Hello,

I am working on an old comparator, and I have changed the light circuit to 12VAC to use an FDT halogen bulb. The bulb is 12V 100W, and I am using a 120V to 12V 150VA control transformer to power it. The bulb is burning out right around once a week. Can anyone give me an idea as to why? Any direction would be greatly appreciated!

~Thanks

 

Sounds like the transformer output voltage may be too high.
Do you have a multimeter to measure the voltage?

 

Transformer output is 12.36V. I measured current to the load on both wires, and it is 8.1A and 7.5A

 

Did you touch the bulb with your hands?

 

Nope. I use the plastic that it comes in or a Kimwipe, which is like a small paper towel.

I'm wondering if it isn't the socket. I'm trying to find a replacement, but it's proving to be difficult.

 

Transformer output is 12.36V. I measured current to the load on both wires, and it is 8.1A and 7.5A

There's something wrong with your current measurement.
The current on both wires has to be the same since they are in series.

I don't see how the socket could be a problem.

What is the problem is a real curiosity.

Who is the bulb manufacturer?
I had my original halogen bulbs on a new microwave burn out prematurely.
The name brand bulbs I replaced them with are lasting a lot longer.

 

These lamps usually only have an average life of about 50 hours or so.
a lot of halogen lamps in the last couple of years have really dipped in their life expectancy quality.

how long are you running this lamp for and is it for sustained periods or is it intermittent use?

I work in the lighting industry so i can help maybe with the lamp side of fault finding.

Soogs

 

It is an Eiko FDT bulb

 

When you mount the bulb. Is the filament in a vertical or a horizontal position? Hint: horizontal is always better.

Also, low voltages tend to affect a halogen bulb's useful life.

 

Replace with an LED and be done with it..

 

As @cmartinez points out, a halogen bulb relies on high temp, thicker glass (usually quartz) with that cools slowly an some halogen gas in the tube - this allows the tungsten to re-deposit on the filament each time it is turned off. So, short cycling of a halogen bulb will kill (turning it off before the glass has time to warm up). Likewise, running it at low voltage so it never warms up will also kill it. Also, running it in an area with forced cooling if the bulb was designed for ambient will kill the bulb. To see if any of these three issues are shortening the life of the bulb, look for dark/black/gray deposits inside on the glass (tungsten vapor depositing on the glass instead of back onto the filament.

Running in small enclosures will kill it (Because it overheats or, if forced air cooling, it never reaches operating temperature).

Vibration is also bad.

 

@mcgyvr.. I've looked into it, and I can't find an LED that puts out 3000 lumens in such a small package.

@GopherT... I will make sure it doesn't get cycled without proper warm up. It is in a smaller space with not much air flow. The glass looks like it has a dark gray blotch of paint on it when it blows. It isn't just breaking the filament.

 

I don't see how the socket could be a problem.

The sockets are responsible for getting rid of a significant amount of heat. Corrosion causes more heat at the contact point instead of less heat.
I would also mention that the power line voltage at my house is 250.1 VAC, rated 240VAC +/- 5%.
Putting a buck transformer in series with my 115V rated HPS lamps increased their lifespan from 2&1/2 years to, "I don't know". I've never burned one out in the 13 years since I bucked the power voltage down from 125 to 109 VAC.

 

I am working on an old comparator,

I'm assuming this is an optical comparator, we left ours on all day once it was light. The heating and cooling of the bulb was harder on it than leaving it on.

 

Interesting point (in #13, from #12!). At my house, my HF meter shows ~119.5±1V every time I've ever looked over the last 25 years. It might be even tighter than that.

Where did the nominal voltages for our power come from? I mean we call it 110 or 120 interchangeably, or 220 or 240. Why is the nominal voltage so fuzzy?

 

Why is the nominal voltage so fuzzy?

Because it has changed several times over the decades. There is a Thread here (somewhere) with charts.

 

Where did the nominal voltages for our power come from? I mean we call it 110 or 120 interchangeably, or 220 or 240. Why is the nominal voltage so fuzzy?

I am with you on this question... You forgot to mention 115 and 230 volts...

 

Because it has changed several times over the decades. There is a Thread here (somewhere) with charts.

Yeah, I vaguely recall that. So the current nominals are 120/240 and the lesser values show up because of older equipment still on line?

 

I have transformers marked, "120/208/230"
I have water heater elements marked, "240 VAC".
I have a Fender Guitar amplifier with an accessory outlet marked, "115 volts".
My 1979 Clothes dryer had to be converted to a 120V rated Calrod heater instead of 115V rated coiled nichrome so the heater would last more than 3 weeks.
Engineering is always a series of compromises.
If you live in Gnaw Bone Kentucky, you have no reason to expect the same voltage as La Vegas.