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Branch Connector Location?

DenverGuy

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Apr 18, 2021
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I now have four PVs on my garage roof and am going to wire them up today in parallel. (I had one PV in place already with two batteries. I now have four batteries, so the one 100W panel is doing all the heavy lifting.)

As the one PV was already in place with its own hole, we drilled another hole for the three new panels.

I have read that the MC4 connectors are weatherproof. But how about the branch connectors? Should I run the wires into the garage and attach the branch connectors there, or should it be done on the roof?
 
I'll put 'em in series. Should the branch connectors go inside or outside?
 
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I'll put 'em in series. Should the branch connectors go inside or outside?
All in series you need to make sure the temp adjust Voc (x4 if all in series) is 15-20% what your SCC max input voltage is. Usually 2 in series, then commented in parallel neat the panels is easiest. This requires 1 pair of Y connectors.
 
To answer your question...they are listed as weather tight connections. So basically they can get rain on them but should not be submerged in water.
 
MC-4 and branch connectors have various ratings IP65= don't get wet, IP68= good and waterproof. Allowing water to run down a wire to any connector is a bad idea, almost as bad as allowing them to sit in water. Given a choice, I say bring them inside.
On my ground mount array I eliminated the connectors altogether by wiring directly into the Junction box. Probably wouldn't be much fun for you.
 
If shading is a big factor, inline fuses will run you $14 each or less Delivered to your door. You’ll need 4.

If this is a roof just big enough for panels with anything shading, parallel 4p could be better. IMO, RV roofs should be in parallel as much as possible because of antennas, vents, and hoods.

You also want to be sure not to exceed 30 amps, the limit for MC4. So, 4 panels 100 watts each is fine, around 26 amps, but can’t add another string nor upgrade down the road to 120 watt or bigger panels

If shading is not a factor, the more in series the better up to the point where the voltage exceeds the SCC limits, to include calculating for cold.
 
If shading is a big factor, inline fuses will run you $14 each or less Delivered to your door. You’ll need 4.

If this is a roof just big enough for panels with anything shading, parallel 4p could be better. IMO, RV roofs should be in parallel as much as possible because of antennas, vents, and hoods.

You also want to be sure not to exceed 30 amps, the limit for MC4. So, 4 panels 100 watts each is fine, around 26 amps, but can’t add another string nor upgrade down the road to 120 watt or bigger panels

If shading is not a factor, the more in series the better up to the point where the voltage exceeds the SCC limits, to include calculating for cold.
I switched from a PWM controller to MPPT. Will I see any advantages in parallel? Thanks.
 
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i switched from a PWM controller to MPPT. Will I see any advantages in parallel? Thanks.
That’s about it. Another disadvantage could be voltage loss in parallel panels. All depends on how long it is.
 
No real advantage, then? I thought they were more efficient in general.
Same power output in parallel or series after taking into account voltage loss and shading.

If the roof is shaded from an antenna or tree parallel is probably better. Otherwise series will cut down on voltage loss. The math needs to be done to be sure.
 
This is a really sunny roof with no trees. None of the wires are longer than 7 feet. It might be a toss-up. I just thought the MPPT units were higher efficiency.
 
This is a really sunny roof with no trees. None of the wires are longer than 7 feet. It might be a toss-up. I just thought the MPPT units were higher efficiency.
I am pretty sure they are more efficient. The side by side comparisons I have seen show that in the data. Nope, I won't be searching for the data.
 
I am pretty sure they are more efficient. The side by side comparisons I have seen show that in the data. Nope, I won't be searching for the data.
I remember looking that up before. It was not so much that the panels were in series or parallel but the input to the SCC from the panel voltage was at the proper ratio to the charge voltage to reach peak efficiency. Input voltage really depends on how much each individual panel puts out and then how many are in series with clouds etc…

I found it in the Victron manual for an SCC. There was a sweet spot for charging voltage versus input voltage on the MPPT. The sweet spot was panel voltage about twice the charging voltage. I remember the difference on the graph being about 10%.

I consider that 10% fairly insignificant. About 6 minutes extra per hour to charge something.

Others may need that 10%.

I also remember more in series allows me to get some production on cloudy days. I have one set of panels that normally provides 40 volts to charge at 27.6 volts and my SCC needs 32 volts in to charge. So when it’s cloudy, that set may not get enough volts to charge. Even if the panels are charging on cloudy days, it’s not a lot, but likely enough to keep me from turning a generator on.

I guess there are a couple more advantages to series panels.
 
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