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Burning halogen bulbs

Posted by robobass (My Page) on
Wed, Sep 8, 10 at 17:32

My wife has a fancy halogen lamp in her office. The original dimmer burned out. Replacement dimmers were unsuitable because of noise, and since she always ran the lamp at full, I wired a simple on/off switch. The problem is that now the $14 bulbs (Euro PSD 05/07) last only a few months. I figured that the switch was causing the problem, and that the bulb wasn't built to deal with instantaneous full-on voltage. A friend in the lighting industry told me this was nonsense and that premature burnout must be coming from excessive handling and vibration of the lamp. Anyone know if this is true? If my intuition is correct, could I modify the switch (with a capacitor, perhaps) to decrease the shock to the bulb?


Follow-Up Postings:

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RE: Burning halogen bulbs

My view is that it is never safe to modify a UL-listed device and hope you aren't creating a fire hazard, and possible insurance problem. Just my paranoid outlook...


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RE: Burning halogen bulbs

I have seen many UL listed devices so poorly made that I am amazed that they work for 15 minutes without bursting into flames and/or electrocuting someone.
With due consideration to that fact, I agree to a point with kudzu9's statement. If after you modify a device you "hope you aren't creating a fire hazard", you probably lack the knowledge and skills to do so. For the purpose of this post, I will say you know how to replace a dimmer with a simple switch. BTW, I have heard rumors about residential insurance policies that prohibit non listed devices, but have never seen one.

If it were my wife and her "fancy halogen lamp" I would find a Variac rated at or just over the needed current, set it at 90% or thereabouts and put it someplace out of sight. The combination of the impedance of the Variac and slightly reduced voltage will make the lamp last much longer.


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RE: Burning halogen bulbs

Turning an incandescent lamp on with a dimmer will indeed make it last much longer. It limits the inrush current drawn by a cold filament.

I couldn't find any info on the net about a "Euro PSD 05/07" lamp. However, it's possible that that particular lamp is designed to operate with a dimmer which never quite delivers full voltage. So with a switch you may be not only hitting it with inrush current it wasn't designed for, but also overdriving it.

That said, underdriving it consistently isn't necessarily the right thing to do either. A halogen lamp has an internal chemical reaction which causes the tungsten evaporating off the filament to be re-deposited onto the filament, instead of just condensing onto the (cooler!) lamp envelope (quartz bulb). This makes the filament last longer and slows darkening of the bulb. But this reaction only "goes" if the lamp temperature is high enough. Dim it too much, and the temp gets too low for the reaction to work.

Of course, if it's dimmed way down, the lower filament temperature vastly reduces the tungsten loss anyway, so there's less need for the halogen reaction. But then the lamp becomes less efficient in terms of lumens per watt.

Lots of blab here, I guess, sorry, but the bottom line is that I'm suggesting you buy an original factory part dimmer and put it back in.


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RE: Burning halogen bulbs

"My view is that it is never safe to modify a UL-listed device and hope you aren't creating a fire hazard, and possible insurance problem. Just my paranoid outlook..."

I think you are being a bit paranoid. By your reasoning, one should never replace a faulty plug on the end of a cord. Better to be safe and legal and just throw the device away. Note: the plugs and switches you buy a Home Depot are UL approved.

"Turning an incandescent lamp on with a dimmer will indeed make it last much longer. It limits the inrush current drawn by a cold filament.
I couldn't find any info on the net about a "Euro PSD 05/07" lamp. However, it's possible that that particular lamp is designed to operate with a dimmer which never quite delivers full voltage. So with a switch you may be not only hitting it with inrush current it wasn't designed for, but also overdriving it."

This is what I'm getting at. Is it a fact that certain halogen bulbs should not be exposed to instantaneous "full on" current? I don't know whether your second statement is true or not, but my instinct is that the ramped startup is a factor, even though my friend who works in the industry said it is flatly false. He said that there was nothing wrong with a simple on/off switch.

To all: I read and contribute to various forums, and try to provide knowledge when I have knowledge to provide. When I don't I stay silent. Why is this format spoiled by people who know nothing about a topic but must chime in anyway with idiotic safety warnings and other nonsense. I must say that the usefulness of web forums has greatly decreased in the last ten years.


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RE: Burning halogen bulbs

... not all safety warnings are idiotic, first.

That said, one of the sites related to repairfaq discussed "soft-start" circuits and found that they do not significantly increase the lifespan of lamps. There was a theoretical explanation of why. I'm not tearing my hair out trying to find the site again - you can take my word for it or google it yourself.

As far as overdriving the lamp: the official rated voltage (as well as expected life) should be printed on the box. I can't find your lamp either, although I found reference to a PSD-05-24 Halogen lamp on an absolutely un-navigable Chinese website.


A capacitor on AC will not create a soft-start circuit. Depending on its rating and how you attempt to wire it, it will either make the lamp altogether dimmer, change the power factor, trip a circuit breaker, or explode and smell real bad.

I can find you a soft-start circuit online if you insist (or you can find one), but by the time you've built it, you've already paid for the new dimmer.


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RE: Burning halogen bulbs

robobass-
Yes, I'd replace a faulty plug with the equivalent...but that's not relevant to my point. I was talking about potential issues in modifying a device, not simply repairing it. UL-listed lamps typically go through a testing process that determines their operating safety based on the specs of the original components. It may or may not be safe to change one of those components out and replace it with something that has different specs or operational characteristics.
I was not trying to be unhelpful. I was trying to make sure that the OP was aware that a modification of the type he was describing had the potential to cause him a problem.


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RE: Burning halogen bulbs

I hope you not touching the bulb with you bare fingers while you're installing the bulb. this will shorten the life of the bulb. just for a test can you find a diode with the proper spec to place in series with the lamp? this should reduce the voltage to lamp and make it last longer. Don't consider this for a long term solution only fact finding. if it works, find the better dimmer and uses that. try changing the leads on the dimmer.

dimmers do increase the life the light bulbs. we've been using the same light bulbs since we moved into our house '94.

-dkenny


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RE: Burning halogen bulbs

Ah! I finally tracked down the original bulb. It's called Osram Ceram with B15d socket. I read a detailed description of the bulb and no mention is made of the need for a dimmer. I think that it was a combination of too much handling (My wife was moving her office space around during renovations) and using a knock-off replacement bulb which caused the shortened life. Yes, she knows not to touch the bulb. It would be impossible to replace the dimmer exactly, as the burnt one is long gone, and the lamp itself has no name or model# on it. I think I'll buy an original bulb and stick with the simple switch, and only add a dimmer if the problem continues. My wife absolutely hates dimmer buzz, and always runs the lamp on full anyway.

Thanks everyone!


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