Buck Gizmo -Volts vs Amps ? UPDATED
Update 5 Nov. (It didn't work out as hoped) I got my little gizmo, see close-up photos here http://www.ebay.com/itm/DC-DC-15A-Converter-Buck-Adjustable-4-32V-12V-to-1-2-32V-3-3V-5V-24V-Step-Down...
Forum Discussion
What a mess!
The solar panel is a current source. It has an output current of Isc.
In a pwm controller, when the battery voltage is low, this controller shorts panel to the battery. If Isc = 10A and the battery is at 12.0V then the output power of the panel is equal to the input power of the battery (neglecting efficiency) P = 12.0V * 10A = 120W. When Vbat increases to 13.0V, input and output power is 130W.
When the pwm controller goes into absorption mode, the controller converts the solar current source to a voltage source. The controller regulates output voltage to perhaps 13.7V. As long as the current demand out of the controller is less than Isc, it will maintain 13.7V regulation. That means, if the battery takes 5A, the output and input power to the regulator is 13.7V * 5A = 68.5W. If you turn on a 3A light, solar current will increase to 8A while the controller maintains the 13.7V regulation.
The mppt controller is different. In boost mode, it converts the solar current source into a voltage source. In the example above, when Vbat = 12.0V, the panel outputs 120W and when Vbat = 13.0V, the panel outputs 130W. You can see, the higher the voltage the more watts the panel outputs. The mppt controller measures panel current and voltage and therefore can find the maximum power point. That may be 160W. When Vbat = 12.0V, the battery current is 160W/12V = 13.3A. When Vbat = 13.0V, Ibat = 160W/13V = 12.3A.
Once the mppt controller gets out of boost, it should work like the pwm controller.
To keep it simple controller efficiency is 100W. Battery input power equals solar output power.
The solar panel is a current source. It has an output current of Isc.
In a pwm controller, when the battery voltage is low, this controller shorts panel to the battery. If Isc = 10A and the battery is at 12.0V then the output power of the panel is equal to the input power of the battery (neglecting efficiency) P = 12.0V * 10A = 120W. When Vbat increases to 13.0V, input and output power is 130W.
When the pwm controller goes into absorption mode, the controller converts the solar current source to a voltage source. The controller regulates output voltage to perhaps 13.7V. As long as the current demand out of the controller is less than Isc, it will maintain 13.7V regulation. That means, if the battery takes 5A, the output and input power to the regulator is 13.7V * 5A = 68.5W. If you turn on a 3A light, solar current will increase to 8A while the controller maintains the 13.7V regulation.
The mppt controller is different. In boost mode, it converts the solar current source into a voltage source. In the example above, when Vbat = 12.0V, the panel outputs 120W and when Vbat = 13.0V, the panel outputs 130W. You can see, the higher the voltage the more watts the panel outputs. The mppt controller measures panel current and voltage and therefore can find the maximum power point. That may be 160W. When Vbat = 12.0V, the battery current is 160W/12V = 13.3A. When Vbat = 13.0V, Ibat = 160W/13V = 12.3A.
Once the mppt controller gets out of boost, it should work like the pwm controller.
To keep it simple controller efficiency is 100W. Battery input power equals solar output power.
