![]() Now go back to Figure 12 and look at the green wire designated W3. Take a pencil and trace the path of the charge current from the output, positive terminal of the 24 volt charger, through the wires, and the batteries, through W1 and back to the output, negative terminal of the 24 volt charger. Interestingly enough, if the connection at battery D positive terminal is moved to battery C positive terminal, without changing the connection at battery A negative terminal, then a voltage imbalance will exist. Figure 13 shows two wires highlighted, the blue one designated W1 and the green one designated W2. Just one more comment about voltage imbalance while charging current is being applied. In some larger systems, these types of considerations could have an impact on both economics and system reliability.įigure 13: Four Batteries in Series / Parallel (Example 2), One Charger That one extra connection makes the difference between being able to use two 12-volt chargers effectively instead of having to use one 24-volt charger. Recall that example 1 shown in Figure 4 had two sets of two batteries, first connected in series, then each series connected in parallel by 2 wire connections.įor those mathematics buffs that are into topology and n-dimensional spaces, etc., one might consider the fact that there is one more piece of wire connecting the batteries in example 2 (5 pieces of wire total) compared to only 4 pieces of wire in example 1. In this case, it is perfectly acceptable to use a single charger for each of the parallel-connected sets of batteries without worrying about the voltage imbalance discussed with respect to example 1. Then those two parallel-connected sets of batteries are connected in series by a single wire connection. What you have is two sets of two batteries each connected in parallel. But this battery pack is configured like example 2 in the previous section. Again, the blue wire designated W1 serves the same charge voltage drop imbalance function that it did in Figure 9.įigure 12 again shows two 12 volt chargers connected to a series / parallel battery pack. Even without those special charging features, the single 24-volt charger in this arrangement does a better job than two 12-volt chargers would. There are some intricate details of charging algorithms that are specifically optimized to account for and eliminate the individual battery voltage imbalance in large series strings. This method is definitely better than the arrangement shown in Figure 10 because the imbalance in individual battery voltages is not as much of a concern. The diagram shown in Figure 11 is an acceptable way to charge a combination series / parallel battery pack. Notice that the total battery pack voltage is 24 volts and that the total battery pack capacity is 40 amp-hours.įigure 11: Four Batteries in Series / Parallel (Example 1), One Charger The string A and C is in parallel with the string B and D. In this type of arrangement, we refer to each pair of series connected batteries as a "string". ![]() Example 1, shown in Figure 4, has 2 pairs of series connected batteries joined in a single parallel connection. In each of the examples, the 4 batteries are identified as A, B, C, and D. Just to get an idea of how these connections can be made, we'll look at two examples, with 4 batteries each, using 12 volt, 20 Ah batteries. ![]() It is not uncommon to have battery packs with several hundred volts and several hundred amp-hours. This is common practice in many battery power appliances, particularly in electric vehicles and large UPS systems where the battery packs require large voltages and amp-hour capacities. ![]() There are many ways to connect a group of batteries in both series and parallel at the same time. ![]()
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