18650s in 2 C cell LEDs?

I recently 3D printed adapters to run 2C and 3C cell LED lights on a single 18650, I figure there shouldn't be a problem with the 3 cells since they are designed for 4.5V nominal from alkalines, but what about the 2 cell version?

Is the Voltage of an 18650 too much for a 2 cell C (or D) LED light?

Anyone here have experience running 18650's in 2 cell C or D LEDs?


Thanks!

It depends on the light. If it's a cheap light (such as a mag) that is depending on the internal resistance of alkaline batteries, then it might get over-driven if you use a high-power battery like an 18650, even if the (resting) voltages match. That will certainly be true if you're replacing a 2C battery, where the 18650 will be both higher voltage and higher power (low internal resistance).

What about LiFePO4? Not necessarily the sought-for solution for OP, or for most of us who are stocked with Li-ion 18650s, but I have given similar things some furtive, wispy thought now and then ...

OP - is there room for a 3.3v voltage regulator in those 3D printed adapters? Why not adapt the voltage as well as the size?

x8353 said:

What about LiFePO4? Not necessarily the sought-for solution for OP, or for most of us who are stocked with Li-ion 18650s, but I have given similar things some furtive, wispy thought now and then ...

OP - is there room for a 3.3v voltage regulator in those 3D printed adapters? Why not adapt the voltage as well as the size?

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I thought about LiFePO4's, should work better in the 2C adapter, but I don't have any in 18650 size.

Good idea about building a Voltage regulator into the 3D print! I had not thought of that. As it is now, the adapters are just a 2 or 3 C cell sized tube with a hole for a 18650 in the rear and a smaller hole through the front for a brass bolt to make the positive connection.

I checked the current on some low cost 3C lights: a Defiant 850 lumen triple LED, a 200 lumen Rayovac "Indestructible" and a Mag ML25 - all draw the same current from a 18650 as they do off of Duracell Ion Core NiMH's (which is what I normally use in C cell lights place of alkalines), so I don't see a problem with a single 18650 in a 3C light that can handle NiMH's.


I am still researching of use 18650's in a 2C Mag ML50LX, apparently the 2D ML300 uses a buck/boost driver which should be OK up to around 5 Volts, if the 2C cell ML50 has the same driver, it should be good to go as well.

Why not use 26650 cells for the additional capacity?

fivemega said:

By my experience, most of modern LED flashlight driver can tolerate 50%~60% extra input voltage so single 18650 will be OK on 2 cell ML50LX

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Thanks much for the info - very much appreciated!

Timothybil said:

Why not use 26650 cells for the additional capacity?

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2 reasons:

1 - I don't have any 26650's at the moment.

2- I am not sure if 26650's would fit in the C cell lights that I have?

I actually printed a 2C to 2D adapter (so that I can use the 18650 to 2C adapter in a 2D light). I left the diameter of the 2C cell chamber on the large side so that 26650''s could be used in 2D cell lights in the future, but I would have to make another adapter to bridge the length difference between 2C cells and a 26650 to make contact.

Timothybil said:

Why not use 26650 cells for the additional capacity?

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26650 will not fit inside "C" barrel without boring.