diy solar

diy solar

From Harbor freight special 12 Volt Off Grid learning system, to new ground up build off grid solar build plan.

Actually I don’t thing I’m not misunderstanding at all. The Nominal wattage from the panels will be 740 W. Minus the resistance of the cabling from the panels to the controller that will deliver approximately 35 A of current at +/-21 V to the charge controller. Charge controller will convert that (~35A @ 21V+\-) into the appropriate trickle charge the batteries depending on their state of charge and temperature. As long as I don’t exceed 120 total panel voltage supply going into the charge controller The charge controller can handle the rest.
I have not looked at the specs for the SCC you mention. However many have a PV input amperage maximum. Since your Voc is 120v I would guess that the controller is MPPT style which basically is going to act as PWM if you go all parallel.

ETA: Pardon me if my replies came off poorly. I was not trying to impugn your thinking about this. It can be easy to miss a specification when looking at components to assemble into a PV system. Every time a conversion is done from one voltage to another the input specs of a device and the output specs for Voltage and amperage change. 10a at 120v is the same power as 100a at 12v. But the amperage of the 12v unit makes for different sizing criteria for components.
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Keep in mind, anytime you put over 2 strings in parallel, you have to fuse that string.
Fusing a 40W panel wastes 5 watts from the connections to the fuse resistance...
Series 3, parallel 3, only 3 fuses...
But you need a real mppt controller.
Okay I see! That’s why series run panels are favored. OK good info to know about fuses in parallel groupings. And Yes I have my heart set on the morning star 120 VOC 60 amp MPPT charge controller.
How do I make sure I don’t exceed the maximum input to the charge controller? Is The maximum input to the charge controller strictly limited by the top end VoC number Number rated for the charge controller or does it matter how many amps the panels are delivering to the solar charge controller as well?
The MPPT effectively provides infinite resistance, i.e. open circuit, at night. When the sun hits the panels in the morning voltage jumps to Voc. If Voc is too high it can fry the MPPT. And Voc increases as it gets colder, so you must be careful.

With infinite resistance, the initial panel current and power is zero. So the startup risk is only from voltage, not current. After startup the MPPT controls current (and power) by decreasing the effective resistance in search of the max power point. Since the MPPT is in control it won't let current exceed the danger point. You can safely "overpanel".

For example, the Midnight unit you mentioned is 700W nominal and can charge a 12V battery at up to 800W. But it allows 1100W of panels. As the datasheet says:

* The PV array power rating may exceed
the controller’s Max Nominal Output
Power specification. The controller will
limit battery current and prevent damage.

As long as you watch your Voc you could probably hook up even more than 1100W. But it's kinda dumb since the MPPT won't let the array produce more than 800W.