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. For this, we use 5kΩ and 2kΩ potentiometers as we have a fixed 270Ω sink resistor.There are many ways to connect a group of batteries in both series and parallel at the same time. We need some resistors at the adjust pin of the IC to control output voltage. You can select the LM338 or LM350 according to your current capacity requirements. Knowing this, we need a circuit in which we can adjust the voltage over time, so it would be easier to control it with the help of a potentiometer or we can use a microcontroller of the task.Ī LM317 voltage regulator IC is the first thing that comes to mind for these applications. Its absorption voltage is 14.1V to 14.3V and float voltage is 13.6V to 13.8V. Let’s talk about a normal 12V, 7Ah battery. You can leave battery charging in this state forever and no harm occurs to the battery. Here, voltage is reduced and a current of less than 1% of the battery's capacity is applied. In the float stage, the charger tries to maintain the fully charged battery in the same state indefinitely. Permanent sulfation occurs when a battery has been in a low state of charge for weeks or more and restoration of the battery is then impossible. In this case, the battery might have permanent sulfation. Sometimes, however, the current does not drop as expected. Here, the charger feeds the constant current same as the absorption voltage of the charger, which depends on charging options and this current consumption decreases until the battery is fully charged. Absorption StageĪt the absorption stage, the remaining 20% of the battery is charged. Remember to check out the charging recommendations from manufacturers, some batteries also specify 10% of the capacity. You can increase the current to the battery more than 25% of its capacity, which will decrease the charging time but also may decrease battery life so it’s not recommended to apply a higher current than specified. For example, in the case of 100Ah battery, 25A of constant current is fed and voltage increases with time. Here, a constant current of 25% of the Ah rating is provided. Bulk StageĪbout 80% of the battery is charged in the bulk stage. Doing so is like giving a slow death to your batteries! The Three-stage Charging ProcessĪs the name states, there are three stages in this charger: bulk, absorption, and float. You might have seen people charging lead-acid (or other expensive) batteries with a constant power supply. As mentioned earlier, these chargers increase efficiency and provide a longer life to batteries. Some chargers have a recovery stage for recovering flat batteries. The float stage which is also referred to as trickle charging happens when the battery is charged at a self-discharging rate. Here, the bulk stage is generally referred to as the boost stage in which the battery is charged at high currents for a short amount of time. You can observe these stages on a common mobile battery charger controller circuit. These battery charging technologies usually rely on microprocessors for anywhere from 2- to 5-stage regulated charging.Ī two-stage battery charger has (obviously) two stages: bulk and float. Multi-stage battery chargers sense the battery’s requirements and automatically switch to CC-CV mode, guaranteeing optimum efficiency and longer battery life. For the more expensive lead-acid battery, this three-stage charging process keeps the battery healthy.īefore getting into three-stage battery charger circuits, we must understand more about multi-stage battery chargers and why they are used. Ideally, however, all battery types should be charged with three-stage chargers. They are high-quality chargers and are popular for charging lead-acid batteries. Three-stage battery chargers are commonly referred to as smart chargers.
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