Fuse between solar panels and MPPT controller?

[scr0che]

Hi,

Been reading around on wiring/fusing for solar panels. I understand the need to put a fuse between the controller and the batteries, but is one needed between the solar panels and the controller? The reason I ask is because Renogy suggest it is needed as per this article - albeit it's quite old, but I've not read that requirement anywhere else:

How to Fuse your Solar System

I currently have a Victron MPPT 100/30 smart controller connected to a 30A breaker, then on to the battery which is right next to it. Planning to use 6mm cable from the panels (2x 175w) connected in parallel via a branch down to the controller, a run of ~5m. Is a circuit breaker needed there?

Steve...

 

[TernVI]

A lot of solar panel manufacturers seem to demand a fuse of about twice the short circuit current of the panel.
The short circuit current is often only about 10% more than the working /MPP current.
Clearly the panel isn't going to blow this fuse on its own, but they must have in mind a system fault.

 

[VicS]

The maximum safe current rating of your 6mm wiring is well in excess of the maximum combined output current of your solar panels. It's 50 amps. The maximum ( short circuit) combined current from you two panels will be no more than 20 amps Therefore no fuses or circuit breakers are necessary.


However if you are planning to use 6mm cable for a combined 5m run to the controller look again at that.
I think that should be at least 10mm

 

[VicS]

A lot of solar panel manufacturers seem to demand a fuse of about twice the short circuit current of the panel.
The short circuit current is often only about 10% more than the working /MPP current.
Clearly the panel isn't going to blow this fuse on its own, but they must have in mind a system fault.

I think you will only need fuses if there are a number of panels ( more than about 5 or 6 ) wired in parallel using wiring sized to the individual panel output)
Taking the OPs 175 watt panels, which will probably have a short circuit current of about 10 amps each. If they are interconnected with 6mm ( 50amp) cable the combined short circuit output could be nearly 60 amps from 6 panels which is over the rating of 6mm cable

 

[TernVI]

I think you will only need fuses if there are a number of panels ( more than about 5 or 6 ) wired in parallel using wiring sized to the individual panel output)
Taking the OPs 175 watt panels, which will probably have a short circuit current of about 10 amps each. If they are interconnected with 6mm ( 50amp) cable the combined short circuit output could be nearly 60 amps from 6 panels which is over the rating of 6mm cable

That's not quite the way panel manufacturers are thinking.
Check the spec of the panel and see if they require a fuse, and what size.

 

[rogerthebodger]

That's not quite the way panel manufacturers are thinking.
Check the spec of the panel and see if they require a fuse, and what size.

In my view if the current carrying capacity of the cable from the solar panels to the regulator is higher than the short circuit current of the panels the is no real need to a fuse between the two.

Also the size of the cable needs to be large enough to reduce any volt drop between the panel and the regulator to keep the efficiency up.

In saying that there is no problem in putting a fuse in the cable as close to the solar panel as possible.

 

[scr0che]

Thanks for the advice re cable sizes, I'll go up to 10mm - it will be run through inch and a quarter radar arch tube, should be ok. I plan to run the cable just below deck, then put an MC4 connection in - just in case the arch ever has to be removed - then run it on to the controller.

Q: Will my hex battery cable crimping tool crimp the 10mm connectors ok? It crimps from 6-50mm, and has a slot for 10mm.

Q: Will a standard MC4 branch connector connect to the 10mm connectors or do I need specific 10mm branches? Can't seem to find any reference to those.

Doesn't sound like I need the fuse.

 

[lustyd]

While the current may not exceed the cable right now, there's nothing stopping someone fitting more panels in the future, or reusing the wiring for other things like a wind gen. The fuse is to protect the wiring and the boat, so add a fuse sized to the wiring. If you've bought a controller, cable and panels, the extra £1 won't break the bank

 

[VicS]

That's not quite the way panel manufacturers are thinking.
Check the spec of the panel and see if they require a fuse, and what size.

The OP does not say what make of panels he is using but he does mention a Victron controller
Supposing he is using Victron panels...
I see no mention of fuses or circuit breaker in the spec or user manual for them.

 

[rogerthebodger]

While the current may not exceed the cable right now, there's nothing stopping someone fitting more panels in the future, or reusing the wiring for other things like a wind gen. The fuse is to protect the wiring and the boat, so add a fuse sized to the wiring. If you've bought a controller, cable and panels, the extra £1 won't break the bank

Any thing is possible in the future so are you proposing to design the system to cater for what the future may bring.

Yes an extra pound wont break the bank but it could cause the solar system to fail due to unnecessary extra equipment.

KISS

 

[noelex]

All solar controllers need circuit protection between the controller and the battery. Some solar installations also need circuit protection on the input side of the solar controller. With only two panels this is not generally needed, so your system is almost certainly OK without this added protection.

However, having the ability to easily disconnect the solar panel input can be useful, especially as it is sometimes necessary to disconnect the input first to prevent damage to the controller or even other equipment. Many users incorporate a circuit breaker for this function.

 

[noelex]

In my view if the current carrying capacity of the cable from the solar panels to the regulator is higher than the short circuit current of the panels the is no real need to a fuse between the two.

The problem and potential fire risk that needs to be comsidered when discussing circuit protection between the controller and the panel generally comes from the internal wiring used within the solar panel. These internal wires are kept relatively fine to reduce the shading of the cell.

 

[lustyd]

Any thing is possible in the future so are you proposing to design the system to cater for what the future may bring.

Yes an extra pound wont break the bank but it could cause the solar system to fail due to unnecessary extra equipment.

KISS

No I’m saying you should fuse all circuits to protect the wiring whether you think it could go over current or not. All it would take would be someone upgrading panels and it could lead to fire. Simple is great right up until it’s not!

 

[rogerthebodger]

No I’m saying you should fuse all circuits to protect the wiring whether you think it could go over current or not. All it would take would be someone upgrading panels and it could lead to fire. Simple is great right up until it’s not!

Yes if some upgraded the panels the wiring should also be upgraded.

When I built my boat I fitted 4 solar panels and later added 4 more but ran separate wired back to a new second regulator as I needed to have a higher rating for the extra panels .

If you are going to do it in the first place how do you decide how much extra wiring to include.

With a MPPT regulator you can increase the voltage thus keeping the current at the same level.

I would also like to know how many fires have started at a solar panel setup.

 

[pvb]

The OP does not say what make of panels he is using but he does mention a Victron controller
Supposing he is using Victron panels...
I see no mention of fuses or circuit breaker in the spec or user manual for them.

In the Victron MPPT controller manuals there's a specific warning that the PV input isn't isolated from the battery circuit, so presumably there could be a problem with a short in the cables to the panel.

And in the installation circuit diagrams, there's a breaker between the panel and the controller.

 

[lustyd]

Yes if some upgraded the panels the wiring should also be upgraded.

When I built my boat I fitted 4 solar panels and later added 4 more but ran separate wired back to a new second regulator as I needed to have a higher rating for the extra panels .

If you are going to do it in the first place how do you decide how much extra wiring to include.

With a MPPT regulator you can increase the voltage thus keeping the current at the same level.

I would also like to know how many fires have started at a solar panel setup.

The point is that people think the wiring through when first installing but the next owner might not when upgrading panels. You wouldn’t add more wiring just a fuse to make certain the wiring can’t get too much current.
Plenty of fires with solar although I wouldn’t expect many from lack of fuses. Doesn’t mean it won’t happen, fusing is a well proven safety measure and doesn’t need justification.

 

[PaulRainbow]

The point is that people think the wiring through when first installing but the next owner might not when upgrading panels. You wouldn’t add more wiring just a fuse to make certain the wiring can’t get too much current.
Plenty of fires with solar although I wouldn’t expect many from lack of fuses. Doesn’t mean it won’t happen, fusing is a well proven safety measure and doesn’t need justification.

Can you post a few links to these please ?

It makes no sense whatsoever to fit over size cables to anything on your boat, in case the next owner might fit something bigger. How about some nice 240mm battery cables, in case he fits a big bow thruster ? Perhaps some 10mm cable up the mast in case he wants some halogen spreader lights ? Maybe run some cabling to the heads in case he wants an electric toilet, ah, better make it extra large in case he adds a bidet.

 

[PaulRainbow]

Hi,

Been reading around on wiring/fusing for solar panels. I understand the need to put a fuse between the controller and the batteries, but is one needed between the solar panels and the controller? The reason I ask is because Renogy suggest it is needed as per this article - albeit it's quite old, but I've not read that requirement anywhere else:

How to Fuse your Solar System

I currently have a Victron MPPT 100/30 smart controller connected to a 30A breaker, then on to the battery which is right next to it. Planning to use 6mm cable from the panels (2x 175w) connected in parallel via a branch down to the controller, a run of ~5m. Is a circuit breaker needed there?

Steve...

No need for a fuse between the panels and the controller for this setup. The fuse between the controller and the batteries should be at the batteries, it's there to protect the cables.

If you are running cables down from each panel separately (rather than joining them in parallel above deck, 6mm is perfectly adequate.

 

[john_q]

I have just fitted a MorningSta Pro-Star Gen-3 30 amp solar controller and it specificlly states in the manaual a 40 amp fuse between the Controller and the Battery (within 6 inches of the battery) and a 40 Amp fuse between the controller and the solar panels, with breakers to disconnect the battery and the solars

And, by chance, last night I was shown a Vitron controller where the positive input from the solars to the controller has melted the controller plastic/solder. The only fuse in the whole circuit was in the controller itself which does not appear to have blown.

 

[lustyd]

Can you post a few links to these please ?

It makes no sense whatsoever to fit over size cables to anything on your boat, in case the next owner might fit something bigger. How about some nice 240mm battery cables, in case he fits a big bow thruster ? Perhaps some 10mm cable up the mast in case he wants some halogen spreader lights ? Maybe run some cabling to the heads in case he wants an electric toilet, ah, better make it extra large in case he adds a bidet.

Plenty of posts in solar on a boat on Facebook showing various fires caused by panels, usually flexible ones on biminis. If you read my post, and I assume you didn't, I said that there probably aren't any related to fuses. I also not only didn't say to fit larger cables, I said don't fit larger cables.

You then go on to say there's no need for a fuse since it's there to protect the cables. I literally said the fuse is to protect the cables, and if someone upgrades the panels then the fitted cables may have an issue so £1 of fuse is probably a wise investment. These forums are littered with people upgrading panels who don't spare a second thought to also uprating their cabling. A fuse might protect them.