Bosch battery charger (for a drill)

I have been given a Bosch battery charger (along with a battery) for a fairly chunky looking battery powered drill.
The problem apparently is that the charger does not charge batteries. The battery appears to have about 15vdc (marked as 24v 1.2Ah). I have popped the covered off the charger, and there is about 35vdc across the charging terminals.
However when I attach the battery, the voltage drops to about 15vdc - as if the charge has no current supply.
I have had a quick look at the circuit board and it looks ok. There is also an LED attached to the board which briefly flickers when the battery is attached and then goes out again.
I was lead to believe the LED is meant to flash until the battery is charged and then remain on to show 'fully charged'.
The details I have for the unit are: Typ 1617 224 006 (then 820 in an ellipse) prim: 240vac, 50/60Hz, 30w sek: 24vdc, 0.6a, 15va
Any suggestions?!
Cheers, Matt
ps. device is apparently a bit over a year old, but has not had much use.
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Matthew Ames wrote:

This charger is the same as mine, which is for my GBH24 VRE 24Volt Hammer Drill. I doubt that there is anything wrong with the charger itself, rather, the battery is knacked. This is precisely the same effect I had with my original battery which went the same way.
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rather,
There was a second battery in the box with the drill, and we tried that - same result - the LED just flickered once and that was it.
what sort of life would you expect to see from the batteries?
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rather,
Just put an amp meter inline with the battery and it appears to be charging at about 100ma
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Hammer
charging
How long are you leaving the batteries in the charger ? The batteries won't charge in five minutes if they've been left discharged for any length of time or are new. New batteries should be left on charge for at least eight hours before being used, and if the batteries have been left for months without charge, then they'll probably need the same treatment.
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won't
eight
So far, not very long. I'll leave one in over night and see what happens. If I can fix this, then I can get a free riding lesson :-) I will report back tomorrow. My only concern was that the LED did not seem to function as I was told (by the owner) it would... but there again!
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Right. Sub C cells are usually between about 1500 and 2500 mAh capacity, and the safe basic charge rate is 1/10th of the capacity for 14 hours. So 100mA sounds rather low - unless the system is old when batteries *may* have had a lower capacity than today. Also, you said earlier the charger was marked as 0.6 amp which seems a bit generous if it's only charging at 100mA.
However, if things aren't overheating etc, I'd leave it on overnight and check the current again in the morning.
I'd be willing to bet though that it's simply the battery that's knackered.
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Dave Plowman wrote:

I would too. Some of the cells will have grown internal whiskers that will have shorted them out. This often happens with NiCads that are left for months discharged. Sometimes I've fixed them by blasting a current into each cell from a controlled power supply, but you have to get at each cell to do this..
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A Ni-Cad charger - assuming a non intelligent one - will (or should) be constant current, so the voltage will vary a lot according to the condition of the battery and what the charge rate is set at (hours). So you really need to measure the current going into the battery, and know how long it's meant to take to charge. A simple overnight charger would deliver *about* 200 milliamps.
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