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
You got yer IV curve for the panel. On it you find a point near the "knee" that when at that voltage ( Vmp) the panel is at max watts. That point is known as the Max Power Point. Whatever the amps turn out to be at that watts and that voltage is a by product sort of, called Imp.
The buck converter doesn't care about input amps. It only knows the input watts and voltage. The output voltage being lower with the same watts makes for higher amps in the output. The amps you get is sort of accidental by-product. So my 230w panel rated at 8.3a Isc (less for Imp) will do 15 amps as output from the controller's buck converter with the battery in the high 12s. If battery voltage is higher amps are lower.
Meanwhile with a 12v panel and a PWM controller, you get Isc as its output passed through the controller which does not start controlling until Vabs. (the CV set on the buck, down from the panel's voltage of something higher.)
In this case Vmp and Imp are totally meaningless. Only apply to MPPT.
You go out and disconnect the 12v panel and measure Isc. Say it is 7 amps at the moment (it changes all the time) now connect up and you should get 7 amps to the thirsty battery.
With a 24v panel you go out there and measure Isc (panel disconnected) and you get say 7 amps or whatever. But now connect up and with the big intake buck the controller has, you get say 14 amps to the thirsty battery out of the same watts with the lower voltage.
The charging amps you get is entirely accidental by-product of what watts divided by voltage happens to be at the output of the buck converter. The watts is a bit less than the watts at the intake.
This is where I get lost. The watts intake at the buck converter is a bit less than what the panel COULD do but is actually only what is "demanded" which could be a lot less than what the panel could do.
I cannot grasp how the increased load demand on the buck converter makes it do more amps with the same voltage so its watts must be more. It has to get those watts from the input, which must get them from the solar panel. That means you open up a greater potential difference. except that is volts talk , not watts talk? Increasing the load does make the voltage drop (loaded voltage) so that would widen the spread.
You are not setting the buck converter. Its output voltage is whatever the load's voltage is. Somehow that works back through the buck converter to the panel and makes its output go up if the load increases. There are wattage limits but everything seems to be a bunch of moving goal posts; drives me crazy :(
The buck converter doesn't care about input amps. It only knows the input watts and voltage. The output voltage being lower with the same watts makes for higher amps in the output. The amps you get is sort of accidental by-product. So my 230w panel rated at 8.3a Isc (less for Imp) will do 15 amps as output from the controller's buck converter with the battery in the high 12s. If battery voltage is higher amps are lower.
Meanwhile with a 12v panel and a PWM controller, you get Isc as its output passed through the controller which does not start controlling until Vabs. (the CV set on the buck, down from the panel's voltage of something higher.)
In this case Vmp and Imp are totally meaningless. Only apply to MPPT.
You go out and disconnect the 12v panel and measure Isc. Say it is 7 amps at the moment (it changes all the time) now connect up and you should get 7 amps to the thirsty battery.
With a 24v panel you go out there and measure Isc (panel disconnected) and you get say 7 amps or whatever. But now connect up and with the big intake buck the controller has, you get say 14 amps to the thirsty battery out of the same watts with the lower voltage.
The charging amps you get is entirely accidental by-product of what watts divided by voltage happens to be at the output of the buck converter. The watts is a bit less than the watts at the intake.
This is where I get lost. The watts intake at the buck converter is a bit less than what the panel COULD do but is actually only what is "demanded" which could be a lot less than what the panel could do.
I cannot grasp how the increased load demand on the buck converter makes it do more amps with the same voltage so its watts must be more. It has to get those watts from the input, which must get them from the solar panel. That means you open up a greater potential difference. except that is volts talk , not watts talk? Increasing the load does make the voltage drop (loaded voltage) so that would widen the spread.
You are not setting the buck converter. Its output voltage is whatever the load's voltage is. Somehow that works back through the buck converter to the panel and makes its output go up if the load increases. There are wattage limits but everything seems to be a bunch of moving goal posts; drives me crazy :(
