Hot Batteries

[sam fisher]

Who the hell says amperage anymore. Is it even a correct term?

 

[nubie]

I hope you are saying his math is right.  Remember, you have to add Voltage in series, add Amperage in parallel.

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I knew physics teachers who would go crazy if you said amperage rather than current...

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Strange. . . . .

"The strength of an electric current expressed in amperes."

according to Dictionary.com

I guess it is a correct term.  Perhaps more proper would be

"add mAh (milli-amp-hour) rating in parallel."

But it just becomes semantics, not mathmatics, at this point .

 

[tevildo]

maH are milli-amp-hours - charge on the battery, not current. The correct (SI) units are coulombs. But now i'm just being pedantic

However, you do sum the charge when the batteries are in series. You also sum the maximum rated current (or thereabouts, there are extra inneficiencies).

 

[nubie]

maH are milli-amp-hours - charge on the battery, not current. The correct (SI) units are coulombs. But now i'm just being pedantic

However, you do sum the charge when the batteries are in series. You also sum the maximum rated current (or thereabouts, there are extra inneficiencies).

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I see you are right, but I think these people need to know the difference between max current and max charge .

The Current does indeed increase, but only as a function of increased voltage overcoming resistance.

The max current isn't 2.5A, at least I don't think so, you could try it but the batteires would explode. . . sooner or later :blink:

 

[BradN]

Interestingly, the max current doesn't increase when you have batteries in series, but the max current you can use to maintain a given voltage will increase (but a given current will still cause the same percent of voltage drop). If we had some device that needed 1.0V, that only allows for 17% voltage drop if we use a 1.2V battery, but if we used 2 in series, that allows for a 58% voltage drop, so more current could be used. Of course this would be foolish, because if the voltage drop is 58%, this also means that 58% of the power is being burned inside the battery as heat.

I tested one of my NiMH batteries for max current by just shorting it out on the tester and I got about 8 amps, but of course the max usable current is way less than this, since this is 8 amps at 0V - delivering no power effectively, and just generating a metric assload of heat (9.6 watts) inside the battery. But if I tried 2 batteries in series, I'd still get the same 8A, just with heat being generated in both batteries at once.

It's funny how much a real battery can vary from the "ideal" representation - supposedly a NiMH AA has about .03 ohms of internal resistance, and using V/R=I (1.2/.03=I), this suggests the max current is really 40(!) amps, but the battery chemistry just can't react fast enough to produce this much current.

Eeek, I better stop, I'm turning this thread into a circuit analysis class.

 

[tevildo]

2.5A isn't that unreasonable - i routinely drag 5-8A out of one of my sets and they don't seem to mind. Just make sure if you want that kind of current, buy the right batteries - mine are (apparently) fine up to 10A, but i'm not going to test that.

 

[Willei]

Just a little update; I've not have the problem again using the same set of batteries, and I've not noticed any drop in capacity on them either. Since I've got no grounding in electronics, I'm happy to assume it probably won't happen again!

 

[Radek]

Just a little update; I've not have the problem again using the same set of batteries, and I've not noticed any drop in capacity on them either. Since I've got no grounding in electronics, I'm happy to assume it probably won't happen again!

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Here is (imho) good website talking about NiMH batteries.

 

[DynaMight]

My GP2X have had the same problem too, One battery really hot and the other not touched and it showed on my charger that one battery was totally drained while the other was untouched. only happened a few times.... strange tho.

 

[RSilvergun]

hmm... mine are warm... both of them...

AA -> 2500
AAA -> 900

AA wins!

 

[Mr. Anderson]

hmm... mine are warm... both of them...

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warm is normal, hot is not

Good batteries will get warm but not hot. Weak(2000mAh might not be enough) or old ones however may get hot and burn out of energy, nimh don't like too high temperatures and may suffer the "lazy battery" effect. If that happens you need to charge and discharge the batteries about three times to get them back to "life"...

 

[capnhack]

just thought id add a little something i found out. if your rechargeables run down and you stop off to get some standards at a shop, do not buy duracell plus. they should be able to handle the power drain of the gp2x but instead they get far too hot to touch, so no good for extended playtime. ill test out some duracell ultras if i can find any and see if they suffer the same problem.
really didnt expect this from such a quality brand

edit: forgot to mention that they last for ages, if you can put up with taking them out of the unit every once in a while to let them cool..