Convert 3-AAA Flashlite to Lithium

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Introduction: Convert 3-AAA Flashlite to Lithium

About: I like to tinker and experiment with electronics, robotics, programming, and photography. Along with my latest interest in Steampunk.

I like having a small flashlight with me when working. Especially one with a nice pocket clip, but don't like those with 3 AAA cells. After noticing a 14500 lithium cell is very close in length to those 3 AAA cell holders, It got me to think if can I make work with it. A 14500 cell is close in voltage to 3 AAA cells.

Step 1: Compare Sizes

If you remove the battery holder from the flashlight (this one is a Lowes Utilitech), you will see the sizes are almost the same. Just the diameter of the AAA holder is larger.

Step 2: Make a PVC Sleeve

To compensate for the larger diameter of the AAA holder, cut a piece of schedule 40, 1/2 inch PVC pipe. The length is just a little over 2 inches. Try 2-1/16 inches. The 14500 cell will slip inside the PVC pipe. You may need to adjust the length to minimize rattle.

Step 3: Add a Piece of Shrink

To help enlarge the sleeve diameter, shrink down a piece of heat shrink tubing over the PVC tube. You could just add a layer of tape instead. This will prevent the tube from rattling inside and center the battery better.

Step 4: Place Inside Flashlight and Test

Slip the adapter and battery inside your flashlight. Remember to face the Positive End toward the front of the flashlight. The flashlight should work now. When using lithium cells, try not to over discharge the cell so as not to damage it. Charge the cell before it reaches 2.5/2.7 volts. Using cells with built-in protection is recommended.

1 Person Made This Project!

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27 Comments

0
dpeddle
dpeddle

2 months ago

One thing to note here. 3 alkaline or lithium disposable batteries in series gives 4.5v when new. A lithium ion will give 3.7v (we're talking nominal voltage, not voltages you charge up to) and a LiFePO4 will give 3.2v. This means the lower voltage will not give you peak brightness from your flashlight as compared to fresh alkaline or lithium disposable batteries. While the alkaline batteries have a constantly decaying curve, the lithium disposable will stay almost horizontal during it's lifetime and then suddenly die, similar to rechargeable lithium. So, most likely, best luminance is achieved with lithium disposable, but cost maybe better with rechargeable lithium. Trying to improve on the lithium rechargeables will mean installing a boost circuit at the least, but that will reduce capacity, since, depending on design, you most likely are looking at 75% to 85% (if you're good) efficiency. Food for thought! 😉

0
botronics
botronics

6 years ago

The lithium cell shown is a common lithium ion 14500 Ultrafire that charges at 4.2 volts. The 18650 you mentioned will not fit the flashlight and can't be used. Only use a 14500 size cell. When in use, the cell voltage will be about 4 volts.

0
JerryA38
JerryA38

Reply 6 years ago

Why replace the AAA with a battery that has less voltage and less storage capacity?? I use rechargeable Sanyo E's which have a voltage around 3.75 and a reserve of 2400 ma. Your conversion is 3.7 to 4 volt with 900 to 1400 ma reserve.. Did I miss something???

0
jtepper
jtepper

Reply 6 years ago

Actually, yes, you did. The absolute LARGEST capacity AAA NiMH cell I have seen available is 1350mAh, and that is unlikely to be a credible rating. Most are something in the 1000mAh range, and in particular the Eneloops. In my experience, the charge life of the lithium cells eclipses even alkaline AAA batteries, and the higher potential and current provide a bit brighter performance, without burning out the LEDs. 14500 lithium cells are also available in the 2000-2200mAh range.

0
JerryA38
JerryA38

Reply 6 years ago

I think you also missed something. He is replacing (3) batteries with (1). My Sanyo have a 800 ma rating so you times that times (3) batteries and you get an easy 2400ma. Alkaline have even higher rating so I get back to my original question. Why replace with a lower power and lower reserve battery??

0
dpeddle
dpeddle

Reply 2 months ago

You don't multiply the battery capacity by the number of batteries in series. You only multiply the voltage. Only batteries in parallel you multiply battery capacity by the number of batteries in parallel and voltage doesn't change. So a 3S1P configuration where each cell is 1.5v and 800mAh would be 3x1.5v = 4.5v battery voltage and 1x800mAh = 800mAh battery capacity.

0
botronics
botronics

Reply 6 years ago

You can't just add the mAh rating of 3 AAA cells together. Since the current is in series, the mAh rating would be no better than one cell. The best you can get from a single NiMh cell would be 600 to 800 mAh for a AAA cell. With a good quality 16500 lithium, you can get 600 to 900 mAh and have 4 volts to start with. So in terms of power, there is an advantage. The Ultrafire cell shown is probably one of the worst 16500's around with at best, 300 mAh of capacity. I only got it to try this little experiment out. With only dealing with one battery, its easier to change out the battery instead of messing with 3 cells in a holder.

0
JerryA38
JerryA38

Reply 6 years ago

14500 or 16500 ???

0
botronics
botronics

Reply 6 years ago

Oops, 14500 cells. My mistake. One thing I wish is that Instrucables would allow the author to make edits on their own posts.

0
JerryA38
JerryA38

Reply 6 years ago

Ah Ha-- The right answer! Thank You Sir.. Now it all makes sense to me...Forgot that series doesn't compound the ma!

0
dchall8
dchall8

Reply 11 months ago

Hi JerryA38, I realize this is an old post, but another reason to replace the 3AAA design is because you dropped the flashlight, and the only thing that broke was the flimsy battery holder.

0
appsman
appsman

Reply 6 years ago

Actually AAAs are are pretty horrible when you consider they have about 1/3 the capacity of AAs and cost EXACTLY the same. All but the tiniest flashlights made with AAAs are a crime against all that is good. Any attempt to removed a AAA powered device from service should be lauded.

0
jtepper
jtepper

Reply 6 years ago

While the 18650 won't fit most of these cheap lights, I really like using the 18500 size. They have a larger charge capacity, somewhere between the 14500 and 18650, but fit nicely inside. They are commonly available in four-packs for about $10, for use in solar pathway lights.

0
antekar
antekar

6 years ago

Very good idea. I have used this method with success. Please note that Li Ion replacement battery is 18650 and charge limit is 4.2 volts. I use 14500 (AA) size in miniature flashlights that use 1.5 volt or 1.2 volt rechargeable batteries. I find that these batteries charge to 4.2 volt limit in a cheap dual AA chargers. Example Use a blank short circuit instead of one battery in series. The older Li PO4 type 14500 batteries are charged to 3.2 volts. Be careful not to overcharge the batteries. May overheat, leak, explode or become non rechargeable.

0
dpeddle
dpeddle

Reply 2 months ago

You're confusing nominal voltage with maximum charge voltage. LiFePO4 nominal is 3.2v, but it's charge voltage is somewhere around 3.7v. The more volatile lithium ion batteries nominal are 3.7v but charge to 4.2v. You can look at it like LA batteries; automotive is nominal 12v, but FLA is charge to 16v and AGM is charged to 15.4v. resting voltages after charge for all the above is somewhere between nominal and full charge voltage. Usually closer to nominal.

0
JohnW51
JohnW51

Reply 6 years ago

If you've got two 4.2 v cells in series, you're using 8.4 v (at max charge) in a flashlight designed for 4.5 v (with new cells). I'm sure that makes the light a lot brighter, but it may overheat the LED and cause premature failure (as in a few minutes operation instead of years).

0
antekar
antekar

Reply 6 years ago

Sorry for my omission. Yes in this case use 14500. My flashlight is older type, larger with aluminum body. I adjusted the length by pressing down on negative terminal extension, then it fit, used a thinner insert. Another flashlight type 1200 lumen has a 15 mm screwed extension that allows for 18650 Li Ion battery or 3 type AAA cell cartridge.

0
antekar
antekar

Reply 6 years ago

By the way, that flashlight allowed the 18650 battery to slide 12 mm inside the screw base. I bought it at Costco in 2 pack, in 2005. It was just right for this conversion.

0
botronics
botronics

Reply 6 years ago

Did you have to modify the flashlight to fit the 18650?

0
lugiasean19
lugiasean19

1 year ago

I just used a 18500 battery it’s the same diameter as the 18650 but shorter. Works great, you can add or make a sleeve for a tighter fit but most likely it won’t be necessary. You can also just wrap a buildup of scotch or electrical tape around the center to make your desired tighter fit if you prefer. Just make sure to get the lithium not the Lifpo4 because of the voltage difference but either will still work.