# Connecting Cells in Parallel: Effects of Series Resistor

• IntuitioN
In summary, connecting two cells with different emf in parallel along with a resistor in series can potentially cause a large current to flow through the batteries, which can lead to damage. This is especially dangerous in high voltage batteries. However, standard 6V and 9V dry-cell batteries have high enough internal resistance to limit the current to safe levels. Once equilibrium is reached, the 6V battery serves no purpose.
IntuitioN
what happens if you connect two cells with different emf in parallel along with a resistor in series

eg:

l---100Ohm--l
l-----6V-----l
l-----9V-----l

Stop! Don't do it. The loop containing the 9V and the 6V battery is a "short circuit"
(as in "Don't blow your fuse.") . The imbalance is 3V which would give a large current
through each battery: I=3/r, where r is the (usually very small) internal resistance of the batteries. The 1 kOhm resistor would have a current of I=3/1000=.003 Amp.
But the batteries would quickly burn out.

It generally won't blow anything up, but it won't be good for either battery. The 9V battery will be trying to "charge" the 6V, but the 6V vattery cannot ever charge to 9V. It can potentially draw a large current from the 9V battery for a period of time, but the equivalent series resistance of both batteries will limit the current to levels that wouldn't be considered dangerous. Once the system reaches equilibrium, the 6V battery will serve no purpose, neither sourcing nor sinking any current.

- Warren

Have you ever shorted a 6 V car battery?

I have seen a 360 V electric car battery pack get shorted, and that's definitely messy. I assumed he was talking about standard 6 V and 9 V dry-cell batteries, though, which have high enough ESR to prevent a dangerous amount of current.

- Warren

## 1. What is the purpose of connecting cells in parallel?

Connecting cells in parallel allows for an increase in the total current output of the circuit, as the cells work together to provide a larger flow of electricity.

## 2. How does a series resistor affect the connection of cells in parallel?

A series resistor is used to balance the current flow between the cells in parallel. It helps prevent one cell from draining all of the current and causing an imbalance in the circuit.

## 3. What happens if a cell in the parallel connection fails?

If a cell fails in a parallel connection, the remaining cells will continue to function and provide current to the circuit. However, the total current output will decrease due to the loss of one cell.

## 4. Can different types of cells be connected in parallel?

Yes, different types of cells can be connected in parallel as long as they have similar voltage outputs. It is important to note that the cells will only work together efficiently if they have similar characteristics.

## 5. What are the advantages of connecting cells in parallel over series?

Connecting cells in parallel allows for a larger total current output, as well as a more reliable power supply. In a parallel connection, if one cell fails, the others can still provide power, whereas in a series connection, the entire circuit would fail if one cell fails.

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