Bosch cordless screwdriver problem

[JH]

Hi,

The battery in my Bosch PSR 3.6 VS cordless screwdriver doesn't recharge anymore, I suspect the problem is the battery is in deep discharge as it is outputting 0 volts when measured with a multi-meter. Although I'll also mention that when plugging the screwdriver into the re-charger unit the recharge LED does not come on, not sure if this is relevant though.

First thought was to simply replace the battery pack but after doing some research on the web it appears the old pack may be recoverable by connecting a more powerful DC battery to it briefly.

1) Does anyone know the validity of such an approach? I.e. do I just connect a 12v car or bike battery for a second or two and that's it? Sounds a bit dodgy to me but I'm willing to give it a go.

2) If the old pack cannot be recovered, what is the best source for a replacement pack?

3) Whilst taking the screwdriver apart the drive mechanism "auto disassembled" onto the floor :-(. I've reassembled most of the parts but cannot figure out where two small metal rollers go (about 5mm long by 3mm in radius) . Here's two pictures and . Any ideas?

Thanks

Jules

[mike ring]

"JH" wrote in news:AEYAd.331$X% [e-mail]:

Got no idea whether it will work, but surely it's got to be tried......!

mike

[Ian Stirling]

When you measure the output of the charger, what does it measure?

When was it last working.

I'd say that it's a bad idea to directly connect to a larger battery,

Do you have a 10W (or so, 5-25W will be fine) 12V bulb, and a 12V battery?

Connecting these in series with the 3.6V battery (in the correct direction!!!) and then seeing what happens will tell you lots.

[JH]

0 volts too when measured with a multimeter. If it's toasted I dare say it will be more economical to buy a new screwdriver.

It has been disconnected for a couple of months.

I think I get the idea, don't have the parts specified but adding another

3.6V battery in series and measuring the voltage with a meter I get 4.07V - the same reading I get without the dead cells in series.

Jules

[Ian Stirling]

Err, actually, I meant to charge it.

If you've got a charged 3.6V battery, then connecting it in parallel with the dead one (- to - and + to +), should charge it enough to measure.

[JH]

Left overnight to charge and battery still reads 0V

[Ian Stirling]

Just to confirm - you're not meaning on the charger are you?

Ok. Is the 3.6V other battery you have similar to the screwdriver one? In other words, could it (temporarily) be substituted for the not working one, to test the charger?

[Andy Dee]

OK, the battery is internal short circuit. The method of recovery is to use a car battery with heavy leads (jump leads) and momentarily "flash" this accross the cells. This should be done to each cell individually. The idea is that the high current that flows, blows the internal chemical trails from accross the cell. !!!!! HOWEVER, THERE IS A HIGH RISK THAT THE CELL COULD EXPLODE !!!!!

Even if this recovers it, the chances are that this will happen again or the cell will fail in some other way. Get a new battery pack or screwdriver. A

[JH]

I've now got to the bottom of the problem. After shorting the dead battery (0 volt reading) a few times across a 12V bike battery I got a reading of

4.07 Volts. I then recharged the resurrected battery using a mobile telephone charger, which has a similar rating to the screwdriver charger, as a source. Reassembled the screwdriver and it now works again.

So basically the re-charger part of the unit broke at some point in the past few months which caused the battery to deep discharge. Which leaves a couple of queries

1. I dare say the battery, whilst now working, needs replacing, any recommended sources?
2. Clearly I need to replace the re-charger, which I'm considering simply sourcing from an old phone charger for free (e.g off a friend who replaces their phone every 12months). Does this sound like a sensible approach?

Thanks

Jules

[Bob Minchin]

It is ususally quite easy to cut open the battery pack and fit new cells. Quite often these are sub C size. CPC are often a good source.

Chargers often appear on Ebay quite cheaply. These will interface correctly to the temperature sensor in the battery pack that is important to regualte the fast charging process.

Bob

[stu]

Lidl or Aldi sell spare 18v rechargeable drill battery packs for about

7quid. Inside are 15 rechargeable 1.2v cells.