Solar system disconnect ?

Maine Sail · Jan 26, 2014

Bob 04 H260 said:
I am looking at a 300w solar system and looking for two disconnects. One for the panel (8 amps) and one for the controller a TS MPPT 45. I will need fuses or breakers as well. Is there anything on the market designed for this application or do you just combine a fuse holder and switch from Bluesea in a plastic box ?
Thanks, Bob

What will these disconnects be used for? Generally at the panels MC-4 connectors would be used.

Fusing goes within 7" of the positive battery post.

Each controller manufacturer will dictate where to disconnect before, or after the controller..

If you have not yet looked at the Rogue line of controllers I would suggest doing so... Also MidNite solar is coming out with the MidNite KID in a month of so...

seadaddler · Jan 26, 2014

Blue sea

I had some blue sea circuit breakers and used one close to where the solor controller wire goes to house bank and the other circuit breaker between the controller to panels.
Pretty sure my Blue Sky 3024 controller suggested 1 breaker like i did.
Nick

Bob846 · Jan 27, 2014

I've got 3 permanently mounted panels and 2 removable that add up to 370 watts. Each panel is wired into a 6 position Blue Sea fuse block. You can get this with the older style glass/tube fuses or the newer blade fuse. Thus, if I want to disconnect a panel, just yank the appropriate fuse. The fuse block is then wired to the controller. Obviously, yanking all the fuses shuts down the controller (Blue Sky 3024i) too (thinks it's night).

Best of luck on your project!

Maine Sail · Jan 27, 2014

Bob 04 H260 said:
Thanks for the information.

The panel will be mounted over the bimini aft of the Hunter arch. The panel connectors will be inside the s/s box on the arch, it requires tools to open. I thought a quick way to disconnect power from the panel was a safety feature. Also the controller needs the battery power turned on first before the power from the panel is applied. So if the boat were powered down for some reason it would be easy to remove the panel output so the controller could be powered up first.

The controller will be mounted very close to the batteries. I am looking at a Bluesea surface mount breaker that would also function as a battery disconnect.

I'll put my fuse for the panel in the s/s arch box and mount a single pole switch for a panel disconnect beside the controller. I will be using #10 wire from the panel to the switch at controller. I have not seen a fuse holder or in-line fuse that will accept a wire this size and an 8 amp fuse ?

The Rogue controller looks like a very good price. It was not clear to me from their website if it is an MPPT controller. The price seems to indicate a PWM controller. The max panel voltage on it is 40 V, my panel is 39.8 V. I think the panel voltage will go down with temperature increase, can it go above 40V in cold weather ? Also the Rogue has no battery temp. input, should this be a concern to optimize the charge as well as a safety issue if the batteries started to over heat ?

Thanks again, Bob

Bob,

#1 No need for a fuse between panel & controller on land this is a requirement because you are running 100+V arrays and is an NEC requirement. On a boat you can short the panels into the wire all day long and not cause an issue as the wire should be sufficiently sized to handle the entire current of the panel. It is a wasted fuse that only adds more voltage drop to the system.

#2 There must be a fuse close to the batteries to prevent short circuits at the "source" end . Batteries are always the "source" for over current protection. This fuse is always sized towards the max ampacity of the wire. Running a smaller fuse than wire ampacity results in unnecessary voltage drop.

#3 The Rogue is a super high quality MPPT controller and built to the highest possible standards. It comes standard with features that cost extra with the other guys including STANDARD battery temp sensing.. Please take the time to read this link before making a choice: http://www.roguepowertech.com/documents/RogueDifference.pdf

sea_casper · Jan 27, 2014

Maine Sail said:
Bob,

This fuse is always sized towards the max ampacity of the wire. Running a smaller fuse than wire ampacity results in unnecessary voltage drop.

Did you really mean this?

The maximum "ampacity" of a wire depends on its diameter (gauge), its length, and allowed temperature rise, you certainly don't wan't someone to misinterpret your advice and size for the "fusing" (absolute maximum) current for a particular wire gauge.

You want the fuse to blow before the wire can heat up substantially. I think you should have said the fuse should be sized to the "maximum safe" or "maximum recommended" current for that length of wire.

Maine Sail · Jan 27, 2014

sea_casper said:
Did you really mean this?

The maximum "ampacity" of a wire depends on its diameter (gauge), its length, and allowed temperature rise, you certainly don't wan't someone to misinterpret your advice and size for the "fusing" (absolute maximum) current for a particular wire gauge.

You want the fuse to blow before the wire can heat up substantially. I think you should have said the fuse should be sized to the "maximum safe" or "maximum recommended" current for that length of wire.

Sizing over current protection for the wires ampacity rating should always take all of that into account plus bundling, engine spaces and jacket temp rating.

My point was the last thing you want to do is size your over current protection for an 8A load with an 8A fuse. Doing so will create undue voltage drop and the fuses won't last long being run at 100%.. Ideally they should be run at 80% or less, preferably much less.

You don't need to size for "max" ampacity but you want a fuse large enough to minimize unnecessary voltage drop and protect the wire at the same time. A 10GA wire can handle a max ampacity for OCP of about 50A inside an engine space and 60A outside but this is 105C wire not bundled.