Fuse rating for solar installation

[FairweatherDave]

The manual recommends I install an inline fuse between the battery and the solar charge controller. The manual is generic for various sizes of panel and therefore says "the fuse rating should be chosen according to the maximum power current/short circuit current of your solar panel".
The back of my 50 watt panel says "Current at Max power (imp) 2.84A" and also "short circuit current (isc) 3.07A.
My instinct is a 5A fuse (unless there are 4 Amp fuses commonly available). Or should I be getting a 3 Amp fuse, which I guess is a bit too close to the max power.
Hope this is a simple question! Thanks for any pointers

 

[VicS]

The manual recommends I install an inline fuse between the battery and the solar charge controller. The manual is generic for various sizes of panel and therefore says "the fuse rating should be chosen according to the maximum power current/short circuit current of your solar panel".
The back of my 50 watt panel says "Current at Max power (imp) 2.84A" and also "short circuit current (isc) 3.07A.
My instinct is a 5A fuse (unless there are 4 Amp fuses commonly available). Or should I be getting a 3 Amp fuse, which I guess is a bit too close to the max power.
Hope this is a simple question! Thanks for any pointers

There are two considerations. The maximum charging current you could see ( with an MPPT controller it could be slightly more that the short circuit current of the solar panel itself) and the max safe working current of the wiring.

The fuses must have a continuous rating a little greater than the max current you'll see but be less than the safe rating of the wiring

Hopefully in order to minimize volts drop the wiring will in practice have a much higher safe rating that the max output from the controller so only this will need to be considered.
4 amp fuses are available. Personally Id probably opt for 5 amp though.

The fuse(s) should be as close as reasonably possible to the battery connection to protect the wiring fully

Type of fuse ?????? Inline fuse holders with glass tubular fuses generally considered no a good chcoce. Blade fuses better.

See https://www.12voltplanet.co.uk/fusing-circuit-protection.html

 

[FairweatherDave]

Thanks VicS, really helpful.

 

[Richard10002]

The manual recommends I install an inline fuse between the battery and the solar charge controller. The manual is generic for various sizes of panel and therefore says "the fuse rating should be chosen according to the maximum power current/short circuit current of your solar panel".
The back of my 50 watt panel says "Current at Max power (imp) 2.84A" and also "short circuit current (isc) 3.07A.
My instinct is a 5A fuse (unless there are 4 Amp fuses commonly available). Or should I be getting a 3 Amp fuse, which I guess is a bit too close to the max power.
Hope this is a simple question! Thanks for any pointers

Surely the fuse between the controller and the battery should be sized for the current and the cable that runs between the controller and battery, and not the current from the panel to controller? In addition, isn't the fuse to protect the cable from the unlimited current that could come from the battery, rather than the limited current that comes from the panel and controller - given that the cables will be rated to carry more than the maximum that the panels and controller can possibly produce?

Which begs the question.... what size cable runs from your controller to the battery bank?

As an aside, I find it useful to have a switch between panels and controller, and I actually use a 50A circuit breaker for 2 x 245W panels in parallel.

 

[Mikedefieslife]

A fuse it pretty important especially if like most people you have your solar controllers hooked up to a charging bus rather than directly to the battery. In such a case it might be possible to switch the batteries off (from loads) but still have the loads running through the charging bus. A high load like a starter or windlass would totally destroy the wiring.

As others have said, a fuse should be sized to protect the wiring. You didn't say what size wire you are running, but a doubt it's so small it can't easily carry 5amps a reasonable distance.

Additionally, fuses should be as close to the battery as possible, but never in the same compartment if running FLA batteries. Theory is, if the batteries are gassing, a blowing fuse could be enough to ignite the hydrogen.

 

[FairweatherDave]

Thanks for the further posts. The simple truth is I am installing from a kit supplied by Photonic Universe so I have not needed to get into the details of wire size. I am following instructions to the letter and therefore there is no fuse other than the one I posted about and the wires go direct from the controller to the battery terminals (no bus bar).

 

[Graham_Wright]

To muddy the waters or clarify my understanding, does shorting the output of a solar panel damage it? Is it duration limited?

I can't see the point of protecting the connection between the panel and the controller as the cable size will have been chosen to avoid excessive drop and be far greater than the 3 amps quoted.

 

[FairweatherDave]

To muddy the waters or clarify my understanding, does shorting the output of a solar panel damage it? Is it duration limited?

I can't see the point of protecting the connection between the panel and the controller as the cable size will have been chosen to avoid excessive drop and be far greater than the 3 amps quoted.

I suspect you are directing that at Richard as my fuse is between the battery and the controller. That said, I can see the virtue of a switch between panel and controller purely so that if you disconnect the batteries you know the leads are definitely dead. (There is no switch on my controller).

 

[VicS]

To muddy the waters or clarify my understanding, does shorting the output of a solar panel damage it? Is it duration limited?

I can't see the point of protecting the connection between the panel and the controller as the cable size will have been chosen to avoid excessive drop and be far greater than the 3 amps quoted.

"does shorting the output of a solar panel damage it? Is it duration limited?"

To the best of my knowledge, "No" to both questions

The purpose of the fuse is to protect the wiring, and the controller, from the hundreds of amps that the battery could deliver in the event of a fault. It should be located close to the battery connection for maximum benefit in protecting the wiring. Hence the recommendation from Photonic Universe

If the controller to battery distance is kept short the use of excessively heavy wiring can be avoided, but the greater it is the heavier the wiring will have to be .

 

[Richard10002]

To muddy the waters or clarify my understanding, does shorting the output of a solar panel damage it? Is it duration limited?

I can't see the point of protecting the connection between the panel and the controller as the cable size will have been chosen to avoid excessive drop and be far greater than the 3 amps quoted.

No need to protect the cable between panel and controller as the Amps are limited by what the panels can produce. However, it is useful to have a switch between panels and controller, and I have found the most convenient is actually a circuit breaker type switch.