Neon sign transformer testing - Page 1
Forum section: electronics / beginners

author: poot36
author_rank: Frequent Contributor
timestamp: July 17, 2015, 02:54:12 am
content: I have a neon sign transformer that I am trying to see if the secondary winding is intact but with the sign unplugged I measured the resistance between the two outputs and I get nothing. I also measured between the earth pin and each output and still got nothing. When I measured the capacitance between earth and each output I got 0.06nf on one side and 0.14nf on the other. I have tested the resistance of the primary and it measures around 45 ohms. I do not want to do any tests that require the sign to be plugged in because I do not have the appropriate high voltage testing equipment available. The sign is rated at 7500V and 30ma and is made by Franceformer in 1982 and says secondary mid-point grounded on it.

author: BennVenn
author_rank: Regular Contributor
timestamp: July 17, 2015, 03:34:46 am
content: Secondary mid-point grounded should read around 1kohm between the GND lug and any one of the secondaries, atleast on mine it does.

author: poot36
author_rank: Frequent Contributor
timestamp: July 17, 2015, 03:41:47 am
content: Ok, so I am going to assume that my transformer is most likely broken. It did come from a fixture with a broken tube so it could have gone over voltage. Do you think that there is any merit to trying to use fluorescent light transformer to try and zap the presumably broken windings back together?

author: NiHaoMike
author_rank: Super Contributor
timestamp: July 17, 2015, 06:31:24 am
content: Clip some wires to the output, set the ends maybe 1/4" apart, then plug it in for a moment while keeping well clear of the wires. It should arc if it's good.

author: poot36
author_rank: Frequent Contributor
timestamp: July 18, 2015, 08:19:08 pm
content: Ok after some zapping with the fluorescent light transformer I am now getting 250K ohms between one winding and ground and 800K ohms on the other. When I supplied the input of the transformer with 6V AC I got 180V from one winding to ground and 195V from the other winding to ground. Is this good or bad?

author: SeanB
author_rank: Super Contributor
timestamp: July 19, 2015, 02:26:46 pm
content: Good enough to now try with mains via a current limiter, like a 100W lamp as a dim bulb tester. No band and light is not at full brightness is a pass.Funny enough yesterday I was just hooking up my neon sign collection. I wanted a sign, but the painters butchered it off with a sledge hammer and an axe.

author: Stray Electron
author_rank: Super Contributor
timestamp: July 24, 2015, 08:06:07 pm
content: Neon sign transformers are now some kind of switcher design with a voltage tripler type circuit on the output and I don't think that you can check them by measuring the resistance across the output and they also won't work in a lot places where a realtransformerwould. If that one doesn't weigh at least 15 or 20 pounds then it's a switcher and not a transformer.

author: poot36
author_rank: Frequent Contributor
timestamp: July 25, 2015, 04:46:09 pm
content: The date I found on the case is 1982 so I think that it is a transformer. As well when I tried to open it up it was all potted in black goo.