Just wondering - 18500 => 3-AAA carrier adapter?

Biker Bear

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Just wondering if anyone's ever made an adapter to run a light that uses 3 AAAs in a carrier from an 18500 cell. My "just curious" solution - wrapping the cell in some thin foam and using a 5mm thick magnet on the tail (negative) end works, but isn't very "cool". ;)

Granted, I understand not wanting to spend as much or more for a battery adapter than one paid for the flashlight...!
 

mvyrmnd

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OOPS!

I just re-read the op and realised I had it backwards. Please ignore me.

:duh2:
 
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45/70

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The two 3xAAA lights that I still own, from "the early days", I converted to 18500. I just cut to size an old mouse pad, rolled it up and stuck it in the battery tube. Since the 18500 is a bit shorter, I place a few U.S. nickels in behind it to make contact with the tailcap spring. Works for me, and no rattle.

One thing you have to watch when substituting an 18500 for 3 alkaline AAA cells, is that the voltage under load when using an 18500 is going to be considerably higher than that of 3xAAA alkaline cells. This is true also when using 3 AAA NiMh cells in place of alkaline cells, although to a somewhat lesser degree.

The voltage drop under load when using alkaline cells is significant, in most lights, compared to NiMh cells, and even less when using an 18500. Depending on the driver in the light, this may, or may not be a factor. I've blown quite a few 5mm LEDs in 3 AAA lights that were direct drive, using NiMh cells, and even more with 18500 cells. So, if the light has some sort of regulation you might be OK, but I would avoid trying this in a direct drive 3xAAA light. Most 5mm "shower head" 3xAAA lights are direct drive, single emitter high power LED lights can go either way.

Dave
 
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Biker Bear

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tylernt: I've discovered that the 3-AAA carriers do vary a fair bit - some just have a button, others have a spring as the + terminal - so you're quite right that any adapter would at least have to be intended to replace a specific carrier, and possibly a specific light/carrier combo.

45/70: I'm using the inexpensive LiFePO4 18500's from W*lmart - $5/4-pack. As their nominal voltage is lower than LiCo or LiMn cells, there should be much less chance of burning out the lights I'm using. And while they're "only" rated at 600mah, in the light I'm experimenting with I got 2+ hours of decent light out of a cell as it came out of the package (I'm still waiting for my charger to arrive, so not entirely sure of the state of charge of the cells). I sure wish I had something that could test capacity of lithium cells the way my Maha C-9000 does for NiMH cells.
 

45/70

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Biker, yeah the LiFePO4 cells from WallyWorld, should probably be OK.

On another note, LiFe cells are extremely difficult to determine remaining capacity. The voltage changes ever so slightly during discharge, ie. the discharge curve is so flat, compared to LiCo cells, that the only real way that I've found to determine remaining capacity, is to completely discharge the cell(s) and see what was left.:) It doesn't help either, that cells from the various manufacturers all have slightly different discharge curves, as well.

Dave
 

Biker Bear

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Biker, yeah the LiFePO4 cells from WallyWorld, should probably be OK.

On another note, LiFe cells are extremely difficult to determine remaining capacity. The voltage changes ever so slightly during discharge, ie. the discharge curve is so flat, compared to LiCo cells, that the only real way that I've found to determine remaining capacity, is to completely discharge the cell(s) and see what was left.:) It doesn't help either, that cells from the various manufacturers all have slightly different discharge curves, as well.
In terms of device performance I love flat discharge curves - and am willing to put up with the difficulty in assessing charge level.

In terms of the setup I'm working with, the adapter could be as simple as a 22.5mm diameter disc of plastic with a 6mm long conductive post through the middle. I may have to make myself look odd by carrying my digital calipers around with me looking for some plastic item that's just the right size for me to put a conductor through the middle of!
 

HotWire

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I just rolled up some cardboard and stuck in an 18500. Works great! Will it work like that with all? Don't know....Run time shoud be greatly increased.
propeller.gif
 
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