power tool – Richard Mudhar

We standardised on 18V Makita NiMH cordless drills at the farm. NiMH is older tech and heavier than LiIon, but the price/performance seemed to be about right there. We’re not hauling these up ladders or carrying them for miles. The trouble with cordless drills, well the NiMH ones, is that you have to stop using the drill as the battery runs down – when you hear the change in note as the power fades, switch the battery. If it’s you who will be paying for the replacement battery you will do that, but if it’s something used by many people that doesn’t happen, because it’s hassle to go get another battery.

Under the harsh load of a drill, that means as the voltage of a cell falls to 0, soon current gets forced backwards through the weakest cell and it dies. So you get a pack with a few duff cells in them, and have to junk the whole thing. The moral of the story is change the battery as soon as the sound changes and the power drops…

Continue reading “Adapting A Makita Universal Charger For Other Nimh Batteries”

Cordless power tools often die not because they’re worn out but because the battery fails, or only holds a charge for a short time. Every tool’s battery pack seems to be different, either from the sheer cussedness of consumerism making you buy a new tool, or because nobody has standardised battery packs, You can fight back, because though the battery packs are all sorts of sizes, the parts inside are usually drawn from standard sized parts, they’re merely packed in different ways.

I had a cordless strimmer, once advertised years ago in the Guardian, from a no-name supplier with two battery packs. Both of which are now duff – a strimmer is a fairly hard life for the battery packs with about 50-100W. Here’s how I remanufactured the battery packs. These are NiCd battery packs – the key issue to to replace like with like. You can replace NiCd with NiMh but don’t cross any other chemistries.

Continue reading “Remanufacturing a 12V power tool battery”