what is the minimum charging current for a lead-acid battery.

Generally it is said that a lead-acid battery charging current is 0.1C during float charging. so if a battery capacity is 75AH at 12V it require 7.5A DC voltage at 13.8VDC.
But i think that current will be determined by the difference of voltage between charger and battery. The more voltage difference drains more current to battery. so current is not a fixed value during charging.
so, my quary is what is the significance of 0.1C? and what is the minimum charging current for a 12V 75AH lead-acid battery.
Thanks.
Sanjoy

sanjoy said:

Generally it is said that a lead-acid battery charging current is 0.1C during float charging. so if a battery capacity is 75AH at 12V it require 7.5A DC voltage at 13.8VDC.

Click to expand...

Lead Acid batteries are charged with constant-voltage, not constant-current!!!! Unless otherwise stated by the battery maker, 0.1C is the MAXIMUM current that should flow into a LA battery during charging. You purposely build the charger such that it is BOTH current-limited and voltage-regulated.

sanjoy said:

But i think that current will be determined by the difference of voltage between charger and battery. The more voltage difference drains more current to battery. so current is not a fixed value during charging.
so, my quary is what is the significance of 0.1C? and what is the minimum charging current for a 12V 75AH lead-acid battery.
Thanks.
Sanjoy

Click to expand...

During the early phase of charging, the charger's current-limiting protects both the charger and the battery and the voltage rises slowly as the battery charges. During the final part of the charging cycle the charger holds the voltage constant, and the current naturally decreases asymptotically toward the leakage current of the battery (assuming no other load is connected).

Read this: Powerstream

so a charger having 3A Capacity will capable to charge a 75AH, 12V battery since 0.1C is max current flow for constant voltage charger.

sanjoy said:

so a charger having 3A Capacity will capable to charge a 75AH, 12V battery since 0.1C is max current flow for constant voltage charger.

Click to expand...

Sure, it will just take twice as long as a charger limited to say 7.5A. If the charger just being used for "floating", then either one will work provided that the voltage of both is limited to the values shown in the PowerStream link, above.

By the Way, flooded-cell lead-acid batteries will tolerate a maximum charging current of up to 0.7C. For example, your car likely has a 80aH battery and the alternator can charge at a 50A rate.

Only Sealed Lead Batteries (SLA) or Absorbed Gas Mat (AGM) batteries have a lower maximum charge rate. For SLA or AGM, consult the battery maker's Data Sheet for the specific battery you are buying to see what the max allowed charge rate is...