Charging with a Power Supply
With technical knowledge, batteries can be charged manually with a power supply featuring user-adjustable voltage and current limiting. I stress manual because charging cannot be left unattended; charge termination is not automated. You need to observe the state-of-charge according to voltage and current behaviors. Lower the charge voltage or disconnect the charge when the battery is full. Because of difficulties in detecting full charge with nickel-based batteries, I recommend only charging lead acid and Li-ion batteries manually.
Before connecting the battery, calculate the charge voltage according to the number of cells in series, and then set the desired voltage and current limit. To charge a 12-volt lead acid battery (six cells) to a voltage limit of 2.40V, set the voltage to 14.40V (6 x 2.40). Select the charge current according to battery size. For lead acid this is between 10 and 30 percent of the rated capacity. A 10Ah battery at 30 percent charges at about 3A. Starter batteries charge at lower currents, and an 80Ah pack would charge at about 10 percent of the rating, or 8A. Higher currents are possible.
Observe the battery temperature, voltage and current during charge. Charge only at ambient temperatures in a well-ventilated room. Once the battery is fully charged and the current has dropped to three percent of the rated Ah, the charge is completed. Disconnect the charge. High self-discharge (soft electrical short) may prevent the current from going to the anticipated low current level when fully charged. Disconnect the charge also when the current has bottomed out and cannot go lower. If you need float charge for operational readiness, lower the charge voltage to about 2.25V/cell.
You can also use the power supply to equalize a lead acid battery by setting the charge voltage 10 percent higher than recommended. The time in overcharge is critical and must be carefully observed. When using the power supply to perform equalizing, refer to the previous article entitled Equalizing Charge.
A power supply can also reverse sulfation but there is no guarantee of success. When applying a charge, a totally sulfated lead acid may draw very little current at first, and as the sulfation layer dissolves the current will gradually increase. If you must increase the charge voltage above the recommended level, set the current limiting to the lowest practical value and observe the battery voltage. If the battery does not accept a charge after 24 hours, restoration is unlikely.
Lithium-ion charges similarly to lead acid and you can use the power supply also but use extra caution. Set the voltage threshold to 4.20V/cell and make certain that none of the cells connected in series exceeds this voltage. (The protection circuit in a commercial pack does this.) Full charge is reached when the cell(s) reach 4.20V/cell voltage and the current drops to three percent of the rated current, or has bottomed out and cannot go down further. Once fully charged, disconnect the battery. Never allow a cell to dwell at 4.20V for more than a few hours. Read more about Charging Lithium-ion.
I do not recommend charging nickel-based batteries with a power supply. Full-charge detection is difficult to assess because the voltage signature varies with the applied charge current. If you must charge, use the temperature rise on a rapid charge as an indication for full charge. When charging at a low current, estimate the level of remaining charge and calculate the charge time. An empty 2Ah NiMH will charge in three hours at 500mA. The trickle charge must be reduced to 0.05C. Read more about Charging Nickel-based batteries.
Comments
Give a brief idea of charging Lithium Yitrium based batteries
can you send me information on how long should any cell phone charge fo
hi thanks a lot for the information you are providing.
i would like to know about dead cell and cell reversal or polarity reversal.
Can you explain rapid pulse charging? I want to know how i can charge cell phones quickly in 10 mins.
Joel, the faster the charge, the more damage you are doing to the battery
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I want to pose a question here….. Plz help..
If I have 2 lead acid battery packs of 24V 26Ah each, and I want to charge them. Which one of the following techniques will take lesser time????
1) I connect them in series to make a 48V 26Ah unit, and charge this pack using a suitable charger for 48Volts.
2) I charge the 2 packs of 24V 26Ah simultaneously using two suitable chargers of 24 volts.
700Ah
It is a bit surprising that you can charge a 2Ah(=2000mAh) battery using a 500 mA and a charging time of 3 hours.. 3h * 500mA = 1500 mAh.
The battery is heating up during charging so one would expect e.g. a 500 mA connected in e.g. 5 hours.
Please clarify. One answer could be that you should never discharge a 2Ah to more than 50% of full charge.
Please clarify. I have tried for 3 months to get an answer to this question and also how much energy (in%) is lost (to heating the battery) during decharging the battery