24 volt to 12 volt converter
Looking to run 600 watts of solar to my 40 amp MTTP controller at 36 volts. I have 4-6 volt batteries. So I need to get my 24 volt battery bank down to 12 volts to my Magnum 2012 inverter charger. ...
Forum Discussion
"now, your 40 A controller is too small for a 12 V system unless you intend to throw those watts away.. 40A*12V=480W and you waste 120W ! not an ideal situation"
I am not understanding this at all. I posted earlier how his 600w array would work out.
The big thing is that the over-panelling in the morning is an advantage, because the sun is not high enough yet to get the full wattage anyway. By the time you get to mid-day high sun, battery voltage is up, and amps are down to what the controller can do, so his 40 amp controller is just fine IMO.
Repeated:
"Your output amps come from the output watts. You divide the output watts by the battery voltage to get your amps.
... Your 600w array might be putting out 540w on a nice day. ( You lose about 10% due to panel heating in the sun--those panels get hot.) You lose another percent or two on the wires going to the controller's input. So input watts might be 540 -11 = 529w
So you have 529w on the input with the controller doing say 30v at Vmp ( example) so the input amps is 529/30 = 17.6a. (wire gauge for that) The controller efficiency is say 96%, so output watts is 508w.
Now your batteries are starting in the morning at say 12.5v, so they will get 508/12.5 = 40.6 amps --wire gauge for that-- (but the controller rated at 40 will keep the amps at 40, not letting the amps get higher.)
Later after the batteries are recharged some, their voltage is now 13.5v rising, so amps now (assuming same watts--actually with higher sun at noon watts might be higher--depends if panels are flat or aimed at sun all day) anyway 508/13.5 = 37.6a
As battery voltage rises, amps go down with the same watts.
With the 600w you are slightly "over-panelled" for that 40a controller, but that is a good thing for your over-all daily AH haul since you will get to use all the array can do earlier and later in the day when the sun is lower."
I am not understanding this at all. I posted earlier how his 600w array would work out.
The big thing is that the over-panelling in the morning is an advantage, because the sun is not high enough yet to get the full wattage anyway. By the time you get to mid-day high sun, battery voltage is up, and amps are down to what the controller can do, so his 40 amp controller is just fine IMO.
Repeated:
"Your output amps come from the output watts. You divide the output watts by the battery voltage to get your amps.
... Your 600w array might be putting out 540w on a nice day. ( You lose about 10% due to panel heating in the sun--those panels get hot.) You lose another percent or two on the wires going to the controller's input. So input watts might be 540 -11 = 529w
So you have 529w on the input with the controller doing say 30v at Vmp ( example) so the input amps is 529/30 = 17.6a. (wire gauge for that) The controller efficiency is say 96%, so output watts is 508w.
Now your batteries are starting in the morning at say 12.5v, so they will get 508/12.5 = 40.6 amps --wire gauge for that-- (but the controller rated at 40 will keep the amps at 40, not letting the amps get higher.)
Later after the batteries are recharged some, their voltage is now 13.5v rising, so amps now (assuming same watts--actually with higher sun at noon watts might be higher--depends if panels are flat or aimed at sun all day) anyway 508/13.5 = 37.6a
As battery voltage rises, amps go down with the same watts.
With the 600w you are slightly "over-panelled" for that 40a controller, but that is a good thing for your over-all daily AH haul since you will get to use all the array can do earlier and later in the day when the sun is lower."
