16.8 Battery Charger Electronics - needed
 

I like my Sears 16.8 volt drill kit with two batteries but my charger
has gone south. It works fine when the batteries are only slightly
discharged but if they get too low, it won't work. The cost is

I opened it up and there is a small circuit board with 6 or 7
components on it, and none are marked. One device gets hot and the
charging light goes out so I suspect this device has partially failed.
I can cool it and it charges the batteries longer but I'd like to
replace the circuit with something else. Any ideas?

Look he
..
http://www.bobvila.com/ProductServic...hlights-2.html

Dave M.

On Thu, 07 Apr 2005 16:55:37 GMT, "David Martel"
wrote:

Look he
.
http://www.bobvila.com/ProductServic...hlights-2.html

Dave M.


All well and good, but click on the item I need and you will see that
it is NOT available at this time.

On Thu, 07 Apr 2005 12:06:51 -0500, PJx wrote:

On Thu, 07 Apr 2005 16:55:37 GMT, "David Martel"
wrote:

Look he
.
http://www.bobvila.com/ProductServic...hlights-2.html

Dave M.


All well and good, but click on the item I need and you will see that
it is NOT available at this time.


I think I will remove that component that is heat sensitive and
epoxy it to a cpu heat sink and hook it back up with wire. That
should help.

PJx wrote:

I like my Sears 16.8 volt drill kit with two batteries but my charger
has gone south. It works fine when the batteries are only slightly
discharged but if they get too low, it won't work. The cost is

I opened it up and there is a small circuit board with 6 or 7
components on it, and none are marked. One device gets hot and the
charging light goes out so I suspect this device has partially failed.
I can cool it and it charges the batteries longer but I'd like to
replace the circuit with something else. Any ideas?

My bet is on the battery rather than the charger. Can you borrow a
battery, run it down and see if your charger will bring it back? Or, if
you really like the tool, buy a replacement battery. That way, even if
your first battery is good, you will end up with two useable batteries.

PJx wrote:
I like my Sears 16.8 volt drill kit with two batteries but my charger
has gone south. It works fine when the batteries are only slightly
discharged but if they get too low, it won't work. The cost is

I opened it up and there is a small circuit board with 6 or 7
components on it, and none are marked. One device gets hot and the
charging light goes out so I suspect this device has partially failed.
I can cool it and it charges the batteries longer but I'd like to
replace the circuit with something else. Any ideas?

Isn't Sears cordless stuff usually rebranded Ryobi? Easiest solution might be
to pick up a used charger on fleabay.

On Thu, 07 Apr 2005 13:22:57 -0400, "William W. Plummer"
wrote:

PJx wrote:

I like my Sears 16.8 volt drill kit with two batteries but my charger
has gone south. It works fine when the batteries are only slightly
discharged but if they get too low, it won't work. The cost is

I opened it up and there is a small circuit board with 6 or 7
components on it, and none are marked. One device gets hot and the
charging light goes out so I suspect this device has partially failed.
I can cool it and it charges the batteries longer but I'd like to
replace the circuit with something else. Any ideas?

My bet is on the battery rather than the charger. Can you borrow a
battery, run it down and see if your charger will bring it back? Or, if
you really like the tool, buy a replacement battery. That way, even if
your first battery is good, you will end up with two useable batteries.

I've been down that path already. I did find a bad cell in one of
the two batteries and replaced it with a cell from an old 9.6 volt
battery. That fixed it but charger only works when the voltage is
above 15.5 volts (on either battery).

I took the bottom off the charger and have a fan blowing on the
electronics and it works great. It charged one battery from 14 volts
to 19 volts without a hiccup. The other one is charging now. I'm
looking for a heat sink as a temporary fix and for replacing the
circuit with a more sophisticated one for a permament fix. I love my
drill.

Battery Charger Circuits:
http://www.discovercircuits.com/B/batt-chrg.htm

PJx wrote:
On Thu, 07 Apr 2005 12:06:51 -0500, PJx wrote:

On Thu, 07 Apr 2005 16:55:37 GMT, "David Martel"
wrote:

Look he
.
http://www.bobvila.com/ProductServic...hlights-2.html

Dave M.


All well and good, but click on the item I need and you will see that
it is NOT available at this time.


I think I will remove that component that is heat sensitive and
epoxy it to a cpu heat sink and hook it back up with wire. That
should help.

Epoxy's a lousy heat conductor. Typically, you want some thermal paste with
some mechanical clamping. Without a picture of the board and components, I'm
just whistling in the dark beyond that...

On Thu, 07 Apr 2005 17:57:59 GMT, Andy Hill wrote:

PJx wrote:
On Thu, 07 Apr 2005 12:06:51 -0500, PJx wrote:

On Thu, 07 Apr 2005 16:55:37 GMT, "David Martel"
wrote:

Look he
.
http://www.bobvila.com/ProductServic...hlights-2.html

Dave M.


All well and good, but click on the item I need and you will see that
it is NOT available at this time.


I think I will remove that component that is heat sensitive and
epoxy it to a cpu heat sink and hook it back up with wire. That
should help.

Epoxy's a lousy heat conductor. Typically, you want some thermal paste with
some mechanical clamping. Without a picture of the board and components, I'm
just whistling in the dark beyond that...

Thanks, Good idea.
I think I can wedge the component (which looks like a resistor) in
between the fins of a cpu fan heat sink.

JimL/PJX

Is that a peak charger, you may be defeating the peak function on 2 bad
packs. It could be the batteries.

On Thu, 7 Apr 2005 13:53:17 -0500, (m Ransley)
wrote:

Is that a peak charger, you may be defeating the peak function on 2 bad
packs. It could be the batteries.

It's a sears. $69 for the two batteries and drill.

I love it.

Andy Hill wrote:
PJx wrote:
On Thu, 07 Apr 2005 12:06:51 -0500, PJx wrote:

I think I will remove that component that is heat sensitive and
epoxy it to a cpu heat sink and hook it back up with wire.

Epoxy's a lousy heat conductor. Typically, you want some thermal
paste with some mechanical clamping.

Epoxy is a perfectly fine heat conductor for an application like this
(the charger was supposedly designed to keep the chip cool enough
without any heatsink), and I do include ordinary epoxy lacking any
particles intended to improve its heat conduction. Furthermore the
chip package itself is epoxy and will impede heat flow much more than
any thin layer of epoxy between it and a heatsink. Even a small
heatsink, like this one:


http://www.radioshack.com/product.as...%5Fid=276-1368

will likely at least double or triple the heat flow between the chip
package and the surrounding air, whether it's attached with ordinary
epoxy or silicone rubber adhesive (RTV).

Tool chargers typically fail when an electrolytic capacitor dries out
or the switching transistor shorts (MOSFET or bipolar, may be built
into the charging controller chip), and since cooling the hot device
makes your charger work again, I suspect a capacitor. Adding a
heatsink will not fix this but may prevent it from happening in the
first place. Any replacement capacitor must be rated for at least as
much voltage as the original and for approximately the same
capacitance. It's also important that it be designed specifically for
high frequency switching operation (low ESR). www.digikey.com and
www.mouser.com carry suitable replacements. The charging controller
chip is often made by www.maxim-ic.com or www.linear.com (their web
sites have schematics that may help you diagnose your charger), but
many use a general-purpose microcontroller (CPU), which can't be
replaced (but it should always have a separate switching transistor
that can be).

Chargers are not typically transformer isolated from high voltage, so
take great care when operating yours with its cover removed. At the
very least, plug it into a GFCI-protected wall outlet.