Anyone got a B&D BD602 cordless drill?

I have been given an old cordless drill (Black and Decker BD602) without a charger.
It is only 7.2V so no problems if it must go in the bin, but a spare is always useful, if only for mixing paint.
I can make a charger if someone can let me know the voltage and polarity of theirs. I am guessing that with it being a B&D there are going to be loads of them about. Equally, if someone has one that they no longer need, please name your price.
Thanks, Rob
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I've had one of those for, well, must be about 15 years I should think, and it's still going strong (on its original battery too!). I can't claim that it has been used every week of its life, but more like heavy use - often as a powered screwdriver - for a few days now and again as each DIY project comes and goes. It would be a crime to use it as a paint stirrer !!!
The charger bears the legend "8.7v 480 mA" with the little symbol of a continuous line above a dashed line which I presume to mean raw unsmoothed DC. The centre pin is positive and the output measures 9.6v off load (on an old but accurate moving coil voltmeter). If 'twere me, as a best guess without knowing what cells are in the battery pack, I think I'd take note of the "480 mA" rating and build a constant current charger of about 400mA. Actually, no, on second thoughts, I don't think I would - I'd probably want to open up the battery pack to see what size the cells are and make a more informed guess at their rating and build a constant current charger to suit!
HTH.
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The accepted safe charge rate from an unintelligent charger is 1/10th the capacity for 14 hours. Sub C cells are usually 1500-2200 mAhr, so I'd make a constant current charger 150mA for starters.
Your one has probably just a simple series resistance so will vary the charge current rather unpredictably. ;-)
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Dave Plowman snipped-for-privacy@argonet.co.uk London SW 12
RIP Acorn
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wrote:

Thus reinforcing my point about wanting to see the cells first ... thanks Dave. JFYI, back in the dark ages (!) I stumbled across an ingenious circuit that Hewlett Packard used to use for their calculator battery chargers employing just two transistors and two resistors in which the forward voltage drop across a conducting transistor junction acted as a controlling reference for the current through the load across a wide range of voltages. Therefore, 30v input to the circuit would deliver (say) 50 mA through 1, 5 or 20 cells connected as a load. It was like a 'minimalist' current limit protection circuit on a laboratory power supply. In a 'universal' version of the circuit - of which I built many over the years - changing the value of one resistor would control the current delivered to suit the capacity of the cells being charged. Simple but very effective.
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On Tue, 4 Nov 2003 10:31:44 -0000, "Mike Faithfull"

The voltage across the base and emitter of a transistor is pretty much stable once the junction has started conducting - it's only a diode in that sense, and once the current flow has gone past the "knee" point then the amps to volts gain is almost infinite.
I spent 4 years working at Mullards Semiconductors in Southampton....oh the memories.... ;)
PoP
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The CC circuit I use for drills etc is at its simplest one transistor, two diodes and two resistors. I add a couple of LEDs for status. It will work ok at virtually any voltage (more than the voltage of the cells) but of course needs a larger heatsink if the difference is great. I can't remember where I found it, though, to give them a credit.
I've got a charging area in the workshop with a few 13 amp outlets all fed off a 14 hour one shot timer.
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Dave Plowman snipped-for-privacy@argonet.co.uk London SW 12
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Dave Plowman wrote:

Any chance you could knock up an ascii circuit diagram?
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Toby.

'One day son, all this will be finished'
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a
and
that
as
an
of
want
suit!
Thanks to all for your help. I have 'roughed' it a bit by plugging in a 9V 150mA PSU. I realise that the current is low but it didn't get particularly hot so perhpas there is some current limiting in the drill.
How long would you charge it for?
Cheers Rob
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