re-celling batteries

[Dave Plowman (News)]

They're capable of several hundred amps to start a car - so I'd say the performance will be ok. But of course you shouldn't deep discharge them.

[Bruce]

Starting a car doesn't deep discharge them?

I should have thought that deep discharging was what they were designed for.

[Andy Burns]

Continually cranking an engine over, and over, and over, when it refuses to start, until the battery is flat, *THAT* is deep discharge.

Deep discharge batteries (aka leisure batteries) are designed for e.g. mobility scooters, golf karts, UPSs, caravans, and expect to be more or less flattened each time they are used, before re-charging.

[Dave Plowman (News)]

If it did, it wouldn't start.

Better than car batteries, possibly, but no lead acid likes to be fully discharged. Indeed few batteries do.

[ijon tichy]

Tim,

I would either buy a replacement pack with similar contacts/geometry and modify it slightly, or rebuild the pack using new cells. mixing old and new cells is a bad idea.

as people noted, the charger makes the difference. simple timer-based chargers are not the best. proper chargers monitor the change of current flowing through the cell to detect the point of optimum and usually have two modes for charging, fast and slow. for NiCd and NiMH the slow mode saves the battery life a little bit. I used MAX charge controllers before and they are relatively easy to plug into an existing charger.

depending on what type of charger you got, you can replace the cells with any cells of the same geometry. if the charger is smart and IC-based and the IC can charge NiMH, you can even change from NiCd to NiMH. again, in this case you can put a higher capacity cells there. if the charger is dumb, however and simply works on a timeout, you either have to adjust the RC circuit to increase the time, or stick with the same capacity.

hope this helps.

/ijon

[Tim Lamb]

In message , ijon tichy writes

Yes. Price is a major issue though! The 24V Direct Power battery pack does not match any commercially available replacement (AFAICT)

This is a *smart* charger but I don't think it would do anything other than Ni-cd.

The basic message seems to be that re-celling can be done but at a cost more than a complete discounted drill kit. Oh well! Back to global warming:-)

regards

[Pete C]

On May 19, 10:31=A0am, Tim Lamb > The basic message seems to be that re- celling can be done but at a cost

How many cells are gone?

cheers, Pete.

[Bruce]

Thanks Dave.

[Man at B&Q]

What's global warming?

MBQ

[ijon tichy]

proper charger controller ICs can usually do both NiCd and NiMH.

I don't know how expensive the set of decent cells is. you can still make a better pack yourself.

/ijon

[Tim Lamb]

In message , Pete C writes

None AFAICT. The packs seem to *self discharge* over a few days without use.

A few charge/use cycles and they recover but having to anticipate using a drill by the battery charge time is tedious.

regards

[meow2222]

Its self discharge that makes them 'gone.' Charge the pack, leave it for a week and measure the v across each cell. You'll find one or possibly more that are very low.

Since your priority is cheap, there are 2 options that work:

1. Remove any bad cell(s), wire across where they were and continue at 22/23v.
2. Re-cell it using poundland AA 25p each cells. Yes, I know... but its very cheap, and will work at reduced power and capacity for sod all money, =C2=A35, if its ugly but cheap you want.

NT

[Pete C]

Just charge the pack as much as can be, leave it a few days, then run the drill til it fades and check out what's happening with the cells, while the drill is running.

It sounds like you only have one pack for the drill. How flat do you run the pack before recharging?

cheers, Pete.

[The Natural Philosopher]

Classic dying nickel problem.

Yup.

Go A123 or lithium. Nickels were always crap at self discsharge. Leving them flat is the killer usually.

Lithiums and 123s destroy themselves instantly if allowed to go flat, so they have protection to make sure they never do!

[Tim Lamb]

Umm.. There are two inaccessible cells in the *plug* part of the pack otherwise OK. Running the drill without load is not going to draw much current.

No. There are two supplied. Pretty flat. Usually until no more useful work is achieved.

Having discovered the cost of better quality cells, I intend to buy another drill. I will then be *failure proofed* to the extent of 4 batteries:-)

regards and thanks to all who contributed.

[John Rumm]

Worth bearing in mind that recelling with decent cells may make a dramatic improvement to the drills performance, which you won't get with a new one.

[meow2222]

:

Thats probably why they died. Capacity and self discharge varies from cell to cell, and by the time youre getting no more useful work, some cells are getting reversed at high current, and they really dont like it. Best to stop running thme as soon as they start to fade. rather than when theyre finished fading.

NT

[Tim Lamb]

I'll remember that for the next set:-) Currently in despatch at Screwfix!

I have purchased a replacement battery for my 9.6V Bosch so I can hack in to the cells on the old one and find out what happened there. Just hope it isn't a charger issue!

regards

[Tim Lamb]

Yes. Extended drilling jobs seem the worst for battery drain. Most of my recent work has been installing roof sheets using self drilling Tek screws where battery operation has been adequate and much more convenient than mains.

regards

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