3x 1.2 AA.... 1x18650 - will it work?

[JimmerG]

I've got a flashlight - its got a 3 mode CREE Q5, and its currently being powered by a battery pack containing 3x AA Nimh batteries. Do we think this same torch could be powered by 1x 18650 battery?

The AAs are 1.2 volts each
The 18650 will be 3.7 volts.... should work - shouldn't it!?

Thanks

J

 

[old4570]

Yes , should work ...

 

[Oddjob]

Don't see why not.

 

[45/70]

Actually, if your light was designed to use 3 AA NiMH's and you don't have a problem physically replacing them with an 18650, it should work fine. The voltage and current delivery of 3 AA NiMH is very close to an 18650 LiCo cell.

A bit OT, but I've run 18500 cells in a couple lights that were designed for 3 AAA alkaline cells in a carrier. The problem you can run into here, is that under load, an 18500 (or an 18650 If you can fit one) will deliver a much higher voltage under load than three alkaline AAA, or even somewhat higher than 3 AAA NiMH. This can burn up the LED(s) if their Vf isn't high enough to handle the increased voltage. Of course, if the light has a regulated circuit, it would probably be fine.

Dave

 

[Black Rose]

The AAs are 1.2 volts each
The 18650 will be 3.7 volts.... should work - shouldn't it!?

18650 will be 3.7 volts when empty and 4.2 volts hot off the charger.

 

[45/70]

18650 will be 3.7 volts when empty and 4.2 volts hot off the charger.

That's true, Black. I'd just like to point out that 3 NiMH cells in series, hot off the charger would likely be 4.2 Volts, and 3.6 Volts when "dead".

Dave

 

[kramer5150]

Yes but only if the host has very good thermal cooling characteristics, and the 18650 cell does not have unusually low internal resistance.

But it will work for short burst kind of applications, if you monitor emitter temps.

I have been punnishing a Q2 XR-E in a cheap host(pic below), direct driven off some Samsung 18650 cells. I just turn it on and let it burn, I ceiling bounce it and use it as a desk light. It gets HOT, even with high resistance 18650 cells. I think the light does have decent thermal cooling properties, but even then after several months of torture I think the LED has dimmed a little. But I think its still in the ~150 Lumen range.