Replace 3x AAA with 18650 Li-ion Battery

thingiverse

Some LED flashlights powered by three 1.5-volt alkaline AAA batteries mounted in a cylindrical adapter may be retrofit with a single rechargeable 18650-type Li-ion battery. In most cases the LED flashlight's electronic circuitry will be able to handle the voltage difference between Li-ion (3.7 volt) and 3x AAA (4.5 volt).Read and follow the CAUTION section below to become aware of the caveats.====================================================================Update 3 Januar 2024:You may find protected 18650 Li-ion batteries athttps://www.keeppower.com.cn/or at resellers, relieving you of most of the CAUTION issues detailed below. Please note that due to the integrated protection electronics these batteries have a length of 69 mm instead of the standard 65 or 66 mm.====================================================================Disclaimer:You are using my design and advice at your own risk. Li-ion batteries may explode and/or catch fire (burning furiously and inextinguishably at very high temperature until all combustible material is consumed). My advice may be incomplete, erroneous, misunderstood, and I am not aware of your LED flashlight's particularities.Using the retrofit LED flashlight may void its warranty.Prerequisite: The LED flashlight's triple-AAA battery adapter must approximately be of the same length as the 18650 Li-ion battery (65 mm). Some very short LED flashlights may have a very short triple-AAA battery adapter unsuitable for this retrofit (unless the spring still manages to compensate for the length difference by being more compressed).The flashlight must be a LED flashlight. The old incandescent bulb flashlights are not suitable for this retrofit even if their triple-AAA battery adapter matches, see CAUTION below (Li-ion deep discharge not detectable).The LED flashlight's genuine triple-AAA battery adapter must have only a single electrical contact at each end. If the adapter has more than one contact at either end, then this LED flashlight is unsuitable to be retrofit with standard 18650 batteries. In this case stay with the triple-AAA alkaline batteries.Which 18650?Buy a quality product like the Sony/Murata type US18650VTC6 (data sheet e.g. athttps://asset.conrad.com/media10/add/160267/c1/-/en/002362039DS00/datasheet-2362039-murata-us18650vtc6-non-standard-battery-rechargeable-18650-high-current-loading-li-ion-37-v-3000-mah.pdfor athttps://www.omnitron.cz/_dokumenty/792019133205264/sony-us18650vtc6.pdf )Do not trust some sellers' capacity deliriums. Significantly more than 3'000 mAh is physically impossible in an 18650 package. So "12'000 mAh" clearly is a scam. The real capacity of this scam-18650 may even be significantly lower than 3'000 mAh (me being the proud owner of such a collector's device). Weight is a good indicator of capacity. The above US18650VTC6 weighs about 45 grams.CAUTION: LED flashlights designed to be powered by 1.5-volt alkaline batteries do not contain the deep discharge protection circuitry required for or Li-ion batteries. Li-ion batteries must never (not even once!) be discharged below about 3 volt per cell. Some quality cells may survive a minimum of 2.5 volt under favourable circumstances (e.g. specific discharge current and temperature). When the Li-ion battery has been discharged below this level (even once), then the Li-ion charger will have to refuse to recharge the cell, because recharging the cell from deep discharge may cause the cell to explode and/or burn furiously at very high temperature during or after recharging. When the voltage is approaching 3 volts, then the voltage will continue to drop faster and faster. The marginal remaining energy obtained in this voltage region does not pay off compared to the risk of permanently damaging the Li-ion battery.It is therefore your own responsibility to avoid discharging the Li-ion battery below about 3 volts. Depending on the particular LED Flashlight, the LED flashlight may go out as soon as the voltage drops to around 3 volts. You may fathom the go out supply voltage of your LED flashlight with a variable voltage laboratory power supply by starting at 4.5 volt (never expose your LED flashlight to a higher voltage than 4.5 volts) and continue downwards. If the flashlight goes out at 3 volts, then you may use this as an indication of when to stop discharging the 18650 battery any further.When, during operation, the LED flashlight goes out or refuses to light, then immediately remove the 18650 battery from the flashlight in order to avoid any (possibly inadvertent) deep discharge, because in this situation it may not easily be possible to determine whether the switch is currently on or off. If it is on, then the discharge will continue towards destructive deep discharge.For the same reason, leaving such a Li-ion retrofit LED flashlight both on and unattended is a bad idea. Do not use a Li-ion battery on an incandescent bulb flashlight designed to use alkaline batteries, because incandescent bulbs will not show a clear go out voltage to indicate a certain voltage level. Further, incandescent bulb flashlights do not have the electronic circuitry to raise the Li-ion’s 3.7 volts to the nominal 4.5 volts of their triple-AAA battery pack.18650 means "diameter of 18 mm and length of 65 mm". In practice, this is accurate to about 0.5 mm in diameter and about 1 mm in length. But please do not measure the length of your 18650 battery with a metallic calliper as this will lead to a short circuit with potentially dramatic results (e.g. welding of the calliper to the battery terminals followed by explosion and fire).Do not allow other people (including children) use the retrofit LED flashlight if they are not fully aware of all of these points.So far about the dangers. Now wipe the cold sweat from your brow and move on.The diameter of the original triple-AAA battery adapter may vary depending on the LED flashlight type. It is always larger than the diameter of the 18650 battery. I am therefore supplying a number of adapter-.stl files with a range of outer diameters: Some LED flashlights have a single contact spring at its negative terminal (usually located inside the end cap) and no spring at the positive terminal (usually located towards the LED). In this case my 3D-printed adapter is a simple 65 mm tube of suitable outer diameter. Other LED flashlights have a contact spring at the positive terminal (usually located towards the LED) or even at both ends (LED side and end cap side). In this case it is important to centre the spring to the positive 18650 battery terminal, which my other adapters exhibiting a cone do (see cutaway view).As always, I include the OpenSCAD source file for you to adapt and/or improve:Download and install OpenSCAD from https://www.openscad.orgLaunch OpenSCAD and open the enclosed OpenSCAD source file (/File/Open).Amend the parameters at the top of the source file or even code.Save your changes (/File/Save).Render the design (/Design/Render).Export the rendered design e.g. as a .stl file (/File/Export/Export as STL).Slice and print.See my other designs athttps://www.thingiverse.com/thinger13/designs