Strange frequent blowing of 500w lamps in a church

[gball]

I look after the lighting in a church, which is basically a set of around 20 500w halogen lamps in fairly old open reflectors.

The lamp life of these seems rather short, I'm changing them after what can't be more than a couple of hundred hours use.

Now I am 99% sure this is just luck, but I wondered whether there are any possible other explanations for the short life. I can't see how noisy mains could affect lamp life (unlike say computer equipment), but thought I would check with the experts.

These are true 500w lamps, not the economy ~400w variety, in an open reflector. Typically it seems to be the wire at the cap end (ie within the glass, not the lamp tungsten itself) which goes.

The other twist is that we had 3x LED floodlamps (50W) fitted a couple of years ago, which also failed. Again that could just be a bad batch, but it does seem slightly odd!

They are all run off a straight set of switches, no dimmers.

 

[securespark]

Could be a bad batch...Have you tried Osram? I swear by them.

Or have you tried a low-energy equivalent: CFL or LED?

If your incoming voltage is higher than the rated lamp voltage, that could shorten lamp life.

 

[RF Lighting]

It might be the pins on the lamp holders are corroded. This will cause a high resistance joint which will generate excess heat at the end of the lamp.

Also try using quality branded lamps, especially the ones designed for use in theatres, such as Philips Broadway

 

[gball]

That's the problem - I haven't been scientific enough to note which ones I changed, and which lamps were from which mfr. With hindsight I should have taken a careful note (especially as half of them are about 20m up from the ground!)

The LED failures were what prompted the thought - they should last 10 years, but started to flicker and failed after 2 years. Again, that could be a bad batch too though!

Thanks RF Lighting on the thought about lamp holder wear, I hadn't thought the heat of a bad contact might cause premature failure. Is that a 'known' failure mode for old high-wattage fittings, or just an suggestion for explanation? I had assumed the lamp end was blowing where there was some sort of internal fuse, but that was a guess. And having an internal fuse link on a linear lamp does seem silly now...

 

[RF Lighting]

Yes it can become a problem with older halogen fittings. When you remove a failed lamp have a look at its ends. They should still be bright and shiny. If they've gone dark / pitted / burnt / rusty then this could well be the problem.


What make were your led fittings? There's some dreadful quality ones around if you're not careful with what you're buying.

 

[Taylortwocities]

If the lamp ends are dirty/pitted, you'll need to shine them up, and the contacts in the lamps fitting itself.

 

[flameport]

Frequent switching will shorten the life considerably.
If they are left on for extended periods, replace with some other lighting such as metal halide.

 

[deadshort]

Hi, your not next door to a Sub station are you ?

DS

 

[gball]

Thanks for the help so far. I will check the lamp ends next time I replace one (in fact one blew yesterday, so good timing)

The Substation was a crazy idea that crossed my mind, but I couldn't believe the voltage spikes were that high. The nearest step-down transformer is only 80 yards away, but I don't think any of the neighbours change their bulbs every month.

Now the other random point: The hall next-door* has infra-red radiant heaters on a manual thermostat (with contactor obviously) - which cycles these heaters on and off. That's about 25kW of resistive load (100A) getting turned on and off with alarming rate. That was my first suspicion, but that should cause a voltage drop, not a spike.

* They are two independently supplied buildings, but the hall is 3 phase, so potentially the heaters are on the same phase as the church (single phase) itself.

 

[stillp]

Are the heaters in the hall balanced across the 3 phases?

 

[gball]

Nope. The heaters in the main hall are on one phase; the heaters in the other hall are a second phase (but much smaller - perhaps 8kw total); the lighting, cooker and all sockets are on the third.

Aha! so could a large switched load on one phase actually cause a voltage increase across the others, if it causes the 'neutral to float'? (I'm sure there is a better word to describe that)

 

[stillp]

Aha! so could a large switched load on one phase actually cause a voltage increase across the others, if it causes the 'neutral to float'?

Maybe. If it's happening every time the heaters switch, it wouldn't need much overvoltage to shorten the lamp life.

 

[333rocky333]

I second Rf regarding the pins, especially when running 500w lamps, also the heat sometimes tends to make them loose there springyness making the situation worse.
you can if you feel its worth it change the lampholder insert.

 

[Echo the husky]

It would be better to fit new lights if the existing ones are open fronted, don't want bits of hot glass from an exploding lamp showering onto the congregation!

 

[RF Lighting]

Yeah I'm not sure how allowed open fronted floods are these days, or how / if you'd code it on an eicr. I've never seen them for sale in all my time in this trade.

My local church had the same lights until about 10 years ago when we replaced them all with 70W HQI fittings to save energy and reduce maintenance.