Breaker or fuse between solar panel and controller?

[MichaelG]

Hi all, I have bought a small solar kit from a supplier. It's a Victron 215w panel and a Victron 15a smartsolar controller which the paperwork suggests is good for panels upto 220w. The kit also comes with the wiring between the panel and controller and the controller to the batteries. The wiring from the controller to the batteries is fitted with a blade fuse type fuse holder. There is no breaker or fuse for installation between the panel and controller included in the kit. I'm wondering if it advisable to fit a breaker or fuse between the panel and controller or is that not required?

[robtheplod]

I don't think its required, but I've seen it recommended lots so you can isolate your panels easily and quickly. You might find this video interesting:

 

 

[nicknorman]

1 hour ago, MichaelG said:

Hi all, I have bought a small solar kit from a supplier. It's a Victron 215w panel and a Victron 15a smartsolar controller which the paperwork suggests is good for panels upto 220w. The kit also comes with the wiring between the panel and controller and the controller to the batteries. The wiring from the controller to the batteries is fitted with a blade fuse type fuse holder. There is no breaker or fuse for installation between the panel and controller included in the kit. I'm wondering if it advisable to fit a breaker or fuse between the panel and controller or is that not required?

The fuse between the controller and batteries is necessary because the batteries could supply thousands of amps if the wiring developed a short circuit, causing the wiring to go on fire etc.

 

However the panels cannot supply thousands of amps under fault conditions, they can only supply their rated output regardless of fault, short circuit etc. Therefore the wiring should be able easily too withstand eg a short circuit, no fuse  or breaker is needed. It might however be advisable to install some kind of switch to be able to isolate the panels from the controller, in part because one should never disconnect the controller from the batteries whilst the panels are still connected and in sun. But it would be for convenience, not for safety.

[Kudzucraft]

The thng to keep in mind is that fuses protect the wire, not necessarily the device it is connected to. It prevents the wire from overheating and possibly causing a fire. I have seen wires overload glow bright red!

 

It might not be necessary but a properly sized fuse  is good idea and cheap insurance

Edited November 4, 2021 by Kudzucraft

[nicknorman]

6 minutes ago, Kudzucraft said:

The thng to keep in mind is that fuses protect the wire, not necessarily the device it is connected to. It prevents the wire from overheating and possibly causing a fire. I have seen wires overload glow bright red!

 

It might not be necessary but a properly sized fuse  is good idea and cheap insurance

There is only any point in installing a fuse if there is something to protect against. In this case there is nothing, unless you can explain where this source of current to create overheating and fires is coming from? Maybe when the sun goes supernova?

[David Mack]

39 minutes ago, nicknorman said:

It might however be advisable to install some kind of switch to be able to isolate the panels from the controller, in part because one should never disconnect the controller from the batteries whilst the panels are still connected and in sun. But it would be for convenience, not for safety.

But how often do you disconnect solar from the batteries? It's not an every day occurance. It's almost as easy to disconnect one of the solar cables from the terminals on the controller. 

[nicknorman]

12 minutes ago, David Mack said:

But how often do you disconnect solar from the batteries? It's not an every day occurance. It's almost as easy to disconnect one of the solar cables from the terminals on the controller. 

I agree, hence my point that it was an optional convenience.

[MichaelG]

Thanks for the advice. I wasn’t sure if or why one would be required but had seen a couple of set ups that did have them so thought I’d check if they were required for safety reasons. I get the point about being able to disconnect the panels should I need to disconnect from the batteries but as that should be an infrequent requirement I’ll go without the breaker and just disconnect at the controller terminals if required. Thanks again for the advice.

[MichaelG]

Hi, sorry just thought. I was aware that you must connect the controller to the batteries before the panel. What happens if the batteries aren’t connected, for example if the inline fuse between the batteries and controller blows.

[Alan de Enfield]

3 minutes ago, MichaelG said:

Hi, sorry just thought. I was aware that you must connect the controller to the batteries before the panel. What happens if the batteries aren’t connected, for example if the inline fuse between the batteries and controller blows.

 

Be happy - 'blowing up' your panels is a small price to pay. The fuse has blown for a reason and that just may have saved your life / boat exploding / boat burning up.

[nicknorman]

4 minutes ago, MichaelG said:

Hi, sorry just thought. I was aware that you must connect the controller to the batteries before the panel. What happens if the batteries aren’t connected, for example if the inline fuse between the batteries and controller blows.

Depending on the controller, if the fuse blows then the controller MAY be destroyed if the panels are producing power and the controller to battery wires go open circuit. Some controllers are protected from that, some aren’t. However one has to consider WHY the fuse blew, and the main reason is because there was a short circuit between the controller and the fuse. So in that case, the controller to battery hasn’t gone open circuit, it’s gone short circuit. And with that, there is almost certainly no damage.

 

So what is to be avoided is to select a fuse that is close to the rated output of the controller, which will consequently run hot and may age and fail prematurely. The fuse should be selected according to the current rating of the cable, and since voltage drop is normally the predominant factor in selecting cable size, the cable’s max current rating will always be well above the max output from the controller.

[MichaelG]

Thanks for the sensible advice Nicknorman, much appreciated.

[Tony Brooks]

1 hour ago, David Mack said:

But how often do you disconnect solar from the batteries? It's not an every day occurance. It's almost as easy to disconnect one of the solar cables from the terminals on the controller. 

 

The answer is never unless the solar is disconnected first. If you do odd things may happen to the controller like magic smoke or setting itself for a 24 volt batter bank. That is why it is convenient to have  away of isolating the panels, be it by switch or pulling a fuse out.

[PeterF]

1 hour ago, David Mack said:

But how often do you disconnect solar from the batteries? It's not an every day occurance. It's almost as easy to disconnect one of the solar cables from the terminals on the controller. 

When you have one of the Epever Tracer controllers having a switch between the panels and controller can get used more as these controllers can get stuck at a low output if there is intermittent sun and shade. Stopping the current flow from the panels caused the controller to do a new maximum power sweep and get back to full output. Gone Victron now and no more switching the panels on and of a couple of times a week.

[Chewbacka]

7 hours ago, MichaelG said:

Thanks for the advice. I wasn’t sure if or why one would be required but had seen a couple of set ups that did have them so thought I’d check if they were required for safety reasons. I get the point about being able to disconnect the panels should I need to disconnect from the batteries but as that should be an infrequent requirement I’ll go without the breaker and just disconnect at the controller terminals if required. Thanks again for the advice.

If you have several panels in parallel then fuses may be required but this is not common on boats

[john.k]

Cheap solar battery chargers have caused fires that damaged a number of vehicles,when the battery current was allowed to fry the lektrics......Fuse the battery leads.

[reg]

My installation notes, long since list, stated that before disconnecting the solar charger from the batteries the solar panels must be disconnected from the charger first. Only after disconnecting from the solar panels should the battery connections be broken

 

Basic Internet search will confirm this rule and in some cases explain why. So

    always disconnect solar panels first 

 

I do mine via blade fusesl