Its chemical reaction , they always involve some heat , the faster you chagre them the more heat you get, this is the limit of charging speed. Charge them too fast and they get too hot and explode , simple as that.
I think it's to do with the amount of energy involved and cost of chargers and associated wiring. Some rechargeable are after all very quick to recharge - take the lead-acid cell in your car. Maybe it's 50Ah capacity. If you know that chargng is 70% efficient then you need to put in 1A for 50h/0.7, or about 70 hours, from fully flat. That's 3 days on a cheapo Halfords charger. Alternatively the alternator will bang in 50-70A, so even from totally flat (which it never is) it will only need an hour to be full, and will be operational after 15 minutes or so. The snag here is that an alternator is a big beast, the wiring is costly and 70A at 12V is 840W. You'd need a big, beastly power supply to deliver that.
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Wow, you're my long lost brother. Quite a few years ago (decades even), I used to race 1/12th scale on-road and 1/10th scale off-road. For stock-class, the preferred battery was Sanyo 1,200mAh SCR Nicads, which could be fast charged in 15-20 minutes with a peak detection charger. Those were fun days ...I use Lithium Polymer (LiPo) batteries in electric radio controlled cars. These are very good at massive discharge rates with peaks of over 300A and continuous of 60A and are recommended to be balanced charged so you match all the cells voltages whilst charging.
Like the previous technology Nickel Metal Hydride they have better life if you charge at a lowish rate. The rule of thumb is the max amperage you try to stick down them is their amp/hour rate. Therefore for a 5000 mah (milli amp hour) you charge at 5 amps and it will take 1 hour to charge, for a 2200 mah you charge at 2.2 amp for 1 hour and so on. This charge rate is known as the C rate so my examples are 1C. You can charge at higher C rates but with reduced life as Steve mentioned above.
Lipo's are great as you can top them up and have no memory effect but they really do not like being overcharged and several accidents and major fires have occurred due to accidental shorting and overcharging so much so that most race meetings mandate placing them in a fireproof bag for charging.
Its chemical reaction , they always involve some heat , the faster you chagre them the more heat you get, this is the limit of charging speed. Charge them too fast and they get too hot and explode , simple as that.
Wow, you're my long lost brother. Quite a few years ago (decades even), I used to race 1/12th scale on-road and 1/10th scale off-road. For stock-class, the preferred battery was Sanyo 1,200mAh SCR Nicads, which could be fast charged in 15-20 minutes with a peak detection charger. Those were fun days ...
Ahh wow, so what is the optimum time for the biggest bang?
Ahh wow, so what is the optimum time for the biggest bang?