Solar Charge Controller
Posted: Mon Mar 03, 2014 3:03 pm
In reading this article I noticed an error in the discussion about reverse power flows:
"FETs will also conduct both ways, thus creating a potential that the batteries could discharge through the solar panel. To prevent this, an algorithm is used, and when the solar voltage drops below the battery voltage the unit disconnects from the solar panel. This prevents discharge when the sun goes behind a cloud or the sun goes down."
The problem is that simply controlling the gate of the FET will not prevent the reverse power flow because there is a diode between drain and source of the power FET that will conduct even if the gate turns the device off.
To correct this problem you need another device in series. You could use a simple diode but that results in power loss. The alternative is another power FET but this time with the drain and source connections reversed. You can see that in this charge controller.
"FETs will also conduct both ways, thus creating a potential that the batteries could discharge through the solar panel. To prevent this, an algorithm is used, and when the solar voltage drops below the battery voltage the unit disconnects from the solar panel. This prevents discharge when the sun goes behind a cloud or the sun goes down."
The problem is that simply controlling the gate of the FET will not prevent the reverse power flow because there is a diode between drain and source of the power FET that will conduct even if the gate turns the device off.
To correct this problem you need another device in series. You could use a simple diode but that results in power loss. The alternative is another power FET but this time with the drain and source connections reversed. You can see that in this charge controller.