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Old 01-22-2020, 10:59 PM   #1
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Join Date: Dec 2017
Location: Frisco, Texas
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Year: 1998
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Chassis: International 3800
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Need help with fuse / circuit breaker sizing

I've got most of my solar and electrical setup all hooked up, and I'll be finishing it this weekend once I get the proper fuses / breakers and make the last connections. This part gets confusing pretty easily so I was hoping somebody might be able to help me figure out what I need for my setup.

Here's what I got.
4x 245 watt solar panels. 2 in series, 2 in series, then paralleled together. (imp: Current at Max Power (7.6A))
40A mppt charge controller
9x nissan leaf battery modules (3 groups of 3 in series for 24v, wired in parallel for 24v battery bank)
24v 3000w inverter / charger
24 volt to 12 volt converter
30A shore plug
6 bay load center
24volt LED lights
12volt roof vent/fan
12volt water pump

I know I'll need a 30A breaker between shore power and inverter/charger
I have my breakers in the load center already wired up (20a and 15a, depending on circuit, not all of them being used but may add later)
I'll have a 12v fuse box for those 2 loads
Planned on wiring 24v LED right to the batteries with a small fuse (switches inline up front) as it's my only thing needing 24v, but I'm not sure if I should just wire those to the output of the charge controller


What i need help figuring out is the proper size fuses/breakers to put in between -
solar panels - charge controller (20A circuit breaker with disconnect option?)
charge controller - battery bank (unsure)
inverter / charger - load center (unsure)
battery bank - inverter charger (charging output current of inv/ch is 50a, so 60amp fuse/breaker?
battery bank - 24v/12v converter (converter is rated 40A, so i assumed 40a fuse/breaker)


Also, am I missing anything or is that everything I'll need?
attached is a rough sketch of my setup, and the couple pictures i took of some of the stuff

in advance. Any help is much appreciated.
Attached Images
File Type: jpg 20200122_164046.jpg (135.1 KB, 9 views)
File Type: jpg 20200120_000604.jpg (277.1 KB, 9 views)
File Type: jpg 20200120_202008.jpg (287.8 KB, 7 views)

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Old 03-06-2020, 09:37 PM   #2
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As a general rule of thumb size your fuses to protect your wiring, and aim for roughly =>125% of the device/circuit max load.


The manuals for your components will often give a fuse recommendation, look there first.



Once you understand the theory of fuses/protection devices, its easier to figure out the specifics.


This thread, these links, and this video is a good place to start
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Old 03-06-2020, 10:00 PM   #3
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As for specifics (with the caveat that I'm still learning too, and that my advice should be take with a grain of salt or two, and that the recommendations in your manuals are better than any advice you'll get on the internet):



solar panels - charge controller - There is disagreement on how useful a fuse is here, but a breaker or switch is advisable.

charge controller - battery bank - Check your controller documentation, for a 40a controller a 50-60a breaker sounds about right
inverter / charger - load center - Check your documentation
battery bank - inverter charger (charging output current of inv/ch is 50a, so 60amp fuse/breaker? - check your inverter/charger documentation. I suspect you would need a much larger breaker, 60-75a would work for the 50a charger but what about the inverter? My guess is that the inverter draws at least 80a maybe upto 160. Best bet here is to read the manual and follow manufacturer recommendations.
battery bank - 24v/12v converter (converter is rated 40A, so i assumed 40a fuse/breaker) - 40a fuse would be okay as long as you don't intend to ever use all 40a (which is probably smart).
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Old 03-07-2020, 07:18 AM   #4
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