What rate can SLA's be charged at?

[carbon.nanotube.capacitor]

I am contemplating purchasing Soneil chargers. The company claims that a rate of 5 amps constant-current can safely charge a 20ah battery. It would take around 4 hours, roughly half the time a 2.5 amp stock charger takes. My concern, other than the batteries overheating, is that they will be slightly overcharged, causing the electrolyte to boil away a little each charge. This would reduce the batteries lifespan, which would not be desirable. I was told that a battery can be charged at a current level up to 25% of the batteries amp-hour rating. This would mean a 20ah battery could theoretically be charged at 5 amps, at least with an intelligent charger.
Can anyone confirm or deny this? Clearly if batteries are overcharged slightly, they will have shorter lifespans and need more frequent replacing, which would be good for battery suppliers, but customers, not so much. Perhaps I'm being cynical.

-C

 

[snowcrow]

I was told that a battery can be charged at a current level up to 25% of the batteries amp-hour rating. This would mean a 20ah battery could theoretically be charged at 5 amps, at least with an intelligent charger.
Can anyone confirm or deny this? Clearly if batteries are overcharged slightly, they will have shorter lifespans and need more frequent replacing, which would be good for battery suppliers, but customers, not so much. Perhaps I'm being cynical.

-C

Charge SLA's at .1C or 10% of amp-hour rating for max. cycle life, but you can go as high as .2C or 20% of amp-hour rating without damaging the battery, but you may loss a little in lifespan. Blessings, Snow Crow

 

[PaulM]

I have a pair of 18 AH batteries here that list an initial current of less than 5.4 amps for CV charging. My 20 AH set lists an initial current of less that 8.0 amps.

 

[carbon.nanotube.capacitor]

Thank you. We have here at the bike shop after market 20ah batteries with maximum constant current charge ratings of 6 amps. The batteries that come with our bikes have maximum ratings of 3 amps. So we have settled on 3.5 amp chargers, which would be .175C, or 17.5% of capacity. So we should be safe. For our 12ah batteries we have chosen 2 amp chargers at .166C or 16.6% of capacity.
Theoretically, at 3.5 amps a 48 volt charger will recharge a 48 volt 20ah battery in approximately 5.71 hours. The charger puts out 168 watts, and the battery totals 960 watt-hours. 960 divided by 168 is roughly 5.71, which is the time in hours for a 168 watt charger to fill a 960 watt hour battery.
This math does not take into account things like temperature or battery age or condition, but using the same formula with the stock chargers for our bikes has proven true thus far: Charger 48 volts at 2.5 amps is 120 watt output. To charge the 960 watt hour battery takes roughly 8 hours. In my experience the longest these batteries will take is 10 hours - this is a battery so deeply discharged as to rest at 37 volts (9.25 per 12 volt battery) at 20°C. So a normal-level discharged battery generally takes 8 hours.

 

[dak664]

Theoretically, at 3.5 amps a 48 volt charger will recharge a 48 volt 20ah battery in approximately 5.71 hours.

It's not that simple for lead-acid batteries. If you limit the charging voltage the current will drop as the battery charges, and much of the charge will be at less than peak amps. You need that extra time to drive the ions into the interior of the plates, and keep sulfates from forming. I would double the time estimate, assuming the charger uses the right absorption voltage. If the voltage is too high the batteries will lose water.

 

[snowcrow]

Theoretically, at 3.5 amps a 48 volt charger will recharge a 48 volt 20ah battery in approximately 5.71 hours.

It's not that simple for lead-acid batteries. If you limit the charging voltage the current will drop as the battery charges, and much of the charge will be at less than peak amps. You need that extra time to drive the ions into the interior of the plates, and keep sulfates from forming. I would double the time estimate, assuming the charger uses the right absorption voltage. If the voltage is too high the batteries will lose water.

If he is buying a Soneil smart charger, he shouldn't have any problems. Because it is only a two stage, I agree, he would benefit by leaving the batteries at "float stage" for a few hours to insure a full charge.

Blessings, Snow Crow

 

[Mathurin]

Soneil = 4 stages.
http://soneil.com/48_volt.html

 

[snowcrow]

Soneil = 4 stages.
http://soneil.com/48_volt.html

I guess you could call it a 4 stage if you like, but it looks like a 3 stage to me. Stage 4, as they call it, is a common feature on all 3 stage chargers and is NOT really part of the charge cycle itself. My guess is that "Soneil" is just trying to justify the asking price.

Blessings, Snow Crow