OT: Cold batteries question

I have a 12V 60Ah, vented cell NiCd battery. I tested this at

-40degrees with a 500A load and got 5min to a 9V end point. A theoretically perfect 60Ah battery would have given 600A for 6min so this is truly impressive performance.

My question: I hear from many sources that modern NiCd and NiMH cells have very poor cold weather performance in GPS receivers and digital cameras. Does any one know what the difference in chemistry and/or construction is that leads to the poor performance?

Ted

Reply to
Ted Edwards
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I'd run this by the folks over at...

sci.chem.electrochem.battery

I've been reading it off and on for a while out of curosity... seems to be some sharp people there.

Good Luck!

Erik

Reply to
Erik

I'd take a WAG that your 500 amp load raised the internal temperature of the battery pretty quickly, helping the performance.

In contrast, the currrent draw in a GPS receiver is probably low enough so no sizable internal heating of the battery takes place, and a camera's load is pretty intermittant, so again, not much useful heating.

Just my .02...Stemming from what may have been just an urban legend...from the days of hard starting cars in the winter...Turn the headlamps on and count to 100 before attempting the first cold start on a frosty New England morning. The headlamp's current draw is supposed to warm up the battery and lower its internal resistance ..... or something like that...

Happy Thanksgiving guys,

-- Jeff Wisnia (W1BSV + Brass Rat '57 EE)

"If you can keep smiling when things go wrong, you've thought of someone to place the blame on."

Reply to
Jeff Wisnia

IIRC, the battery still felt cold to the touch at the end of the run. Of course, that wasn't -40 anymore. Internal loss would be on the order of 1000w for 5 minutes. The battery weighs 60lbs but it would be hard to estimate the average specific heat.

My GPS-II+ runs about 10C internal temp (according to its thermometer) above ambient due to the somewhat insulating nature of the case.

Yeah. I've heard that too but internal resistance of a decent car battery has to be on the order of 10mOhms. Let's say your headlights draw 20A. I^2xR is then about 4 watts. I can't see 4 watts for 2 minutes doing much to all that lead, water and acid.

Ted

Reply to
Ted Edwards

What was done in the frigid north was to short the battery with a booster cable for a few seconds to warm the internals.

What I do is just use the starter motor. I recall one VERY cold morning when I pushed the starter and nothing happened. I thought about it for a few seconds and decided the problem was the cold, so I held the starter in. Soon the engine groaned over, then started cranking faster until it caught. In that cold I wasn't worrying about overheating the starter for 30 seconds.

Reply to
Nick Hull

Technical term is "boot strapping"

A jumper cable or other short would work better than the starter, but is nowhere as convenient.

Dick

Reply to
D.B.

Somebody shoulda told me this 45 years ago! At that time, if I wanted to start the 1950 Austin A-40 at anything below 0 deg.F. I got out the hand crank; below -20, pour a half cup of gas down the carb. then crank; below -40, forget it completely! Gerry :-)} London, Canada

Reply to
Gerald Miller

You *really* don't want to do that with the NiCds I described! :-)

I once came out to go home after working late - winter in Edmonton. There were two cars in the parking area, mine and a VW. A very dejected individual was standing beside the VW in the -40 cold. He asked if I could give him a boost. I said I could if he had cables. See, I had put mine (00 superflex welding cable with BIG solid copper clamps) in my wife's car and hadn't had time to make another set.

He had a set of Canadian Tire specials (UGH!!). I looked at them but figured it might be an advantage in this case (6volt VW). I hooked up one cable and one end of the other and told him to get in his car, turn on the ignition and hit the starter and *under no circumstances* was he to let off the starter until the engine started or I yelled. He did as he was told and as soon as I heard a feeble grunt from his emgine, I touched the other end of the cable I was holding to my battery post.

Well, I'm not sure whether it was the cranking speed or whether that engine was scared into starting but it had never been turned over that fast by electricity! As soon as I heard engine-running noises, I instantly disconnected but I needn't have worried. See, there was a fuse in the circuit - one of the jumpers had parted and was dripping molten aluminum. Needless to say, all the insulation on both cables was a black mess. But the car was running.

Moral: Don't **ever** short a set of 60Ah sintered plate NiCds.

Ted

Reply to
Ted Edwards

Agreed, but maybe the heating occurs just where it can do the most good, and those areas get warmer than the case felt?

Where's the battery design engineering maven when we need him?

Happy Holidays,

Jeff

Reply to
Jeff Wisnia

I read from what you said that your vehicle had a NiCd battery?

If so, I'm really out of touch, I thought all conventional gas and diesel engined cars still used lead acid batteries. I can't recall seeing NiCds advertised for that purpose.

I have been reading recently that it won't be long before we'll start seeing

42 (or is it 48) volt batteries become the standard for gas engined cars.

Please bring me up to date.

Jeff

Reply to
Jeff Wisnia

Yep, I get 30A out of a 7-cell sub-C 2Ah pack in my 2 meter glider, and that isn't shorted. Competition electric powered gliders are known as "flying welders" for the same reason. They routinely operate at 80A. When something goes wrong, they usually burn.

It is also recommended that you don't carry stick NiCd packs in your pocket; too may stories of change, short circuits, and pants on fire.

Pete Keillor

Reply to
Peter T. Keillor III

This was an elderly Caddillac. I was living in Edmonton, Alberta at the time. The car had a standard lead-acid battery. I ran two heavy cables from the engine battery terminals to the trunk where I installed my NiCd battery during the winter. I left the lead-acid battery in place. It wasn't contributing much at those temperatures.

Ted

Reply to
Ted Edwards

That may well have affected my test but with that battery in the trunk as wired, the car started so quickly, even at extremely low temperatures, that there couldn't have been much heating in the battery.

Ted

Reply to
Ted Edwards

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