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.

Reply to
Eric Smith
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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.

Reply to
mc

beleive

4 are

LEDs are

I'm

substantially,

can see

on

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.

Reply to
Watson A.Name - "Watt Sun, th

It's fairly common that it doesn't.

Best regards, Spehro Pefhany

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Reply to
Spehro Pefhany

I just got a 4 white LED flashlight that uses 3 AA cells from Harbor freight. I measured the current at 127 ma and and that leads me to beleive they are direct wired. Looking inside as best I can it looks like all 4 are in parallel and connect directly to the 3 cells in series. I think LEDs are supposed draw a lot less current if they have a dropping resistor. I'm guessing that a dropping resistor would reduce current draw substantially, increase led life and not reduce light output significantly. But I can see were I could easliy install a resistor. I also know just about zero on leds. tnx

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73
Hank WD5JFR
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Reply to
Henry Kolesnik

more

damaged.

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.

Reply to
Watson A.Name - "Watt Sun, th

beleive

all 4 are

LEDs are

I'm

substantially,

can see

on

Your assumptions are wrong.

Reply to
Watson A.Name - "Watt Sun, th

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.

Reply to
Fred Bloggs

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.

Reply to
Si Ballenger

beleive

all 4

think

resistor.

significantly.

just

sided PCB

AA is

parallel. The

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.

Reply to
Watson A.Name - "Watt Sun, th

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?

Reply to
mc

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

Thanks, Rich

Reply to
Rich Grise

Watson *knows* LEDs. You might want to do a little research - perhaps find a flashlight with a LED such as you describe - before trying to challenge him.

Personally, I have never owned, seen or heard of a flashlight that uses an LED where the LED includes what is necessary to operate at the correct voltage.

Ed

Reply to
ehsjr

The Electronic Goldmine sells a 4 white LED flashlight for $1.99. Item # G15184 Watch for the line wrap:

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You didn't specify the Item # for the Harbor Freight flashlight - I assume it is ITEM 3653-0VGA

Based on the catalog pictures, it looks like the Harbor Freight light has a metal body, while the Goldmine's is plastic. But I'll bet they use the same LED's. I have the Goldmine unit - there is a bluish tint to the light it produces. Does yours produce a bluish tint?

As Watson mentioned, overdriving LEDs does reduce their life and their light output, so your thinking seems right on target. But for either a $7.00 or a $1.99 4 LED flashlight, it's probably not worth the effort to incorporate a dropping resistor - unless experimentation, rather than function, is the goal.

Ed

Reply to
ehsjr

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

127ma/4 LEDs=31.75ma per LED,that's a bit high for the Nichia white LEDs;IIRC,they have a 25ma max limit.

Are there now other white LEDs that have a higher current rating?

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Jim Yanik
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Reply to
Jim Yanik

The Harbor Freight number is 3653 and if there's any blue tint to the light I can't see it. tnx

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73
Hank WD5JFR
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Reply to
Henry Kolesnik

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

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Reply to
Spehro Pefhany

Yes, that would be good way to market it. ;-) It does make the design sensitive to battery type. I have one that does not work properly with CR123A Lithium batteries that otherwise fit (it's a 5W Luxeon module with no series resistor that puts out less than a 3W type unless you use special batteries).

Best regards, Spehro Pefhany

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Reply to
Spehro Pefhany

I just made a probe out of solid No. 12 house wire and measured the resistor at 8 ohms on my Fluke 87. So I^2*R=0.127*0.127*8=0.129 watts. I guessed the reisitor looked like 1/8 but I was using my recollection of what 1/8 watt radial lead resistors look like for size. I should have done all this with my original post and not wasted all those resources. But hind site is 20

20.
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73
Hank WD5JFR
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Reply to
Henry Kolesnik

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

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Spehro Pefhany

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