Originally Posted by
Slunnie
Solar panels and the controller discharge batteries?
Used to be a problem once upon a time, especially for those who think it's a good idea to connect a solar panel directly to the battery with no controller. Some solar panels come with a series connected forward biased diode in the connector box on the back of the panel. This solves any potential 'nightime discharge' issues and protects the panel from inadvertent reverse connection.
An issue with constant float 'set and forget' connection is that float voltage is usually set at 13.5 - 13.8 volts depending on the battery/controller which is above the gassing voltage for many lead acid batterys. Ultimately this can wear the battery out as electrolyte may be slowly depleted, re-combination type battery or not. Leaving a battery on constant float can also aid sulphation (where insoluble lead sulphate forms on the plates reducing battery efficiency).
To overcome this some quality controller manufacturers eg. Victron can have a maintenance mode in their charging profile which drops the float voltage from say 13.5 V to 13.2 V which is below the electrolyte gassing voltage so holds the battery fully charged without gassing. To prevent sulphation and electrolyte stratification in a flooded cell (where electrolyte becomes layered with different levels of specific gravity) every so often the charger goes into charge mode and stirs things up. This is probably the 'gold standard' and can be relatively expensive to set up as these controllers aren't cheap.
Another potential hazard of the 'set and forget' maintenance mode is that when cheap controllers fail it's often the output voltage regulation that fails leading to overcharging and eventual destruction of the battery(s). It may be cheaper and more reliable in the long run to buy a 240 volt battery maintenance charger instead.
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