Replace D Cell LED Lantern With 18650's

linuxrunner · Aug 22, 2018

I have a led lantern that takes 8 D cell batteries. after it got left on a few times over night and ran through 16 D cell batteries in 1 weekend ($$$) i figured this would be an easy project to convert to 18650's with a little USB charge controller so i could plug in the lantern to recharge. I searched the forums a bit but didn't see a bunch of other posts with the same thing.

originally i just assumed that a 18650 cell would stomp a D Cell battery in amp hours, but after a bit of checking it looks like a D Cell battery is between 12000 - 18000 mah (depending on load)? so it looks like i might actually lose run time if i swap out the D cells.

lantern seems to run on 6v (not confirmed yet) given that it will run on only 4 batteries installed.

DIWdiver · Aug 23, 2018

Hi, and welcome to the forum!

Agreed, if the lantern will run on 4 cells, it's definitely set up for 6V. The other 4 cells just add to run time.

There are bigger differences between 18650s and Ds than capacity. 18650s are LiIon cells. Most of them are 3-4V per cell through discharge, while Ds are alkaline, and 0.8-1.5V. So changing the batteries without re-wiring the light would likely burn out the bulb quickly if not instantly. You you might be able to change to a 12 or 15V bulb, which would work.

Also, 18650s are slightly to significantly longer. If you get protected ones (and you definitely should), they are typically around 67-68mm long, as opposed to 60mm for the D.

Also, the D is around 3 times the volume of the 18650, so it shouldn't be surprising that it's got 30-50% more energy. But that's only if you discharge it very slowly. If your load will drain the cell in 10 hours, the advantage disappears. For heavier loads, the 18650 would stomp the D.

linuxrunner · Aug 24, 2018

DIWdiver said:
Hi, and welcome to the forum!

Agreed, if the lantern will run on 4 cells, it's definitely set up for 6V. The other 4 cells just add to run time.

There are bigger differences between 18650s and Ds than capacity. 18650s are LiIon cells. Most of them are 3-4V per cell through discharge, while Ds are alkaline, and 0.8-1.5V. So changing the batteries without re-wiring the light would likely burn out the bulb quickly if not instantly. You you might be able to change to a 12 or 15V bulb, which would work.

Also, 18650s are slightly to significantly longer. If you get protected ones (and you definitely should), they are typically around 67-68mm long, as opposed to 60mm for the D.

Also, the D is around 3 times the volume of the 18650, so it shouldn't be surprising that it's got 30-50% more energy. But that's only if you discharge it very slowly. If your load will drain the cell in 10 hours, the advantage disappears. For heavier loads, the 18650 would stomp the D.

Thanks for the reply, yes i do know that LiIon cells are higher voltage, was originally going to try it with 2 liIon cells in series to get around 6 volts but after seeing the capacity difference i am going to need more cells. perhaps some type of series parallel hybrid arrangement? 4 cells 2 groups in parallel and then those 2 groups wired in series to get 6v.

sounds like i need to measure the current draw of the led's to get a better idea of how useful this would be. i almost always leave it turned down to the lowest intensity (very dim) so my guess is i am looking at very low current.

DIWdiver · Aug 24, 2018

Do you know how long it runs with a new set of Ds? That should give us a fair idea what the current is.

Replace D Cell LED Lantern With 18650's

linuxrunner

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DIWdiver

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linuxrunner

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DIWdiver

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