Harbor Freight 4 LED $7.00

LEDs have a more or less fixed forward voltage drop. If you supply more voltage than that to them, they draw more current (and produce more light). But beyond a certain amount of current, they will be damaged.

I'd be surprised if the flashlight has no current limiting resistor.

Light output is nearly a linear function of current. If you increase the resistance, you will decrease the current, and hence the light output. This will increase the LED life, but the life was probably good enough already.

Sounds like they are using the battery internal resistance to limit the current. Four LEDs at 30mA/ea gets your ~120mA with Vbatt pulled down to maybe 3.5V at that current. And it probably has a "good enough" graceful degradation with battery run down causing the current to taper off exponentially after a point-reducing battery discharge per use. It does require the LEDs to be matched to some degree.

White LEDs require about 4 to 4.5 volts. That is about what comes out of the AA cells. The internal resistance of the LEDs is probably sufficient. Newer LEDs have more internal resistance than older ones.

beleive

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Seems like everything is made for the flashlight that has the profile of the Mini-Maglite. It has two cells, and fits into all sorts of holsters, pockets, carriers, etc. So if you get it, or a similarly sized flashlight, then you're home free. Of course the Mini Maglite has a halogen bulb, so it sucks. I bought the MagmaLED and Opalec Newbeam conversion kits for mine, and I'm happy with them. I've seen the three cell flashlights and I would much prefer that mine not be that long, three cells is just too long.

Dorcy sells some four LED, two cell flashlights, for under $16. I bought a couple and They work but the rubber gtrips fall off - no big thing.

One other disappointing thing about three cells lights is that if they are direct connected, then you can't use Ni-MH rechargeables in them. Some flashlights with the V boost circuitry can run on Ni-MHs, possibly at reduced light output.

It's fairly common that it doesn't.

Best regards, Spehro Pefhany

I would assume that LEDs that are now made for flashlights have built in pulse circuitry to get the brightest output from the LED. They would include what is necessary to operate at the correct voltage.

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I agree. The ones that I've seen without a resistor are mostly the ones that use a CR2016 or CR2025 button cell, basically those keychain lights that you squeeze. The cells have enough internal resistance to limit the current.

But alkaline AA cells are capable of delivering more than an amp. I don't know what the internal resistance is, but it's very low. The multiple LED Altoids box lights that I've built use 33 ohm resistors, and I've put as many as 8 LEDs on a set of 3 AA cells, and they're _bright_. More commonly I do 6 LEDs, each with a 33 ohm resistor, and I consider that a minimum for a decent source of light.

By using 4 LEDs and no resistors, the light output is probably greater than my 6 LED lights, but from what I've seen over just a few hundred hours, the light output from these flashlights will drop off after only a few hundred hours or less when pushed to this high a current. But it may take more than a year and several sets of AA cells to put a hundred hours on a flashlight, and by that time, the warranty has expired. :-( This is a dirty little secret that no flashlight maker wants you to know.

beleive

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Your assumptions are wrong.

"Henry Kolesnik" schreef in bericht news:8ovje.1965$ snipped-for-privacy@newssvr11.news.prodigy.com...

Hank,

Adding a resistor will not be that difficult. A thin piece of two sided PCB and some handiwork with a fret-saw and a fraise will do the trick. As AA is pretty small you may need to use two or more SMD resistors in parallel. The round piece of PCB should be place between a battery and its press spring.

petrus bitbyter

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spring.

My dictionary says a fraise is "an obstacle of pointed stakes driven into the ramparts of a fortification in a horizontal or inclined position". Which I don't think is what you had in mind. Maybe you could explain. Thanks.

He clearly means a strawberry.

Pearce Consulting

And your proof is...? ;-)

I don't know about *his* proof, but I've never seen such things on the component market. They'd be handy if they existed. I've seen LEDs with built-in flashers and with built-in current regulators to run from much higher voltages.

Also, if pulsing were going on, you'd see stroboscopic effects when you moved the flashlight quickly, wouldn't you?

A google search comes up with "fraise toestel", but it's not clear to me what exactly it does. Cut a donut in the PCB?

Best regards, Spehro Pefhany

On Fri, 20 May 2005 22:57:44 -0400, Spehro Pefhany wroth:

If you think about it, the batteries do have an equivalent series resistance and the LEDs are not perfect voltage clamps either. There IS a series resistance even though there is no discrete resistor in the circuit.

Jim

Exactly. That's why they work. Maybe not as perfectly as some would like, but good enough to sell.

OTOH, an LED backlit LCD graphics display I have uses some sophisticated white LED driver chip arrangement. The backlight snaps on as the voltage is ramped up, almost like a fluorescent.

Best regards, Spehro Pefhany

Heck, I'm still stuck on 'fret-saw'. )-;

Thanks, Rich

"Watson A.Name - "Watt Sun, the Dark Remover"" schreef in bericht news: snipped-for-privacy@corp.supernews.com...

Milling cutter. (Dutch -> Frees).

LOL, it is indeed one of the meaning of "fraise" in French. One of the other ones is "milling cutter", which I guess is a good version. Source is