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SentinelAeon 12-25-17 01:47 PM

Convert cordless drill from Ni-Cd to Li-ion conversion

I have a couple of old laptop battery packs and i would like to do a fun little project and would like your opinion/advice. Ni-Cd Batteries in my old backup drill died and i threw them away. I saw online a couple of ni-cd to Li-ion battery pack conversions. The reason i didn't do it yet is that Li-ion batteries are kind of tricky and i would hate to see them go up in flames.

I do know that laptop batteries aren't heavy duty and i am ok with my cordless drill being less powerfull after the conversion - it being a backup for some easy tasks while my main cordless drill is charging. I was thinking of taking 4 of those batteries and connect them in series to get 14.8V to replace my old 14.4V pack. I would charge the batteries individualy (i have 4 small chargers that charge 1 battery at a time).

Now my main dilema is this: will the fact that those batteries are made for laptops and not for drills mean that cordless drill will simply be less powerfull, or will they overheat and go up in flames ? I am ok with the first thing, the second one, i would like to avoid. I would like it to be as simple as possible but if really necesary, i would include some safeties. I was thinking of some overheat protection (a switch that will turn off when batteries reach a certain temperature, or simply some heatsinks on batteries). I dont think i need low voltage protection since those batteries are old anyway and this is more of a fun project then a long term solution.

So what do you think, can this be done without serious fire hazard ? I love doing projects like this, but the nature of lithium batteries is what worries me.

oil pan 4 12-25-17 08:58 PM

I bet you can do it.
I converted an old spot light I got back around 2000 from lead acid to LiFePO4. But I have not tried to charge it yet.
It had a 2.5ah 6v acid battery. Now it has 8ah of lithium stuffed in it.

I don't know if the laptop top lithium ion are suitable for drill use. I know something like LiFePO4 would be.

jeff5may 12-26-17 06:54 AM

The danger of running lithium battery cells happens when trying to discharge them completely. Unlike the nickel chemistry type, the lithium cells can never be discharged to near zero volts. If the cells are discharged, they polymerize and liberate heat in the process. In the case of tablets or phones (or an ever-increasing number of compact high-drain devices), the battery can melt or burn its enclosure.

Running laptop cells (18650) to power hand tools is a common industry practice. Naturally the top tier manufacturing companies are going to use a different cell in the Shell just so they are difficult to swap out. The big dogs couldn't charge 75 dollars or more for a battery if they had common cells inside: the aftermarket would undermine the price.

The single most important thing to include in the battery pack is a BMS, or battery manager system. These are a combination of a smart charger and a smart discharger. All of the laptop battery packs have one in them in order to meet safety and liability standards in Europe and America. They can be found as cheap and barebone or expensive and snazzy as you desire on the normal auction websites. More discharge current and higher voltage BMS cost more than low voltage and low drain. Just figure out your peak current draw and max voltage and order accordingly.
Cheaper than dirt $3
Still cheap $7
Not cheap $22

oil pan 4 03-28-21 06:36 PM

Hey I found lithium ion upgrade batteries for my old Dewalt tools. There's 2 types. One uses the original NiCd-NiMH charger and the other type comes with its own charger. I have had the battery for about 6 months and it actually holds a charge really well. I keep that one on my 18v Dewalt 1/2 inch impact.

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