I bought a nice cordless drill in a junk shop for $2. They couldn't
get it to charge, so sold it off cheap. The problem was the wall
charger was dead. So, I cut the cable off the wall DC power supply
and put a current limiting/voltage dropping light bulb (12v in case
the cord gets shorted to ground) in series with the + lead to the 12V
house battery. The bulb is rated 12V at 6W for a low voltage sidewalk
light at hardware stores. The drill battery pack is 7.2V. If the
battery pack is nearly charged up, 13V minus 7.2V equals 5.8V across
the bulb. Now, the bulb draws .5A at 12V (6W/12V=.5A). At half
voltage, it'll draw about .25A, half current. (Bulbs are not linear
but for charging drill motors noone cares.) This charging current is
far below the C cell Ni-MH desired charging current in any case so I
get a nice trickle charge and the battery pack gets barely warm at
full charge. The light bulb is quite bright when the battery is dead
and dims as the battery pack voltage rises towards full charge, giving
me a coarse indication of its charge status. I use the drill, mostly
as a screwdriver, then simply plug it back into the light bulb when
I'm done with it. Slow charging gives you LOTS more capacity...(c;

You can't charge a 12V Ni-Cd from 12V reliably. Ni-Cd and Ni-MH cells
are CURRENT charged, not float voltage charged. It would be hard to
get a good grip on a series resistance that would give you stable
current for them.



On Tue, 23 Mar 2004 07:50:53 +0100, "Jürgen Spelter"
wrote:

Hi AD,
take a look at the data sheet or instruction manual of that charger, you
want to buy with your new drill. Some chargers have a wide area of voltage,
because they are sold all over the world. The modern chargers use switching
power sypply and the it is no problem to built them for for voltages between
60 and 240 V.

I´m planning to use my old cordless drill on my boat too. Because I have
only battery power supply, I´m going to connect the drill directly to my 12
V power. Maybe that`s another idea for you. Drill voltage must be the same
as onboard voltage and the cordless drill gets a cord. That cord will make
only problems on a ship of some 100 m og length....


Jürgen



"AD" schrieb im Newsbeitrag
...
Hi all,

looking to replace my cordless drill on the boat with something a bit
better. I am looking at a panasonic and have found the prices extremely
cheap in the US but I need to get the charger to work with 240 volts not
110volts. Is it possible to modify a battery charger to do this or would
I
need to use a step up type voltage converter?

TIA

AD






Larry W4CSC
POWER is our friend!