Knowledgeable battery advice needed

Josh Hassol said:

OK, all you EE types . . .

My headlights short-cicuited last week. After the lamps suddenly died,
I rode for about 5 minutes before noticing that the wiring was hot, and
I unplugged the battery. The wiring in the lamp heads is cooked, but
that's easily repaired.

The battery still works (that is, it will light up a 15W halogen), but
it obviously got hot during the episode: melted through the bottom of
the water bottle holder it was in. It is a 14.4V, 4000 milliamp-hour,
NiMH battery pack.

My question: If there is no leakage from any of the cells in this
battery pack, is it safe to run it down and then try recharging it? Or
am I asking for trouble?

You may have reduced the capacity and future number of recharge cycles
of the battery, but it should be fine to run it through a
discharge/recharge cycle and see how well it works.

peter said:

You may have reduced the capacity and future number of recharge cycles
of the battery, but it should be fine to run it through a
discharge/recharge cycle and see how well it works.

Thanks. I'm going to peel the plastic shrink wrap off the battery pack
and take a good look at all the cells before I do anything.

Josh Hassol said:

peter said:

You may have reduced the capacity and future number of recharge cycles
of the battery, but it should be fine to run it through a
discharge/recharge cycle and see how well it works.

Thanks. I'm going to peel the plastic shrink wrap off the battery pack
and take a good look at all the cells before I do anything.

Good idea. Sounds like you're gonna have the battery apart no matter
what you do (since it melted its water bottle). Just don't get
yourself in a situation where you have to depend on the light lasting
its normal run-time to get you home in the dark (at least not until
you've got a few rides with it in).

Mark Hickey
Habanero Cycles
http://www.habcycles.com
Home of the $795 ti frame

Quoted message said:

Quoted message said:

Quoted message said:

You may have reduced the capacity and future number of recharge cycles
of the battery, but it should be fine to run it through a
discharge/recharge cycle and see how well it works.

Good idea. Sounds like you're gonna have the battery apart no matter
what you do (since it melted its water bottle). Just don't get
yourself in a situation where you have to depend on the light lasting
its normal run-time to get you home in the dark (at least not until
you've got a few rides with it in).

Regarding the battery, I don't know if it would be safe or not. There
may be increased risk of cell rupture. As another poster indicated,
I'd run it through a charge/discharge cycle (typical load) and measure
the voltage output over time. Do this in a 'safe' area and check for
reasonable battery temperature. If the voltage/temps/burn time seem
reasonable, then I'd continue using the battery.

FWIW, I build my own bicycle lights using off-the-shelf parts. Due to
the risk of short circuiting, I used to use automotive blade fuses.
This was a problem if I happened to get a short, as the fuse needed
replacement.

I have started using something known as a polyfuse. This is a tiny
passive device that looks something like a disc capacitor. When a
short-circuit occurs, the device acts as a breaker and stops current
flow. When the short circuit is corrected, the polyfuse resets itself,
allowing you to turn your lights back on without damaging your battery
(or lights). They're fantastic little things!

If your light is factory-built, it shouldn't be too much trouble to
make a connector segment with an inline polyfuse.