Why is my battery pack melting?!

skater252000 · #1 01-25-2003, 08:12 PM

Here's the deal. I've got a dual 150 mah battery setup with a 3.5 motor in a bit and made a stand alone charger for it. Just a standard pack that holds 4 double A batteries that I got from Radio Shack. Every time I hook it up to my bit to charge it gets really really REALLY hot and the metal spring that holds in the (-) side of the AA battery melts through the plastic. I dunno if I wired it wrong or what but can somebody please help cuz I can't even run my bit anymore!

BTW- I think I wired the batteries right but correct me if I'm wrong. I went from the (+) end of one battery to the (-) end of the other battery.

hogjowlz · #2 01-25-2003, 08:52 PM

either you are charging too long or you wired wrong

Namuna · #3 01-25-2003, 09:02 PM

I just edited the title of this thread...Keep it clean skater.

skater252000 · #4 01-25-2003, 09:14 PM

Well I know I'm not charging too long cuz doesn't a 2.4 volt bit take like 2 to 4 minutes to fully charge. Anyways It starts melting after about a minute at most. BTW, sorry bout the title Namuna.

Anyone else know what's wrong?

hogjowlz · #5 01-25-2003, 09:29 PM

it depends on your charger. 4aas going straight to it is quite a bit of power. my 4aa charger has a timing capacitor.
if it runs after you charge for a minute its not the wiring. id guess you are overcharging.

#6 01-25-2003, 09:47 PM

So let's get this straight - you've got 6 volts (unregulated) dumping into a 1.2 volt cell, and your wondering why things are getting hot?

Just use the charger that's built in the transmitter until you've done a little more research on charging NiCd or NiMh batteries.

I use a 1/10 scale RC battery charger to charge my Bits at a lower charge rate than the built in charger. It takes longer to charge, but the cars run over 15 minutes, and the batteries will last longer.

skater252000 · #7 01-26-2003, 12:12 AM

Arceeguy- Alls I know is that I've read at least 5 different instructions on how to modify a bit to use dual 150's, and all of them have said to use a battery pack that holds 4 AA batteries. And I'm not sure if this matters or if it's correct, but isn't it dumping into the eqivalent of a 2.4 volt cell? I'm no electrician here you know lol. BTW, supposedly you can't get enough power outta a standard transmitter charger to charge up the dual 150's.

hogjowlz · #8 01-26-2003, 03:05 AM

i think you are overcharging.

ZeroTT · #9 01-26-2003, 07:56 AM

As I understand it, the controller regulates the voltage normally, and can charge dual cells if you rewire the charger past the regulator and timing circuit...

(From Quest for Madness)

My standalone charges dual cells fine with only 2 AAs in the charger, and I believe the theory is to charge at about the same voltage as the rating of the batteries, which is why the stock charger is stepped down. The heat, I imagine, is caused by overvolting the batteries. Try charging with just 2 batteries and see if that works...

#10 01-26-2003, 09:20 AM

I somehow failed to see the "dual cell" in your original post. Anyway, the "if 2AA batteries charge 1 cell, then 4AA batteries can charge 2 cell" thinking is not valid. Anyone else doing this must be melting battery holders too!

If you want to do a "professional" job, check out page 14 of this pdf document from National Semiconductor. Look at the "simple 1A current regulator" circuit. Using this simple circuit will allow you to charge a 1-3 cell Bit at 1 amp regulated charge rate. It won't shut off automatically, so you'll still have to time it - but it will regulate current and prevent melted battery holders! I think all of the parts are available from RS for less than 3 bucks! (You can use a LM317 regulator instead of a LM117 regulator)