Flat battery

Hi Bob.

Sub "C" NiMH are available but a quick price check here in Australia through an electronics outlet would drop about $180 AU out of the bank account to buy the 20 needed to attain 24v.

Yes there are probably cheaper here and in the UK so shop around !

The charger could also be what has killed the batteries as many battery packs don't have the internal temperature thermistor either fitted or connected (that is what the third terminal on the battery is for ) and some chargers don't have this third terminal fitted either .

This is to protect the battery pack from overheating when charging which kills batteries pretty quickly .

An Electonics magazine (silicon chip ) i read did some stories on this and also produced a charger kit that was available through Jaycar electronics but i'm sure Elektor magazine did the same in the UK .

A later edition saw an old battery drill revived with the use of 2 gell cell batteries mounted in a small plwood box with a carry handle on top , it was not as convenient as the drill with an internal battery but still had its uses as you did not need mains power to run it or have to run power leads everywhere .

IAN

You can sometimes rejuvenate a Nicad pack simply by puttibng as much charge as it will take in, then shorting it with a thick wire for a few seconds. As mentioned above you are trying to burn out the 'dendrites' in the shorted cells.

A failed pack is almost always just one duff cell, easy to replace but be aware that another cell will fail in turn.

Hard to run such a drill off a transformer, as they can take 20 amps peak which might be about 300 watts.

Joey

A friendly word of warning.

DO NOT try to replace the Ni-Cads with NIMH batteries and think that the existing charger will be okay

It will not !!

doing this may well result in the batteries exploding.

NIMH battery chargers are designed specifically for NIMH and closely regulate the voltage and current.

Ni-Cad chargers are not nearly so carefully regulated.

Like I said, just a friendly warning

I would hate to see anyone get hurt.

This can also happen if you overcharge NiCad batteries. Don't ask how I know!

Russell.

My recent experience and testing shows that lithium ion cells are much superior to either nicad or nimh cells. They hold their charge extremely well and have excellent output. I recently fiited 2x3.7v cells in parallel to my B&D screwdriver by removing two internal ribs, and the result is most satisfactory. I then fitted another two into a small electric hand drill similarly. I obtained these cells as one pack from a sales basket in a Halfords shop for £3. They were from one of those portable DVD players. I did not charge them and did not use them for nearly six months and when I tested the pack by a quick short out of the leads, they nearly welded together. These cells are nominally 3.7 volts, but are slightly bigger than AA cells, but I see that some Hongkong firms are offering what appear to be sub C sizes. I recently bought a collet chuck and ten ER16 collets from one firm there for about £40 including postage - about one third of the price charged in this country. They arrived in five days and are excellent. So some of these firms can be trusted. Their paper work and communications were in impeccable English. I have been using all types of cells for RC flying since the first Deac cells were introduced, when these were either 250mah or 500mah. These Lithium cells are now being offered with 5000mah capacity- quite amazing. Lithium Polymer is a different kettle of fish. Too much charge and they are junk. Let them run down too far and they are junk. Unless charged and handled with extreme care they can be mini fire bombs.