LED warning?

[R K]

Found this article today…

LED article

I have been using lithiums for this past season and havn’t noticed any problems with my tikka plus. I did notice that it felt quite a bit warmer than normal when using it though.

[paul johnson]

***deleted***

the original content of this post, which linked directly to the Petzl webpage, added no additional info which was only noticed after taking the time to follow links in the article linked to by the previous post. my apologies to all.

[Michael Davis]

I have a Petzl Tikka XP and I was about to buy lithium AAA for an October trip through the White Mountains.

Of course, I could continue with that plan and after the LED’S burned out, I could find navigate with my glowing forehead!

[Chris Jackson]

I wonder whether the warning applies to voltage/current regulated lights such as the princeton tec EOS?

[paul johnson]

Don’t have the PT Eos “owner’s insert” in front of me – this would perhaps be the best source of info to get an answer to your question.

However, a quick trip to the PT website revealed the following info:

1. the webpage for the EOS, the Quad (both 3xAAA) and the older Yukon HL (3xAA) listed ONLY alkaline batts. (emphasis mine).

2. whereas, the webpage for the new Apex as well as the Corona listed multiple battery types, including Li batts.

Hope this info helps.

[Roger Caffin]

If you take three 1.5 volt batteries you have, in principle, 4.5 volts. But the white LEDs want about 3.6 volts. That’s 0.9 volts excess grunt.

The difference between the two batteries types is that Alkaline batteries sag in output voltage when they are loaded, while the Lithium ones don’t. So the alkaline batteries tend to sag down towards the required 3.6 volts anyhow.

Sometimes the manufacturer puts a little resistor in the circuit to limit the current, but in calculating what value resistor to use he assumes that the battery voltage will sag alkaline-style.

So his calculations work OK with Alkaline cells, but are all wrong with Lithium cells. Excess heat, and short life.

However!!!
This only applies to the older cheap and nasty LED headlamps. Some of those rely on the battery sagging enough quickly that no resistor is needed at all. Rough…

The more modern ones have a bit of electronics in there which limits the current more intelligently. The problem is that ‘smart’ costs $$, but at least you can put Lithium cells in them. For instance, the PT Quad will take Lithiums, and this headlamp is currently being tested at http://www.backpackgeartest.org . Caution – I am one of the testers!

The best answer is to use a full switch-mode converter inside the headlamp. However, the cost of the electronics would put the headlamp into the $60-100 category (at least), and this may be too much for the market for one of the little headlamps. It is OK when the headlamp has two 5W super-grunt white LEDs for illuminating half the mountain, but who needs that amount of light around camp? (Yeah, the military, I know …)

The alternative is to make your own bit of electronics. High frequency stuff though. I do this, and power my 2-LED headlamps off a SINGLE lithium AAA cell. This is UL.

Cheers

[Bill Cooper]

Roger,

Did you pull the step converter chip out of your junk box or actually spec it for wattage, packaging, etc.?

[Summit CO]

Roger: circuit diagrams please unless you are doing surface mount through your job or something) :)

[Scott Toraason]

Before I purchased my PT EOS last year I emailed Princeton and received an enthusiastic response from the company to use the new AAA lithium batteries with the light. However it does make more sense as the EOS has a heat sink and current regulation where as Petzl lights have neither except some models (MYO) I believe may have current regulation for their LEDs.

[kevin davidson]

To the Electronically inclined crew—
I’ve had perhaps 150-200 hours of Lithium battery use in me Princeton Tec Aurora and maybe 40 hours w/ the EOS w/ no apparent issues concerning the LED (s). Are heatsinks and or regulation a deterrant to premature LED failure? Or do we need to relegate our lithium AA’s and AAA’s to Davey Jones Gear locker? Yarr.

Fuller documentation from the Manufacturers would be the gentlemanly thing to do or else they may be facing consumer mutiny. Yarr.
(Today’s International Talk Like a Pirate Day—get on board or walks the plank ye scurvy landlubbers.)
http://www.talklikeapirate.com/piratehome.html

[Mark Regalia]

I suspect it would. Lithiums get hot when producing a current. It is one of their biggest limitations. The question would be how much of a thermal barrier there is between the battery and the circuit.

[Rick Dreher]

Avast!

This (lithium-triggered fail-yarrrrs) didn’t seem to be an issue until the newest high-output 5mm LEDs came on line, although it might also be the result of greater market penetration of the lithium batteries themselves.

Petzl’s near complete banishment of lithiums to the desert isle is cause for concern, because it includes both their 5mm and Luxeon lights. I’ll take them at their scurvy word.

Princeton Tec is concise about which of their AA/AAA LED headlights are lithium-approved: Quad, Apex, Corona–all regulated, and the Apex and Corona are heat-sinked. The Aurora isn’t, no surprise because it’s not regulated. The Eos also isn’t, which is a surprise as it is regulated. FWIW I’ve run Li cells in an Eos with no problems, including during our full product review. The same headlamp lives on.

Perrrrrhaps Petzl with get with the program and regulate their lights now? That’d make an old sea captain happy enough to break out the rrrrum.

[kevin davidson]

Aye, there’s a salty Gear Pirate on the BPL staff. Welcome aboard y’ Scalawagg.

[Rick Dreher]

Avast matey!

‘Tis good to be a stinkin’ sea pirate on Pirates’ Day. Now hand over all yer titanium or preparrrrre to walk the carrrrrbon fiberrrr plank!

You can have all these bloody doubloons and pieces o’ eight. They’re tooo heavy, yarrrrrrrr!

[Scott Toraason]

The Princeton Tech web site lists the Eos as having a heat sink.

[Rick Dreher]

Well, sort of. There’s a piece of sheet aluminum inside the lamphead, but it’s nothing like the finned arrays on those other lights and it’s not exposed to the air.

That said, in my experience the Eos only gets middling warm in use.

[Roger Caffin]

Maxim MAX1796, using almost stock circuit per data sheet. DIL switch across part of the divider chain to get high (20 mA) and low (4 mA) current drives. It starts at 0.7 volts input (1*AAA) and has a LOW Vref.

Unfortunately … surface mount. I don’t think you can get through-hole with these sorts of specs. And these particular chips are expensive!!!

I snuck a few PCBs for this into the corner of a sheet of other PCBs for a client. Mostly used up now.

I am looking at some other newer chips which are cheaper, but with similar specs. I would need to get a whole PCB sheet done though – expensive, even at prototype levels. They will be SMD of course.

Cheers
Roger

[Christopher Plesko]

What about just running a BuckPuck from Luxeon to power the LEDs? Or a Shark step up converter if you just wanted to use 1 battery?

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