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
"The MPPT feature just fine-tunes the panel's output for the buck's input, but you still get some sort of panel input with no MPPT."
That's an interesting point.
Hmmm, I was just re-reading page 3 in my 'paralleling made easy' thread, where Salvo was explaining Kirchoff's voltage law. And I thought it applied here, and perhaps explained the advantage of the mppt feature.
Perhaps the mppt only shows its merit during boost, because it recognizes there is 'extra' power available that the pwm does not utilize. In Salvo's example above, the pwm is only extracting 120w at first, but the mppt is extracting 160w. Why is this? Well, it appears the pwm is operating according to Kirchoff's law, and is therefore only extracting just enough voltage to overcome battery Voltage and cable Resistance. So, if the batts are at 12.2v and cable resistance is .3v, the pwm will start at 12.5v in cc/boost mode, just like a typical power supply / 3 stage smart charger.
But the genius of the mppt is that it is not bound to Kirchoff's law, necessarily, because it does not start in cc mode, but rather in a sort of variable cv mode. And that "variable constant voltage" will be whatever is available at the time, from the panel. And when available power (Watts) exceeds that required by a pwm to operate in cc mode, the mppt makes use of this extra power, and thus produces more current.
So, while there is 160 watts available, and Isc is 10a:
... the pwm only uses 125 watts... (12.2v + .3v) x 10a = 125w
But while there is 160 watts available, and Isc is not limited to 10a:
... the mppt uses all 160 watts... (12.2v + .3v) x 12.8a... and thus operates at a slightly higher Charge Rate.
??? What I don't understand is why Isc does not apply when an mppt is employed?
That's an interesting point.
Hmmm, I was just re-reading page 3 in my 'paralleling made easy' thread, where Salvo was explaining Kirchoff's voltage law. And I thought it applied here, and perhaps explained the advantage of the mppt feature.
Perhaps the mppt only shows its merit during boost, because it recognizes there is 'extra' power available that the pwm does not utilize. In Salvo's example above, the pwm is only extracting 120w at first, but the mppt is extracting 160w. Why is this? Well, it appears the pwm is operating according to Kirchoff's law, and is therefore only extracting just enough voltage to overcome battery Voltage and cable Resistance. So, if the batts are at 12.2v and cable resistance is .3v, the pwm will start at 12.5v in cc/boost mode, just like a typical power supply / 3 stage smart charger.
But the genius of the mppt is that it is not bound to Kirchoff's law, necessarily, because it does not start in cc mode, but rather in a sort of variable cv mode. And that "variable constant voltage" will be whatever is available at the time, from the panel. And when available power (Watts) exceeds that required by a pwm to operate in cc mode, the mppt makes use of this extra power, and thus produces more current.
So, while there is 160 watts available, and Isc is 10a:
... the pwm only uses 125 watts... (12.2v + .3v) x 10a = 125w
But while there is 160 watts available, and Isc is not limited to 10a:
... the mppt uses all 160 watts... (12.2v + .3v) x 12.8a... and thus operates at a slightly higher Charge Rate.
??? What I don't understand is why Isc does not apply when an mppt is employed?
