Something else to use salvaged cells in - powertool packs!

Batteries and Chargers Rechargeable Batteries
1

I’ve been wanting to do this for ages and I’m extremely pleased by how well it turned out.

I have a whole bunch of B&D 18V powertools (drill, sander, saw, strimmer, hedge trimmer, hand vacuum) and although I think the tools are great, I’ve never been very happy with the batteries. The don’t hold their charge very well, weigh a lot, take ages to charge and don’t last very long, especially in the strimmer and hand vacuum. As they all use the same battery, I figured that converting some of them to lithium would fix pretty much all those grumbles.

Also, as some of you know, I’m an enthusiastic battery scavenger and an unrequited skinflint, so I toured the battery recycling bins at work for a few months and (among other things) found 3 macbook pro li-po packs from which I got 5 parallel pairs with an average of 6Ah capacity. Li-po should theoretically deal with high current draw better than the li-ion cells found in laptop batteries, so I went with these as the pilot experiment.

they’re obviously not matched pairs, plus I need some way of monitoring battery charge, so I built the pack with a balance plug wired in using a 5S JST extension from Hobbyking (a few bucks for 10). 12AWG solid copper wire was used for the fly leads and interconnects, also scavenged from work, this time from the machinists recycling bin :slight_smile:

The case was “adjusted” to fit the cells and a port for the female balance plug cut out.

pack wired up and in place

However, as the li-po cells are wider than the nicd cells were tall, the top of the case doesn’t sit flush anymore. So I rummaged around in my pile of scavenged wood (see the theme here?)

cut out a piece the shape of the case

then cut out the spacer using my jigsaw

The case screws are really long, so it all fitted together just fine. The male to male extension was made by soldering together 2 male extension halves and matching the colours of the wires on each half, then wrapped in electricians tape. The voltage monitor is one off eBay for $3 or thereabouts (the most expensive component) and held on with velcro so I can swap it between batteries and even my supercharged mattress inflator (https://budgetlightforum.com/t/-/18754).

installed!

To charge it, I cut off the charging cradle from one of my spare chargers, removed the guts (after I figured out why it didn’t work) and wired it up to a Magicshine female plug I had lying around to that it would plug into one of my charger adapters. Picture was taken before I removed the guts of the cradle, hence the red light :slight_smile:

So how did it work? Freaking awesomely! One of the main spurs in building the pack was that I wanted to clear a section of overgrown trail on a really cool mtb bike route I rode a couple of months ago. The underbrush had grown together over the trail so that riding through it was like getting the skin flayed off your legs. So I figured that I’d strap my hedge trimmer to my camelbak and ride up Tuesday evening (usual ride time, but my buddies were all away) to clear it. Well, after climbing for 50min or so in 30C+/90%+ humidity I finally got to the clogged section and around 3h later I was finished :slight_smile: The pack lasted about 2 1/2h before bank 1 started dropping below 3V, so I switched over to my spare NiCd pack to finish off. Then I packed up, switched my helmet light on and rode back down to the car :slight_smile:

I charged up the pack last night and it took 4.5Ah, so I think that I used most of the capacity. It’ll be interesting to see how it fares with the strimmer, but even if I get 1h out of it, that’s more than enough to do my whole garden. Next up is another pack with li-ion cells, perhaps 5S1P to see if I can make a lighter pack that works with my drill (the li-po pack is about the same weight as the NiCd pack). I’ll also seal up this pack a bit better and paint the wood black or something :smiley:

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very nice!

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Slightly off topic , but I’ve just recently used my hobby charger to charge my Ryobi NiCd drill battery, I first did discharge cycle then a charge cycle and amazingly the Ryobi battery is now holding a decent charge , the chargers they provide are sh1t to put it plainly.

4

thanks!

I agree, they’re just simple dumb chargers that charge at a low enough rate not to cause the cells to vent.

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Nice work! I did this a while back to some B&D packs. Unfortunately, the standard Li-Poly cells used in laptop packs are not high-drain (usually 2C) and did not last very long in my drill or nail gun. I got about three cycles before some of the cells started to gas (visible bulging of the cell). After that they are more of a hazard than anything. :frowning:
Hopefully your cells are better than the ones I used, although they look very similar.

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hmm, thanks for the feedback relic. I did wonder about the max drain rate of those cells, especially as it’s not like Macbooks have to fly or anything. I’ll keep a close eye on them, especially after using the pack with the strimmer. Going by the trail session, the hedge trimmer was drawing 2-3A, which is well within 2C (~12A), so that should be fine.

I can also see how the load is pulling the voltage down in real time too, which should give me an idea if I’m stressing the cells too much. The hedge trimmer took a while to go below 4V per cell, which is a super light load, whereas the strimmer pulled it down to ~3.8V instantly. The drill I’ll have to keep an eye on too as the load varies massively, from nothing (wood) to lots (thick steel).

As an aside, the 2S4P ~8Ah pack in my mattress inflator gets pulled down to ~3.5V/cell instantly and I can only use ~1/4 of the capacity before voltage sags below 3V/cell. I don’t even want to know how much current that 6V motor is pulling :slight_smile:

7

String trimmers are brutal when actually cutting. For light duty, that pack should be OK.
I rebuilt a Ryobi Ni-Cad pack using a Turnigy RC 5S 40C pack and it’s rock solid. Only thing it’s missing is a low battery cutoff. I use it as a backup now as I have three Ryobi Li-Ion packs.

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yeah, if I was going to do this properly I would have just bought a high drain li-po pack. Then again, that would actually entail spending money, something I find difficult to do :slight_smile: Plus I like reusing stuff that would otherwise have been trashed.

I’ll update the thread once I’ve used the pack with the strimmer and done a few charge/discharge cycles. I was sort of hoping that the hot weather would kill off the lawn so it wouldn’t grow again until it gets covered with snow in winter, but that was just wishful thinking…

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You mean I'm not the only one who thinks this way?

-Garry

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Nice work.

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:slight_smile: first snow is awesome! Although the chore of mowing the lawn is replaced by the chore of shoveling snow off the driveway, I somehow find the latter much more satisfying.

I never get people who actually water and feed their lawn, it seems like you’re working to make more work for yourself.

thanks!

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well it's been a while and I've had a chance to use this battery quite a bit. Sadly, it kicked the bucket one afternoon when I went to use the strimmer. After grumbling about how crap the original NiCd batteries were (took 3 to do the garden, grr) I stripped the battery down. With some poking around, it looked like the polyswitch tripped on one of the parallel pairs (the mismatched one). Then one of the connections on that cell desoldered and refused to be reconnected - I was too impatient stripping that battery down and didn't leave enough of the tabs. Anyway, crap to that, so I just swapped in another Macbook Pro parallel pair with lovely long tabs :)

Battery is now up and working again, fingers crossed it'll stay that way!

However, it's as heavy as one of the original NiCds (even with 2-3x the capacity) and it tires my arm and wrist when I'm using it on my drill. So, with some other salvaged cells (each a healthy 2.75Ah!) I made a 5S1P battery which is at least half the weight of the other one but still holds up fine.

as an added bonus, the new battery fits into my dustbuster minivacuum and actually gives it enough umph to be useful. Had some fun sucking up metal shavings off the floor :)