Photo Cells and Low Voltage Lighting

[Chamuit]

I have a job where the customer has exterior lights (low voltage, 50W MR16) being operated by a Tork 3010 photocell.

They have had to replace almost 100% of the lamps in less than 6 months.

Is it possible that the photocell is shortening the life of the lamps?

There are two fixtures per living unit fed by the power in that unit. The power source for the fixtures is different from unit to unit.

 

[broadgage]

I very much doubt it.
The photocell simply switches the lamps on and off via a relay or perhaps a triac, neither of these will increase the supply voltage which is the principle cause of short lamp life.
Excesive temperatures or vibration, or poor qaulity lamp holders can also reduce lamp life, but are not influenced by the use of a photocell for switching.

If the lamps are lit all night, then 6 months seems a fair life and failures are to be expected.
The average life of 12 volt MR16s varies from about 1000 hours for cheap imports to several thousand hours for reputable brands, therefore 6 months which is about 2,500 hours of all night use is not bad.
10,000 hour MR16 lamps are available in the UK and presumably elswhere, but are not widely used.

 

[Dennis Alwon]

MR 16 bulbs don't last very long, IMO, esp. the 50 watt bulbs. If the fixture is enclosed I would install an MR- 16 35 watt and see if that helps.

 

[Chamuit]

Thanks guys. I was thinking a 130V lamp might help too. Hadn't thought of lowering the wattage too.

 

[Electric-Light]

Magnetic low voltage transformer steps down voltage and low side is proportional to line voltage, so if the line voltage runs high (i.e. 126v all the time) the low-side is also going to be about 5% high and halving the lamp life. If there is no taps to change, go with electronic transformer.

 

[Dennis Alwon]

Thanks guys. I was thinking a 130V lamp might help too. Hadn't thought of lowering the wattage too.

130v for LV??? Why would you need 130V lamps for a lv system--- 12v for 12v-- now your transformers may be putting out 13 or 14 v and that could be the problem.

 

[Chamuit]

130v for LV??? Why would you need 130V lamps for a lv system--- 12v for 12v-- now your transformers may be putting out 13 or 14 v and that could be the problem.

You don't think that will work?

Sorry brain-fart there. That's why I talk to y'all. I look like an idiot here instead of in front of the customer. :roll:

 

[John120/240]

We want to see how red your face gets. The advantage of an anyomuous place

to discuss ideas.

 

[Chamuit]

Okay, so I go to this job. I plug my DMM into the socket of the LV fixture and get nothing. Just an ohm or two or zero. Plug the lamp in. It works. Plug another DMM tester in. Nothing. What am I doing wrong? Did I forget something?

Both testers read from 0.1V +

 

[Chamuit]

Oh, another thing. They are getting around 60 days of life (or less) out of these lamps. I thought about setting up a receptacle (aka plug) on to the back of one of these fixtures. (They are wired inside the garages in EMT and 4squares.) Then plugging in my Voltage Performance Monitor in and leaving it for about a week. See if anything shows up on that.

 

[Chamuit]

Excesive temperatures or vibration, or poor qaulity lamp holders can also reduce lamp life, but are not influenced by the use of a photocell for switching.

These lamps are failing at the high rate even through our mild Phoenix-metro winter.

 

[broadgage]

Okay, so I go to this job. I plug my DMM into the socket of the LV fixture and get nothing. Just an ohm or two or zero. Plug the lamp in. It works. Plug another DMM tester in. Nothing. What am I doing wrong? Did I forget something?

Both testers read from 0.1V +

I consider it likely that electronic transformers are fitted.
With the lamp removed and therefore no load on the transformer, no or very little output is produced.
Even measuring the output on load wont help much, the fact that the lamp lights is proof that at least roughly the correct voltage is present on load. The output is at very high frequency and most testers wont measure this accuratly.

It would be worth measuring the AC line voltage input, if this is at the upper end of the range, then the output voltage will probably be increased in proportion, and that would shorten the lamp life.

What brand lamps are used ? for cheap ones I would consider 60 days reasonable.
Here in the UK, and presumably elswhere, ultra long life MR16s are available that are claimed to last 10,000 hours.
I am not certain that they last that long, but they definatly last longer than regular name brands, and MUCH longer than el cheapos.

 

[Chamuit]

Even measuring the output on load wont help much

I even tried that. What if I placed my tester in series to the lamp? could I make that work?

The output is at very high frequency and most testers wont measure this accuratly.

Darn!

It would be worth measuring the AC line voltage input, if this is at the upper end of the range, then the output voltage will probably be increased in proportion, and that would shorten the lamp life.

Should I test until the next failure? Or just for a week or so? I'm thinking of picking the house with the highest failure rate to monitor.

What brand lamps are used ? for cheap ones I would consider 60 days reasonable..

They have use several brands including and open xenon bi-pin. They just started tracking the failures at the beginning of Feb.


Thanks!

 

[Electric-Light]

Here in the UK, and presumably elswhere, ultra long life MR16s are available that are claimed to last 10,000 hours.

Those are the equivalent of higher-than-nominal rated, such as 130v bulb even though no such nominal voltage exists in the US. They're a good solution when you have a line that is consistently running around 125v.

Long life bulbs are basically the same thing. The filament life is increased exponentially with reduction in filament temperature which is changed by voltage.
10,000 hr incandescent will run the filament at lower kelvin, have a lower efficacy, in trade for longer life.

Electronic transformer is not like a magnetic transformer. It is more like a switching power supply, so it should have a better control of output even with a variation of input.
If you want to measure the output, Fluke 18x and 289 are good to 100KHz.

 

[broadgage]

Agree, the extra long life MR16 lamps to which I refer are in effect 12.5 or 13 volt lamps, though to avoid confusion they are refered as "12 volt"
I would expect them to be less efficient, though they seem very similar to regular lamps in light output.

I could recomend a UK supplier if that would help, they cost ?1 each if purchased by the hundred. Might be worth the cost of air mail if you cant obtain locally ?
They are available in 20, 35, or 50 watt.

 

[Electric-Light]

They're probably available through Alibaba or Tradekey.

I have a 50W MR16 lamp with no brand that was sold for 97 cents.
It's made in China, as you expect. It's a private label promo item from The Home Depot. The SKU is 955-201 and it says Distributed by Home Depot USA,, ATL, GA