Unregulated LED flashlight + NiMH, runtime plot

Since I haven't really seen many runtime plots of unregulated LED used in conjuction with NiMH's, here it is...

Light under test: Cateye HL-EL300. 6 5mm LEDs in parallel driven through a 10 ohm resistor.

Power source: LaCrosse 2.0Ah AA NiMH x 4 in series

tested for current over change in time. It starts at around 175mA with freshly charged NiMH batteries and 270mA with new alkaline batteries. I'm not running a test with alkalines, because I don't have any batteries to waste and I'm not about to go buy some just to waste them.

Thanks for the test and plot. That is pretty flat performance.

Interresting! Seems like with NiMHs there's really no regulation necessary!
I'd be interrested in a comparable chart with normal batteries and the same flashlight...

Thanks,

I had that suspicion from my work using NMHi batteries in digital cameras... work well then suddenly go from near full voltage to near zero.

Holland

Ice said:

Interresting! Seems like with NiMHs there's really no regulation necessary!
I'd be interrested in a comparable chart with normal batteries and the same flashlight...

Click to expand...

You could take a look at a few graphs available on flashlightreviews.com to get an idea of the runtime of unregulated flashlights' runtime curve looks like with regular batteries.

http://www.flashlightreviews.com/reviews/ld-34_diving_torch.htm

The actual time depends on the current draw, but the basic shape stays the same. As I said earlier, my light draws 270mA with new set of batteries while it only draws about 175mA with freshly charged NiMH.

With regular batteries, the current drops to 175mA ish with very minimal use and you can also see this pattern in the review site's graph as well. The marketing brightness figure is usually the output you get for the first ten minutes or so with brand new alkaline batteries.

You will get a longer useful runtime with alkaline batts, because the way the voltage drops with the depletion of available energy dims the light down and reduce the power usage.

With NiMH, you get less time, because the LEDs are maintained at higher power throughout most of the useful capacity.

stjohnh said:

Thanks,

I had that suspicion from my work using NMHi batteries in digital cameras... work well then suddenly go from near full voltage to near zero.

Holland

Click to expand...

Yep yep. The relatively flat discharge curve is the characteristic of both NiCd and NiMH and it is both a disadvantage and an advantage. It is a disadvantage, because you can't monitor the voltage to gauge the remaining battery capacity. It is an advantage, becauase the device gets a quite stable power and allow effective use of available capacity.

The disadvantage can be overcome with a mAh counter in the device. It could either count the charge going in and out or... have a user programmable setting that lets you set the mAh of their fully charged cells and compared the usage against the program.

For example, you set the menu for "2,000mAh". The camera/device would assume your newly charged cells have "2,000mAh" and subtracted the used capacity from 2,000 to estimate the available capacity. This isn't dead on accurate, but can give you an estimate in full, 3/4, 1/2 and 1/4 ish..

Thats pretty close to the same shaped curve I got with another light using Ni-MH cells. My curve is for light output rather than current, but they pretty much directly follow each other.

Its amazing how level the curve is with them

Handlobraesing said:

You could take a look at a few graphs available on flashlightreviews.com to get an idea of the runtime of unregulated flashlights' runtime curve looks like with regular batteries.

http://www.flashlightreviews.com/reviews/ld-34_diving_torch.htm

The actual time depends on the current draw, but the basic shape stays the same. As I said earlier, my light draws 270mA with new set of batteries while it only draws about 175mA with freshly charged NiMH.

Click to expand...

That's actually a rather optimistic graph for unregulated alkaline (or is it carbon zinc? the batts are "extra heavy duty"), probably due to the low output of that light. If you look at the Mags it's much crappier - drops to 50% almost instantly.

When you say your ni-mh draws much less initial current, is that an unregulated light? If so, then that's probably only because of the lower voltage.

RoyJ said:

That's actually a rather optimistic graph for unregulated alkaline (or is it carbon zinc? the batts are "extra heavy duty"), probably due to the low output of that light. If you look at the Mags it's much crappier - drops to 50% almost instantly.

Click to expand...

Hence the "LED" in the title.

When you say your ni-mh draws much less initial current, is that an unregulated light? If so, then that's probably only because of the lower voltage.

Click to expand...

Hence the "unregulated" in the title. Yes, it's becauase of the voltage and I'm just pointing out that you won't get the "oh wow" output you'd get with fresh set of alkaline batts.