Ultra budget system 12v passive battery Vs what panels?

[Kbeam]

Hi all. I was looking at this video of our host

I think what he is missing is the solar panel system for such budget setup, so I'm asking here instead:
Is it safe to connect a, say, 40v-max-rated panel to that "dumb" 12v battery? I guess not (if it does not fry the battery, then it may fry the inveri?)...
Or does the charge controller do that stepping down of the voltage? I think they don't do that...
But then that means quite a few 12v panels in parallel, right? I found that on the market the larger and more powerful panels are typically around 30-40v.
Am I missing something?

 

[Rednecktek]

No, you should almost NEVER be connecting the panels straight to the battery. The SCC is there to turn the higher voltage, low amperage 40v DC and convert it to lower voltage higher amperage battery friendly DC. Think of it like this, if you were to take the USB cord for your phone, cut off the head, and fish the bare wires into a wall outlet, how would your phone battery take it? Magical orange smoke.

Most used panels come off of someone's house when they got solar and it's cheap enough to replace them, so the higher voltages are perfectly normal. That's what the MPPT controller is for.

As a rule of thumb, for a 12v system you'll want 10a of SCC per 100w of solar panel. So, if you had a 400w panel you'd want a 40a SCC for your 12v setup.

 

[Kbeam]

Got it! I thought those Victron solar converters have similar (almost no) functionality to those 8 USD solar "convertors".
But it seems that those actually step down the voltage. Great!

 

[Rednecktek]

You're thinking of MPPT and PWM. The MPPT are DC-DC converters that take high voltage and low amperage and convert them to low voltage high amperage. So if you had a 100w panel that does 50v @ 2a, that's 100w. The MPPT will convert that to 14v @ 7a into the battery.

On the other hand, the 8 dollar PWM controllers are basically just a fast switch that cuts off any voltage above the battery, so your same panel would send 50v @ 2a to the PWM, but the PWM would just cut off any voltage above 14 and send 14v @ 2a to the battery, or 28w, a 70% nerf in your power! EEK!

Fortunately there are many, many brands of MPPT controller that will convert the power over, you don't have to use Blue.

 

[pollenface]

A friend of mine connected panels straight to the batteries. All his batteries died very quickly