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xray transformer

Posted: Wed Jun 27, 2018 10:17 pm
by David Lloyd-George
My friend and I recently bought an X-ray head from eBay and I took it apart. I will be ohm metering the wires soon. I found that the transformer was quite small and am unsure if it will be suitable for proper fusion work. The label says that it outputs 65kV at 10mA however is only suitable for 2sec max.
I think it may work with a good cooling system, and a putting the primary winding in series with a resister to limit the current however I am unsure.
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if you guys have any questions, comments or concerns, please respond.

Thanks,
David

Re: xray transformer

Posted: Thu Jun 28, 2018 4:15 am
by Richard Hull
Would you be the Earl of Dwyfor and former PM of Great Britain.

Richard Hull

Re: xray transformer

Posted: Thu Jun 28, 2018 9:49 am
by Dennis P Brown
Most such x-formers in those units worked for very short time periods and were not designed for any long term operation. As such, putting it in oil and then pulling a vacuum (to remove any trapped air), might be a good idea to improve its cooling as you indicate. A proper ballast resistor would also be critical in order to protect the unit when 'open circuit' situations occur in fusor start up. Running at as low a current as possible would certainly be helpful - as such, a proper milli-amp meter would be essential so you can monitor its actual output.

Re: xray transformer

Posted: Sun Jul 01, 2018 4:04 pm
by Rich Feldman
David, a forum search will show you reports by people (including successful fusioneers) using dental XRT's.
IIRC, most unrepairable burn-outs were from internal arcing, not from overheating.
The 2 second limit might come from the heating of a tiny x-ray tube anode, instead of transformer windings.
When you know the resistances, you can figure the power loss in primary and secondary windings at, for example, 5 mA.

We are still skeptical about your real name. You gave two.
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Re: xray transformer

Posted: Wed Jul 04, 2018 6:47 am
by David Lloyd-George
Quick update, I measured the resistance of the primary coil of the transformer and got 1.4 ohms. This seemed quite low and after i did a quick current calculation with 120V, I found that the current running through the primary should be 85 amps!!! this is way to high so I figured that my multimeter must be getting the resistance wrong or I was measuring through the wrong wires which is doubtful. since the transformer is rated for .9KVA which I assume is 900W, the current through the primary should be about 8amps instead of 85.

Also Richard, I am related to David Lloyd-George the prime minister and am named after him. He is my great great grandfather. This is a little off topic but I thought that since you mentioned him, I should satisfy your curiosity. In regards to the transformer issue, if anyone has any thoughts, please share them.

Thanks,
David

Re: xray transformer

Posted: Wed Jul 04, 2018 6:52 am
by David Lloyd-George
another update,

I tested the transformer by applying a dc voltage of around 1.3 volts and got 1.1A of current indicating that the previous resistance measurement is correct.

Re: xray transformer

Posted: Wed Jul 04, 2018 8:44 am
by Rex Allers
Simple ohms law doesn't apply on a transformer. The ohms you are measuring are at DC. The primary will have a large inductance. At the intended operating frequency of the transformer, hopefully that inductance will provide inductive reactance that won't draw the kind of power your DC calculation seemed to say.

I happened to have a medium-small transformer sitting near me and just measured it. It's 115 V pri and 12V at 8A secondary, so OK for about 100 watts. The primary resistance at DC is less than 5 ohms. Ohms law would say more than 20 A or about 2.6 kW. But in reality it will draw very little unless there is a load on the secondary.

Ohm measurements will help you figure out the coils and possibly taps. Then for testing you should have a variable autotransformer and probably even connect that to a step down transformer (like the one I just mentioned). Apply only very low AC voltages first to see if the voltage ratios, primary to secondary make sense. Then you can start cranking up the primary in a safe configuration, oil etc.

Re: xray transformer

Posted: Wed Jul 04, 2018 6:46 pm
by Richard Hull
Rex is correct AC and DC are different animals. Inductance to invariant DC is equal to a carbon resistor. To AC, its inductance acts as a reactance which has a totally different form of resistance to AC based on the frequency.

I would be amazed if this transformer will function over the period needed to develop a fusion system. As the die is cast, it should be worth the effort to try.

Richard Hull