NiCad battery discharge rate?

[KC]

I don't recharge NiCads until they're 80-90% discharged. (Definitely don't want to discuss the pros/cons of that!) My question is what is a reasonable discharge rate to get the batteries down to that level? For example, for a pack of 2800mah batteries, a bulb pulling 300ma takes a long time to draw them down. Can I safely up the load to 1 or

1.5A to discharge them faster without causing damage to the batteries?

Why? Typically I'll have usage on a battery pack at the end of the day, but want to start tomorrow with a fully charged pack.

KC

[Tony Hwang]

Hmmm, Discharge rate depends of current draw.

[Richard J Kinch]

Sure. The RC toy applications draw tens of amps from such batteries.

[RicodJour]

Switch to NiMH or Li-ion.

R

[Steve Barker]

Really, only experimentation will tell the story. The higher the discharge rate, the hotter they will get. You don't want them hot. And when they do get warm, you'll want them to have a complete cool down before putting them on the charger.

[KC]

Not to be glib, but that's why I asked the question. "Hot" is a relative term - more than room temp, to hot to touch, etc, etc. So how hot is too hot? I had hoped there was someone who could point me to a spec sheet on these things since experimenting at $38 a pop is not good. My battery charger somehow senses battery temp since it has a mode "Charging delayed - battery hot", and I have seen it go into that mode when the battery case only felt lukewarm in the hand.

KC

[Jim Yanik]

KC wrote in news: [e-mail]:

there's a thermoswitch inside the battery pack,the third terminal is the sense terminal.It opens when the temp goes higher than the switch rating. IIRC,the NiCds used for RC apps get VERY hot in use(discharging),too hot to hold.(unless you are into pain)

My 9.6V Makita packs get warm but not "hot" when recharging. You can hold them without discomfort.

[Andy Asberry]

I sure just mentioning this will bring the battery gods down on me. I received a Makita drill with NiCds for Christmas 1989. I was flying RC planes then and marked the date on the batteries as was customary. The charger crapped out about 5 years ago so I bought a new drill which was only $50 more than a charger. It came with NiMH batteries. They died about 2 years ago. I thought, heck I'll try the NiCds which had been sitting for 3 years. I've been using them for 2 years now.

--Andy Asberry--

------Texas-----

[KC]

I saw that in there but just assumed it was a charging current limiting resistor. Learn something new every day! Thanks.

KC

[mm]

Just about every rechargeable battery pakc, even the seemingly simple ones, going back for more than a decade has a three pin connector. Are thyey always a thermoswitch, or what other uses might they have?

[Jim Yanik]

mm wrote in news: [e-mail]:

possibly a thermistor;a temp sensitive resistor,it can be either positive coefficient or negative.

pos thermistor increases resistance(R) with increase in temp,neg decreases R with increase.

I'd guess that thermistor sensing is rare.It requires a more complex circuit.

[mm]

Thanks a lot.