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Enclosure for small X-Ray transformer ?

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sparky99

Mon Dec 24 2007, 01:47AM

Registered Member #1159 Joined: Fri Dec 07 2007, 02:10AM
Location: Hudson Valley of NY State
Posts: 84

Merry / Happy to all! I have a dental X-ray transformer, 100KV @ 20 ma. Its a fairly small xfmr & I'd like to get some ideas for an enclosure. I'm thinking a 5KVA pole pig can is going to be way too big. An OCR (oil circuit recloser) would be the right size, but I've only seen one offered on eBay. Plexiglass or some other hi-tech plastic is also a possibility, but I've never worked with this kind of stuff
& would need some "how to do it" help. I'm trying to avoid the transformer in a 5 gallon bucket filled with xfmr oil.
Any ideas or suggestions?

Thanks,
sparky 99
Bob

J. Aaron Holmes

Mon Dec 24 2007, 07:46AM

Registered Member #477 Joined: Tue Jun 20 2006, 11:51PM
Location: Seattle, WA
Posts: 546

Where are you located, Bob? And what are the dimensions of your transformer?

I have an OCR: http://silicon-arcana.com/remote_pics/OCR.jpg

I *might* be persuaded to part with it. It's about as small as they come, though, and may in fact be too small for your transformer! Inside the can, the bushings extend about halfway down, leaving only the bottom half available. Anyway, if you want to talk seriously about getting it, let's first talk about your transformer a bit more and see if it seems like the right size. Also, I think you'll have a good challenge on your hands installing any kind of low-voltage bushings. Off hand, I don't know what I'd do...maybe come down through the top? You'd want them to be really low-profile in that case...

EDIT: And really, 100kV between these two little bushings is probably going to flash right over! But maybe if you keep it down

Using a plexy/acrylic tube, or else some other kind of transparent enclosure would be really cool too. I've always wanted to do that with a HV transformer.

Cheers,
Aaron, N7OE

sparky99

Mon Dec 24 2007, 04:18PM

Registered Member #1159 Joined: Fri Dec 07 2007, 02:10AM
Location: Hudson Valley of NY State
Posts: 84

Hi Aaron,
That looks like the same one I saw on eBay! I'm a bit familiar with the inside of the OCR. The ceramic insulator inside the can would have to be cut back to fit the transformer. The plexi tube over the insulators would work fine & not look bad. I could always try to retrofit a set of 34.5KV insulators, if I could find 'em. The transformer is small, 8" x 6" x 5". Here's a few pictures:

I'm located in NY state, about 60 miles north of NYC. Those are some nice looking potential transformers in the picture

. One other question, do you know if the oil inside that thing is PCB free? I finally got to check the oil in the big X-Ray transformer I have with a DEXSIL test kit. Results came back negative.

Please let me know if you think it will fit & if so, what you're looking to get for the ocr.

Merry Christmas & Happy New Year & 73 de bob (aka sparky99)

J. Aaron Holmes

Mon Dec 24 2007, 06:20PM

Registered Member #477 Joined: Tue Jun 20 2006, 11:51PM
Location: Seattle, WA
Posts: 546

sparky99 wrote ...

I'm a bit familiar with the inside of the OCR. The ceramic insulator inside the can would have to be cut back to fit the transformer. The plexi tube over the insulators would work fine & not look bad. I could always try to retrofit a set of 34.5KV insulators, if I could find 'em. The transformer is small, 8" x 6" x 5". Here's a few pictures:

True; you could put some bigger bushings on there. I expect it would be easier at that point to just make your own lid, though! I have a few larger transformer bushings lying around, but not a nice matched pair.

sparky99 wrote ...

One other question, do you know if the oil inside that thing is PCB free? I finally got to check the oil in the big X-Ray transformer I have with a DEXSIL test kit. Results came back negative.

Yes, the oil in the can is non-PCB (Shell Diala AX) because I added it myself. I got it un-oiled from U of WA Surplus about 15 years ago and filled it only fairly recently. I can't honestly certify what was in it before, but I'd like to think the Surplus folks wouldn't have just dumped out PCB!

And actually, I would be emptying it out again before shipping. That way I can just break it down completely and stick it in a box. I really don't want to ship it with oil. If you have no other oil source, I might consider sending along some Diala separately, but that still sounds like a potential mess!

The history of this particular OCR is a bit interesting, actually: It was part of a scientific instrument aboard a ship. The instrument was basically a large cabinet with a 10kV three-phase transformer and huge capacitor bank, and was apparently used to take depth soundings at great depth. The capacitors would be discharged across a pair of electrodes trailing the ship, producing a huge "BOOM" under water. However despite what you might expect, the OCR was actually just connected between the capacitor bank and a couple of very large resistors, and the lever on it was connected to a rod that extended out the top of the cabinet and had a big red knob on it. I believe the purpose of the OCR was simply to permit discharge of the bank when not in use or else for servicing. The OCR looks just like what you'd see on a pole, though, except that the mounting bracket has been removed.

sparky99 wrote ...

Please let me know if you think it will fit & if so, what you're looking to get for the ocr.

Give me a day or two more to de-can the thing and take some measurements. I'm all caught up in the holiday at the moment and will get major spouse-demerits for hanging out in the garage!

I'll get back to you shortly and include some more pictures, too. If you decide you want it, how does $50 + s/h sound? If it doesn't work out or if you decide you don't want it, no biggie!

Cheers,
Aaron, N7OE

sparky99

Tue Dec 25 2007, 03:30PM

Registered Member #1159 Joined: Fri Dec 07 2007, 02:10AM
Location: Hudson Valley of NY State
Posts: 84

Hi Aaron,
OK, no rush. If you think the transformer will fit, I'll definately take it.

Nice, sunny Christmas day here. Hope yours is the same!

73,
bob
n2oam

J. Aaron Holmes

Wed Dec 26 2007, 04:38PM

Registered Member #477 Joined: Tue Jun 20 2006, 11:51PM
Location: Seattle, WA
Posts: 546

And a belated Merry Christmas to you!

It was a not-clear, not-sunny, not-atypical Seattle Christmas day. We had a pretty good snowstorm going at one point, but no accumulation except on the lawn. My three-year-old daughter's hopes of building a snowman were dashed

I saved a couple of present boxes that look like they'd be a good fit for this sucker. I'll empty it out either tonight or tomorrow night, take some measurements, a few more pictures, and then post them for final inspection. We can keep it all here in this thread until then, since I think pictures of the guts might be amusing to more than just you, and then if you still want it you can PM your address and all that jazz.

Cheers,
Aaron, N7OE

J. Aaron Holmes

Fri Dec 28 2007, 06:03AM

Registered Member #477 Joined: Tue Jun 20 2006, 11:51PM
Location: Seattle, WA
Posts: 546

Ok...

...well, it's going to be TIGHT! Inside, the can is 9-1/2" tall, and just shy of 7" in diameter. How thick is the core, front to back? I know you said the width was 6", but if the core is too thick, the widest measurement may be greater than 7". The height poses another potential (no pun intended) problem: Where do the HV leads come from? It would be nice not to have to chop the HV bushings off right under the lid, but if the HV leads come out on the same side of the transformer, at least one of them will have to pass in between the top of the core and the lid, which seems problematic for such a voltage. I guess the speculation ball is back in your court!

(EDIT: From your pictures above, it looks like the core is about 1-1/4" thick or so. Dusting off my trig skills: That would make for a widest measurement of about 6-1/8")

Here are some pictures of the little thing, freshly de-oiled. You'll notice in a couple of pictures you can see some black rubber that I zip-tied to the structure behind the contactor. I'd forgotten about that. I added that shortly after buying the thing because I didn't like how the contactor arm would smack the plastic support behind it when it was opened. That is not original equipment!

...if the pics make you think of more questions, fire away!

Cheers,
Aaron, N7OE

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