In this post we learn about a simple battery current sensor with indicator circuit which detects the amount of current consumed by the battery while charging or by any other load and displays it through discrete LEDs.
Battery Charging by Detecting Current
Commonly most battery charging indicators utilize the voltage level of the battery to indicate its charging condition, here instead of voltage the current (amps) magnitude is used for measuring the charging status.
Using current as the measuring parameter enables a more accurate assessment of the battery charging status. The circuit is also capable of indicating the instantaneous health of a connected battery by translating its current consuming capability while its being charged.
Referring to the shown circuit, we can see four opamps configured as comparators where each opamp has it own presetable current sensing inputs.
A high watt resistor Rx forms the current to voltage converter component which senses the consumed current by the battery or the load and translates it into a corresponding voltage level and feeds it to the opamp inputs.
Setting up the Presets
P1 upto P4 are adjusted such that the A1 to A4 opamp non-inverting inputs become higher than their respective inverting inputs in response to the decreasing current consumption by the battery as it reaches it full charge status.
For instance P1 may be adjusted such that A1 pin3 becomes slightly higher than its pin2 when the battery consumes the highest amount of current (a known specified level), that is when its fully discharged.
P2 may be adjusted identically when the battery gets charged to some a slightly higher voltage level and its current consumption is reduced proportionately.
Similarly P3 and P4 may be adjusted for the next lower voltage levels across Rx in response to the battery's increased charge level until it's fully charged.
These various current consumption levels from maximum to minimum is indicated by the corresponding LEDs connected across the outputs of A1 to A4 in a sequential manner, wherein only a single LED lights up at any given instance for indicating the relevant battery current levels.
Parts List for the proposed battery current indicator circuit
R1----R5 = 1k
P1-----P4 = 1k presets
A1-----A4 = LM324 IC
Diode = 1N4007 or 1N4148
Rx = 0.6/specified battery charging current
How to set up the circuit
Initially keep all the preset slider arms towards the ground end.
Disconnect the P1---P4 connection with Rx and connect it with an external variable voltage source which can be simply made with a 1K pot.
For making the variable power supply, take a 1K or a 10K pot, connect its outer terminals with the supply rails and connect its center terminal with the free end of P1---P4 which was disconnected from Rx.
Adjust the pot and create a 0.7V at the center lead of the pot.
Now adjust the P1 such that the white LEd just lights up.
Increase the pot center lead voltage to 1V and set P2 such that the yellow LED just lights up, shutting off the red LED.
Next, increase the pot center lead voltage to 1.3V and subsequently to 1.5V and adjust P3 and P4 identically as done for P1, P2.
Once the setting is completed the pot may be removed and the P1----P4 end reconnected to the Rx point.
The above range of 0.6V to 1.5V will be subject to the selected Rx value and the desired current range, where 1.5V may be assumed to the maximum voltage across Rx generated for an equivalent maximum desired charging current for the battery or any other load.
For example, a 1 ohm resistor selected for Rx will generate 1.5 V across it when a current of 1.5 amp is passed through it, whereas the same voltage will be generated for a 5 amp current if Rx is selected as 0.3 ohms and so on.
The formula for selecting Rx = 1.5/maximum charging current.