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How to measure battery charge

How to measure battery charge

Battery capacity - the time during which the battery can power the connected load.

Standard capacity is measured in ampere-hours, and for small batteries - in milliamps-hour.



The quantity of electricity (charge) of the battery is called capacity. The charge is measured in coulombs, 1 pendant is 1 Amp x 1 second. To find the capacity battery, Charge it fully and discharge after a given current I and measure the time T, for which will complete discharge. Multiply the time (T) to the current (I), and you get the Q - Capacity battery.


Fully charge the battery and to check theconnect it to this unit. Clock set on the record & lt-0 & gt- and turn on Start. Now the relay should close the contacts 4-5 and 5-6, and the battery begins to discharge through a resistor the R, the clock voltage is applied. The voltage on the battery itself and the resistor begins to slowly decline, when the resistor, it will drop to 1V, the relay opens the contact, the discharge stops and the clock stops.


On discharge battery Managing the current passing through the contacts 1-2relay 8 drops to 2 mA. If the drive current is 3 mA in power, the contacts 4-5 and 5-6 the resistance is less than 0.04 ohms (value low enough not to take it into account when measuring the current). If you need a current of 1A discharge, use a resistor R = 1.2 ohm.


After the discharge is stopped, the battery voltage starts to rise to 1.1-1.2 V, this occurs because of the internal resistance of the cell. Consider the fact that the capacity of the newly charged battery will be higher, because after some timethe charge is lost sight of self-discharge. In order to calculate the amount of self-discharge, measure the capacity immediately after charging, and then after about a week after that. Some self-discharge of batteries can be up to 10% per week or more.


If you are working on this scheme, try to reduce the contact resistance battery and connectors. If the current is 0 is valid.5-1 A, you can get at a very high measurement accuracy (lose on the contacts of 0.1 V or more). It also can cause loss of precision steel spring, which is used in some of the holders batteryTherefore it contacts and other steel shunt with a copper wire.

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