Hammond X-Ray Transformers

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Mark Rowley
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Hammond X-Ray Transformers

Post by Mark Rowley » Sat Apr 06, 2019 6:09 pm

Late last year I picked up two of these Hammond x-ray transformers which came from a system built in 1975. I’ve found visually similar units on the web that are rated at 70kV at 10ma but I have yet to find anything specific to this particular Hammond.

I’m wondering if anyone here has familiarity with these units and knows what the actual current rating is. I’m also wondering if operating these in parallel (under oil) is a viable way of doubling the current. I’ve read a few previous posts on the topic but they don’t appear to be specific to this type of transformer.

This would be for fusor use and not for the pinch tube I discussed earlier.

Thanks!
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Rich Feldman
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Re: Hammond X-Ray Transformers

Post by Rich Feldman » Sun Apr 07, 2019 1:03 am

Nice set of transformers you got there.

Sounds like a good guess about the current rating.

Remember that in a dental X-ray generator, HV current is a factor in calculating exposure times. But the machines are designed to run for less than one second out of every minute. Continuous operation at nominal current would overheat the transformer. (The tube would overheat much faster.) How about starting by measuring the DC resistance of secondary windings, and figuring their power dissipation at, say, 10 mA average load current? The HV rectifier topology matters. You could also get a feel for the copper loss by running 5 or 10 mA DC through a secondary winding, and see how many minutes it takes to get hot to the touch. Don't ignore possible overheating of primary windings, whose current will be measured in whole amperes; they have much less thermal mass.

Regarding parallel operation: Good way to halve the transformer current, for a given load current, to reduce heat per transformer by a factor of four. If it were my project, I'd make the parallel connection downstream from the rectifier diodes, and monitor the HV currents separately. Then if one secondary winding failed by internal arcing, it would be less likely to take out its parallel partner.

In case you missed many forum posts about measuring the voltage ratio: If you apply 120 or 240 volts on a secondary winding, and measure voltage on other windings, take the opportunity to determine the relative phasing of primaries and secondaries. For a less unrealistic magnetization level, you could put low voltage AC on the primaries (start at 1 volt or less). See how much it takes for voltage on one secondary to reach the limit of your AC voltmeter. It's what I did with my first XRT, many years ago. Its coils and core are still sitting in a bag on my workbench, like some people have pistons from a long-dormant engine project.

Have fun. Play safely.

p.s. just visited your post with picture of sparky alpha particle detector. Nice work! When that thread was active I got me some fine tungsten wire on ebay. No wire has been unspooled since that day.
Mike echo oscar whisky! I repeat! Mike echo oscar whisky, how do you copy? Over.

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Mark Rowley
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Re: Hammond X-Ray Transformers

Post by Mark Rowley » Sun Apr 07, 2019 6:28 am

Thanks for the advice Rich. I’ll spend the next few days measuring the windings and conducting some low voltage tests.

Tbh, I’m kinda skeptical about assembling these transformers for Fusor use. Seems that quite a few older posts report failures after a few runs.

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