# Charging Voltage and charging current for 12V 1.3Ah battery

#### Siv77

Joined Jul 17, 2021
13
I have a lead acid battery of 12V 1.3Ah battery used for a solar charger circuit. I need to know the charging current and voltage for it. if it is connected to the panel always.

#### Dodgydave

Joined Jun 22, 2012
11,234
12V sla batteries are charged at 13.8V constant voltage, the current will alter automatically as the battery is charging.

#### Siv77

Joined Jul 17, 2021
13
12V sla batteries are charged at 13.8V constant voltage, the current will alter automatically as the battery is charging.
How will current change automatically can you please explain

#### LowQCab

Joined Nov 6, 2012
3,929
If you have a Big-Panel, You could overheat the Battery, and eventually damage it.

Generally, You can charge a Lead-Acid-Battery at its rated Output,
in this case, 1.3-Amps.

Will your Panel generate more Current than that ?

If You routinely discharge the Battery to a very low State-of-Charge,
it may pull too much Current, that is, if your Panel can deliver more than 1.3-Amps.

To be completely safe, use the following Circuit,
but change the Current-Limiting Resistor so that it will limit
the maximum Charging Current to less than 1-Amp. .............................
.
.
.

#### Dodgydave

Joined Jun 22, 2012
11,234
How will current change automatically can you please explain
The battery draws what current it needs , a 1.3aH sla wont draw more than 600mA on charging.

#### Siv77

Joined Jul 17, 2021
13
If you have a Big-Panel, You could overheat the Battery, and eventually damage it.

Generally, You can charge a Lead-Acid-Battery at its rated Output,
in this case, 1.3-Amps.

Will your Panel generate more Current than that ?

If You routinely discharge the Battery to a very low State-of-Charge,
it may pull too much Current, that is, if your Panel can deliver more than 1.3-Amps.

To be completely safe, use the following Circuit,
but change the Current-Limiting Resistor so that it will limit
the maximum Charging Current to less than 1-Amp. .............................
.
.
.
View attachment 243794
I am using a 17V 5W solar panel in this case so i think the current should not exceed 0.29A

#### Siv77

Joined Jul 17, 2021
13
The battery draws what current it needs , a 1.3aH sla wont draw more than 600mA on charging.
I am using a 17V 5W solar panel in this case so i think the current should not exceed 0.29A
So what you are saying is i dont need to mind the current voltage should be the only consideration. Am I right?

Also I read some where that 0.3 of total Ah rating is the maximum limit of the charging current.

I am new to this so please forgive me if I am wrong.

#### Dodgydave

Joined Jun 22, 2012
11,234
Yes you only need to manage the Voltage , the battery will set the current as it is charging, a bad battery will draw the maximum current, and will probably trip the chargers current limit.

If you're using a Solar panel i would use a buck converter or mosfet opamp to keep the voltage at 13.8V,. a linear regulator will waste heat.

#### Siv77

Joined Jul 17, 2021
13
Yes you only need to manage the Voltage , the battery will set the current as it is charging, a bad battery will draw the maximum current, and will probably trip the chargers current limit.

If you're using a Solar panel i would use a buck converter or mosfet opamp to keep the voltage at 13.8V,. a linear regulator will waste heat.
Do you know the output voltage of fully charged 12V lead acid battery

#### Ian0

Joined Aug 7, 2020
9,436
Sealed lead acid batteries should be limited to a charging current of 0.2C (that's 0.26A for a 1.3AH battery)
If it is for cyclic use (i.e. you wish to discharge the battery regularly, not just once in a while when some power source fails) then it should be charged to 14.70V, then swapped to 13.65V when the charge current has fallen below ~26mA.
Generally batteries designed for "cyclic" use, don't care much for being left on "float" charge for extended periods of time.

#### MrAl

Joined Jun 17, 2014
11,250
I have a lead acid battery of 12V 1.3Ah battery used for a solar charger circuit. I need to know the charging current and voltage for it. if it is connected to the panel always.
Other members here have some good ideas too, but to know the max charging current and stuff like that you have to get that from the manufacturer's data sheet for that very battery.

The float voltage is made for keeping the battery charged when it is not being used. It is meant to compensate for the self discharge of the battery. The self discharge is the discharge when the battery is not connected to any load or to any charger. It means the battery discharges over time and because of this the battery is often kept on float charge. it keeps a little current going into the battery all the time.
If you keep it connected to a solar panel indefinitely the key issue is what current does it deliver during that time. If it is a small current similar to what we would see in float charge, then it is ok but if it is too high it will overcharge the battery and ruin it.

Modern chargers have at least 3 stages you should probably look into that.

#### Ian0

Joined Aug 7, 2020
9,436
Other members here have some good ideas too, but to know the max charging current and stuff like that you have to get that from the manufacturer's data sheet for that very battery.
Invariably 0.2C in the datasheet. (Though some battery manufacturers have told me that they will withstand the same charge current as the maximum discharge current, provided that they are kept below the gassing voltage and recombination is not required)
The float voltage is made for keeping the battery charged when it is not being used. It is meant to compensate for the self discharge of the battery. The self discharge is the discharge when the battery is not connected to any load or to any charger. It means the battery discharges over time and because of this the battery is often kept on float charge. it keeps a little current going into the battery all the time.
If you keep it connected to a solar panel indefinitely the key issue is what current does it deliver during that time. If it is a small current similar to what we would see in float charge, then it is ok but if it is too high it will overcharge the battery and ruin it.
Yes, if it is designed for float, not if it is designed for cyclic use.
Batteries designed for float use have a specified life on float, either 5 years, 10 years etc. They are meant for emergency power usage, they are only intended to be discharged very infrequently.
Batteries designed for cyclic use will dry out and have a very short life kept on float charge. They will last rather longer if allowed to self-discharge then once in a while topped up with a charge to 14.7V
A solar panel cannot keep a battery on float charge because the sun doesn't shine at night. During the night the battery will discharge; when the solar power returns, the battery should be recharged to 14.7V. Recharging it only to the float voltage will mean that it is never fully charged and will shorten its life.
The float voltage should also be temperature compensated by -3mV/°C/cell
Modern chargers have at least 3 stages you should probably look into that.
Yes, constant current bulk charge (0.2C) followed by 14.7V absorption charge, followed by 13.65V float charge, as I said.

#### MrAl

Joined Jun 17, 2014
11,250
Invariably 0.2C in the datasheet. (Though some battery manufacturers have told me that they will withstand the same charge current as the maximum discharge current, provided that they are kept below the gassing voltage and recombination is not required)

Yes, if it is designed for float, not if it is designed for cyclic use.
Batteries designed for float use have a specified life on float, either 5 years, 10 years etc. They are meant for emergency power usage, they are only intended to be discharged very infrequently.
Batteries designed for cyclic use will dry out and have a very short life kept on float charge. They will last rather longer if allowed to self-discharge then once in a while topped up with a charge to 14.7V
A solar panel cannot keep a battery on float charge because the sun doesn't shine at night. During the night the battery will discharge; when the solar power returns, the battery should be recharged to 14.7V. Recharging it only to the float voltage will mean that it is never fully charged and will shorten its life.
The float voltage should also be temperature compensated by -3mV/°C/cell

Yes, constant current bulk charge (0.2C) followed by 14.7V absorption charge, followed by 13.65V float charge, as I said.
Float charge is meant to replenish the self discharge, it does not need to be constant. In fact, i have found that it is better to charge at a lowish charge rate for some time and then let it 'rest' for some other time, then repeat. So a solar charge could be used in that way.
With a set of NiCd's i used in a power drill i had it charge for some minutes and then turn off for 12 hours, them back on, then repeat. They lasted a long time like that. The 'on' time and the 'off' time can be calculated knowing the equivalent self discharge current and the charge efficiency.