Adding Second Solar Panel Questions

[penra]

I have an existing solar panel which I can plug the new one into but have some questions.
What sealant should I use to cover the screw holes? Dicor self-leveling? Any tips on installing it?
The wiring says "do not disconnect under load", how do I remove the load before I disconnect?
The new panel will be on the other side of the roof, should I cover the wires across the roof with sealant to keep them down? Cover completely or every 8 inches or so?

[Hblick48]

When I installed my second panel, I got two "Y" connectors. They enabled me to plug both panels into the existing leads to the charge controller: https://www.renogy.com/mc4-parallel-...-mmf-ffm-pair/

When connecting panels to the charge controller, first connect the batteries, and then the panels. When disconnecting, reverse the procedure and disconnect panels first, and then batteries.

I have always used Dicor self leveling.

[penra]

Originally Posted by Hblick48

When I installed my second panel, I got two "Y" connectors. They enabled me to plug both panels into the existing leads to the charge controller: https://www.renogy.com/mc4-parallel-...-mmf-ffm-pair/

When connecting panels to the charge controller, first connect the batteries, and then the panels. When disconnecting, reverse the procedure and disconnect panels first, and then batteries.

I have always used Dicor self leveling.

Thanks.
So disconnect the trailer batteries and then disconnect the solar panels?

[Hblick48]

Disconnect panels, then disconnect batteries. Perhaps turn off charge controller first so there won't be any load on the panels.

[PNW Fireguy]

This is a very good example as to why a disconnect should be installed between the PV array and the charger. It allows you to isolate the array should you need to work on it. No need to disconnect batteries. Also prevents any backfeed from a poorly designed charge controller.

[penra]

Originally Posted by PNW Fireguy

This is a very good example as to why a disconnect should be installed between the PV array and the charger. It allows you to isolate the array should you need to work on it. No need to disconnect batteries. Also prevents any backfeed from a poorly designed charge controller.

I could install a cutoff I guess, great suggestion.

When it comes to finding the roof rafters to screw the panels into, do you just use a normal stud finder? I was going to try to place it directly opposite of the existing panel.

thanks!

[PNW Fireguy]

Most folks simply screw into the roof sheeting. I think it would be pure luck if the panels lined up with the rafters/stringers. The sheeing with proper screws (length, size and type) has been strong enough for me and I have residential panels installed. I have been in high wind areas like the Q and the Badlands with no problems.

[jetskier]

I unplug the panels on the roof and leave the batteries connected. If it's full sun, I cover the panels first so they aren't producing a lot of power or do it when there's low sun angle as to not surge the controller.



You can see the joints in the plywood through the rubber roof. I found it wasn't always a clean 16"o.c. from the joints to the trusses. I found a bay @ 21" when I moved a roof vent on this new rig! If you don't over tighten the mounting screws, try to anchor the trusses on the front of the panel and ,if you are forced to, into the roof sheathing only on the back. The roof sheathing is 3/8" OSB. That provides enough hold down resistance when traveling since the front can't lift as easy. For some reason, the mounting hardware for the panels doesn't conform to the wood framing world. The lap sealant locks and seals everything down fairly well. I've never had an issue doing it this way on any of the installs I've done for myself or others.

[penra]

Originally Posted by jetskier

I unplug the panels on the roof and leave the batteries connected. If it's full sun, I cover the panels first so they aren't producing a lot of power or do it when there's low sun angle as to not surge the controller.



You can see the joints in the plywood through the rubber roof. I found it wasn't always a clean 16"o.c. from the joints to the trusses. I found a bay @ 21" when I moved a roof vent on this new rig! If you don't over tighten the mounting screws, try to anchor the trusses on the front of the panel and ,if you are forced to, into the roof sheathing only on the back. The roof sheathing is 3/8" OSB. That provides enough hold down resistance when traveling since the front can't lift as easy. For some reason, the mounting hardware for the panels doesn't conform to the wood framing world. The lap sealant locks and seals everything down fairly well. I've never had an issue doing it this way on any of the installs I've done for myself or others.

Thanks! Exactly what I was looking for.

[Greg n Tracy]

So, when do you reach the point of "overloading" the existing preinstalled wiring that goes to the charge controller? In other words, how many watts can you send thru the preinstalled solar set-up?

2019 Montana Legacy 3130RE
2016 F350 6.7 DRW

[jetskier]

Originally Posted by Greg n Tracy

So, when do you reach the point of "overloading" the existing preinstalled wiring that goes to the charge controller? In other words, how many watts can you send thru the preinstalled solar set-up?

around 360W-400W. That's based on 12-13.4V * 30A on the output of the controller.

[66 Galaxie]

Originally Posted by Greg n Tracy

So, when do you reach the point of "overloading" the existing preinstalled wiring that goes to the charge controller? In other words, how many watts can you send thru the preinstalled solar set-up?

2019 Montana Legacy 3130RE
2016 F350 6.7 DRW

The wire is 10 awg and rated for 30 amps DC from the panel to the battery bank.

Amps x Volts = Watts.
30a x 12v = 360w.
30a x 45v = 1350w.

PWM chargers are usually good to 25v on the panel side and MPPT chargers can go above 100v. If you go higher than a 30 amp charger you'll need to change the wiring and fuse from the charger to the battery but not necessarily the wiring from the panel to the charger.

[Charlie W]

Go buy you some 1/4" self tapping wood screws, I got mine from Ace hardware. do not use the self tapping metal screws. Put a battery cutoff to your panels and a fuse.
Also depending on your charge controller if it will handle it I would hook the panels in series. To kick up the voltage. But that depends on if your charge controller will handle the voltage and if it's an MPPT controller. MY 2¢

[PNW Fireguy]

Without getting too far in the weeds here the basic formula provided earlier is correct to convert watts to amps. Your overcurrent device is to protect the wire not the charge controller. How the panels are installed is another factor to consider. If the panel is installed in parallel with the existing panel then the current of the additional panel is additive to the original existing panel. If the panel is connected in series with the existing panel then the rated current is common in the circuit. The temperature on the roof (which can be significantly higher than ambient temp) is indirectly proportional to the current the PV wires will carry due to the direct relationship between temperature and resistance. Now from a practical standpoint it may be best to fuse the panel wiring and use a disconnect to isolate the charge controller on the input side. A second overcurrent device on the output sized to protect the size and type of wire that will carry the rated output current of your charge controller.


The OEM PV wire is 10AWG. 10AWG wire unless specifically allowed for in specialty sections of the NEC is not to carry more than 30A. However your panels are installed the calculated current is limited to 30A. As mentioned connecting the new panel in series will raise the output voltage and thereby reduce the output current from the PV array.