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rickp avatar image
rickp asked

Warning: Solar Newbie question... Fuses/Breakers/cable for my system

I am building a solar/battery portable system for emergency use. It is based on 4 Battle Born 12V batteries, in series pairs and parallel for 24V, 200AH total. I am using a Multiplus 24/3000/70 Inverter Charger and a 150/85tr Solar Controller (This is being upgraded to a 250/100, due to your comments. Thank you!). I will also be using a Victron 24/12/40 step down converter for 12V loads, which I expect to be few but thought I should account for, nonetheless.

I need to protect the systems with fuses or breakers, but am having a time determining the proper amp ratings, and exactly where to place them. Diagrams I have read don't agree, so I am guessing there are many ways to do this.

Can someone help, or provide a reference to information that would shed a little light on this subject? I am not totally new to electricity, but am new to solar powered systems and am not ashamed to ask for help when I need it. I'm not going to connect a wire until I know what I am doing!

Thank you in advance...


UPDATE:

I am including a diagram I did today showing the items I have (except the breaker on the Pos battery line, that one is a guess), and how I envision them to be connected. I have a feeling more fuses or breakers are required, and I am totally open to comment or suggestion on cable sizes or other needed additions or changes.

UPDATE 5/27:

Drawing updated to show upgrade to Solar charge Controller, per comments. Also added a slight upgrade in 24-12 converter capacity (40 to 70).

System Drawing V4 5-27-2020.pdf

fuses
system-drawing-v4-5-27-2020.pdf (449.2 KiB)
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klim8skeptic avatar image klim8skeptic ♦ commented ·

Wire your panels 2 series x 2 parallel.

Renogy panel

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rickp avatar image rickp klim8skeptic ♦ commented ·

Thanks for the input. Can you help me understand the advantages of this, or the dangers of them being in series as shown?


EDIT: I see the problem. I’m going to up the solar controller to the next level. Drawing has been updated. Thanks!

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Kevin Windrem avatar image Kevin Windrem rickp commented ·

4 panels in series will exceed the maximum input voltage for the 150/85 MPPT controller

As temperature goes down, open circuit voltage goes up. Any voltage above spec will destroy the MPPT whether or not you are drawing power from the panels!

Check out the calculator at:

https://www.victronenergy.com/mppt-calculator

Use -0.5%/C for the voltage temperature coefficient and set your expected minimum temperature.

Series vs parallel is a huge topic. The design of the panel affects how it will perform under shading of one or more panels or of a part of one panel. The best way to know for sure is to try the system in various series/parallel configurations shading entire panels, one cell, rows and columns of cells.

The cost of a 250 volt MPPT is about double the one in your diagram so 2 panels in series then those strings in series is the best you could do with the controller and panels you have called out.

A lot depends on your possible expansion plans. Again, the calculator referenced above will allow you to quickly try different series/parallel combinations.

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rickp avatar image rickp Kevin Windrem commented ·

Thats great information. I was looking at the wrong voltage line, and didn’t realize it. The charge controller has not shipped yet, so I am raising it to the 250/100. Buy once, cry once...

Drawing updated.

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2 Answers
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michaelvausr answered ·

Hi Rick, can you also tell how long your cables have to be? The fuse and the cable type depend on that

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rickp avatar image rickp commented ·

Yes, thanks. The entire system (except panels, of course) will be in the same location... one moveable enclosure. I can't imagine a single run over 3 feet on any connection.

Thank you!

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rickp avatar image
rickp answered ·

The last of the items will arrive next week. I’ll let y’all know how it comes out. I’m excited for the possibilities.

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