On Dec 4, 3:51*pm, terry wrote:
On Dec 4, 1:21*pm, "WW" wrote:

Quote: *"Heck, I've got some old batteries lying about, I might just
try building a
small DC power supply to fit in the scooped-out innards of one."

Been thinking the same!

An excellent basic idea; although I wish batteries were 'Universal'!
And yes a power supply MIGHT be built into a dud battery case to power
a cordless; although it would have to supply a much higher current
capacity than that for just recharging a typical cordless battery,
continuously, over a few hours!

Welcome any comments on the Calcs. below.

Also see my previous post about setting up two old truck batteries to
power our 24 volt computer UPSs. And extending that to our main work
bench. Our good neighbour mentioned recently that he's thinking of
replacing his four transport truck batteries again; before, or during
this winter. So although we have three of his previous ones they'd do
fine. We also have an heavy old-timer 26 volt DC battery charger
supply than can be modified etc.

If the 24 volt proves too high for a couple of the older 12/14 volt
cordless drill with dud batteries and dud chargers am thinking of a 12
volt tap (to keep it simple) or a voltage regulator circuit to step
down to say 18 volts.
To date experiments seem to show that several of these older 12 volt
cordless work fine on anything from 10 to 18 volts; although how much
torque they'd have at 10 volts not yet checked.
The idea being that the now useless cordless drills be used at the
bench; we have some other newer cordless with good batteries and
chargers that still work for outside/portable work. Typically a
replacement Bosch charger was $70+, two new batteries around $50 each,
total $170 plus shipping etc. for a Bosch set (including carrying
case) originally bought for $150! Answer go out and buy new! Price
planned obsolescence? We didn't buy another Bosch however!

Calcs: Typical cordless drill takes say 60 watts? That's 12 volts at 5
amps = 60 watts. Or maybe 100 watts, that's around 8 or 9 amps. If a
typical cordless battery is 2.5 ampere hour it will last about 2.5/ 5
to 2.5/8 = 0.5 to 0.3 hours ( 12 to 30 minutes say) running time? So
somewhere around 5 to 10 amps (at 12 to 18 volts) sounds about right?

Obviously a good idea brewing? And even if a typical cordless required
say 150 watts that's still only 1.2 amps at 'mains supply voltage of
120 volts' .So lightweight lamp cord (18AWG) could be used for an AC
wall plug-in part of it!. Certainly a lot bigger than a Wall-wart but
sounds technically feasible?

Oh btw; tried running a cordless without any battery on DC from a
small supply such as those supplied to power a CB radio. The PS was
rated at around 3 amps.
And it worked OK, without load on the drill. And proper polarity +/-
was needed.
Also tried same voltage AC (Approx. 12 volts RMS) and while the drill
rotated and would reverse it obviuosly didn't like it; probably the
speed controll/trgger not designed for AC! Same results with three
cordless of different manufacturers.