Serial & Parallel Connections

Joseph Lopez

Wednesday, March 26, 2008

Battery packs are configured to suit their proper voltage (power) and amperage (run time) by connecting its cells in different series. A single cell holds a fixed voltage and amperage on its own, however; these cells are combined in different ways to form a battery pack that generates the desired rating.

Let’s say we’re dealing with 1.2V, 1000mAh single battery cells, (fig. 001) and we need to combine them to create a battery pack with a certain voltage and amperage. In order to do this we need to know the 3 different configurations and the rules associated with each of them.
Serial Configuration (fig. 002) When two or more cells are connected in a string, it is called a serial configuration. This connection increases the voltage, however; the amperage stays constant. Notice how the negative ends are connected to the positive ends.
	Parallel Configuration (fig. 003) When two or more cells are connected side by side it is called a parallel configuration. This produces the opposite effect of a serial configuration because it increases the amperage and the voltage remains constant. Notice how all the positive ends are connected to each other (same with the negatives).
Serial/Parallel Configuration (fig. 004) We can also connect the cells in both columns of serial configurations and rows of parallel configurations to increase the voltage and amperage of the battery pack. Notice how there is a mix between positive and negative connections.
With this information we can determine the voltage and amperage of a battery pack by looking at its configuration. For example, the battery pack below (fig. 005) is made of 3.6V 2000mAh lithium-ion cells. What is the total voltage and amperage of the battery pack? Since the cells are in a serial configuration the voltage increases with each cell, however; the amperage stays constant. The 5 cells are rated with 3.6 volts at 2000mAh, so we would multiply the 3.6 (volts) by 5 (cells). 3.6 x 5 = 18 volts The amperage stays constant in a serial configuration, so the total amperage is 2000mAh.
	The battery pack on the left (fig. 006) produces 2.4 volts at 3000mAh. Its cells are in parallel configuration; therefore the amperage of one cell is multiplied by the total number of cells in the pack assuming that all cells are identical. Amperage remains constant.
This battery pack (fig.007) is in serial/parallel configuration, so both the voltage and amperage are increased. There are 3 cells in each column so the voltage of one cell is multiplied by 3 in order to calculate the total voltage of the battery pack. 1.6 x 3 = 4.8V There are 2 rows of parallel cells, so in order to calculate the amperage of the battery pack we would have to multiply the amperage of one cell by 2, assuming that all cells are identical. 1700 x 2 = 3400mAh

This is a single SLA (Sealed Lead Acid) battery. These are connected in serial and/or parallel configurations using the red (positive) and black (negative) terminals. Depending on the configuration type, a cluster of these batteries could either produce more voltage, amperage, or both.
If you wanted to connect SLA batteries in a series to produce higher voltage this is how you would connect them to each other. Notice how the terminals are connected to their opposite currents. Black connects to red, and red connects to black. The two ends of the battery pack would then be connected to the device’s positive and negative terminals.
The picture on the right is how you would connect SLA batteries using the parallel configuration. All the positive terminals are connected to each other using a positive cable, and all the negative terminals are connected to one negative cable.
This would be a serial/parallel configuration since the terminals are connected to both their equal and opposite currents.

When dealing with currents and battery configurations you must remember to follow these guidelines:
-Never connect cells in parallel and/or series that are not designed for that purpose. A cell mismatch may cause overcharge and venting with flame.

- Never charge or discharge the battery without connecting a working protection circuit. Each cell must be monitored individually and the current disconnected if an anomaly occurs.

- Always attach a temperature sensor when charging and discharging the battery. The temperature sensor must disconnect the current on excess temperature.

- Only connect cells that are matched and have the identical state-of-charge.

- Pay special attention when using an unknown brand. Not all brands contain intrinsic safety features that protect the cell when stressed.

- During experiments, place the test battery into a well-ventilated fireproof container.

- Never leave the battery unattended while under charge or discharge.

- Do not charge a battery hat has physical damage.

# comments about: "Serial & Parallel Connections"

1. 4/15/2008 8:29:34 PM | Posted by: hongyan

Well, you explained serial

Serial & Parallel Connections

# comments about: "Serial & Parallel Connections"

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