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Neon Transformers and Removing Shunts

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IamSmooth

Mon Feb 26 2007, 07:16PM

Registered Member #190 Joined: Fri Feb 17 2006, 12:00AM
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Posts: 1567

By removing the shunts I know that one can increase available current. Other than increasing the risk of burning out the secondary is there any disadvantage if one is planning for using these for a TC? What have most of you all done: leave the shunts alone or remove? What were the results (performance and life of the NST)?

J. Aaron Holmes

Mon Feb 26 2007, 07:42PM

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

I have heard of folks removing the shunts from NSTs, however NSTs are not built with overload in mind. In fact, "overload" in NST terms is "normal" in TC terms

The NST secondary wires are hair-fine, and may not last for long at much higher than rated current. I don't know that for certain, though. However, as NST are easily gotten for cheap (in the U.S., at least, and probably in many other places), I'd vote for the tried and true method of paralleling multiple NSTs for higher current over prying them open and modifying them. They are generally covered in tar or (worse) epoxy, and so any modification or, more commonly, repair, is usually a messy, time-consuming process. Often best avoided by just tossing the NST out and getting a new one

My 2c.

Regards,
Aaron, N7OE

Hazmatt_(The Underdog)

Tue Feb 27 2007, 02:17AM

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

Avoid depotting NST's, I've done it 3 times and its a total mess.
Also remenber that depending on the mfgr. you are not guaranteed to have shunt plates in the core. Some mfgr's use a core with the shunt built in with a set air gap. Grinding it down would be a big waste of time because you have 2 shunts per lamination, and close to 200 or more laminations per core.

I'd go parallel with identical NST's as well.

sparky

Thu Mar 01 2007, 07:35AM

Registered Member #530 Joined: Sat Feb 17 2007, 07:56AM
Location: Victoria BC, Canada
Posts: 178

Hazmatt_(The Underdog) wrote ...

Avoid depotting NST's, I've done it 3 times and its a total mess.
Also remenber that depending on the mfgr. you are not guaranteed to have shunt plates in the core. Some mfgr's use a core with the shunt built in with a set air gap. Grinding it down would be a big waste of time because you have 2 shunts per lamination, and close to 200 or more laminations per core.

I'd go parallel with identical NST's as well.

Shunts are 95% accessible in every NST unit I have seen. I spent years recycling NSTs and its now an easy enough science for me, but I must admit I think going with epoxy potting was a dumb idea. I have 2 15kV 60mA NPF NST units that I turned into 200mA units and paralleled them for more power. These units put out 4kW of pure terror!!

Dr. Slack

Thu Mar 01 2007, 08:32AM

Registered Member #72 Joined: Thu Feb 09 2006, 08:29AM
Location: UK St. Albans
Posts: 1659

If you want hairy scary transformer current, then you may be better off seriesing 6 MOT secondaries, centre-tapped to ground, with due control of core potential to minimise the possibilties for insulation breakdown, rather than serious remodelling of existing NSTs. I've had such a 12kV 1000mA "NST" running in air without breakdown for a while now, though admittedly have only powered a JL from it, not had it on a TC, so the insulation has not been seriously challenged. It might need dunking in oil for TC use.

cbfull

Thu Mar 01 2007, 05:42PM

Registered Member #187 Joined: Thu Feb 16 2006, 02:54PM
Location: Central Ohio
Posts: 140

sparky wrote ...
Shunts are 95% accessible in every NST unit I have seen. I spent years recycling NSTs and its now an easy enough science for me, but I must admit I think going with epoxy potting was a dumb idea. I have 2 15kV 60mA NPF NST units that I turned into 200mA units and paralleled them for more power. These units put out 4kW of pure terror!!

I wouldn't mind knowing how you went about converting a 60mA unit to a 200mA unit without melting the secondary. What brand of tranny was it?

I have 4 Magnetek 15/60 units, but with 4 of them I can para them all up to get 240mA so there's really no need to do something like that, but I wouldn't mind boosting them up to 100mA each. I have a big variac that is set up for current limiting service so I would have plenty of control.

Details please!

sparky

Thu Mar 01 2007, 06:39PM

Registered Member #530 Joined: Sat Feb 17 2007, 07:56AM
Location: Victoria BC, Canada
Posts: 178

I have several large cored -older France-former units. Un-potted these NSTs had a large stack of shunts. The primaries were wound with 10AWG - and the secondaries appear to be 26-27 AWG...can't be sure though---. I knocked out a few shunts on either side and ran the NST for a short run on an arc test with the transformers under oil. The secondary current hovered around the 200 mA mark.

These 15kv 60ma unit cores are identical to two cold cathode NST unit I had a while back they were 12 kV 120mA, and one 15kv 120mA - so I guess years ago when metal was cheap france-former used the same core size for all of their units...

Download

Mon Mar 05 2007, 07:33AM

Registered Member #561 Joined: Sat Mar 03 2007, 02:46AM
Location: Adelaide Australia
Posts: 230

i saw a 120ma nst over currented to 250ma one nice arcs to

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