what is rated capacity for State of charge calculations

Do not go by current. Go by end cell voltage to know state of charging. visit: http://hbl.in for more litrature.

Actually ur question is a little confusing. I dont know if ur problem is how to compute charging rate or how to compute charging current. Well be it as it may, if ur battery is 75Ah, you will require 75Amps charging current to get the battery fully charged in one hour. 10Amps charging current will charge it in 7.5Hrs. By deviding the Ampere Hour capacity of the battery to the available charging current you arrive at a time when the battery is expected be fully charged. If ur using 5 Amps for the above battery, u need a time of 15 hours for the battery to be fully charged. Do same for any other capacity of lead acid battery.

Dickson. Abuja Nigeria

From: Tim Hawley Master Mech.

Hello cr4satya,

The rated capacity is related to the size of battery. For example if you compare a car battery to an electric Hi-LOW battery there capacity is very different. The state of charge is related to the status of the peak voltage and current output over charging time period.

If a car battery is dis-charged to a point where it will turn over the engine very slowly but not fast enough to start the engine. You then hookup jumper cables to the stalled car. It will start right away.

If the battery is dead before hand, you must connect the jumper cables and charge the dead battery for several minutes before you can begin to rotate engine over because the dead battery creates a resistive load on the charging circuit between the two(2)cars.

If the battery has some power left in it, then the flash light will come on but the light produced will be dim.

The same applies to charging:

If you charge an average car battery at a rate of 10 amps output from the charger and the battery is in good shape. It will take 5-6 hours to charge the battery to maximum voltage output or 12 volts.

If you charge the same car battery at a rate of 2 amps output, it will take 24 hours to reach the same output voltage potential from the same battery.

Conclusion:

All is related to the batteries resistive load across the charging source. If the resistive load is high it will require more current over time to charge the battery to its peak voltage output capability.

Example: If your charger voltage is a constant 12 volts DC and the resistance of the battery is 10 ohms then the current will be 1.2 amps.

E= voltage R= resistance I= Current (E/R)=I

I hope this helps

Best Regards,

Tim

Use a hydrometer to measure the specific gravity of the electrolyte. There is a special one made for testing lead acid batteries. The electrolyte is a solution of sulphuric acid which becomes more concentrated when the battery is charged. A fully charged battery has an electrolyte density of about 1.265. When it is discharged, it drops to about 1.12. See http://www.batterystuff.com/tutorial_battery.html for more details.

Thank you all for all valuable inputs.

Regards,

Satya

Hi Satya,

To check the Ah capacity you must charge the battery fully which you can check by either the density or by the open circuit voltage (the battery having been "rested" to stabilise the voltage. Note that putting 75A for one hour will not fully charge the battery, it may well damage it. Either charge very slowly with a voltage of about 13.8V or with 14,4V but only for a max of 4hours (from when it reaches 14.4V)

From this fully charged point you then should discharge it at the specified discharge rate, thus in the example you quote for C20 it will be 75/20 = 3.75Amps, or for C5, 13Amps.

Now the voltage at the terminals will decrease over time until it reaches a final voltage, for C20h I suggest you use 10.5Volts, then you multiply the duration of the discharge test by the current. Bear in mind that the current is unlikely to be precisely the calculated amps and that it will change as the voltage reduces.

If you are doing the test over 5 hours then the final figure will be lower (perhaps 10.25V?), check with the manufacturers data sheet.

Hope this helps

Chas