3 different solar panels on rv roof

moonlitsouls

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One last helpful tip - if any wire is too hot to touch (while you're using your system) then the wire needs to be bigger or the fuses smaller :)

what do you think about this 150a as the last line of defense fuse? i can run all my positive wires to this , and then it even includes a small cord to run to the battery

there is so many different type of fuses too , ANL , MEGA , Class T , my heads going to explode
 
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OffGridInTheCity

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what do you think about this 150a as the last line of defense fuse? i can run all my positive wires to this , and then it even includes a small cord to run to the battery

there is so many different type of fuses too , ANL , MEGA , Class T , my heads going to explode
If you mean wires -> buss-bar -> fuse -> battery? Then make sure the wire between the buss-bar and the battery is 2awg. The fuse should not be bigger amps than the wire between the fuse and the battery can handle.

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moonlitsouls

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If you mean wires -> buss-bar -> fuse -> battery? Then make sure the wire between the buss-bar and the battery is 2awg. The fuse should not be bigger amps than the wire between the fuse and the battery can handle.

View attachment 67359
thanks for taking the time to draw this , you're really helpful and i appreciate you

i dont understand why we need a busbar between the fuse and the incoming wires , going to do some more research
 

rmaddy

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Assuming 12v, then 1000w/12v = 83a. So 80a or 100a or 120a. Remember that the fuse should not be bigger than the wire can handle - else the wire will melt (start a fire?) before the fuse will blow.

80a fuse = 4awg wire.
This is not the correct approach. You do not pick a fuse size and then determine the wire. Quite the opposite. Based on the needed load you pick a wire size that can safely handle the current and provide the minimum needed voltage drop. Then you choose an appropriate fuse size that is between the load size and the max size safe for the chosen wire.

4AWG wire would be used for 80-100A loads assuming the wire length isn't too long. The max safe fuse size for 4AWG is 150A if it's a single wire not bundled with others or buried in a conduit. These specific numbers are based on the wire and fuse chart from Blue Sea Systems.

So back to the calculation. 1000W / 12V = 83A. For an 83A load you look at the chart and pick 4AWG wire. Then you look at the fuse chart for 4AWG wire and see the max is 150A. So you want a fuse between the 83A minimum and the 150A maximum. Too close to the minimum and you risk annoying nuisance trips. Too close to the maximum and the wire can get too hot to handle (even if it still "safe"). A common choice is 1.25 times the load. 1.25 x 83A = 104A. Round up to the next available size making sure you don't go over the maximum.
 
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moonlitsouls

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@rmaddy
@OffGridInTheCity

hi guys , so ive been doing a lot of learning today

im going to go with the lynxx distributor instead of individual bus bars and fuses , im in the process now of putting together a wiring diagram , a parts list , and im going to create another post to to get help on proper fuse sizes for the Victron Lynx Distributor
 

Bud Martin

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You also need to factor in 15% Inverter efficiency and system lost, so 1000W 12V will draw about 98A of DC current to produce about 1000W of power on the output side of the inverter.
 

rmaddy

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If you mean wires -> buss-bar -> fuse -> battery? Then make sure the wire between the buss-bar and the battery is 2awg. The fuse should not be bigger amps than the wire between the fuse and the battery can handle.

View attachment 67359
You state "The fuse should not be bigger amps than the wire". That is essentially correct. But the diagram shows the opposite approach.

The wires between the battery and bus bar should be sufficient to safely carry the needed loads. The fuse should then be chosen to safely protect the wire. While the statement in the diagram isn't technically wrong it is backwards thinking. Pick the wire for the loads. Then pick the fuse to protect the wire.

I know much of this is a repeat of my previous post but I wanted to address both of these.
 

OffGridInTheCity

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You state "The fuse should not be bigger amps than the wire". That is essentially correct. But the diagram shows the opposite approach.

The wires between the battery and bus bar should be sufficient to safely carry the needed loads. The fuse should then be chosen to safely protect the wire. While the statement in the diagram isn't technically wrong it is backwards thinking. Pick the wire for the loads. Then pick the fuse to protect the wire.

I know much of this is a repeat of my previous post but I wanted to address both of these.
We're in agreement and in this case I think multiple points of view/comments will help them :). They seemingly wanted to 'add a fuse' to the existing wiring and so the main point I was trying to help with - is that you must not add a fuse that's too large for the *existing* wiring and then point out that if you insist on starting with the fuse - you must then go back and make sure the wiring is capable. I agree - its a bit backwards logic.
 

moonlitsouls

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Base case #1 - If you wire them in series using Vmp you'd have: 20.4v + 20.4v + 16.77v + 16.77v + 17v = 91.34v * (lowest amps = 9.45a) = 863w. This would be 863w/940w (max) = 91.8% of the max.

Base case #2 - If you wire them in parallel you'd have: 9.45a + 9.45a + 11.2a + 11.2a + 11.76a = 53.06a * (lowest voltage = 16.77v) = 890w. This would be 890w/940w (max) = 94.7% of the max.

Then there would be combinations - 1st 2 in parallel ----series---> 2nd 2 in parallel ----- series ----> 5th panel - as an example but the rules should apply - e.g. in series the voltages add up but its the lowest amps that rules and in parallel the amps add up but its the lowest voltage that rules.

In base case #1 you'd be at 91.34v against 100v max of the Victron - likely be OK. In base case #2 you'd be just a bit more efficient (in theory) but you exceed 50a max of the Victron at 53.06a. With 5 in series you'd be subject to loss of power on *any* shading - even 2 x 2 inches kind of thing.

Here's a youtube discussing mixing panels of different types I used as the basis for the above - start at 4:42 for different types:

Personally - 92% vs 95% is no big deal because in real life there are a lot of variables with panels including tilt, shade, clouds, heat etc. However, I would think about shading - for example on my trailer I have each side in it's own string so I can have shade down 1/2 the trailer roof from front to back and still have 1 side producing.
How are you? Everything worked out with the series configuration but I want to add a 5th panel , I just updated my original post with a spec sheet of the last panel,

My MPPT will be maxed at 100 volts and I’ll be just over that if I stay with the series configuration

It’s a 100/50 MPPT

What’s the best way to go about this? 3s2p?

There is 10guage wire from the panels to the SCC so im trying to keep that in place

Really appreciate your help
 
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