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? asked in Science & MathematicsEngineering · 6 months ago

is there a way to detect battery voltage WHILE IT'S CHARGING?

in case you don't understand the question which you probably don't, let me draw it to you, if 12.7v battery is being charged by another 12.7 battery, voltage across the battery that is being charged is always 12.7 (due to other battery) despite the fact it may be at 10.5v or 11v. is there any way to detect it's voltage while it is being charged.

Update:

@billrussell no, i don't mean voltage with the charger not connected, that makes no sense why i would mean that. as i clearly wrote i mean voltage across the battery while it's charged. how do you imagine voltmeter will show it's real voltage when it has 13v across it from other battery or any source. think again.

Update 2:

there is a solution for this by measuring both batteries in series with a voltage controlled switch

Update 3:

"

The only way to see the battery charge level electrically is to disconnect, test, then reconnect" not true and there are MULTIPLE ways to do it

Update 4:

solution is to connect the batteries in parallel and in series at the same time, but make the series connection very high resistance so virtually no current flows.

Update 5:

Anonymous that is exactly what i said in my updates

Update 6:

like i wrote above, most elegant solution is to connect batteries in series too, but put big resistor like 50kohms on both sides to eliminate virtually all current. voltage across any of the two resistors will be 1/2 of two battery voltages which makes easy to calculate the voltage of the battery being charged. https://i.postimg.cc/zBqDcW4s/1.jpg

5 Answers

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  • Rick
    Lv 7
    6 months ago
    Favorite Answer

    don't see how it could be done, no .........................

  • derfram
    Lv 7
    6 months ago

    To determine the battery EMF, as opposed to the terminal voltage, you would need to know the battery's internal resistance and the current flowing into the battery. 

    For example, if you knew the battery had an internal resistance of 1.5 ohms, and were charging it at 0.5 amps, you would be able to calculate that there is 0.75 volts dropped across the battery's internal resistance.  If the terminal voltage was 12.7 volts, you could determine the EMF to be 12.7 - 0.75 = 11.95 volts. 

    Otherwise, you would need to reduce the charge current to zero (by disconnecting the battery from the charger) and measure the terminal voltage.  With no current flow through the internal resistance, the drop across that resistance would be zero and the terminal voltage and EMF would be the same. 

  • Anonymous
    6 months ago

    Put a 100Ω resistor between the batteries.

    Each will show it's charge. At the current goes to zero the V-drop goes to zero.

  • billrussell42
    Lv 7
    6 months ago

    A voltmeter will always measure the actual voltage, even if being charged. That is what voltmeters do.

    But I think you mean voltage with the charger not connected. Answer is NO.

  • ?
    Lv 7
    6 months ago

    The only way to see the battery charge level electrically is to disconnect, test, then reconnect.  Some advanced chargers do this to prevent overcharging.

    However, if it's an 'old-school' lead-acid battery (and some others), you can test the electrolyte specific gravity to determine charge level.

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