish I could be the one to say that I'd dive right into this project, but I have too many other things on the table right now. Have to be choosy.

-Carl
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Re: Modified Transformers

Post by dabbler »

Many thanks, Carl. This is the sort of thing I need to know before
picking up a wrench. I like to plan things out and study options in
advance.

dabbler.
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Re: Modified Transformers

Post by Richard Hull »

So it is sort of back to the good ole cheap, dangerous, easy to assemble 60hz system for 95% of us. My switch mode plans are also far back on the table and I have every component to assemble one on hand, NOW! Like Carl, I just have too many other siren calls in my ears, so I will continue to use my old 60hz supply shown recently in the construction posts.

Richard Hull
Progress may have been a good thing once, but it just went on too long. - Yogi Berra
Fusion is the energy of the future....and it always will be
The more complex the idea put forward by the poor amateur, the more likely it will never see embodiment
DaveC
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Re: Modified Transformers

Post by DaveC »

Been out of the circuit for a day here...power outage last night....

I have a minor dilemma, in that I and another fellow build the entire HV power supplies Switchmode drivers, HF transformers (which we now buy rather than build) and the HV multpliers. The way we build them, makes them rather expensive...but these have a reasonable punch... up to about 120kV at currents of a couple mA. but the design is proprietary.

I will try to put together a generic design, and have already given a number of the more important construction hints.

But as Richard has said, these gadgets are a bit pricey.

The low voltage driver board can be built for about $50 assuming you build and wire or etch your own. The HV transformer uses Ferrite U cores, which can be purchased from one of the major magnetics companies...

The multiplier is simple in general terms... you get about V pk-pk per stage, unloaded. where the Vpk is the peak output voltage of your transformer. The usual circuit is a Cockcroft-Walton 1/2 wave multiplier, but for more output, a full wave requires only one additional capacitor and diode stack, (50% more parts) to get a full 100% power increase.

There is a US company fronting the Chinese HV diode mfr - (about $3 +/-), and caps are available from several sources, including Murata, and HVC in Wisconsin. The latter are a bit larger but not too expensive ( about $4-5 each , if you buy a hundred).
So, .... a 10 stage multiplier will give 5X Vpk-pk and have 10 HV diodes and 10 HV capacitors, for the half wave design. A little less than $100.

The transformer at about 30 -40 kHz, will give about 1-2V per turn. Cores are just a few dollars each, same for the matching bobbins, and then you need wire for primary and secondary, interlayer insulation, permacel tape or Kapton, a bit of patience and some rudimentary sort of winding jig. So setup for winding the transformers, will cost about $50, and then you should be able to produce a few before you have to buy more materials

The real bear will be transformer secondary... which will have a couple thousand turns. Much less than the 60 hz designs. But even with a coil winder, ( what I have used), it take a couple hrs to do transformer. then it needs to be vacuum dried, varnished and baked.

For an oil insulated multiplier, you can build it in a one gal, paint can, mount the transformer in the oil too, and have just one realitvely simple low voltage drive board. I would recommend oil, since you rebuild and repair, and the oil is only a few $ per gallon, versus, about $300 /gal for the solid insulating materials, which cannot be repaired.

Total "production" costs, are less than $500US, which will provide enough parts to build a couple power supplies.

As Richard has already noted above, the multiplier type HV supplies, have very low output capacitance which makes them a lot less hazardous to use. Flashovers can startle, and can, of course BE LETHA;L, but you will not have fiery, barn burning arcs, when something goes haywire (as it alwasy does).

Dave Cooper
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Re: Modified Transformers

Post by Richard Hull »

Thanks for the offer of help with a simple design Dave.

For those eager to look at something, here is a URL which sort of takes you by the hand on making a 1KW switch mode system using IGBT's.

I plan on a half bridge unit, myself as my needs are modest.

http://w5jgv.com/hv-ps1/index.htm

I have printed out the whole site's instruction and schematics group. (~40 pages). There are a couple of short little video clips of this guy fiddling with the system.

I think the deal is to keep the system simple and the number of needless bells and whistles down to near zero.

The normal crazed fusorite looking to hit 10e6 n/s should have little use for more than 50kv @25ma, MAX, with most folks never needing more that 40kv @20ma. Thus, a 1kw to 1.5kw solid supply at moderately high voltages would be adequate.

I have also thrown this cool URL up in the "Links Forum" so it won't get buried in this posting forever.

Richard Hull
Progress may have been a good thing once, but it just went on too long. - Yogi Berra
Fusion is the energy of the future....and it always will be
The more complex the idea put forward by the poor amateur, the more likely it will never see embodiment
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Re: Modified Transformers

Post by Mike Veldman »

Just managed to survive the first week of returning students so I thought I'd look in and see what you guys were talking about. I have a couple of interesting pulse transformers I picked up a while back I thought I'd throw into the mix. I don't know what these were used for and neither did the junk guy I purchased them from. Pictured here are two transformers that are about 14" cubed and weigh around 100lbs. The tag says" Pulse Transformer oil filled, built for Northern Electric Co. LTD. The primary voltage is 250 volts 1 amp, the secondary says 115KV 78 amps. No Kidding! The pulse is 8 microseconds on width, 360 pulses per second. The step up ratio listed is 8.8 to 1. The unit was manufactured by Moloney Electric Company of Canada. Total Weight 590 LBS."
I've not seen the whole system, the container, lead shield and oil were sold off before I came in contact with these. I was told though, by the guy who disassembled these that the transformer and the insulator pictured were all that was in the container. Anyway, something like these might be coaxed into a useful high voltage supply.

mike
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Re: Modified Transformers

Post by Richard Hull »

Mike, You have radar modulator, pulse transformers. These are most often driven by a nice beefy hydrogen thyratron and can't serve as a power supply transformer in the normal sense as they are set up for very short, but very intense pulses at rep rates on the order of 1khz. Almost all have iron cores.

These are just what the doctor ordered for pulse work in fusion though. This is provided they can handle the voltage. Richard Hester supplied some cool designs for pulse "lift" circuits and hydrogen thyratrons a while back when Larry was off chasing that rainbow.

Richard Hull
Progress may have been a good thing once, but it just went on too long. - Yogi Berra
Fusion is the energy of the future....and it always will be
The more complex the idea put forward by the poor amateur, the more likely it will never see embodiment
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Re: Modified Transformers

Post by 3l »

Hi Mike:

The pulse transformers are light to medium duty.
But they will work.
The are usually only worked at 5 microsecond bursts at 100 to 200 cps.
I have not totally given up on pulsed but to go any higher in the stuff requires a good shielded place. I ran out of cord in the shop and I am building a free standing 20 gallon septic tank with a cinder block top for all the support instruments. It is about 250 feet from the shop and buried 30 feet in the ground with a storm drain to extend it to the right depth. I modelled it on the Pontiac
Street Hot Pit. The active parts get lowered down by a truck winch. Exterior vacuum line runs are no fun.

Happy Fusoring
Larry Leins
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