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Help identifying transformer - Newbie

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Bob Jones

Tue Oct 02 2007, 11:19PM

Registered Member #1040 Joined: Tue Oct 02 2007, 10:13PM
Location: San Bernardino, CA USA
Posts: 6

I just joined, and I'll be up front and say I'm not a high-voltage experimenter, but I have a few transformers that might be of interest to someone. First, I need a little help identifying them.

They are made by Hipotronics, and are labeled "high-voltage AC tank". There are connections for the primary on the side of the enclosure and a whopping big red insulator with a center ball contact. I know they were used at 60 Hz by a lab I used to work at and the part number is T725-15MA. The 15MA part is pretty obvious, but the T725 I'm not so sure about. Maybe 7.25 kV, but the insulator looks like way overkill for that. 72 kV maybe? At that voltage 15 mA sounds like way too much. Anyway I have a few of these things that I would like to part with, so if we can figure out what they are I can post them on the classified section if anyone is interested.

BTW, the box is 10"H x 9"L x 8" W and the insulator is 7" long x 3" diameter. The box is oil-filled.

As a clueless newbie, I'll try to attach a jpeg and see what happens...

Myke

Tue Oct 02 2007, 11:38PM

Registered Member #540 Joined: Mon Feb 19 2007, 07:49PM
Location: MIT
Posts: 969

Well 15mA @ 72KV is about 1080W so that seems fine. but I don't know if a 7 inch long insulator seems kind of short because at 110KV it will arc between needles at ~6.9 inches through air. It's a bit overkill I think to have a 7 inch insulator if it's only 7.25KV. See if you can try to connect it up and see when the arc starts. ~1.1KV for every 1mm.

...

Tue Oct 02 2007, 11:39PM

Registered Member #56 Joined: Thu Feb 09 2006, 05:02AM
Location: Southern Califorina, USA
Posts: 2445

The easiest way to find out is to just put a few volts into the primary at 60hz, and see how much you get out of it. If you are expecting 70kv with 100v in, then if you have 1v in you should get about 700v out (which can be read by most voltmeters).

The easiest way is to use a variac, but if you needed you could run a few small transformers in series, like a 120v->12v into another 120v->12v, which would give about 1v out.

Of course this will only give you a very rough estimate, but it will tell you how far away from it you need to be when you power it up ;)

Bob Jones

Wed Oct 03 2007, 12:08AM

Registered Member #1040 Joined: Tue Oct 02 2007, 10:13PM
Location: San Bernardino, CA USA
Posts: 6

Yes, I could do that. I thought about running the output of a variac into a filament xfmr to be certain the voltage couldn't get too high but I thought I'd ask first to see if someone here already knew. I have a small yellow streak when it comes to HV. Once a long time ago I got onto the plate supply of a pair of 6146 amplifier tubes and I didn't like how that felt...

Hazmatt_(The Underdog)

Wed Oct 03 2007, 06:18AM

Registered Member #135 Joined: Sat Feb 11 2006, 12:06AM
Location: Anywhere is fine
Posts: 1735

Wooo! be real careful around that transformer. You may need a 40kv test probe to test the output with low input voltage. Or you could make a HV divider chain of say 10 10M resistors and 1 1k resistor, that would give you 100M:1K. I dunno what that works out to at the moment, its 1k / (10M +1K) is your division ratio. Just be real careful.

Bob Jones

Wed Oct 03 2007, 06:14PM

Registered Member #1040 Joined: Tue Oct 02 2007, 10:13PM
Location: San Bernardino, CA USA
Posts: 6

I will be careful. I have a Tektronix HV probe and I'll keep the input low. The probe is 20 kV max at 60 Hz but that'll let me go high enough to see what the transformer is doing. I've been searching the web and have found some info the suggests this might be a 25 kV transformer. I should've just set up to test it before I asked, but being basically lazy (and something of an HV coward) I thought I'd check.

Since cowardice clearly wasn't going to cut it, I dug out my probe and set up a test. Since the probe tops out at 20 kV rms I ran the output up to about 19 kV rms. At that output the input was about 80 Vrms so it looks like it is a 25 kV, 15 mA transformer. The first two images are the setup, with the left meter on the primary and the right meter on the probe (1:1000). The last one is with the probe on my old scope, with 50 V in and about 30 kV p-p on the scope (5v/div).

Thanks for your comments. Sorry to ask the question when I had the means to answer it myself, but I really am a bit of a coward with HV and I avoid it when possible.

Not knowing much about what you folks do, might anyone be interested in such a transformer?

Note to self: Read rules first, then post.

I went looking for someone who might have a use for these things, so I joined for the purpose of seeing if anyone was interested in them and a few other items. I see that is verboten. I had no ill intent, and it's your board so your rules.

Moderator, feel free to delete this thread and you can kill my membership while you are at it. Sorry if anyone thought I was up to something.

Wolfram

Thu Oct 04 2007, 05:39AM

Registered Member #33 Joined: Sat Feb 04 2006, 01:31PM
Location: Norway
Posts: 971

Relax. We don't ban people for trying to sell things before they have 15 posts.

I'll let this thread stay, as it's a relevant thread.

You can make a sale thread for the transformers when you have more than 15 posts.

Please don't double post. I just merged your three posts into one.

Anders M.

Steve Conner

Thu Oct 04 2007, 08:59AM

Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706

Hey, I'd buy one from you if it weren't for the cost of getting it shipped across the pond to the UK.

Like Anders said, all you need to do is make your 15 posts relevant to HV and then you can pimp your items for sale as much as you like. We have this rule to discourage people joining up for the sole purpose of advertising things for sale. It's not that we don't like selling things, but there are a lot of spammers who join forums just to post ads for OMG $99 (fake) Motorola RAZRs and the like.

Bob Jones

Thu Oct 04 2007, 04:49PM

Registered Member #1040 Joined: Tue Oct 02 2007, 10:13PM
Location: San Bernardino, CA USA
Posts: 6

I checked after posting and only saw one. Sorry for the multiple post.

It wasn't that I expected to be banned, it's just that I don't really want to get involved in yet another web forum (too many already) just to try to create some sense of credibility so I'm OK to post a for sale ad.

The xfmrs will no doubt show on feebay in the near future.

Cheers

Wolfram

Thu Oct 04 2007, 08:32PM

Registered Member #33 Joined: Sat Feb 04 2006, 01:31PM
Location: Norway
Posts: 971

Post a link here when you put them up then, I'm sure many people here would be interested.

Anders M.

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Moderator(s): Chris Russell, Noelle, Alex, Tesladownunder, Dave Marshall, Dave Billington, Bjørn, Steve Conner, Wolfram, Kizmo, Mads Barnkob