Solar voltage drop calculations, new question
Using a calculator: I like this one When figuring wire size from panels to controller for "12v" panels in parallel and PWM controller, we should use 20v as our input, right??? I see writeups wher...
Forum Discussion
It is not really the voltage drop itself that matters as a chunk out of the voltage, but what happens to the current you want to get through the battery as battery voltage goes from 13 to 14.8.
The voltage you use is the compromise voltage between the battery and panel when connected as they try to "middle" their voltages. You have the R of the wire which is fixed. V=IR so with voltage held and R fixed it is all down to current how much voltage drop there is. More I, more drop.
At first you have say your 0.5v drop with 13 at battery and 13.5 at panel. With the current through the battery, chemical reaction, battery voltage rises. As battery nears full current acceptance drops so I is less, so voltage drop is less, say 0.25 now and battery is 14.5 and panel is 14.75.
Meanwhile the diff between battery v and panel v is less than before so current is less from that too at some point.
Meanwhile the panel's own current output gets less as seen in that IV curve as battery voltage rises.
You are trying to pick a wire R that is low enough to keep I going as V rises within that range 13-15 volts where I=V/R
Now also this is solar, so you need enough I to get it done before dark too. Lower R helps keep I up and keep the battery chemical reaction going to raise its V sooner
The voltage you use is the compromise voltage between the battery and panel when connected as they try to "middle" their voltages. You have the R of the wire which is fixed. V=IR so with voltage held and R fixed it is all down to current how much voltage drop there is. More I, more drop.
At first you have say your 0.5v drop with 13 at battery and 13.5 at panel. With the current through the battery, chemical reaction, battery voltage rises. As battery nears full current acceptance drops so I is less, so voltage drop is less, say 0.25 now and battery is 14.5 and panel is 14.75.
Meanwhile the diff between battery v and panel v is less than before so current is less from that too at some point.
Meanwhile the panel's own current output gets less as seen in that IV curve as battery voltage rises.
You are trying to pick a wire R that is low enough to keep I going as V rises within that range 13-15 volts where I=V/R
Now also this is solar, so you need enough I to get it done before dark too. Lower R helps keep I up and keep the battery chemical reaction going to raise its V sooner
