Replacement Fuses for Neon Sign

[kbuhagiar]

Hello folks,

I have an old neon "NO LEFT TURN" sign which was used on the streets of San Francisco up through the mid-80s. It is very similar to the common "WALK" - "DON'T WALK" signs of that era, but the twin segments read out "NO" and "LEFT TURN". (For you locals, these were the ones installed along Lombard Street on the US 101 corridor leading up to the Golden Gate Bridge.)

(See attached picture - EXACTLY like this one but with 'left' instead of 'right' - and minus the hoodlum.)

My particular unit was acquired NOS - never installed but cleared out of inventory after the city obsoleted all neon traffic signs. It is mounted in my garage and I light it up very occasionally, MAYBE 4 or 5 hours a year. Although it has low usage, it's still old, pretty sure it was manufactured sometime in the mid-1970s.

Transformer specifications are as follows: "FRANCEFORMER power factor corrected", manufactured by France Manufacturing of Cleveland, Ohio.
Part #7560PLK07
Input 115V, 60 cycles, 250 VA
Output (secondary) 7500 volts, 60 MA

There are two in-line fuses on the line, one each for hot and neutral. They are Bussmann MIN-5 5-amp quick acting indicator-style fuses. Both of them are blown and need replacement; this just happened out of the blue last week.

Before I start replacing fuses I want to see if I can figure out what caused this, as I hate to just pop in a new fuse before determining cause, not to mention that the replacements I have found so far are north of $10 apiece.

Questions - Could this be indicative of a transformer failure? If so, what is the best way to check the windings? Can I use some other kind of (cheaper) fuse in place of these?

Thanks in advance for your time and trouble.

 

[cybrdyke]

France is still in business. You can look them up at www.sfeg.com . I'd recommend calling them and asking about it.
I'd be verrrrry leary about trying to "check the windings" of a 7500 volt transformer. Be careful!
CD

 

[wyliesdiesels]

If the fuses are on the line side, it could be the transformer.

You would need a megohmeter to test the windings, which are not cheap. Only problem is the 7.5KV rating. Im not aware of a megometer that would be rated for the voltage needed to test that.

 

[kbuhagiar]

France is still in business. You can look them up at www.sfeg.com . I'd recommend calling them and asking about it.
I'd be verrrrry leary about trying to "check the windings" of a 7500 volt transformer. Be careful!
CD

CD,

Thanks for the response. I certainly won't be anywhere near that transformer output (or input FTM) when energized. Perhaps 'check the windings' was a poor choice of words...would there be any risk in testing a completely de-energized and disconnected transformer?

 

[kbuhagiar]

Follow-up question:

Is it normal for fuses on both sides of the circuit to blow at once?

Or is it indicative of a bigger problem?

We had been having some local POCO (PGE) problems with slightly fluctuating line voltages (caused by failing old lead cables in local UG feeds, which have since been resolved) just prior to the fuse failures.

 

[wyliesdiesels]

how much did the line voltages fluctuate?

 

[mattblast]

It’s easy to test a neon sign transformer. I’ve done this several times as I’ve repaired signs and bought a few in unknown condition and needed to test them.

At 7500 volts, it will jump a fraction of an inch. You can connect a wire from one of the high voltage terminals until about 1/4” from the other terminal. Then stand back and plug in the line voltage. If you see a spark buzzing between the two terminals then it works. Unplug.

I’ve used a metal hanger to test as you can shape it so it will hover just by the second terminal without touching.

In my sign it turned out that the xformer was fine. The tube leaked gas. Gas tubes can be tested using a mini Tesla neon tester. (Or a full size Tesla coil will light it up too but that is harder to build). Blown tubes can be refilled at a local neon shop.

 

[kbuhagiar]

how much did the line voltages fluctuate?

Wylie,

I couldn't give you a precise voltage measurement, but everyone in our neighborhood had been experiencing lights flickering regularly throughout the day for about a week. Then one day the power failed completely and we were out of service for approximately five hours. Since then the flickering has been gone...for now, anyway.

I expect that we may encounter more of the same problems in the near future...our neighborhood was one of the first to have been planned with all-underground utility service when it was built in 1947. As I was told by PG&E there are still sections of the original lead cable in place which are prone to these types of failures. At some point they expect to have all of the old lead cable replaced, but apparently they will only replace it as it fails.

 

[dogdog]

I say if the fuses are not too expensive, just give them a shot first... I think transformers you diag/measure with inductance meter... normal multimeter don't have that functions...

This guy shows you how to measure the transformers...properly. Lots of math though.

 

[cybrdyke]

would there be any risk in testing a completely de-energized and disconnected transformer?

I dont think you could learn anything by trying to test a de-energized transformer.

Follow-up question:

Is it normal for fuses on both sides of the circuit to blow at once?

Or is it indicative of a bigger problem?

We had been having some local POCO (PGE) problems with slightly fluctuating line voltages (caused by failing old lead cables in local UG feeds, which have since been resolved) just prior to the fuse failures.

It is certainly possible for an overvoltage event to blow both fuses....also to kill the transformer. It wouldn't be normal for a transformer failure to cause the death of the fuses, but I suppose it's theoretically possible.
If I had to speculate, it sounds like a voltage surge got you.
CD

 

[kbuhagiar]

I dont think you could learn anything by trying to test a de-energized transformer.

Thanks CD, that's good to know.

It is certainly possible for an overvoltage event to blow both fuses....also to kill the transformer. It wouldn't be normal for a transformer failure to cause the death of the fuses, but I suppose it's theoretically possible.
If I had to speculate, it sounds like a voltage surge got you.
CD

I found an inexpensive source for the elusive MIN-5 fuses, so my next course of action will be to replace the fuses and see if that fixes it...keeping my fingers crossed, but if that doesn't do it I've identified a couple of sources for a replacement transformer.