My solar plan—thoughts please

rmaddy

Full-time Solar-powered Trailer Life
Joined
Nov 16, 2019
Messages
3,424
Location
USA
Okay, so for a new charge controller, I need something that can handle around 30v from the solar. I haven’t researched charge controllers (obviously 🙄) as much as other components, so are there any other specs I should be looking for?
There are two main values to worry about when choosing a solar charge controller (SCC). 1 - the max input voltage and 2 - the max charge current. When you look at Victron charge controllers you will see models such as the 100/20 or the 150/45. The first number is the max input voltage and the second number is the max charge current.

The max input voltage is based on the Voc of the solar panel arrangement. You must NEVER exceed this value. If you put two panels in series you need to support twice the Voc of a single panel. Also note that Voc goes up as the temperature goes down. The Voc can be about 20% higher at -40º.

The charge current is simply the total wattage of your panels divided by the battery voltage. So 200W on a 12V system is about 17A. It's OK if you exceed the max charge current of the SCC. At least within a reasonable amount. Maybe 20%. Any extra potential from the panels will simply be lost.

So think ahead. If you know you will never get more than 200W of solar then you only need to support 17A of charge current. You could actually get a controller that only handles 15A because you'll likely never actually get the full 200W out of the panel. But if you think you might upgrade to 400W then you should get a SCC that can handle 34A (though a 30A controller would be fine). Then you don't need to buy a new SCC just because you want to add a 2nd panel.
 

KateC

New Member
Joined
Dec 25, 2021
Messages
16
There are two main values to worry about when choosing a solar charge controller (SCC). 1 - the max input voltage and 2 - the max charge current. When you look at Victron charge controllers you will see models such as the 100/20 or the 150/45. The first number is the max input voltage and the second number is the max charge current.

The max input voltage is based on the Voc of the solar panel arrangement. You must NEVER exceed this value. If you put two panels in series you need to support twice the Voc of a single panel. Also note that Voc goes up as the temperature goes down. The Voc can be about 20% higher at -40º.

The charge current is simply the total wattage of your panels divided by the battery voltage. So 200W on a 12V system is about 17A. It's OK if you exceed the max charge current of the SCC. At least within a reasonable amount. Maybe 20%. Any extra potential from the panels will simply be lost.

So think ahead. If you know you will never get more than 200W of solar then you only need to support 17A of charge current. You could actually get a controller that only handles 15A because you'll likely never actually get the full 200W out of the panel. But if you think you might upgrade to 400W then you should get a SCC that can handle 34A (though a 30A controller would be fine). Then you don't need to buy a new SCC just because you want to add a 2nd panel.
Perfect. This was so concise. Thank you!
 
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