Is Heat the only problem with 15 Minute Chargers?

[LightScene]

If you could keep your batteries cool while they charge at 7.5A in an Energizer 15 Minute Charger would there be any other drawbacks?

 

[SilverFox]

Hello LightScene,

That is an interesting question...

I think that there is more to it than just the heat. The process of ramming the electrons back through the separator may be causing excessive wear on the separator which will lead to cell breakdown and failure.

On the other hand, if you could keep the inside of the cell cool, this may also reduce the damage to the separator.

I think you would still do some damage to the cell, but I don't know for sure.

Tom

 

[Hitthespot]

Is the Cell Damage from the heat, or is the heat from the Cell Damage. LOL

Offered as a Rhetorical statement only.

Bill

 

[45/70]

On the other hand, if you could keep the inside of the cell cool, this may also reduce the damage to the separator.

I would think, that while trying to keep the cells cool externally, the reaction creating the heat, internally, would still be about the same. I'm not saying it wouldn't help, it probably would, but marginally.

A perhaps poor analogy, the internal cylinder temperature of an internal combustion engine during combustion stays relatively the same during a set load, rpm etc. regardless of how well the engine's cooling system is working. Additional cooling in this example will provide better cooling throughout the rest of the engine and it's components, but the the internal cylinder temp will stay the same.

Dave

 

[AlexLED]

There might be another problem besides the heat, as stated in the Sanyo Twicell documentation: the oxygen consumption of the negative electrode may not keep up with the generation at the positive electrode, leading to gas leakage.
Not sure if this can be prevented by just keeping the temperature low.

 

[Fallingwater]

You'd probably do a bit less damage, but just a bit.
Stay away from 15-min chargers.

 

[mdocod]

I think it's a great question, and the only way to find out a true answer would be to run a few tests...

2 separate groups of cells would have to be cycled repeatedly, one group charged in a refrigerated environment, ideally with a fan mounted to blow on the cells, with the other group charged at room temperature. A few dozen cycles, possible more would be required. Before and after capacity and self-discharge and internal resistance measurements would have to be taken for comparison.

This would be an interesting test, wish I had the equipment to perform a valid test of this :)

Eric

 

[degarb]

I think it's a great question, and the only way to find out a true answer would be to run a few tests...

2 separate groups of cells would have to be cycled repeatedly, one group charged in a refrigerated environment, ideally with a fan mounted to blow on the cells, with the other group charged at room temperature. A few dozen cycles, possible more would be required. Before and after capacity and self-discharge and internal resistance measurements would have to be taken for comparison.

This would be an interesting test, wish I had the equipment to perform a valid test of this :)

Eric

I have been laying charger batt side down on ice pack since 2007. So, batts get fan and ice cooled. Final temp usually room temp or lower. A package of wife's finest ground turkey works well. And cooling works better if you tear off the thermal and electrical insulator on cell.

I know it can help alot, as long time before cell rejecting in charger, and I have 2006 1800 ma cells that still work in the charger. Probably, some damage, but less than a wall charger without voltage cut off-by far. And it doesnt matter, since many operations are impractical without this kind of charger.

 

[qwertyydude]

I use the energizer 15 minute charger. It is a battery killer, I tend to have to get a new set of cells after a year as the charger will reject them. One thing I also do to fool the charger into charging cells it normally would reject is to fast charge the batteries for about 30 seconds by shorting it across a 4.8v high current battery pack. This gets the cell nice, warm, conductive and boosts the voltage. This usually lets me charge these marginal cells.

Now some things to keep in mind, I have a high powered fan I place on top of the batteries while they're charging, the first generation of these chargers used to have a powerful fan that kept the batteries cooler but they switched some time ago to a quieter fan supposedly from all the noise complaints. But with the quieter fan came the battery roasting problem. Forget about anything they say about these things monitoring battery temperature. It simply doesn't happen. I've had cells boil over and vent while charging, it got so hot the shrink wrap split and came off. So 15 minute chargers definitely do benefit from fan cooling but even with extra cooling your cells will not last more than about 100 cycles. Oh and cheap cells with high internal resistances also heat up a lot more than good cells so cheap cells also will get killed faster than good cells. Another note to keep in mind is high capacity cells, 2500 mah and over aren't good to fast charge either, they're not built as rugged as 2000 mah cells so their cycle life will also be drastically shortened.

 

[jasonck08]

I'm not sure why anyone would use a 15 minute charger these days. Just get an extra set or two of LSD Ni-Mh cells (eneloopes) and keep that extra set charged and ready to go, so there is no need to quick charge.

 

[lightseeker2009]

I was given a Rc monster truck for my birthday about 7 years ago. It might even be 9 years ago. The battery is a Nimh 3300mah 7.2V pack.
Now firstly we read all the time that you should not charge nimh batteries is series. Well with these packs you don't have the option to charge them seperately.
Secondly, I bought a car charger for it, simply because it was 3 times cheaper and could be used in the field, and of course because it was charging the pack way faster than the AC charger would have. So its also basically a 15-20 minute charger. And I can confirm that these batteries are still like new. I still get the same runtimes with it.
I have since upgraded to Lipo packs. This ''retired'' 6-cell Nimh pack is currently doing duty in a spotlight I've converted to work with a 5-led DX drop-in.
So I don't know if the rate of charge and heat really drastically reduces the lifespan of AA Nimh batteries. It does not seem to do so with Sub-C cells.

 

[degarb]

Firstly, qwertydude, do I understand you correctly: you keep a 4 aa pack around and charge 1 aa cell for half a minute and put it on 15 minute charger to breakdown internal resistance?

Well, I use 15 minute charger, for two reasons: firstly, at 3-4 watts per worker per hour times 8-10 hours times 3-5 guys = one heck of alot of batteries (I realized the other day, that I carry about 100 cells daily with me to work each day), and the 15 min charger fills the slack when your 5 other chargers cannot keep up; secondly, it simply doesn't do as much damage as most my other chargers do, when batteries are resting on ice pack, because virtually all store bought chargers lack a voltage cut off (overpriced batteries plus, excepted). And unless the charger charges at least 16 cells, paying more than $20 for the charger doesn't make sense for heavy battery users.

I was hoping that they would have improved these (never owned a duracell 15 minute) the throttle down to 30 minute for cells with high internal resistance. Also, they could add a switch for slower/cooler charge, when time isn't as important. But these guys are the same that make chargers that cook your cells with slow chargers. (For example, last night I put 4 aa on a slow charger, and found them simmering--way hotter than an ice pack and a 15 minute charger. The kicker is they cooked for hours, not just last 7 minutes on a 15 minute charger.)

Also, not discussed or referenced here is the modification people can make to the 15 minute charger to trick the charger into thinking aa cells are aaa cells, for a slower charge, even on cells with higher internal resistance. I did the mod once, I was too lazy to open up the charger and just melted a slot in the side of charger to slid my index card in. I helped on a few rejected cell, but not all. Maybe, I didn't line it up correctly. I guess I need to open it up, and do it again more precisely on a different 15 min charger.

 

[qwertyydude]

It's not just 4AA cells in a holder. It's a 4 cell sub-c nimh pack from an rc car they're soldered together in a very low resistance pack. Very high amperage goes through the cells, about 25 amps. It warms the batteries to like 120 degrees in 30 seconds. The boost in voltage tricks the charger into thinking the cells are in good condition.

 

[jasonck08]

I was given a Rc monster truck for my birthday about 7 years ago. It might even be 9 years ago. The battery is a Nimh 3300mah 7.2V pack.
Now firstly we read all the time that you should not charge nimh batteries is series. Well with these packs you don't have the option to charge them seperately.
Secondly, I bought a car charger for it, simply because it was 3 times cheaper and could be used in the field, and of course because it was charging the pack way faster than the AC charger would have. So its also basically a 15-20 minute charger. And I can confirm that these batteries are still like new. I still get the same runtimes with it.
I have since upgraded to Lipo packs. This ''retired'' 6-cell Nimh pack is currently doing duty in a spotlight I've converted to work with a 5-led DX drop-in.
So I don't know if the rate of charge and heat really drastically reduces the lifespan of AA Nimh batteries. It does not seem to do so with Sub-C cells.

Thats odd that some of the sells charge in parallel. The reason why this is bad is because the charge method most Ni-mh chargers use, which is -dv termination. If there are two cells in parallel with slightly different capacities, the voltage on each cell may be different and the charge termination may not work properly, leading to over or undercharged cells. Secondly, those Ni-mh RC packs are designed differently than consumer grade cells. These are lower resistance cells and are designed often for high discharge currents of 20-60C or so. And they can handle faster charge currents as well.

 

[qwertyydude]

RC car batteries charge in series. As long as the capacities are well matched and the pack is not over discharged the cells don't tend to get out of balance. The nimh chemistry can withstand a little bit of overcharging and that's how they are self balancing. When the low capacity cell fills up, it starts to heat up and it's voltage starts dropping, usually by this time a well matched pack should have all the cells topped up so there's usually no damage. But if you overdischarge nimh packs the real damage occurs as the weak cell gets reverse charged. That's what usually kills these, not overcharging, especially if you use a proper smart charger.

 

[degarb]

The nimh chemistry can withstand a little bit of overcharging But if you overdischarge nimh packs the real damage occurs as the weak cell gets reverse charged. That's what usually kills these, not overcharging, especially if you use a proper smart charger.

Interesting... Also, how would a 6 volt car charger work at warming up a cell to quick charge?

I wonder what available brand/capacity of battery works best over long run with quick charging. And theory to back it up. I have had best luck with 1800 ma, but no theory as to why, other than cramped electrons need space to roam and be free. Free range cells, I guess.

 

[Launch Mini]

I did the same years ago, before I knew the danger of this. Once, a cell did not explode, but it got sooo HOT, the cell ruptured and was smoking inside my car. Last time I ever did that

 

[qwertyydude]

A 6 volt car charger probably will be enough but keep in mind that this basically shorts whatever power supply is being used so if that charger has built in protections it may trip as this can draw in excess of 20 amps, or it may even break the charger. Just use a battery pack it's safer, you can even solder 4 AA nimh batteries in series, it'll work as good.

 

[davec]

You are trying to push the chemistry a lot faster than it likes to go. As you do this other reactions, unwanted ones, are more likely to happen, this reduces the life of the cell. It's similar to the LiPo thing where if you bring a cell to a full state of charge e.g. 4.2V, then you might get 300-500 cycles, but only charge it to 4.1V and you may get 1500+ cycles out of the cell. The more you "push" the charge into the lithium cell as it reaches the full state of charge, you keep pushing and unwanted reactions have more likelihood of happening and the cell ages faster.

It's another reason why if you discharge a Lithium cell down to say 1.4V, as long as it's not down there too long (a week or less), you can often bring it back with careful charging and of course some sanity checks to ensure the cell is safe. e.g. A very slow charge (0.1C) 200 ma or less if you can and watch the cell voltage, to ensure it rises quickly, if it doesn't then perhaps it won't be safe to recharge as it could be shorting out internally. Get the cell to about 3.3 volts then take it off charge and see if it holds the voltage (within .1 or ,2V, or drops very low), the cell should be left for a few hours or overnight. If it;'s OK the next day then charge it up, put it aside for a day or two and check it's not self discharging. Fully discharge and recharge it, check the cell doesn't get too warm on discharging or charging. Suprising how many cells are fine after this.