Lithium batteries & Xenon bulbs

A friend of mine is a Search & Rescue professional & tells me that he can't use lithium AA batteries with a Petzl Myo headlamp because the batteries will burn out the Xenon bulb.

He probably knows what he's talking about, but now I'm scratching my head as to why that would happen. I thought the device would just pull what it needs, but I guess it gets too much current from these more potent batteries.

The batteries are just 1.5 volt.

http://www.tigerdirect.com/applications/SearchTools/item-details.asp?EdpNo=720594

Here's the headlamp.

http://www.altrec.com/shop/detail/15924/

If anyone knows of high intensity Xenon powered headlamps that can use lithium batteries, I'd sure like to pass that info. on to him. He needs the lithiums because of the extended runtime & their ability to work in cold weather.
He's in Canada, heh.

I use lithium AA batteries in my Petzl Duo and haven't had any problems with burning out the high beam (xenon) bulb. Lithium AA batteries do have an open circuit voltage of 1.7-1.8v and I have experienced early bulb failure when using them in mini-mag lights. With fresh Lithium AA batteries in a min-mag light I find that mechanical shock when the lamp is on will often cause the lamp to burn out. With the 0.5A xenon bulb in a Petzl Duo I have not had any problems and I expect that the high drain of these lamps pulls the Lithium AA batteries down from their open circuit voltage of 1.7-1.8v to more like 1.5-1.6v.

I am also using lithium AA batteries in a UK 4AA with the 4 watt lamp:
http://www.candlepowerforums.com/ubbthreads/showflat.php?Cat=&Number=479232&page=&view=&sb=5&o=&fpart=1&vc=1

Actual open circuit voltage from a lithium battery (L91 AA or L92 AAA) is about 1.72 volts. These batteries normally operate at 1.6 volts even with fairly heavy loads. This is compared to the normal 1.6 oc volts, 1.5 loaded volts from an alkaline battery. I don't know if he's tried it or if Petzel has warned against it, but it is probably true. I wouldn't hesitate to try it in an emergency, but I would attemp to start with USED L91s if possible.

As you can see, the lithium battery may have 10% higher voltage in use than the xenon bulb is designed for. And they are usually designed close to the performance limit at the expected operating voltage (alkaline, or 1.5v batteries). I have used xenon bulbs at up to 10% overvoltage but I do recognize that I may ocassionally fry one.

That drawing 'only the required current' works only if the voltage is held to a fixed level (or a design maximum). Current draw is actually determined by the applied voltage and the impedence (resistance for DC) of the entire circuit as well as the load. That's why we often need to use a voltage or current regulator, sometimes the voltage or circuit characteristics vary too much in a particular application.

Thanx Guys,
I'll pass this along to SARHound...

Streamlight has a new luxeon star headlamp that runs on AAA's, called the Argo I think. BTW, it's eh, not heh, eh?

Tell him to get one of the older style Petzl headlamps (Zoom Zora, Duo, Micro) instead of the Myo. Their bulbs are terribly yellow and ugly. With lithiums, they should work pretty well. The newer Myo has a bulb color that is much improved, but they expensive and not easy to change, especially with cold hands. Better bulb color = driven closer to the bulb limit.

Black Diamond's headlamps might work better with litiums. I have only tried Lithiums in mine once, but they worked fine.

BD Supernova, lithiums are ok'd by the manufacturer. And in my experience they work great in it.

Last year I used lithiums in my PT Vortec. The light stayed brighter a lot longer than alkalines, and the headlamp was more comfortable because of less battery weight. BTW, I was using the stock halogen bulb, I think that the Mag xenon bulbs are less tolerant to overdriving.