Why do rechargeable batteries take so long to recharge?
- Thread starter Blzebub
- Start date
Mullardman
Moderately extreme...
I can only assume that the chemical processes involved are not especially quick.
There's always a downside.
Mull
There's always a downside.
Mull
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.
Right, and connected with this is the fact that as the temperature of a battery rises, the voltage falls. As the voltage falls, the voltage sensor in the charger thinks it needs to add even more power to lift the voltage. Unless the charger is equipped with a temperature sensor (most aren't), the result of unrestricted fast charging can be thermal runaway followed by an explosion/fire.
And all that is still limited by the amount of heat that will be generated , you still have to limit the charge rate , theres a regulator in the charging circuit , you can be sure it wont pump 50/70 amps directly to the lead acid battery of the car.
sq225917
Bit of this, bit of that
Bzle, because you are using a 'dumb' cheap charger. Netter chargers with active sensing charge faster. I have a Sanyo Eneloop AA charger than will fully charge 4 x AA in about an hour. In fact if you are looking for AA batteries I recommend the Sanyo Eneloop XX, they are the best rechargeables I've ever used and I hammer them in the camera grip for my 7D. They even hold full charge for 6 months sat in my camera bag between trips. Not cheap but worth every penny.
steve watkins
pfm Member
It does depend on the type of battery you are charging but generally the faster you charge the less the battery enjoys the experience so the shorter the life.
Batteries generally charge fairly quickly even on a slow charge to 80/90% of their capacity. It is the remaining 10/20% that takes the time. You can force the issue but you end up with shorter battery life.
Modern smart chargers are much more sensitive to the batteries needs and switch off when critical temperatures, voltages, currents are reached rather than just carry on pumping in charge which is just wasted as heat and buckle the battery plates in the process.
Pulse charging is the fastest way to charge. Very high but short energy bursts can be used so the battery does not overheat. This system also has the benefit of breaking down any crystals which form between the plates and may internally short the battery.
Modern metal couples like Lithium Ion are now much more capable of accepting charge at a faster rate and at any state of the duty cycle than say the older Ni-Cad technology which required complete discharge before recharge to avoid memory effect and premature failure. Another reason for the longer charging cycle.
For example a Ni-Cad battery charged at the standard rate may last for 1000 cycles. Charged at half the rate for twice the time may gain as many as 250 to 500 extra cycles. whereas charged at twice the rate may only last for 500 cycles and at four times the rate may only last 100/200 cycles.
In multi cell batteries it is the best cell in the pack which will bring down the others because it never uses all of its capacity becomes slow to accept charge and fails first. So in critical applications manufactures will form and capacity match all the cells in a pack so that no one cell is better than another within about a minute of complete discharge. Any two cells taken off the production line may vary by as much as 1/2 hour in capacity over the stated minimum, so for many applications capacity matching makes pefect sense. The lower capacity items become general consumer product that meets the spec but little more.
Most rechargeable batteries must be in relatively constant use to keep them active or again they will fail prematurely.
The Float battery generally used for instant backup power is the exception. They have long life and great power but can only be used for a few cycles.
Some rechargeables can be brought back to life and it is sometimes possible to recover what appears to be a dead battery by giving it a shock. An appropriate voltage, high current applied for a second or two will often revive a Ni-cad or nickel metal Hydride cell and bring it back to life again.
Batteries generally charge fairly quickly even on a slow charge to 80/90% of their capacity. It is the remaining 10/20% that takes the time. You can force the issue but you end up with shorter battery life.
Modern smart chargers are much more sensitive to the batteries needs and switch off when critical temperatures, voltages, currents are reached rather than just carry on pumping in charge which is just wasted as heat and buckle the battery plates in the process.
Pulse charging is the fastest way to charge. Very high but short energy bursts can be used so the battery does not overheat. This system also has the benefit of breaking down any crystals which form between the plates and may internally short the battery.
Modern metal couples like Lithium Ion are now much more capable of accepting charge at a faster rate and at any state of the duty cycle than say the older Ni-Cad technology which required complete discharge before recharge to avoid memory effect and premature failure. Another reason for the longer charging cycle.
For example a Ni-Cad battery charged at the standard rate may last for 1000 cycles. Charged at half the rate for twice the time may gain as many as 250 to 500 extra cycles. whereas charged at twice the rate may only last for 500 cycles and at four times the rate may only last 100/200 cycles.
In multi cell batteries it is the best cell in the pack which will bring down the others because it never uses all of its capacity becomes slow to accept charge and fails first. So in critical applications manufactures will form and capacity match all the cells in a pack so that no one cell is better than another within about a minute of complete discharge. Any two cells taken off the production line may vary by as much as 1/2 hour in capacity over the stated minimum, so for many applications capacity matching makes pefect sense. The lower capacity items become general consumer product that meets the spec but little more.
Most rechargeable batteries must be in relatively constant use to keep them active or again they will fail prematurely.
The Float battery generally used for instant backup power is the exception. They have long life and great power but can only be used for a few cycles.
Some rechargeables can be brought back to life and it is sometimes possible to recover what appears to be a dead battery by giving it a shock. An appropriate voltage, high current applied for a second or two will often revive a Ni-cad or nickel metal Hydride cell and bring it back to life again.
cutting42
Arrived at B4 Hacker Ergo
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.
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.
Use them or lose them
btw, to which do you refer?
lead acid
Nicad
Nimh
lithium ion
lithium polymer
Most modern appliances using rechargeable packs have reasonably effective charge management but less us know more about your particular issue and maybe we can assist..
James
Lord of the Erg\o/s
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 ...
naimplayer
Aspiring to be a halfwit.
Ahh wow, so what is the optimum time for the biggest bang?
cutting42
Arrived at B4 Hacker Ergo
That's funny, Can't help wondering what else we will find in common
Getting more OT!
I used to race RC bikes back 25 years ago and mess about with cars as well but got back into it when my son recently started getting interested. The technology has moved on massively with brushless motors and LiPo battery technology and the electronics in the speed controllers.
I currently race 1/10th off road with 4400 mah LiPo a 10.5T motor, 60A ESC and 2.4Ghz radio (no crystals needed and no glitching)
cutting42
Arrived at B4 Hacker Ergo
t = 0
cliffpatte
Speed camera anarchist
if you could change the electrolyte between the anode and cathode you could get pretty close to T=0, although it would be more of a refill rather than a recharge I guess.
cliffpatte
Speed camera anarchist
Darth Vader
From the Dark Side
Zenner has it. It comes down to Chemical Thermodynamics:-
ΔE=ΔG+ΔH-TΔS
For now ignore that last term and you'll see that E=G+H. What that means is that a certain amount of energy is split into Gibbs Free energy G that does useful work and the Enthalpy H that is wasted as heat.
It comes to pass that if you use the energy infinitely slowly you can end up with just G i.e. its all done useful work. But the faster you use the available energy more is converted to heat thus less is available to do useful work. Think of a car engine and the harder you drive it the hotter ot gets but you also do less mpg because more energy is wasted as heat than doing useful work.
So charge your battery faster and it gets hotter and you use more lecky to charge it. Also the heat shortens the life of said battery. My Heli and Quad copter can bring a LiPo to its knees rather quickly.
Ah that last term TΔS T of course is the temperature and S is that wonderful 'arrow of time' Entropy a measure of disorder. The Universe is going from a highly ordered state to utter disorder. Everything we do increases this disorder and the faster we use energy the more disorder there is. Its a measure of 'lost' energy or the energy used to create disorder.
You can do a simple experiment to see the relationship between energy and entropy with a simple wide rubber band. Hold band between fingers and touch on forehead now rapidly stretch the band and it will get warm. Now still holding the band stretched remove from forehead hold for a mo and then return the band to the relaxed state and touch your forehead, It will now feel cold as heat is absorbed. The structure in the band is disordered as long twisted molecular chains. Stretching straightens those chains but when they again become disordered heat is absorbed.
Cheers,
DV
ΔE=ΔG+ΔH-TΔS
For now ignore that last term and you'll see that E=G+H. What that means is that a certain amount of energy is split into Gibbs Free energy G that does useful work and the Enthalpy H that is wasted as heat.
It comes to pass that if you use the energy infinitely slowly you can end up with just G i.e. its all done useful work. But the faster you use the available energy more is converted to heat thus less is available to do useful work. Think of a car engine and the harder you drive it the hotter ot gets but you also do less mpg because more energy is wasted as heat than doing useful work.
So charge your battery faster and it gets hotter and you use more lecky to charge it. Also the heat shortens the life of said battery. My Heli and Quad copter can bring a LiPo to its knees rather quickly.
Ah that last term TΔS T of course is the temperature and S is that wonderful 'arrow of time' Entropy a measure of disorder. The Universe is going from a highly ordered state to utter disorder. Everything we do increases this disorder and the faster we use energy the more disorder there is. Its a measure of 'lost' energy or the energy used to create disorder.
You can do a simple experiment to see the relationship between energy and entropy with a simple wide rubber band. Hold band between fingers and touch on forehead now rapidly stretch the band and it will get warm. Now still holding the band stretched remove from forehead hold for a mo and then return the band to the relaxed state and touch your forehead, It will now feel cold as heat is absorbed. The structure in the band is disordered as long twisted molecular chains. Stretching straightens those chains but when they again become disordered heat is absorbed.
Cheers,
DV