Charging storage batteries
Charging the storage battery bank is a critical process; incorrect management of the charging process will damage the storage battery bank and may reduce its working life by half or more, and the storage battery bank is the most expensive single component in a hybrid independent power plant.
The charging process
The process of charging the storage battery bank is designed to maximise efficiency, and to maximise the life of the storage battery bank.
In normal circumstances the charging process starts when the charge in the storage battery bank is reduced to 65% of its full capacity. The storage battery bank can be discharged more than this if necessary; however it is best to avoid this to maximise its life.
Charging storage batteries is a three-stage process. The charging process looks like this:
The charging process starts at the highest amperage available, without exceeding the recommendation of the storage battery manufacturer. As the charge in the storage battery increases the charging voltage increases to maintain the amperage.
This stage of the charging process is called the bulk stage; it will charge the battery to 80 – 85% of its capacity.
As the charging process continues the charging voltage will eventually rise to a value that is called the absorption voltage. The absorption voltage is the highest voltage that the storage battery may be charged at. The charging voltage is maintained at this value, and the amperage progressively falls as the battery charges.
This stage of the charging process is called the absorption stage; it will charge the battery to nearly 100% of its capacity.
As the battery continues to charge at the absorption voltage the amperage will progressively fall. When the amperage falls to a specified value the charging voltage is reduced to a value that is called the float voltage, which keeps the battery fully charged. This stage of the charging process is called the float stage.
The charging process may be controlled by one of several different types of equipment. A PowerMaker generator incorporates a controller that manages the charging process; a solar controller manages the process for solar panels, and the charging process may also be performed by a mains-powered battery charger.
Not all charging equipment performs the full three-stage process. The very simplest and cheapest equipment doesn’t control the charging process at all, and relies on the user to switch it off before the battery is overcharged.
Better equipment produces a regulated charging voltage (the absorption voltage) and stops the charging process when it is fully charged, without a float stage. More sophisticated equipment, such as a good quality battery charger will perform the complete three-stage charging process.
A generator, such as Eniquest’s PowerMaker, does not perform the float stage as this would require its engine to run continuously with a very low load to maintain the float voltage, which wastes fuel and may damage the diesel engine.
Independent power plants
- Independent energy solutions overview
- Generator sets for independent power plants
- Hybrid independent power plants
- Sizing your independent plant
- Independent energy system components
- Using a conventional generator set
Independent energy system components
- Control system
- Solar panel
- Solar controller
- Storage battery bank
- Battery charger
Independent energy system concepts
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