Fuse in small solar setup

dlochner · Oct 29, 2021

At a minimum the fuse should go between the unregulated power source and whatever else. Which means a fuse should be between the controller and the battery or bus bar.

If you think about this, it makes sense. The maximum current the solar panel can produce is around 3 amps, however the battery can dump many more amps out if there is a short. That could cause a fire or at a minimum the wires to overheat, the insulation to melt and who knows what else.

The MC4 connectors should be crimped with a crimper designed to crimp those connectors in order to get a good connection. You will also need the tool to separate the connectors if you plan to disconnect the panel. You can't just pull them apart.

For a high current/high voltage panel, it is best to use properly installed MC4s. For a smaller a panel I might think otherwise, but I won't advise you to do that.

dmax · Oct 29, 2021

Regarding the wiring, the Renogy panels come with MC4 plugs already installed, you'll want to get an adaptor kit to go from the panel to the controller, the kits have MC4 plugs as well: Solar Panel to Charge Controller Adaptor Kit

Ken Cross · Oct 29, 2021

I purchased a Renogy 100-watt portable panel. That allowed me to use it on the boat as well as on my travel trailer. It works well, no, it works beyond my expectations, but I question if the steel frame will last in a marine environment. I like the portable system because the controller is attached to the panels and I can just unplug and go. I positioned it on the cabin top when I wanted to use it, then unplugged it and stored it away when not in use. I built an adapter to just plug it into the vehicle plug on the trailer so It is connected to the recharge line. For the boat, I attached a 2 conductor 12awg cable to a fuse directly connected to the batteries.

DArcy · Oct 29, 2021

I wired a fuse between my 30 Amp solar controller and the battery. I would hard wire between the controller and the fuse and then from the fuse to the battery, not use connectors for this location. From the panel to the controller the MC4 connectors are good. You can get custom length battery cables made up or buy standard lengths off the shelf for an application like this. Or buy a proper crimper and DIY.

Don't forget to consult the wire gauge chart to get the proper size for your run length, and remember the run length is total wire length so add the +ve and -ve wire lengths to get total run length.

https://www.bluesea.com/resources/1437

dmax · Oct 30, 2021

Instead of the Renogy fuse, you want an in-line fuse with just plain wire pigtails like this: https://www.amazon.com/Blue-Sea-Sys...ocphy=9001874&hvtargid=pla-524531232225&psc=1
Make sure the Wire size is appropriate through the whole thing as others have said. I have a 50 watt Renogy panel and used 10 AWG wire.

Ken Cross · Oct 30, 2021

Ours came with giant alligator clips. I only get around 5 amps, so I cut them off and installed one of these type plugs. For the battery, it's just a ring terminal. Since the connector is 16 gauge, keep those leads short. https://smile.amazon.com/Fastronix-...words=2+conductor+plug&qid=1635601949&sr=8-16

Stu Jackson · Oct 30, 2021

Ken Cross said:
I like the portable system because the controller is attached to the panels and I can just unplug and go.

For the OP, read the instructions that come with your equipment. Most (generally) require the solar panel to be disconnected fron the controller FIRST. A few (VERY FEW) allow the controller to be disconnected from the batteries with solar still attached to the controller. Just be careful here. What works for Ken may NOT work for your equipment. Just a helpful warning to you.

In addition, you might be interested in these:

Solar Systems: Selection, Installation & Controllers by Maine Sail SUPERB

Installing A Small Marine Solar System by Compass Marine How To

Do I Need a Controller for Solar?

Do I Need A Solar Charge Controller ??

Sizing wiring for solar Wire sizing calculator for Solar Panel Arrays

sesmith · Oct 30, 2021

That Renogy fuse you linked to is one that would be used at the panels. You won't need a fuse at the panels because the panel you're using is small enough it can't put out enough current to fry the wiring with a short. What you do need is an in-line fuse near the battery, between it and the controller. Any decent in-line fuse holder would work for your installation. The fuse size is determined by the size wiring you decide to use between the battery and the controller. The fuse protects the controller wiring from being burned up by battery current if there's a short. The fuse has to be small enough to burn up before the wiring can. There are charts online to determine fuse size.

Ken Cross · Oct 30, 2021

Stu Jackson said:
For the OP, read the instructions that come with your equipment. Most (generally) require the solar panel to be disconnected fron the controller FIRST. A few (VERY FEW) allow the controller to be disconnected from the batteries with solar still attached to the controller. Just be careful here. What works for Ken may NOT work for your equipment. Just a helpful warning to you.

Ours also requires you to disconnect the panels before disconnecting the battery connection.
And I used a 10 amp fuse at the battery.
Ken

heritage · Oct 30, 2021

Renegy states that:
"This Fuse Holder is designed to provide complete single circuit protection to your solar power array. The fuses prevent large currents from damaging the solar panels. Purchase this product for extra protection on your system."

I can't imagine what large current could find it's way to the panel. That's like saying that fuses near your main battery are there to protect the battery.
Maybe a lightning strike that energizes the panel wiring could damage the panel and be mitigated by a fuse?

DArcy · Oct 31, 2021

I have a Blue Sea 5006 fuse holder like this one with a 50A fuse

For a 10A fuse I'd probably just go with an inline blade fuse holder. Don't use the cheap tube fuse holders, they don't last. If the solar controller is close enough to the battery (or +ve terminal block) then you could just crimp the proper size ring terminals onto the fuse holder pigtails and hook it up. If the pigtails aren't long enough then you will need to crimp on a longer wire. All fairly simple to do for this size wire and getting a good crimper is a very good investment.

thinwater · Oct 31, 2021

chriscampbell said:
I'm going to add a small solar panel system to keep my battery charged. I want it to be small and mobile so I can lay it out in the cockpit during the week and stow it in the lazerette when using the boat. I'm about to order a 30watt Renogy with a 10amp controller. I'm having a hard time figuring out all of the parts I will need to set it up. Renogy has been less than helpful in answering my questions.

I think I need:

* the panel
* the controller
* wires to go from the battery to the controller
* 2 sets of MC4 adapters to go from the controller to the panel (I can't tell if the panel comes with them installed...the pic only shows bare wire)

My question is about the fuse. I think I'm supposed to use a fuse between the battery and the controller at a minimum. I cannot figure out what parts I need for this. The 10amp fuse option from Renogy looks like it's supposed to be installed using MC4 connectors, but I can't find any battery cables with MC4 connectors.

I feel like I must be missing something obvious.

If you are going to start wiring stuff, I'd suggest getting a book on the topic and a few simple wiring tools (ratchet crimpers, strippers, and crimp fittings. It will make life simpler. Putting this together would have taken about as long as reading the discussion. A few minutes.

But yes, you have the idea. Very simple. I've done complex solar/inverter/shore power systems, but this should be simple.
Simple solar on an F-24

thinwater · Nov 1, 2021

Mixing wire sizes is not problem. However, crimping two different sizes can be annoying. There are step-down adapters

#16 may be a little small, not in terms of carrying capacity, but in terms of voltage drop. This depends on the distance from the battery to the panel and back (round trip). #14 is better, and there is nothing wrong with #12, other than the fact that #12 takes a different crimp connector size than #16 (14 and 16 use the same size). I'd just use #14. You will also need crimp rings to fit the battery terminals.

The fuse will be smaller than the wire capacity. I'm not sure what the panel suggestion is, but a 50W panel can only put out about 4 amps, so 10A fuse will be safe.

Make certain the panel does not flex (attached with industrial Velcro or sealant to firm deck), you don't walk on it, and that pass-throughs are well sealed (if cored, over drill, fill with epoxy, and redrill). Don't buy a cheap crimper; this is a lifetime tool, and cheap ones ruin jobs.

I think this article is close to what you are trying to do.
Good Old Boat, Small-Scale Solar

Good luck with this intro project!

heritage · Nov 1, 2021

Make sure you put the fuse between the controller and the battery and within 7" of the battery if possible.

sesmith · Nov 3, 2021

The fuse protects the wiring between the controller and the battery. It is sized based on the maximum carrying capacity of that wire. The wiring between the panels and the controller have no bearing on that fuse. You need to size all your wiring based on the distance of each run, and the current you expect it to carry during operation of the panels. Read through the links Stu mentioned above, and I think all your questions should be answered.

That said, as Thinwater mentioned above, a 10A fuse will be less than the maximum capacity of any of the wiring you mentioned using.