4 Stage Battery Chargers Explained
Good battery chargers or charge controllers/regulators will charge your batteries in stages depending on how much charge remains in the battery. Three or four stages are the most common, this article will explain how a four-stage battery charger works. We will also explain why it is important that you use the correct program settings on your charge controller.
How 4 stage charging works
- Stage 1 (Bulk) – If the batteries are at a lower state-of-charge, usually less than 80% full, this is the first stage. When in the Bulk stage the solar panel or generator will put as much Ampere into the batteries as possible. This is the high-speed charging stage, the higher the Ampere the faster the charge.
- Stage 2 (Absorb) – when the batteries reach the “Absorb Voltage” (this number differs depending on program settings but generally around 14.5 Volts for lead-acid batteries), the charger or regulator should go into the Absorb stage. In this stage, the batteries are kept at the voltage set by the program. The Ampere going into the batteries is lower in this stage and the batteries charge more slowly. The Absorb stage can end either after a set time has passed or when the number of Ampere going in drops below a threshold. This is all decided by the charge program settings.
- Stage 3 (Float) – when the Absorb stage ends, the charge controller will drop the voltage to a program defined value and start the Float stage. This stage will kick in when the battery reaches 100% charge.
- Stage 4 (Equalization) – this stage will actually overcharge the battery. But it is only turned on periodically to override the Float stage. This is optimal for lead-acid batteries and will extend the life and performance of the battery.