# Timing Circuit for a battery charger

M

#### Mitch

Jan 1, 1970
0
Ok, this is my first post in this group, and I've done some searching,
but I'll still continue to do so.

I just bought a replacement charger for my battery powered drill and
saw combo. The previous charger crapped out, so I opened it up to see
what it was... All it is, is 4 diodes to rectify the AC, 2 resistors,
and an LED. The resistors only seem to run the led. So the thing is
pretty simple.

When I bought the new charger, I was talking to the guy in the store
and he said that these chargers tend to "burn" up if you put the
batteries on to charge but don't take it off in 3 hours. Not to
mention that it isn't good on the batteries. And since it's an odd
voltage, the batteries are 2x as expensive as common voltage batteries
(Wish I'd known that when I bought it!) So what I would like to do is
design some kind of timing circuit that could turn off the charger
after 3 hours.

I know that the battery I'm charging is 15.6V but I don't know what
the transformer steps the AC down to. (The transformer is where my old
one went bad, and I haven't opened up the new one) So I figured that
if I could rig up something that plugged into the house power outlet,
and then plug the charger into it. The timer would kill the power to
the charger after 3 hours. I don't even need anything automatic
really... I have no problem putting something like a momentary button
to use for a starter switch.

I'm handy with a soldering iron, and I collect pinball machines, so
I'm pretty good with a schematic, and I have kind of a general idea
what a lot of components do, but I'm no where near skilled enough to
try and put something like this together on my own.

If anyone has any thoughts, I'd love to hear them.

Thanks
MitchelWB

R

#### Rich Webb

Jan 1, 1970
0
if I could rig up something that plugged into the house power outlet,
and then plug the charger into it. The timer would kill the power to
the charger after 3 hours. I don't even need anything automatic
really... I have no problem putting something like a momentary button
to use for a starter switch.

Why not just get a couple of X-10 components (if you're not boycotting
them for their annoying web-adverts for their video cameras)?

Might be overkill just for this but something like
http://www.x10.com/automation/timerkit_1deal_a.htm and a couple more
modules can be expanded to a handy way to also turn off the downstair's
lamp or the light in the garage without needing to get up out of bed.
Not that *I'm* so lazy, nope, not me, nosiree...

M

#### Mitch

Jan 1, 1970
0
Not a half bad idea really... and I don't like x10 ads popping up
anymore than the next guy, but at least they usually have some hot
chick to look at for a moment.

Anyway, I think that the biggest difference between that and what I
would like to do is that I don't know what time I'll put the battery
on, or when I would have to shut it off...

So everytime I put on a battery, I'd have to stop and figure out what
time it is, then set the timer to go off 3 hours later (I realize
that's not exactly difficult math) And at what time does that timer
turn the power back on? I would still have to get there in time to
take the battery off before it came back on...

What I'd like is something that when I plug in a battery to charge, it
doesn't even start charging till I poke a button to tell it to
start... Then 3 hours later, the whole thing just shuts off...

I don't even need anything fancy like a way to set how long it runs...
but I wouldn't mind learning how to do that either.

MitchelWB

T

#### the Wiz

Jan 1, 1970
0
So what I would like to do is
design some kind of timing circuit that could turn off the charger
after 3 hours.
[snip]

Thanks
MitchelWB

You want the following, all of which should be available at your local
electrical supply house - maybe even Home Depot.

one 3-wire cord with plug
one duplex outlet
one 4" square electrical box
one box cover with cutouts for a duplex outlet and a wall switch
one windup timer (something like the Intermatic FD or FF series
http://www.intermatic.com/?action=prod&pid=435)

Wire the timer in series with the AC to the duplex outlet.

Plug the charger into the outlet, then turn the timer to 3 hours.

The timer is the most expensive part, but it should be under $20. Home Depot has the 60 minute version (FD50MW) for$15.99 and other time ranges should be
similar.

You may be able to build it cheaper with "electronic" parts (555 timer, PIC of
some type, etc), but the windup timer is the most reliable *simple* device.

VB3 source code: http://thelabwiz.home.mindspring.com/vbsource.html
VB6 source code: http://thelabwiz.home.mindspring.com/vb6source.html
VB6 - MySQL how to: http://thelabwiz.home.mindspring.com/mysql.html
My newest language - NSBasic for the Palm PDA: http://thelabwiz.home.mindspring.com/nsbsource.html
Drivers for Pablo graphics tablet and JamCam cameras: http://home.earthlink.net/~mwbt/
johnecarter atat mindspring dotdot com. Fix the obvious to reply by email.

J

#### Joe

Jan 1, 1970
0
Mitch said:
Not a half bad idea really... and I don't like x10 ads popping up
anymore than the next guy, but at least they usually have some hot
chick to look at for a moment.

Anyway, I think that the biggest difference between that and what I
would like to do is that I don't know what time I'll put the battery
on, or when I would have to shut it off...

So everytime I put on a battery, I'd have to stop and figure out what
time it is, then set the timer to go off 3 hours later (I realize
that's not exactly difficult math) And at what time does that timer
turn the power back on? I would still have to get there in time to
take the battery off before it came back on...

What I'd like is something that when I plug in a battery to charge, it
doesn't even start charging till I poke a button to tell it to
start... Then 3 hours later, the whole thing just shuts off...

I don't even need anything fancy like a way to set how long it runs...
but I wouldn't mind learning how to do that either.

MitchelWB

Maybe you already thought of this, but the first thing that comes to my mind
is a timer that you can buy to turn lamps on and off when you go away. So it
looks like someone is home. It has a circular dial on it and you get a set
of 'thingies' to plug into it at different times of the day to turn things
on and off. You just set up the timer to have the on time preset (anytime)
and the off time preset to 3 hours later. Then you plug the timer into the
wall with the charger plugged into it and turn the dial to activate the 'on'
cycle. It doesnt matter what the real time is.
After 3 hours, it switches off, and you still have about 21 hrs before you
need to come back and unplug it.
I think they cost less then US \$10 and may be all that's required.

hth,
Joe

M

Jan 1, 1970
0

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