Originally Posted by Extemporaneous
Okay, so here is my silly question.
In order for a battery to accept a charge, it needs at least 13.8v.
A full battery is at approximately 12.6v.
When there is a draw/load on your batteries and your solar panels
, does the regulator
put out the 10% extra (13.8v) required to charge the batteries or just flow through the 12.6v and save what would be a 10% waste?
You need to separate what voltage and current
panel/regulator doesn't know what it is connected to or what is drawing current
. If you have a simple regulator, all it does is prevent the battery voltage from going over 13.8 V if that is its set point. If the battery is charged and is therefore drawing very little current, then the regulator will only supply enough current to maintain the 13.8V. If you now turn on a load, then the regulator will supply the current for the load plus whatever current is going into the battery to maintain the 13.8V.
How it actually works is there is a circuit that senses the battery voltage. When that voltage reaches the trigger point, the solar
panel is disconnected from the battery for a short time. The panel is then reconnected again to the battery. The time it now takes the voltage to reach the trigger point determines the duty cycle (% time on) of regulator. If the battery is charged, it takes very little time to turn off again, and so spends most of its time off.
Here's an example of a simple regulator.
A simple solar panel regulator
If you draw more current than the solar panel can put out then the battery voltage will drop below the 13.8 V and the panel output will be continuous. As long as this voltage is above the voltage of the battery associated with its state of charge (not a hard number, varies by battery, battery condition, etc.) then current will still go to the battery and the other load. If you draw enough current with another load, such that the voltage falls below the voltage needed to charge the battery, which is dependent on its state of charge, then the battery will be discharging, and supplying the fraction of the current required by the load that the charger
is not supplying.
So on your other point, 13.8 volts is not required to charge a battery. If you look at your battery volt meter when the battery is heavily discharged and is drawing more current than your charging device can put out, you won't see 13.8 V. As long as the voltage of the charging device is higher than the battery voltage at its state of charge, the battery will charge, but it could take a very long time and might never fully charge. Higher voltage raises the charge acceptance rate of the battery, too high of a voltage causes gassing.
Here's a graph showing how voltage output varies with current output of a solar panel.
Electrical Characteristics of Solar Panels or PV Modules - AltE