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

[mikeo16]

I was just reading an article from Coastal Climate Control Systems (https://www.coastalclimatecontrol.co...ion%20V3.5.pdf) that states "There*should*be*no*On/Off*switch*to*disconnect*the*panels*from*the*batte ry". Is this correct? I am installing a single 160W panel as follows:
160W panel -->Victron MPPT controller --> Positive Bus bar --> MRBF fuse on battery(300 Amp) --> battery. I was thinking of adding a circuit breaker switch just before the solar panel feed goes into the charge controller. Since I am in New England and bring the batteries home for the winter, I was thinking I would need to disconnect the solar panel before the controller - otherwise the panel would be feeding the charge controller which is not connected to a battery for the winter. What is the proper setup?

[john61ct]

If you need a switch, put it between the panels and controller.

Fuse at the battery.

[mikeo16]

Thanks John, I guess the question is "do I need the switch?"

[thinwater]

No, you don't need a switch. If you need to work on the system, throw a towel over the panel. With large, high voltage series systems there are more complicated issues, but not for you.

Why take the batteries home? They won't freeze because the solar will keep them charged, and the cold will actually extend their life. You wouldn't pull the battery out of a car, would you? This is just obsolete tradition, from before people had a reliable way to maintain charge.

So forget the whole process. It's just a good way to hurt yourself with no up-side.

[mikeo16]

good point about just leaving the batteries in the boat, but I seem top recall MaineSail stating that he does not recommend leaving batteries hooked to Solar all winter. For me, that's typically about 7 months - just wondering if that would then mean I would need to check on them once a month (which is why I take them home for convenience, but you are right about lugging those up & down a ladder)

[Pelagic]

In general with a higher current output solar system, they seem to recommend a breaker/fuse.

This from Outback where I have an Outback 80a rated for my 4 high voltage panels.

[Paul L]

Originally Posted by Pelagic

In general with a higher current output solar system, they seem to recommend a breaker/fuse.

This from Outback where I have an Outback 80a rated for my 4 high voltage panels.

Attachment 168313

I don't see what good the breaker does on the solar side of the controller. The panels can never exceed the breaker amp rating.

[mikeo16]

nice diagram! In this diagram, it is showing 2 breakers (one between the solar panel and the charge controller; then another between the charge controller and battery). Does my setup with a single 160 watt panel classify as "higher current output"?

[mikeo16]

I just spoke to Victron and they stated that disconnect switch/breaker is not required, but if you did want to put one in for convenience it should be between the solar panel and the charge controller. They stated that it is perfectly fine to disconnect your battery if you want for the winter and leave the panel connected to the charge controller - it will not do any harm. This seems strange to me, but I am not an expert.

[smac999]

I hope you are not using a 300a MRBF fuse for a 160watt pannel. 15-20a is more like it. just use an inline ATC and save yourself $50. MRBF starts at 30a minamum.

[wyb2]

Originally Posted by Paul L

I don't see what good the breaker does on the solar side of the controller. The panels can never exceed the breaker amp rating.

This. Breakers and fuses exist to prevent excessive current from starting a fire. They serve no purpose where the wiring can handle the maximum current output of the source.

Batteries are capable of supplying huge amounts of current for a short amount of time. Plenty of time to start a fire though.

Originally Posted by mikeo16

I just spoke to Victron and they stated that disconnect switch/breaker is not required, but if you did want to put one in for convenience it should be between the solar panel and the charge controller. They stated that it is perfectly fine to disconnect your battery if you want for the winter and leave the panel connected to the charge controller - it will not do any harm. This seems strange to me, but I am not an expert.

Bold is mine. A switch could be convenient for disconnecting the panels, but a breaker serves no purpose (other than being a switch). On our 200W array we have no way to disconnect the panels other than unplugging them, hasn't been an issue yet. Maybe there is a good reason to have them wired through a cutoff switch that I haven't encountered yet.

[smac999]

Originally Posted by Paul L

I don't see what good the breaker does on the solar side of the controller. The panels can never exceed the breaker amp rating.

Originally Posted by wyb2

This. Breakers and fuses exist to prevent excessive current from starting a fire. They serve no purpose where the wiring can handle the maximum current output of the source.
.

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.

[wyb2]

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.

Good point. But it sounds like the OP is considering the equivalent of placing a 125A fuse/breaker in the 4 awg run between the panels and the controller. If I'm not mistaken that wouldn't protect much of anything.

[donradcliffe]

I think that some of the solar controllers I've used want you to connect the controller to the battery before connecting to the panels, but I routinely violate that and have seen no ill effects.

I agree that the OP should either put a smaller fuse between the bus and the controller, or between the bus and the battery. The 300 amp fuse he contemplates is too big for the solar wiring and the controller. I always tried to remember to pull that fuse before I worked on the panels and their connections. Some times I forgot and had it blow when I shorted out the controller connections.

No need

[sailorboy1]

I don't have switch, but I do have a fuse between the controller and the panel that I can pull.

I also have one at the battery for the controller output line.