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MPP solar fuse question

tfish86

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Dec 21, 2021
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I bought the MPP solar all in one unit for my vintage camper. It is 12 volt with 1000 watt inverter. I am in the process of connecting 200 watts of solar panels but know I will need at least 500watts given of PV given the high idle draw.

I am new to this but having read posts and read his book, I am still having trouble with the fuse and wire gauge. A few questions:

1) If the max amp draw from the unit is 109amps, would I use a 150 amp bolt on fuse and a 4 AWG wire to connect the battery to the MPP unit? Currently I have 6 gauge wire and no fuse b/c that's the impression I got from Will's video.

2) If I want to add a fuse box in this system coming of my 12 volt SOK 200ah battery for dc appliances, do I need a fuse in the wire between the + battery terminal and the fuse box?

Thanks for the help.
 
1) If the max amp draw from the unit is 109amps, would I use a 150 amp bolt on fuse and a 4 AWG wire to connect the battery to the MPP unit? Currently I have 6 gauge wire and no fuse b/c that's the impression I got from Will's video.
Let's do some math.

First, most of the 1000W inverters are not very efficient, so let's assume an 85% efficiency. To put out 1000W, the inverter will draw
1000W/.85=1176.5W. When the battery is low, the current will be as high as 1176.5/12=98A. However, if the manual says 109A, we should use the higher number.

The smallest fuse for the inverter would be 109 x 1.25 = 136A. Depending on what type of fuse, you might be able to find a 140A fuse, but lets use the 150A that you proposed. (The fuse should be mounted as close to the battery as possible) That means the wire needs to be able to handle at least 150A. I always use the 105deg rated marine wire so we can look up the wire gauge in a table for that type of wire.

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So yes, 4AWG Marine grade wire will work.

2) If I want to add a fuse box in this system coming of my 12 volt SOK 200ah battery for dc appliances, do I need a fuse in the wire between the + battery terminal and the fuse box?
I would recommend that.
 
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