NiMH C cells in LED flashlight

I have some 4500mah Powerizer NiMH C cells that I want to use in a new LEDBeam LED flashlight (3 WATT LUXEON III LED)which came with a warning not to use rechargeable or "off brand" batteries, but to use name brand alkaline batteries only.

When I asked the LEDBeam folks, they said that "the flashlight does not have an internal regulator and it is important that the batteries used do not drive the LED with more than 1000ma."

The flashlight takes 3 C cells.

How do I know whether the batteries will drive the LED too much? I don't want to damage this new flashlight.

Thanks in advance!

That is a VERY interesting question!

I have been plying with some lights this morning. Two XM3 and two Garrity 2AA incandescent. Also some NimH AA and some Lith AA.

The incandescent bulbs go very dim and yellow on NimH. They rock on Lith. The XM3s seem to be indifferent about it. I THINK the NimH can/will give more CURRENT but less VOLTAGE.

I don't know if it is recommended or if it is strictly forbidden, but I run 3 Lith AA in a SL TT3AA. It is distinctly brighter this way. But I don't use it regularly and had Alk leak in that light. So I take whatever penalty I get.

I wish I could give you a definative answer!

Try it using a DMM to see about the current. I'm not sure I know how to do that, but it should be easy.

I think I'll try it after while!

I've read that Lithium AA batteries produce 1.7 volts and can be damaging to devices that are depending on no more than 1.5 volts.

> I wish I could give you a definative answer!

Me too. /ubbthreads/images/graemlins/smile.gif

> Try it using a DMM to see about the current.

I have to confess that I have no idea of what a DMM is and I'm guessing that I don't have one. /ubbthreads/images/graemlins/smile.gif

DMM=Digital Multi Meter... used for measure voltage, current and all sorts of other electronic stuff. Get a harbor freight $2.99 one it is a good starter DMM. LEDs can take a certain amount of overdrive if they are well heatsinked, it will usually reduce the life of them possibly substantially if the overdrive is large enough. I wouldn't recommend direct driving with lithiums without checking with a meter because frying LEDs isn't fun.

I like to use a variable resistor and dial down from about 500ohmr or higher while watching a DMM. When you achieve the current you need to the LED you measure the resistance and that will tell you how much overdrive you have using ohms law, or measuring the voltage drop over the resistor subtracting it from the voltage supplied at the batteries.

Welcome to cpf, demogo.

3X C nmh is one of my favorite batt combo's for Direct driving 3 watt luxeons. Kbin vf will draw aprox. 1.2 amps per luxeon from 3x C nmh.

this setup can support 3X three watt luxeon with fair flat discharge rate with excellent runtime.

My Barbolight U-09 is setup exactly as mentioned running 3x 5,000 mah C nmh. draws 2.3amps with fresh charged cells.

Thanks for the tips on the DMM, guys.

Cy,

Assuming that I'm understanding your post correctly, the single Luxeon III LED would be driven at 1200ma by 3x C NiMH - or 200ma above the maximum recommended current.

So it sounds like I don't want to do this because I have no idea of whether there is a heatsink or how effective it will be?

I want to protect this LED.

Thanks!

demogo, not to worry. That 1200mA would be temporary as cell voltage drops overtime. I just now checked Quickbeams's review and it has a nice beefy headsink, according to picture. Also, has a very good overall rating. I would buy, will buy, this flashlight. Use the alkaline C's until you get a DMM. If not too much above 1.2 amps discharge I think it would be safe to use NiMh's, but looking at Quickbeams's runtime chart, it may not be necessary, but something I would probably do.

Bill

I apologize if this is an uneducated statement, but I had thought that putting batteries in series (which I assume is how they are connected in the flashlight) increases the voltage not the current. To get higher current throughput, the batteries would need to be connected in parallel. Besides that, I had always had the understanding that current is drawn based on the voltages applied and the resistance of the circuit. It is not something that the battery pushes.

Am I wrong? If so, please explain before I fry something! /ubbthreads/images/graemlins/smile.gif

ya, and the rechargables will handle a high current draw better, without a voltage drop.

so BASICALLY , the alkalines will start at 1.5V and as you hit them with a high current draw, will drop to about 1.2V then wane down to 1.0 and even .9 during a HIGH discharge rate. the NI-??? will hit at 1.4V hold that for a while, then drop to a 1.2V discharge rate, for the majority of thier existance.

then LITHIUM could be as high as 1.7V hit with 1.5V and actually stay there for a while, then eventually dropd down too.

if i would have FEAR of changing the batteries, it would be Rechargables HOT OFF THE CHARGER, or Lithium.

If any light cannot handle Heat dissipation in the long term, then alkalines would be better, because when the heat gets high to the LED, the alkalines will be weak by then and dropped in voltage.

that does not answer your first question, but to answer it, the best way would be to TEST with an ammeter on the tailcap, before putting it on (assuming you can) by putting an ammeter in BETWEEN the battery and the connection to the led, you could test for a short burst your actual current.

i would gladly overdrive a REAL luxIII 1.2 IF it has heat dissipation capacity, if it doesnt have great ways to remove the heat, then i wouldnt even run it at spec, let alone overdrive.
If its a REAL LUXIII its one hearty creature. if its one of them knockoffs, or doesnt have a way for the heat to leave, worry then.

then lower Vf , means that the LUX is more sensitive, also them higher output ones are oft lower Vf too, the lower the voltage that is required to drive the LED the more likely it will overdrive at some voltage.
Over time, the lower voltage LEDs tend to normalize anyways, so over time (burn-in) the voltage required to get to a specific current will be higher.
that does not mean that (over time) it is any more or less efficient (L/W), or will dissapate the heat of that any better.
it just means that more voltage will run less current through it after its broken in (or aged).

umm, so inconclusion. if the thing aint got no way to remove the heat, then dont put "better" current output batteries in it. because the alkalines will not put out the same current, over TIME.

I smoked 3 LuxIII LEDs in a 4 cell direct drive with NiMh cells. It worked fine with Alkalines. I should have only used 3 cells- they work fine with K bin Lux III's
NiMh cells put out way more current with less voltage drop. I try them and now Lithium Ion in my modded lights. Any kinda light with a real regulator in it should be OK.

oouch, three dead lux's..

when direct driving, objective is to match Vf to VIN. if you can't do so, put a resister for safety.

Kbin vf 3.51 - 3.75V matches 3x C nmh, which has a fairly flat discharge rate. peak current with hot cell drops quickly. so you won't pull 1.1 amps for long with Kbin.

besides voltage one must be aware of amps delivered to lux. there are certain situations where voltage is lower, but will fry lux due to huge amp load delivered.

alk cell's internal resistance will self limit amps delivered. nmh will deliver more amps than alk. li-ion deliver huge amps.

For what it's worth (I'm only a newbie, after all), I've been very impressed with the LEDBeam flashlight. It has an intense, focused beam with a lot of throw for only $30. Battery life is good and it uses cheap alkaline batteries.

Hard to beat for a good general purpose inexpensive flashlight.

Cy,

Can I please impose on you to explain some of the terms you've been using? As someone that just learned what a DMM was yesterday, I have to confess that I'm lost.

What does matching "Vf to VIN" mean?

What does "Kbin vf 3.51 - 3.75V matches 3x C nmh" mean?

And finally, what does "Kbin" mean?

Thanks!

all 3 of the things you just mentioned are Voltages (one way or another)
when you have a higher voltage, more current will pass, through the same ammount of 'resistance'

Vf is the voltage that the LED wants to run at spec (about)
VIN is voltage IN , the voltage that your feeding into the led (or a curcuit).

BINS are different sensitivities of gates on the LED, a low voltage type of LED will overrun faster and generally whatever the "BIN" of the led is, is how you would want to voltage it when trying to run at spec currents.
see http://home.comcast.net/~theledguy/bin_codes/

Bins are more than just how much voltage, there are also bin specs for its coloration, and its supposed ammount of light output (lumens).
but because bins are tagged on whole RACKS of leds the same, it can be highly varied. the bin number is a general idea of how a BATCH of luxes they output will operate, when you test them the first time.

if you really want to "bin" them you will do it yourself on individual units.

DD is Direct Drive, so when you dont have any curcuit stuff in there, like a current controlling curcuit, the voltage that you put IN, and the voltage that the LED itself is, are the critical factors in running it at a 'Spec' current.

so if your batteries are going to put out 3.5V when sending out the ammount of power the led wants, you would prefer to have a LED that enjoyed the 3.5V your sending it.

Vidpro, Cy, everyone else -- thanks for all the tips.

I appreciate the help.