Off-Grid Van Solar System Design Questions

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Old 12-29-17, 11:02 PM
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Off-Grid Van Solar System Design Questions

I'm trying to plan my system. I'm trying to design something with nice components and do not wish to cut any corners. I'm finding a lot of examples but often the explanations are lacking.

I have a few questions about the diagram for a similar system that I'm looking at (image linked below).

First, they put a battery cutoff switch between their battery and inverter. I'm not opposed to doing this but I'm trying to understand what this adds. Isn't the power switch on the inverter a battery cutoff switch? Wouldn't an additional switch just be redundant?

They also put a switch between the charge controller and the battery. What could this be for? To be able to remove the battery without current from the charge controller terminals? This doesn't make sense to me because you are not supposed to have most controllers wired to PV panels without a battery, therefore there should be no charge when disconnecting anyway because the PV panels should be disconnected first.

Will you please explain these switches to me!?!

I'm not opposed to installing them but I don't want to put in unnecessary parts that could increase resistance or add unimportant additional points of failure.

https://gnomadhome.com/wp-content/up...am-correct.png
 
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Old 12-30-17, 12:01 AM
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Will you please explain these switches to me!?!
Keep in mind that the people who posted this diagram are self-admitted novices when it comes to all things electrical. I was mildly curious about the potential exploding charge controller so I located the blog post containing this diagram and read through it to see what they had to say.

They also put a switch between the charge controller and the battery. What could this be for?
Highly technical reason they gave: "This will let us kill the connection the battery if we ever need to."

If what they say about the charge controller exploding is true, then perhaps a DPST switch or some kind of interlock would be better, so the panels are disconnected at the same time as the battery is disconnected.

they put a battery cutoff switch between their battery and inverter
Similar reason given for this one: "so that we can cut the power to the inverter if needed."

If the inverter has a soft on/off button rather than a real switch, then I can see a reason for this. You might need to hard reboot the inverter if it gets confused. Or perhaps the inverter isn't easily physically accessible. I know sometimes companies sell remote switches for inverters, but perhaps this one doesn't have one available.

In either case, I wouldn't fret over tiny details such as this. It's whatever you want to do. You've already pointed out the danger of running the charge controller with panels connected but with the battery cut out, so you've thought it through better than they did.
 
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Old 12-30-17, 12:22 AM
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If what they say about the charge controller exploding is true, then perhaps a DPST switch or some kind of interlock would be better, so the panels are disconnected at the same time as the battery is disconnected.
Right after I posted this I was thinking, if a switch makes sense anywhere, maybe it is between the panels and the controller so that the battery(s) might be disconnected without unwiring the PV panels from the controller.
 
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Old 12-30-17, 05:07 AM
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The two switches appear to me so you can isolate the batteries or the inverter if they ever need to be replaced or serviced.

I think adding a disconnect switch between the PV panels and the controller is a good idea. This is required now for PV building installations in case of a electrical fire so power from the panels can be disconnected.
 
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