Drill battery conversion. But will it work?

If you have been watching some of my previous videos you will have heard me talking about converting an old NiCad drill battery pack to lithium ion power.

And today is the day!
But, of course, the project didn't go exactly to plan. In several ways.

Hopefully someone can learn from my mistake(s)... (I know I did)

Some related videos:

The acquisition of the free drill:

And where I get my free batteries:

And the mailbag where the CC/CV power module came from:
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This isn't the only way to do it.
It's probably not the best way to do it.

But it's how I do it.

[pileofstuff]

Is it really a failure if I learned something from the process?

[generaldisarray]

I'm never disappointed when I watch a pileofstuff video, I either learn a lot, or, I learn something while being highly entertained. Keep up the good work, as the saying goes, show me a person who has never made a mistake, and I will show you one who has never tried anything.

[neilshobbyhq]

Excellent, this is what this hobby we all love is all about

[robertbarr]

Interesting. Thank you. Having seen your bench, I now understand why it's "Pileofstuff".
Good luck.

[GEORGE-jfvz]

That's very close to what I do when my nicad equipment dies. Good reuse of equipment.

[jp-umfr]

U.K. Like you I spent a long time 'faffing' about with fitting all the correct gubbins into the battery shell of an old 7.2V Bosch drill. My efforts not only looked a mess but when the batteries went flat I would not have a drill to use. I ripped the lot apart and went to the KISS method - Keep It Simple Stupid. I made the 2 x 3.7V batteries easy to remove from the old battery case. So that I don't ruin the batteries I put a tiny 2 wire LED volt meter (99P) and test switch in the base of the drill, knowing the state of the batteries helps. I can have the batteries out and new ones in in less than a minute and not wait for over an hour for them to charge. Remember to get the high drain Li-ion batteries - vaping batteries are fine. I have 2 of these drills, both over 20 years old. Single speed, one keyed, one not. They will sink a 100mm screw (4") into wood flush.

[billywhizzy]

The specs of the Samsung ICR1865026F cells have a maximum current output of 5.2A since they are used in laptops and not designed for high current draw. From the spec sheet. Your BMS is a continuous 15A which should do the job with 56A peak current before the overcurrect protection kicks in. Now those are old cells with approx 1/2 the capacity so they probably max out at 3A. Your charging circuit is fine. Your bottleneck is the cells. In LiIon drill packs they use >20A cells. I will still however get a bigger BMS because it is a bit 'on the edge. When I load my liion drill (24v) I get 15A draw and 3A free running. It's an induction motor.

[jerril]

That was still interesting despite it not working. Nice to see a Robbie in action :)

[SeanBZA]

Did the same, just added a small socket to provide the charge current, and connected the drill motor to the battery direct, leaving the BMS to do charge control only. As I was using a single cell no balancing issues either. Good upgrade to a free cordless screwdriver, looking at doing the same to another cordless drill, though my go to drill is now a short cord and a 12V 7Ah SLA battery powered one, which is both portable and has good charge life, especially as I have a few old SLA units to keep cycling though it, and they spend the off time on the solar charge controller getting refreshed.


You need a BMS with a much higher trip point, probably around 30A or so, more than the small ones will do, but you might also experiment with the BMS circuit and add a small capacitor across the BMS gate circuit, so that the disconnection on discharge is very much slowed down, or add extra filtering to the BMS sense input, so it ignores those initial high current spikes from the drill.

[davidcrossley]

I had the same problem with insufficient power from 18650 cells but a lipo pack (and 50A charge controller) worked fine.

[pfb]

Replaced 18v NiCd batteries with LIPO 5S pack. Was a bit longer than battery case but so much torque now! Connected balance connector for charging.

[GeorgeJFW]

This was fantastic these are the type one of videos/projects I wanna do thanks for the inspiration 🍺

[Helmut]

Great tinkering video, like that a lot. Maybe you should connect the laptop charger directly and measure how much current the drill wants? 18650s can deliver a lot of current which is why they are so popular, it must be the BMS holding you back 😁

[SidneyCritic]

Is it possible to put a BMS bypass switch in there so when you drill you get full power. Then it's just a matter of switching from charge to drill.

[GeorgeJFW]

I swear I was thinking about this video yesterday

[dmwtech]

hey, at least you didn't catch your bench on fire. positive right out of the gate. when experimenting with lithium batteries, make sure you have a containment system in case they go into thermal run away.

[SidneyCritic]

Are you going to look into this anymore?
I'm just doing mine now with a 4S 30A - I've got it in 3S2P config -, and I just noticed that there are 100A BMS's cheap, ie, around $10.

[davidpyper]

The battery balancer was a nice thought, but its working against you when using the drill. If you make a circuit to bypass the balancer when the drill trigger is pulled you would get the full amperage allowed by the batteries. Then when the trigger is off the balancer can go to work. But remember not all batteries are equal. Internal battery resistance is going to come into play with projects like this. Your batteries came from a laptop battery. They probably were designed to slowly discharge over time, thus they have a higher internal resistance. Find some that came from an old lithium Ion batter pack. They were made to quickly discharge for instantaneous power, thus they have to have a lower internal resistance. It probably explains why the drill powered up exponentially. That's my two cents. Very entertaining video.

[Leif_YT]

It looks like your BMS protects above 15A. I never measured it myself, but i think during the startup many drills can easily go above 20A. There are some 5S BMS on AliExpress that support up to 30A and also include a charging circuit. If they fit into the case they might be worth a try.

[KARLLARK]

Got to lov the way you try things brill vid thanks, .//., what was the beer make today, .//.,