On/Off switch to disconnect the solar panels from the battery

[john61ct]

If you want to isolate the target bank from the controller, most need to disconnect the panels first.

Yes covering them will work, but not as reliable as a switch.

If disconnecting wires is easy, then no need at all.

CP should be sized to protect the wiring, near the source. So if your SC install says put CP between panels and SC (rare) then a breaker can also act as a switch.

There are also switches like Blue Sea Dual Circuit that will control both sides of the SC with one throw, elegant solution if overkill.

I personally would want to check on the bank at least monthly in storage.

[mikeo16]

Good discussion here - thanks everyone for their input.
SMAC999 - thanks for calling out the need for a smaller fuse - I will add a 20 Amp just after the Positive Bus where the 10AWG wire begins and goes towards the solar controller to ensure I am fusing to protect the 10 AWG wire

[mvmojo]

For safety purposes, you "need" a switch between the panels and the controller due to the danger inherent in DC voltages greater than 30 volts. And, you "want" a switch between the controller and your batteries to protect the solar controller electronics.

Here's the explanation: The microprocessor(s), display, and sophisticated power control electronics in all decent solar controllers are powered by your batteries, not by the solar panels. Because of this, you should connect your batteries to your solar controller to power it up before connecting your solar panels. This allows the controller to run its internal diagnostics and configure itself for your panels before it has to handle the power from the panels. The same thing applies when disconnecting panels. You want to disconnect them first, while the controller is still powered up by your batteries, then shut down the controller by disconnecting it from the batteries.

So, in summary, the switch between the controller and the batteries should be FOLO, i.e., First On, Last Off. And the switch between the controller and the solar panels should be LOFO, Last On, First Off. This insures an orderly start up and shut down of the controller to prevent damage to its electronics.

I use breakers for both switches on my setup which is 1,000 watts of panels, an 80 amp Midnight Solar MPPT controller and 1050 a/h battery bank. The schematic in post #6 is the correct way to wire everything up!

[Paul L]

Originally Posted by smac999

not entirely true. wiring must handle max current of all sources. once you get into multi panel arrays capable of over 30a total. each panel must have it's own fuse / breaker. otherwise a shorted cable in one panel, will draw the current from all other panels as well

IE five 200w panels in parallel each with 10awg wire going to a 100a controller and 125a fuse at battery with 4awg.

one of the 10awg panel wire shorts. 800w of panels feed that shorted 10awg. the 125a will not blow, your roof is now on fire.

My parallel panels use a single heavy gauge wire for the run from below deck to the controller. I don't see putting a fuse near the controller on that wire being useful.
Even with seperate 10awg runs, the wires are rated at over the max 60amps in your example.

[artisanmach]

I installed battery disconnect between panels and mppt controller it's worked well for me

[mvmojo]

Originally Posted by artisanmach

I installed battery disconnect between panels and mppt controller it's worked well for me

That's a better arrangement than just having a disconnect between the mppt controller and your batteries, but, that's not a battery disconnect... it's a solar panel array disconnect. Your solar controller is still powered up by your batteries, and still drawing current from your batteries even though your panels are disconnected. If you want to completely shut down your controller, you have to either disconnect the battery wires from the controller or disconnect from the batteries. A switch between the controller and the batteries is easier than having to disconnect wires. Not absolutely necessary, but more convenient for sure.

[thinwater]

Just remember that covering the panels is the only way to energizer all of the wires.

And battery leads, of course. I'm a little shocked by how many folks (not just on this forum) think you don't need fuses if an item is small. The major power source and the limiting factor in amperage is the battery!

[john61ct]

Originally Posted by thinwater

Just remember that covering the panels is the only way to energizer all of the wires.

Sorry that is not meaningful, typo or poor translation into English?

> And battery leads, of course. I'm a little shocked by how many folks (not just on this forum) think you don't need fuses if an item is small. The major power source and the limiting factor in amperage is the battery.

No one has said CP is not required at the battery side.

The issue here was the CP being sized too large for the wire it's supposed to protect.

[john61ct]

Originally Posted by mvmojo

that's not a battery disconnect...

I read it as "battery disconnect" meaning the category, type of switch hardware.

As opposed to something less robust.

[Emouchet]

It is good practice to disconnect the batteries during winter AFTER they have had a full charge. Especially if say you have 2 or more batteries in parallel.

Personal experience: one winter, I left the 3 batteries together in parallel and connected to the solar controller. One cell in one battery died during winter. The rest of the winter, the good batteries discharged at night into the faulty battery, and got partially recharged during the day by solar (not enough day light to top them every day). Eventually, after so many PSOC cycles, all batteries died and had to be replaced by spring time.

[Pelagic]

This thread frustratingly demonstrates the differences between professional electricians about the installation of Solar.

Switch / No Switch. Fuse/No Breaker

In confusion I asked a professional solar installer how he would wire my 4 Sunpower panels.

His calculations and recommendation were for 2 breakers like these (for both pos and neg wires)


pv is 327wp x 4 = 1308watts

vmp - 54.7 vdc.***** voc - 64.9vdv
imp - 5.98a************ isc - 6.46a
@ parallel Connection 54.7@ 25.84a(isc).
25.84a x 1.56 = 40a breaker
(Between Panels and MPPT)

80a mppt x 1.25=100a or (125a* available @ the market)

So that is what I did for my type of panels.

Its a shame that there is not a standard methodology between all these Solar gurus.

[mikeo16]

Wow, this is really great info. Palagic - I agree with you that after doing some research and seeing all the varying responses, it does really indicate a lack of an industry standard. Based on everyone's replies, I am leaning to the following setup:
160W panel -->Blue Seas 30Amp Thermal Circuit Breaker (I will use it as a disconnect switch) --> Victron SmartSolar 100/20 MPPT controller (I bought this already and now realize it is overkill, but in the event I decide to add more panels I wanted some room. After reading the feedback, it seems that for future expansion I would be better off with adding another controller instead) --> 20A ATO/ATC fuse (I can pull the fuse for winter or if I had a need to disconnect without toughing wires - this becomes in affect a switch by pulling the fuse) -->Positive Bus bar --> MRBF fuse on battery(300 Amp) --> battery.

Thanks again for everyone's help - this has been a real learning experience. Regards - Mike

[patprice]

I do have a switch to isolate the panels. I also have a battery monitor which is very handy for monitoring both power supply and demand to the battery system.
But...with the panels on line and providing charge I cannot see, for instance, what is being taken from the batteries. Just a "nett" figure.

[ccannan]

There are all sorts of benefits to having a switch/breaker between the panels and the controller. The switch/breaker really should be 2 pole (positive + negative). Fully shading solar panels is never easy or secure (towels blow off, etc...), unless you like to work at night. At some point you will want to connect or disconnect your controller (maintenance, testing, replacing, etc...). The smart way to do that is to have the CB between the controller and batteries off, and the CB between the panels and the controller off.

[Paul L]

Originally Posted by Pelagic

This thread frustratingly demonstrates the differences between professional electricians about the installation of Solar.

Switch / No Switch. Fuse/No Breaker

In confusion I asked a professional solar installer how he would wire my 4 Sunpower panels.

His calculations and recommendation were for 2 breakers like these (for both pos and neg wires)
Attachment 168402

pv is 327wp x 4 = 1308watts

vmp - 54.7 vdc.***** voc - 64.9vdv
imp - 5.98a************ isc - 6.46a
@ parallel Connection 54.7@ 25.84a(isc).
25.84a x 1.56 = 40a breaker
(Between Panels and MPPT)

80a mppt x 1.25=100a or (125a* available @ the market)

So that is what I did for my type of panels.

Its a shame that there is not a standard methodology between all these Solar gurus.

In what situation could the solar panel wires have greater than 40 amps to trip your 40amp breaker?