On 2020-07-24 14:20, John Robertson wrote:
On 2020/07/24 10:36 a.m., Adrian Tuddenham wrote:
Brian Struckmeier wrote:

I have new neon sign with a bad transformer (has a short and works
sporadically), it is a 5kv 15MA transformer.Â*Â* I bought a new one
that is
5kv 30ma and the neon fades towards the end of the run.Â* It is nice and
bright the whole run with the original transformer so I am assuming the
30ma vs 15ma is a problem.

Any advice, im having a hard time finding a 5kv 15ma replacement.

The extra current may be damaging the electrodes and causing out-gassing
or overheating the tube so the neon pressure rises.Â* Is there a
possibility that there is an adjustable magnetic shunt inside the
transformer that could be adjusted to reduce the current?

Please be careful - with those sorts of currents and voltages, your
first mistake could well be your last.



Interesting, I did not realize that Neon transformers were current
limiting, behaving somewhat like a ballast on fluorescent lamps:

https://www.richieburnett.co.uk/ballast.html

--------------(quote)---------------------------------------

Neon sign transformers have built-in magnetic shunts which give current
limiting. In its intended use as a supply for neon tube, the high open
circuit voltage of the transformer is used to strike an arc in the neon
tube. Once an arc has formed inside the neon tube, the current must be
limited to prevent overheating of the neon tube and the transformer due
to excessive current flow. (The hotter the arc gets, the more current
flows, so it gets hotter etc€¦)

----------------(end quote)----------------------------------

Thanks for the info! Live and learn, eh?

John :-#)#


HeNe laser supplies are the same way. You have to match them to the tube.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC / Hobbs ElectroOptics
Optics, Electro-optics, Photonics, Analog Electronics
Briarcliff Manor NY 10510

http://electrooptical.net
http://hobbs-eo.com