Battery charging what do bulk absorption and float mean?

Posted Friday 23rd of January 2015 at 17:11


As batteries are charged they go through 3 different states - bulk absorption and float. Here's what is happening at each of these stages and a quick overview of the changing behaviour of the DL-300 charge controller through each of these stages.

1. Bulktroubleshooting
In the first stage of the process current is sent from the wind turbine to the batteries at the maximum safe rate they will accept until voltage is brought up to nearly 80-90 percent full charge level - see table below. During bulkcharge the LED lights on the DL-300 charge controller supplied with the LE-300 and LE-v150 wind turbines blink green there is a long delay and they blink green again.

2. Absorption
In the second stage voltage peaks and stabilizes and current begins to taper off as internal resistance rises. The LED lights at this stage blink green but there is now only a short delay before another green blink.

3. Float
At this point the charge on the batteries is maintained at an optimal level also known as trickle charged. The voltage is reduced to lower levels in order to reduce gassing and prolong battery life. The DL-300 features Pulse Width Modulation (PWM) and sends small short charging cycles or 'pulses' when it senses small drops in voltage. At this point the LED lights are a solid green - no blinking.

As the batteries become fully charged and are no longer able to accept any further electrical energy the battery voltage will rise. When the voltage reaches the regulation level (varies with battery type see below) and starts to dump power the controller's lights are a solid red. This energy is dissipated as heat into the surrounding environment. More or less power is diverted to the dump load according to how much is being supplied to the battery from the turbine.

12V Setpoints
Mode Flooded Sealed
Bulk 14.6 14.3
Float 13.4 13.4

24V Setpoints
Mode Flooded Sealed
Bulk 29.2 28.6
Float 26.8 26.8