Which is Better? Understanding Series & Parallel Battery Connections.
It’s critical to understand the differences between wiring batteries in parallel and series when creating a battery bank or any setup that calls for several batteries. The intended use will dictate how the batteries should be connected in order to properly support the particular load configurations.
So which method is appropriate for a particular setup?
In the case of a simple load or device requiring one battery, then it’s a straightforward task. But when the application requires more power than a single battery can muster, then one of the two configurations might be required.
Both parallel and series connections boost the overall amount of watt-hours available but in different ways. The main difference between the two is that wiring batteries in series increases output voltage, while wiring batteries in parallel retains voltage but increases capacity.
The capacity of a battery, measured in Ampere hours (Ah), is the amount of energy charge that enables 1 amp of current to flow for one hour, i.e., how much amperage it can provide in an hour. However, in both configurations, the total available energy, measured in watt-hours, remains the same.
Simply put, two 12-volt batteries with 100 Ah capacities in series will output 24 volts with 100 Ah capacity, while the same two batteries in parallel will output 12 volts but a double 200 Ah. The total available energy of both configurations is 2400 watt-hours, arrived at by multiplying volts by amp-hours.
i.e.
· 12v x 200Ah = 2400 watt hours (Parallel)
· 24v x 100Ah = 2400 watt hours (Series)
SERIES CONNECTION
When batteries are connected in series, the voltage is doubled, but the ampere capacity remains constant. For instance, two 12 volt, 100 AH batteries will output a voltage of 24 volts, but the amp hours will remain at 100 AH.
Before two or more batteries are connected in a series configuration, they should all have the exact same voltage and capacity rating; otherwise, there is a risk of destroying the batteries.
How to wire the batteries in series
1. The positive (+) terminal of the first battery is connected to the negative (-) terminal of the next battery in the line and this is repeated down the line of batteries in the series.
2. Then the free negative (-) terminal of the first battery is connected to the negative input of the load or application and the free positive (+) terminal of the last battery is connected to the positive input of the load or application.
3. The load or application now receives a sum of the voltages from the connected batteries.
series configuration
Advantages of a Series Configuration
Wiring batteries in series results in a lower system current as the voltage is increased since voltage and current have an inverse correlation. Less current therefore means that not only can thinner cables be used, but there will also be less voltage drop in the configuration.
The power a device draws can be calculated by multiplying its operating voltage by the current it draws, e.g., a 240-watt application using 12 volts will draw 20 amps (i.e., 240 w/12 v = 20 a or 12 v x 20 a = 240 w). If the same application uses 24 volts, it will only draw 10 amps (i.e., 240 watts/24 volts = 10 a or 24 volts x 10 a = 240 watts).
The higher the amps, the higher the current drawn, so a 24-volt application will draw less current. This can be advantageous for larger battery power banks that require higher voltages.
Disadvantages of Series Configuration
Lower-voltage devices and applications cannot be connected to the battery bank without the introduction of a converter to convert or step down the power since series design increases battery voltages. Most DC devices or appliances found in homes and offices operate at 12 volts, thus installing a converter or power step-down device may entail additional costs.
The limit on the number of batteries that can be wired in series depends on the limits of the charge controller or inverter being used. It can also depend on the battery manufacturer, who in some cases does not recommend exceeding a certain limit in series connections.
PARALLEL CONNECTION
When batteries are connected in a parallel configuration, the battery capacity is increased while the voltage remains the same. For instance, two 12-volt, 100 Ah batteries will still output 12 volts but double the capacity to 200 Ah. In parallel, the voltage can be measured from any positive or negative terminal of the batteries connected.
Like the series connections, all batteries connected in parallel ought to have the exact same voltage and capacity rating to avoid the risk of damaging the batteries.
Technically, the number of batteries that can be wired in parallel is unlimited. The catch is that while the runtime is extended, the current is also increased, necessitating heavier, more durable cables and fuses because, without them, there is a serious risk of fire. Additionally, the more batteries added to the bank, the longer it takes to charge.
How to wire batteries in Parallel
1. The positive (+) terminal of the first battery is connected to the positive (+) terminal of the next battery down the line.
2. Likewise, the negative (-) terminal of the first battery is also connected to the negative (-) terminal of the next battery down the line.
3. Then the positive terminal and negative terminal of the first battery (or the last) are connected to the positive and negative inputs of the load, respectively.
parallel configuration
Advantages of a Parallel Configuration
The main advantage of parallel configuration is the increase in the runtime of applications or appliances connected to a parallel battery bank because of the increased capacity. This means if an application could run for one hour on a 12v 100Ah battery, it will now run for two hours on the same two types of batteries and triple the time with three batteries, and so on.
Furthermore in a parallel connection, in the event one battery fails, the remaining batteries will continue powering the application, unlike a series configuration.
Disadvantages of Parallel Configurations
As voltage is inversely correlated to current, lower voltage means higher current draw, which would not only cause more voltage drop but also necessitate the use of thicker, costlier cables.
Furthermore, batteries connected in parallel take longer to charge.
SERIES-PARALLEL
There is a third option for doubling both runtime and voltage, which is a series-parallel configuration. This is achieved by wiring several batteries in series and creating a parallel connection to another series battery bank.
series-parallel configuration
Simply put, it’s connecting two separate series-battery banks in parallel. This is not as straight-forward, and a misconnection could result in a catastrophe, so it should ideally be done by a qualified and knowledgeable individual.
Scenario: Two 12v 100Ah batteries are wired in series to create 24v 100 Ah. Another set of 24v 100Ah battery bank is created. The two 24v 100 Ah banks are wired in parallel to create one 24v 200Ah bank.
Which configuration is better?
Neither configuration is better but depends wholly on the application the battery bank is intended for.
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