18650 to C and D cell adapters

[kilogulf59]

Recently, I purchased my first 18650 powered flashlights. Just outstanding is all I can say. The other lights that I and my family have are mostly various models of Maglites and they're running on disposable D-cells. These work OK because they're not daily use lights, however they don't work well when left in our vehicles. We were running NiMH AA cells (in C adapters) in a Streamlite Waypoint spotlight. This worked great and saved us a lot of money because this is our main, daily use, light.

Any-who, my question is, how well do these 18650 to C and D cell adapters (that I saw on Ebay and pictured below) work? Does it affect the light in any way? Do any of you folks use them?

 

[thermal guy]

Runtime will be shorter and watch your volts. If your running 2X18650 in a 3-D light. Your almost double the voltage. 4.5 for 3 D/ 7ish for 2X18650's

 

[hsa]

CPF member "xxo" makes and uses these extensively. He will have some good input. If the lights are left unattended in temperature extremes them energizer aa lithium in adapters might be a better idea. A single 18650 cell replaces 3 alkalines.
As TG says, you have to match the voltage.

 

[Poppy]

I made a spacer to run a 3C Defiant with a single 18650.
I used a one inch dowel. I drilled it out to accept a bolt cut to size.
I wrapped an 18650 cell with a plastic water bottle that I cut up.

I've been pleased with it.
Some of my 26650 cells will fit in the C light, but most of them don't.

 

[kilogulf59]

If the voltages are higher, won't that burn out the bulb or emitter?

I'm already seeing this as becoming a PITA science project. We can just buy new li-ion lights for the vehicles and keep the old Maglites inside, which most are anyway. Being mainly JIC lights, they hardly get used and are checked every few months. Once a year I test every disposable battery in the house.

 

[xxo]

If the lights are left unattended in temperature extremes them energizer aa lithium in adapters might be a better idea. A single 18650 cell replaces 3 alkalines.
As TG says, you have to match the voltage.

Yeah, AA energizer lithiums are best for little used lights stored in a vehicle or anywhere there may be extremes in heat and cold.

But if you do get some Li-ion adapters for your Mags you may find yourself using them a lot more as quality Li-ions make these lights much more pleasurable to use.

Most 2D LED lights will run fine on 3.6V Li-ions, but some may not so you need to do some research and there may be some risk as a Li-ion cell will put out about 1 Volt more than a fresh pair of alkalines. If your light is an incandescent, you want to use a 3 cell bulb or a LED drop-in rated for at least 3 cells.

For a 3 cell Mag the Voltage of a single Li-ion is perfect.

For two Li-ions in series you need a bulb or drop-in rated for 6 alkaline cells and you need button top protected Li-ion cells for safety.

I currently only make adapters for single protected Li-ions (with built in mechanical reverse polarity protection) as this is safest for lights without low Voltage cut off, like virtually all C and D cell lights.

If you want more runtime than an 18650, I recommend using a 21700 for C cell lights and 26650 for D cells. I make adapter sets to run 18650's or 21700's in 2 or 3 D cell lights, one adapter is a 18650 or a 21700 to 2 or 3 C cells and the other is a C cell to D cell that allows the smaller 18650 and 21700 cells make contact with the larger D cell light's tail spring without doing any mods, The 18650 and 21700 to C cell adapters work in most C cell lights, no problem as they are large enough to make contact with the smaller C cell sized tail springs.

For D cell lights 26650's are generally big enough to make contact directly with an unmodified tail spring, so I make a single adapters for these.

If you want to make your own adapter, check out Old Lumen's (RIP) vid:





If you want to get into more extensive upgrades for your old Mags, also check out Matt Smith's/Lumencraft vids.

 

[alpg88]

The way those adapters work is simple, they fill empty space left by smaller cells, center cells, and in some cases have extended contacts on one end. those adapters have no voltage regulators, and it is up to you to match voltage of old\new cells so the device still works right.
i used to print my own adapters, and entire lights from scratch, among many other things, but cutting a pvc pipe is a lot faster and simpler, than wait hours for a print, and hope the print finishes without failures.
Fortunately pvc pipes fit pretty good for this task.

 

[Poppy]

If the voltages are higher, won't that burn out the bulb or emitter?

I'm already seeing this as becoming a PITA science project. We can just buy new li-ion lights for the vehicles and keep the old Maglites inside, which most are anyway. Being mainly JIC lights, they hardly get used and are checked every few months. Once a year I test every disposable battery in the house.

I was going to suggest that you pick up a few convoy S2+ 18650 lights for about $15 each and call it a day.

Yes, if the voltages are too high, you may burn out the emitter, or bulb.

 

[kilogulf59]

That's probably not a bad idea.

I do have some AA to D adaptors so maybe I can get a box of Energizer lithium. for the truck light. I just hate to see a light go to waste but....

 

[bykfixer]

Figure about 1.2 volts for each AA,C or D disposable battery. Figure about 3.7 to 4 volts for each 18650
So a 2D light used to 2.4 volts may not play nice with an 18650. Now in the case of an incan bulb in that right angle military light you could just use a 3 cell bulb.

I use 1amp 18650's in incan lights.

 

[Lynx_Arc]

I was going to suggest that you pick up a few convoy S2+ 18650 lights for about $15 each and call it a day.

Yes, if the voltages are too high, you may burn out the emitter, or bulb.

This is my advise too. Instead of modding a bulky mag light just buy a decent budget 18650 light. It will be superior in performance, take up a lot less room and likely have a lot more efficiency to boot. Runtime may not be as long but you could consider either tossing a cheap 18650 12v charger setup in with it or get a light with a built in charging port so you can recharge it in your vehicle which to me is a big plus even though alkaleaks will run a long time having 500+ lumens at your command plus it being pocketable and also having lower modes when needed it to me makes a lot more sense. I know people get attached to C/D cell lights but I have a nice Rayovac 2D Roughneck light that I modded to LED that has a very nice beam now and tint but..... I never used it after I got smaller LED lights just as or more powerful I think the batteries in it are from 2004? I have another 2D light that I also converted that sits in a closet near the front door.... I've used it about 3 times in 15 years for about 5 minutes total. I just do not like the size of D cell lights at all any more I mainly liked them growing up because it was needed for incan use as a 2AA light usually had a 222 bulb and was weak in output and limited about 2 hour of good light from it. I've swapped in an LED bulb in a 6V lantern but as soon as the batteries in it are totally gone it is going to take a dumpster dive.

 

[kilogulf59]

Yeah, I'm not so much attached to any of them as it is my hatred of waste. The disposable world drives me crazy, but c'est la vie. I wouldn't toss a working light. I/we just place them throughout the house as JIC lights and check them every so often. Hell, I have my dad's old Eveready captain in a kitchen cabinet.

Buying an adapter, cell or cells, and then figuring out which emitter to get isn't worth the hassle nor the expenditure. I/we are light users, not hobbyists.

Back in December I picked up a Wuben L50 and C3. They're very nice and a good deal, IMO. They come with a protected 18650 cell and have an integral charger. For an EDC I prefer the L50 and the C3 replaced our big, honkin', Streamlight Waypoint. Either light was around thirty bucks and change. Something like that would work I guess.

 

[hsa]

If you throw a Maglite away, those of us who love Mags will sense a shift in the force. We will get together and render your S2+ inoperable or maybe just have a beer and wait for the Wisconsin winter to freeze it to death in your glove box.
Just sayin.

 

[kilogulf59]

The former won't happen, the latter is a good possibility 🤣

 

[bykfixer]

I keep disposables in any just in case lights, just in case the rechargeable self discharges and uh oh, dead battery(s). Afterall, I hardly ever use them so it aint like I'm tossing a bunch of batteries in the trash all the time.

 

[kilogulf59]

I keep disposables in any just in case lights, just in case the rechargeable self discharges and uh oh, dead battery(s). Afterall, I hardly ever use them so it aint like I'm tossing a bunch of batteries all the time.

I do too...and the Energizer D cells last forever if they just sit there inside. Why tie up NiMH's or Li-Ion's doing nothing?

 

[fivemega]

For 2D size, single 21700 or 26650 will work with some spacer at 3.7 volt. (3 cell bulb needed)
For 3D size, pair of 21700 or 26650 will work with some spacer at 7.4 volt. (6 cell bulb needed)
Free Lumens for little cost.

 

[kilogulf59]

Thanks fivemega. Out of curiosity, are there spacers/adapters commercially available or is this something I'd have to make? Also, these lights have LED emitters replacing the bulbs. Is it safe to assume that I would substitute emitter for bulb in you above listed instructions?

 

[fivemega]

Adapters are not commercially available but some people can easily make them even in their garage with lathe.
Voltage of single Li-Ion is pretty close to 3 cell "D" (Alkaline or NiMH) but for 2D size, you need to make sure your module will take voltage of your new set up.

 

[kilogulf59]

Thank you for the explanation.