How do different voltages affect parallel-connected batteries?

[mapa]

Hi,

I wired a 24V battery --which were actually two 12V in series-- parallel with a 12V battery.

The Voltage turned out to be about 18Volts when I measure the 12V Battery side. When I measured the 24V side, it turned out to be about 22.2Volts.

What is going on? Why does the voltage change when different sides are measured? How would I go about calculating voltage when the batteries are in parallel and have different voltages?

 

[Sakha]

Maybe the wire you use to connect the terminals have some resistance causing the voltage drop.

 

[mikelepore]

If batteries were ideal voltage sources, it would be undefined to connect batteries with different voltages in parallel, because the meaning of any components being in parallel is that they have the same voltage across them. With real batteries, the difference between the battery voltages is the voltage that will appear across the battery internal resistance and the wiring resistance, so be careful of the wires getting very hot. Another effect with real batteries is that the battery will fail to put out the advertised voltage, because the voltage produced by a battery is a function of the current. The voltage across a battery is approximately constant if the current is small or zero, but as the current increases the voltage drops.

 

[K^2]

You also have resistance in the wire, so voltage will depend on where on the wire you attach your voltage probes.

By the way, you did create a short-circuit. I hope you didn't leave batteries like that for long.

 

[sardar]

When batteries are connected in parallel, the voltage across each battery remains the same. In this case, the 12V battery will still have a voltage of 12V and the 24V battery will still have a voltage of 24V. However, the total voltage across the parallel connection will be the average of the two voltages, which in this case is 18V. This is because the two batteries are connected in parallel, so the voltage across them is the same.

In your experiment, it seems that there may have been some resistance in the circuit that caused the voltage to drop slightly. This is why you measured a voltage of 22.2V on the 24V side instead of the expected 24V. To calculate the total voltage across the parallel connection, you can use the formula V = (V1+V2)/2, where V1 and V2 are the voltages of the two batteries. In this case, it would be (12V+24V)/2 = 18V.

It is important to note that when connecting batteries in parallel, it is recommended to use batteries with the same voltage to avoid any potential issues with unequal charging or discharging. Additionally, it is important to consider the capacity and internal resistance of each battery to ensure they can handle being connected in parallel.

I hope this helps explain the changes in voltage you observed and how to calculate the total voltage when batteries are connected in parallel. Let me know if you have any further questions.