Making torch brighter with NI-MH?

Hi guys

Ive just brought a new dive light from the US. Its a Underwater Kinetics C4 eLED L2 model and was supplied with 4 C cell Duracell alkaline batteries.

http://www.uwkinetics.com/products/c4-eled-l2#.WgakPGinzMK

The lamp can run (at a big extra cost) with an internal NI-MH battery pack which if I use instead of alkalines will almost double its power but at a much lower runtime.

The specification details show the NI-MH pack to be at 1.2V which is what I would expect given them being NI-MH. My question is how can the unit almost double in light output by running on a rechargable pack and rather than spending a fortune can I just buy a set of C cell NI-MH battries and acheive the same results?

Thanks alot and appreciate any help.

Fivemega, thanks for the reply and warm welcome. Was getting worried my question made no sense.

Ive ordered 4 c cell Ansmann Max-E 4500Mah to replace the alkalines supplied with the lamp.

What I still dont understand is how using a ni-mh pack instead of normal alkalines will give me a 1000 lumen output as opposed to 575 lumen on alkalines? Can anybody shed some light on that excuse the pun lol :twothumbs

Hello UKMG74,

Welcome to CPR.

In my best "light shedding effort..."

It all has to do with internal resistance. Alkaline cells have higher internal resistance. When a load is applied some of the power ends up as heat. When you use a battery with lower internal resistance you end up with higher voltage overall and that results in less heat and more output from your flashlight.

Tom

Hi Tom

Thanks for the welcome and answer to my question :thumbsup:. Its a bit brighter now lol.

So if I understand correctly the standard alkalines have a higher internal resistance compared to the ni-mh which allows the lamp to run at 1.2v for longer. If I have that right then how come the lamp does not emit 1000 lumens instantly before reducing in output as the alkaline voltage reduces?

I might have to get my old school electronics book out

Thanks :thumbsup:

The other thing to remember about alkalines is that due to that higher internal resistance, the voltage sag increases as the draw increases. So to pull the same amount of current from the alkalines that is being drawn from the NiMH cells would cause a larger voltage sag, and thus a much shorter run time due to the extra losses.

My guess is that the designers felt that 500 lumens was a good trade-off giving the use the ability to use alkaline cells and still get a decent run time. If any unenlightened users wanted the higher output they get that without having to worry about chargers and cells and all that rot that we take for granted, being all enlightened and stuff.

UKMG74 said:

So if I understand correctly the standard alkalines have a higher internal resistance compared to the ni-mh which allows the lamp to run at 1.2v for longer. If I have that right then how come the lamp does not emit 1000 lumens instantly before reducing in output as the alkaline voltage reduces?

Click to expand...

That doesn't happen because the driver needed to light up the LED isn't designed to do so. It would take a much more complicated driver to be able to start out at the higher output, and then drop to a lower level as the voltage dropped. Also, as I said in my other note, that high of a drain will really do a number on the capacity of the alkaline cells. Higher cost and reduced run time for a few minutes of extra brightness that most times won't be needed anyway just doesn't seem like that great of an idea.

Thanks Timothy for your advice, much appreciated