primitive early design for battery charging

[giftiger_wunsch]

do u have any experiment for fast charge of nickel base battery with micro?

Nickel-based battery? I may be wrong, but my understanding is that NiMH batteries can be rapidly charged (there are many comercial chargers which can fully charge AA NiMHs in about an hour), but NiCd batteries need to be trickle charged. To which type of battery are you referring?

There are probably ICs available for both, and I'm fairly sure there are ICs available to quickly charge an NiMH battery.

 

[swallow_159]

Not meaning to nitpick or go off-topic, but the Hindenburg actually burned rather exploded, and it was attributed mainly to the composition of the 'skin' rather than the hydrogen content. Hydrogen exploding is certainly very fierce though; when I was in school, we were given a demonstration where 1-part hydrogen and 2-parts oxygen were pumped into a bowl of water, and the bubbles formed were lifted and placed over a bunsen burner.

we can control nimh charge prosess with find inflection point of voltage curve

 

[swallow_159]

Nickel-based battery? I may be wrong, but my understanding is that NiMH batteries can be rapidly charged (there are many comercial chargers which can fully charge AA NiMHs in about an hour), but NiCd batteries need to be trickle charged. To which type of battery are you referring?

There are probably ICs available for both, and I'm fairly sure there are ICs available to quickly charge an NiMH battery.

yes there r many IC that charge nimh and nicd battery with constant current but for my final project I need use brup charge(NPT) for ultra fast charge and control charge prosses with micro like as AVR

 

[audioguru]

Nickel-based battery? I may be wrong, but my understanding is that NiMH batteries can be rapidly charged (there are many comercial chargers which can fully charge AA NiMHs in about an hour), but NiCd batteries need to be trickle charged.

No.
A Ni-Cad can also be fast charged.

Try this: Charge a Ni-Cad and a Ni-MH cell at the same time with the same state-of-discharge and the not-too-high same charging current. The Ni-Cad will actually get cooler while charging but the Ni-MH cell gets warm.

 

[bountyhunter]

The laptop batteries I remembered being recalled because one battery caught on fire . There was no mention of being on his lap and I wonder who made that up. Shoot a link in if you think that is correct.

There's no link because it happened before the internet existed and Apple did a good job of covering it up and containing. I know it happened because I got it from Apple.

 

[bountyhunter]

No.
A Ni-Cad can also be fast charged.

Try this: Charge a Ni-Cad and a Ni-MH cell at the same time with the same state-of-discharge and the not-too-high same charging current. The Ni-Cad will actually get cooler while charging but the Ni-MH cell gets warm.

NI-CADs actually are the BEST cell type to fast charge because the charging reaction itself is endothermic (it gets cooler) as bizarre as that sounds. Even under fast charge, the cell temp drops a couple of degrees and doesn't start warming up until it gets near full charge. The temp rise is a reliable method of charge cut off. The NI-Cd cell voltage also dips a bit at full charge and that can be used for cutoff.

NI-MH is WAYYY harder to fast charge safely because the charge reaction is exothermic so the cell warms up continuously during charging and then gets warmer at a slightly faster rate when it gets to full charge. You have to accurately sense dTemp/dt to terminate fast charge safely.

 

[bountyhunter]

Not meaning to nitpick or go off-topic, but the Hindenburg actually burned rather exploded, and it was attributed mainly to the composition of the 'skin' rather than the hydrogen content;

Dude, the skin was the wick of the candle, the hydrogen was the FUEL that burned. Maybe it doesn't qualify as a bona fide explosion, but it was a hell of a fire.

 

[bountyhunter]

Now thats interesting a,any ideas on why?

LI's normally burn when they develop an internal short and the cell gets super hot VERY quickly as massive current passes through the battery's internal impedance. An accidental external short will do the same thing.

 

[audioguru]

I think a rechargeable lithium cell has thermal runaway. It gets hot which makes it get hotter and hotter and hotter and hotter and ...... fire.

 

[giftiger_wunsch]

NI-CADs actually are the BEST cell type to fast charge because the charging reaction itself is endothermic (it gets cooler) as bizarre as that sounds. Even under fast charge, the cell temp drops a couple of degrees and doesn't start warming up until it gets near full charge. The temp rise is a reliable method of charge cut off. The NI-Cd cell voltage also dips a bit at full charge and that can be used for cutoff.

NI-MH is WAYYY harder to fast charge safely because the charge reaction is exothermic so the cell warms up continuously during charging and then gets warmer at a slightly faster rate when it gets to full charge. You have to accurately sense dTemp/dt to terminate fast charge safely.

I stand corrected.

 

[bountyhunter]

I think a rechargeable lithium cell has thermal runaway. It gets hot which makes it get hotter and hotter and hotter and hotter and ...... fire.

I know the old ones used to catch fire if you drive a nail through them.....

The ultimate "internal short"......

 

[giftiger_wunsch]

I know the old ones used to catch fire if you drive a nail through them.....

The ultimate "internal short"......

Should I even ask why you know that?

 

[bountyhunter]

I've been fooling with batteries for 20 years, but I am not the fool who actually did that.... of course, I know fools who would.

The "nail test" is actually a prestigous event for battery makers. If their Li battery can pass it without burning up, that's actually a huge plus for consumer safety. My buddy is working to develop electric cars and the modern Li technology cells they are using can take the nail without burning up which is pretty impressive.

 

[giftiger_wunsch]

Simple enough to do: just put an empty channel inside the battery and drive the nail through that

I can see why that would be considered a safety plus, though I'm surprised a lithium cell could take a nail without burning up.

 

[Noggin]

yes there r many IC that charge nimh and nicd battery with constant current but for my final project I need use brup charge(NPT) for ultra fast charge and control charge prosses with micro like as AVR

Burping a battery during charging is just the latest fad in fast chargers. It doesn't give you any gains in charge rate or battery life.

If I wanted to make an ultrafast Ni-Cad or NiMh charger I'd just get a micro to accurately read voltage and temperature of each battery and I wouldn't put batteries in series while they're charging. And make sure the micro can turn off the charge current too.

 

[bountyhunter]

Burping a battery during charging is just the latest fad in fast chargers. It doesn't give you any gains in charge rate or battery life.

+1 I have yet to see any compelling evidence that it does anything. IMHO, it's a scam.

 

[tytower]

Just as an adjunct to this conversation I bought some new 9V rechargeable NiMh batterys and after using one recharged it but got the switch wrong on my Lab supply and gave it about half an amp rather than 50 mA as recommended by the manufacturer .

It was on charge for about 3 hours at that and didn't explode but it got very hot and misshaped the plastic shrinkwrap used in its manufacture. Wrecked the battery for use of course so I pulled it apart to see how it was made . Here are the pictures. Demolished battery at the top and another I overcharged but not as badly next to it .
Second is the daisy chain pulled out. Each has about 1.2V ,so 7 off gives 8.4V.

The 4 cells on the negative terminal side of the daisy chain were all useless and showing millivolt readings only , the three on the positive side were salvageable. Might get a use somewhere . Interesting that even though the current flows through each cell ,the cells on the negative side where the electrons enter the battery go first and are damaged whereas the ones on the positive side are not

 

[bountyhunter]

They are all toast. I am sure every cell vented, even if only some of them show catastrophic damage.

 

[Mr RB]

...
Interesting that even though the current flows through each cell ,the cells on the negative side where the electrons enter the battery go first and are damaged whereas the ones on the positive side are not

I'm not sure about the "first electrons" theory. Are you saying the poor little electrons got tired after passing through the first couple of cells?

It's more likely to be a heat issue, the cells that got the hottest show more damage. They probably got hotter becuase they has less ability to dissipate the heat (ie that battery side was down on the table and got hotter or the cells on that side were not as thermally connected to the metal outer case and got hotter).

 

[giftiger_wunsch]

Tytower, you're forgetting that the electrons don't simply start moving at one point and eventually reach the other components; if that were the case then you could well have a couple of seconds' delay when flipping a lightswitch.

The potential difference (voltage) causes the net movement of electrons from negative to positive between the two points; at any given time, electrons are moving at every point along the circuit, and the net movement is from negative to positive.