For example a 5000mAh Nimh battery pack can be safely chargedat 5 amps (1 C). Do
ID: 1722648 • Letter: F
Question
For example a 5000mAh Nimh battery pack can be safely chargedat 5 amps (1 C). Does the charge rate change based oncapacity? For example, if I have two 5000mAh batterypacks and I put them in parallel, could I safely charge it at 10amps? or does it still have to be 5 amps max? *In parallel I know the battery can be charged at the regularcapacity. For example two 5000mAh batteries in series can besafely charged at 5 amps. Please explain. *In parallel I know the battery can be charged at the regularcapacity. For example two 5000mAh batteries in series can besafely charged at 5 amps. Please explain.Explanation / Answer
Theoretically, "n" identical batteries can be charged inparallel with no increase in charging time when the chargingcurrent is multiplied by "n"--think of batteries as chargestorage devices and the charger as a supplier of q/t. Double the qcapacity and the q supply and t remains constant. In practicecharging batteries in parallel can be risky if the batteries arenot matched in terms of internal equivalent series resistance(ESR). Obviously the voltage applied to parallel-connectedbatteries is the same for each cell, but the branch currentswill vary with ESR. The cell with the lowest ESR is going tosink larger current. In the example that you mention where youpropose doubling the charging current when charging twoparallel cells, you will get the desired result if the twocells are matched in terms of ESR. a large difference inESR could result in an unsafe charging condition as the currentavailable from the double current charger will result inovercurrent through the low ESR cell. The failure modesin this case can include heat build up, irreversible chemistrychanges, outgassing, internal pressure, cell deformation, and cellrupture.
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