As mentioned earlier there are two types of charge controllers
.1) Pulse width modulator (PWM) charge controller
.2) Maximum power point tracking (MPPT) charge controller
Before we look at the two types of charge controller I want to discuss briefly the charging process that occurs between the charge controller and the batteries.
There are three basic stages in the charging of a battery.
.1) BULK STAGE
This stage accounts for the major part of the charging process. This is the first stage of the charging process, the battery is charged with the maximum current possible and the aim of this process is to push as much power as possible into the batteries to get them filled up.
.2) ABSORPTION STAGE
This stage occurs when the battery is getting filled up, the charge controller reduces the amount current sent to the battery, this allows the charge controller efficiently monitor the charging process to prevent over charging.
This stage is important in the charging process because if the charge controller continues charging the batteries at bulk stage till the end of the charging process, it may *mistakenly overcharge the battery.
.3) FLOAT STAGE
This stage begins when the battery is almost completely fully charged, at this point the charge controller sends what we call trickle charges to the batteries. This trickle charge is most times equal to the rate of self-discharge of the battery.
In other words, during this process the charge controller is simply topping up the battery, getting to 100%. This is to compensate for the loss that happens due to the internal reaction of the batteries(self-discharge).The charge controller does this by sending very little charges now and then to the battery.
The Charging process can be viewed as this,
When he is still far away, he can drive at the maximum speed possible (BULK STAGE) until he gets closer to the traffic congestion, as he gets to the traffic congestion he begins to slow down (ABSORPTION STAGE) so that he would not mistakenly hit the car(A) that's in front of him. Once he gets close to the car(A) he stops.The traffic congestion eases a little, so the car(A) ahead slowly moves and then stops again, and the driver of car(B) also follows it moving slowly(trickle charge) to cover the gap created between him and the car(A)(FLOAT STAGE).
Though the PWM and the MPPT charge controllers use different techniques to charge the batteries, they still follow this three stages when charging batterieS.