X-ray transformer modifications

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Jim Stead
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Re: X-ray transformer modifications

Post by Jim Stead »

Okay, that's what I'll do, I'll stick with the split supply. I'll get the resistors added, close/vacuum it, and do some testing.

On another note, I am wondering about the purpose of a resistor that was placed on the transformer contactor in the control unit.
X-ray Contactor.jpg
X-ray Contactor.jpg (7.02 KiB) Viewed 8107 times
This contactor uses 30 amp contacts, which are undersized for the current needed. Because of that, they used two contacts rather than one, but they added a limiting resistor on one of them. Why would they do that?
As it is, the contacts being protected by the resistor look to be in good shape. The contacts where the majority of the load is going are pitted and are burning away. I thought the contactor would have had a better chance if the load was equally distributed on the two contacts, rather than being leaned towards one of them.
Jerry Biehler
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Re: X-ray transformer modifications

Post by Jerry Biehler »

Maybe that contact has been adjusted to close first to lessen the power surge as the transformer saturates.
Jim Stead
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Re: X-ray transformer modifications

Post by Jim Stead »

I can't believe how quickly time passes!

I completed the mods we discussed previously, and added a voltage divider while the tank was open. Here's the final schematic and a photo of the finished modifications.
Tank Schematic - Final.jpg
Transformer3.jpg
My next problem is that the transformer was out of oil for 5 months. I don't have the equipment to properly refill the tank under vacuum, so I was wondering what's the next best thing.
I can twist it rapidly CW and CCW as I lower it into the oil, hoping to dislodge some bubbles and force oil into any nooks it can find. I can also move it around each day until I am ready for it (3-4 weeks at least). I was thinking I could put a hot plate under the tank and slowly increase the oil temperature prior to applying a light vacuum. But, I can't apply much of a vacuum because the thin tank wall obviously won't stand it. If that is a viable idea, what temperature can I safely it heat to?

Any other tricks I might try?
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Richard Hull
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Re: X-ray transformer modifications

Post by Richard Hull »

I think you will be Ok if you agitate through a large arc as you lower into the oil. If, after you lower it all into the tank and seal it up, kind of bounce it up and down hard by as little as 1 or 2 inches, this will further help. After all of this, wait a full week and do it again. Only after this time period should you take it up very slowly with a variac to what you think is half voltage and if no arcs, let it sit again for a week and bounce it a bit more and finally take it up under a demo fusor load, playing with it at extended lower high voltages and glow currents for protracted periods. I think it will be OK.

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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Rich Feldman
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Re: X-ray transformer modifications

Post by Rich Feldman »

Not having tanked any XRT's myself,
I think it might be straightforward to process your tank inside a larger tank that can safely handle full vacuum.

Hundreds of vendors sell vacuum chambers made from aluminum stock pots with thick flat plastic lids, used for things like degassing mixed resin.
Here's a 5-gallon size from what looks like a reputable vendor (of course you can save money & make from scratch). http://www.provacusa.com/5-gal-Vacuum-C ... _p_13.html
chamber2.PNG
If 5 gallons isn't deep enough, thick aluminum and stainless pots come much bigger & maybe with taller aspect ratios. Here is a restaurant supply catalog page with pots up to 160 quarts. https://www.hotelrestaurantsupply.com/m ... 0-80-.html

Of course they are not designed for vacuum service, and the flat bottoms come with strength-of-materials issues. Flat-ended cylinders are discussed in David Kunkle's thread about designing his 20" diameter vacuum chamber.

p.s. check out this video of a brand new pole transformer getting its oil. I don't have sound on, so can't tell how much vacuum (if any) is used. Even without full vacuum, I think it helps to put coil-and-core assy into a dry tank, then let the oil level rise slowly. https://youtu.be/sqMGgVZXseA?t=222 Rectangular pad-mounted utility transformers have walls reinforced to withstand full vacuum whenever the oil is installed or changed.

Not to contradict RH, who speaks from experience.
All models are wrong; some models are useful. -- George Box
Jim Stead
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Re: X-ray transformer modifications

Post by Jim Stead »

You are thinking the way I was originally. The X-ray tank is 15.5" in diameter and 2 feet tall, so I was going to need a pretty good sized chamber. I thought I might find a large enough section of used pipe that I could make into a chamber with a steel plate welded to the bottom, and another clamped to the top on thick rubber gasket material. If I lived in oil country, that pipe would've been in my garage by now. But up here in the Northeast, it's super premium stuff. I thought about beefing up a 55 gallon drum for the purpose, and I looked around for a worn out air compressor, or unserviceable propane tank, but nothing jumped out at me. In the end I realized I simply do not have enough extra time to prepare such a chamber, unless it was absolutely necessary.

I was very happy to hear from Richard that I could get away with a simpler method. I imagine this may ultimately limit the overall life span of the transformer, but I can live with that. Sad as it may be for such a beauty. As it is, I've saved it from the scrapyard, so we're already ahead. I expect/hope it will serve many experiments in the near future. In time, I can always pull it back out of service and refurbish it properly, if that seems like the smart move.
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Richard Hull
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Re: X-ray transformer modifications

Post by Richard Hull »

In general, the longer a non-vacuumed transformer sits in its oil, the better. Far better is using it with voltage on it for the high tension will work out bubbles over time and, or, reduce their size. I have seen this way back in the Tesla days. We modified a bunch of high voltage tranaformers and ran them open topped and after a first run at tension, we saw a gang of bubbles come up and later as we used the transformer, the number of bubbles diminished to near zero.

The inter-winding paper has already absorbed oil and will retain it for years. Just resoaking it will re-wick oil all throughout. Vacuuming is hyper important with first dip, bone dry paper right from manufacture.

Just approach max voltage slowly and leave a small vent valve open on top of the tank for a while if you seal the thing up tighly. If the max voltage is 70kv don't go near it for a long time. Work for a while at half max voltage.

No guarantees here, just past experience.

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
Jim Stead
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Re: X-ray transformer modifications

Post by Jim Stead »

I bounced the transformer around some more last night and powered it up slowly with 120v to get close to the halfway mark. It's completely quiet until I get to around 10kv, where the transformer begins its natural hum. At 124v it reached 29.3kv. The hum was smooth and consistent the whole way up, not broken up or varying in any way. No signs or sounds of any arcing. Now I'll let it sit some more.

The schematic for the X-ray setup shows a max input of 300 volts to the transformer, provided by the autotransformer in the control panel. Doing the math from 124v suggests a max output around 70kv as Richard already figured. I'll naturally be at less than half that for a long time while I learn to run a fusor properly.
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Richard Hull
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Re: X-ray transformer modifications

Post by Richard Hull »

Good man Jim!!! You are very wise and the transformer will thank you for your conservatism as the oil insidiously, over time and use, re-insinuates itself into and amongst the windings and paper. It sounds like you have an ideal transformer for fusor work. All the best in your future efforts.

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
Roberto Ferrari
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Re: X-ray transformer modifications

Post by Roberto Ferrari »

Hi Jim

I plan to follow your approach to use just a half of an X-ray transformer.

The last setup you published wiil work as half rectified PS.

How advanced are you in testing it?

I will appreciate any suggestions.

Regards

Roberto
Jim Stead
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Re: X-ray transformer modifications

Post by Jim Stead »

Hi Roberto,

Unfortunately, I have not used the transformer under a load yet.
I continue to "bounce" it occasionally, and have brought power up a few more times.
I'm happy with the way it came out, and I expect that it will work well.
If I was to do this again, the only thing I would do differently is to keep in under oil when I am not actively working on it.

Jim
Roberto Ferrari
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Re: X-ray transformer modifications

Post by Roberto Ferrari »

Hi Jim

You mention that because you had problems with trapped air or just because that way to handle it left you with a unsafe feeling?

Roberto
Jim Stead
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Re: X-ray transformer modifications

Post by Jim Stead »

I haven't had any problems with trapped air yet, but I'm also not operating it under a load or at the higher voltages it's capable of producing.

There wasn't any benefit to leaving it out of oil for as long as I did. I could have easily lowered back into the oil when I wasn't working on it.
That's what I'm recommending. I think it's a mistake to leave the coils exposed to air any longer than they need to be, since that could allow air, and moisture, to work their way deeper into the windings.
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