[KwartzLab] battery pack rebuild: results!

[Andrew Netherton]

It's been a good long while, and I thought I'd post a follow-up.

I recently disassembled a heavy lumber structure in my garage that was
mostly screwed together.  Very high torque to get some of those screws
out, it really gave my cordless drill a run for its money (and in a
few cases, stopped it cold).  I even managed to cycle both packs
through some quick charge cycles.

I managed to get most of the structure apart before one battery pack
suddenly stopped working.  Taking it apart, I noticed that it was the
pack that I had soldered the battery leads directly on to the adjacent
battery.  One such junction had failed, but some of the wiring that
was in the pack originally had also burned through the insulation.  So
that pack is toast.

I continued with the other pack, but within an hour of burning out the
first one, the second one stopped working as well.  This one was the
pack where I soldered the tabs of the battery together (the
replacement cells I had purchased had spot welded tabs top and
bottom).  I did that figuring it might result in a stronger solder
joint, and would prevent any heat damage to the battery cell itself.
Well, in this pack there wasn't any burnt wires, but the pack quite
readily fell apart - many of the solder joints had failed.  Whether
the high current actually melted some I can't say.

So my conclusions are that rebuilding your own cordless drill pack is
entirely possible, and works well for everyday tasks.  Once you start
getting to tasks that really task the drill and put a serious draw on
the battery, however, a pack rebuild with soldered connections likely
won't cut it.  At that point it would be necessary to use a capacitive
spot welder or equivalent to get a permanent connection that is both
mechanically and electrically sound.

I don't think I'm going to rebuild these packs again.  Instead I'm
going to disassemble the pack charger, and hook up the DC output
directly to the drill and see if I can run it as a corded drill.  I'm
hoping I'll get close to full power that way, instead of piddling by
with a wall wart or having to go full-bore with a PC power supply.
I'll be dependent on mains power, but will have a much lighter
(although now imbalanced) drill to use.  If I ever come across a
heavy-duty 12V battery, I might see if I can find a middle ground -
tethered to a large, powerful, non-hand-held battery, but still
portable enough to take anywhere.

Regards,
Andrew

On Wed, Jan 26, 2011 at 8:07 AM, Andrew Netherton
<andrewnetherton at gmail.com> wrote:
> Last night at TON I managed to rebuild one of my two cordless drill
> battery packs.  It was a bit slow going at first, as I had to climb
> the learning curve first, but eventually did get a pack made with the
> new cells I had.  The cells were all soldered together, which worked
> well enough, despite not being especially pretty.  (Next time I'd
> probably just weld tab-to-tab, but that will be pack #2.)  After I got
> home, I got out the charger and popped in the rebuilt pack.  The
> "quick charge" light came on, which was a good sign.
>
> As of this morning, the pack was registering as fully charged, and the
> drill once again turns!  WOO!!  So I'm calling the rebuild process a
> success, and will now just have to wait and see what kind of life I'll
> get out of the pack.
>
> A big thanks to all who helped me with the rebuild, especially Mark
> for his mad soldering skills.  :)
>
> I've already got some process improvements in mind for the next pack,
> but I'm not sure when I'll get out to do that one (my wife's water
> just broke this morning, so I'm home for two weeks). Once it's
> complete and have the process a bit more refined, we can call a meetup
> for rebuilding the DeWalt, and anyone else's packs that may want to
> try their hand at it.  (And if anyone wants to whip up a capacitive
> discharge spot welder in the meantime, PLEASE DO!!)
>
> Thanks again, KWartzlab.  I'm seriously stoked at how well this worked!
>
> Andrew
>