Fuse for solar panels?

[thinwater]

...However, it is handy to have a switch between the panels and controller, and the most convenient I have found is actually a circuit breaker, (50A in my case).

Circuit breakers are nice. For small applications, a blanket laid over the panel also works. Darkness is the only way to turn a PV cell off.

 

[PaulRainbow]

I emailed Photonic Universe regarding the instructions for dual controller, in particular the statement that the fuse should be in each negative cable. Here is their reply ;

Thanks for getting in touch. This is a question we get a lot,
unsurprisingly, for the reasons you've stated! If I'm reading the posts
right, it seems the original poster has one of our dual battery controllers;
in this situation, we absolutely do recommend that the negative cable
between the battery and the controller is fitted with a fuse.

The reason for this is simple enough. Our dual battery controllers are built
so as to have a negative common ground for both batteries within the solar
controller. As a result, the fuse serves a dual purpose in this system - it
serves the standard purpose of protecting the equipment from a system
failure or wiring mistakes as it would in any system, but it also serves to
break the negative link between the two batteries in case of such failures.

That said, if customers are still somewhat nervous they can always fuse both
cables, but ultimately the instructions are correct - due to the internal
construction of the controller, the fuse is recommended to be on the
negative side.

Still seems pointless to me, because there are actually two negative cables going to the controller, one from each battery. It would still require both fuses to blow to acheive " but it also serves to break the negative link between the two batteries ".

Those instructions are still wrong. If they insist that a fuse be fitted to the negative, so be it, but they should still specify fuses be fitted to the positive cables. These instructions are leading people to fit the controllers with no protection to the cables between the batteries and the controller, which leaves the owner at risk.

 

[UK-WOOZY]

ressurecting this thread.

I had to replace my photonic universe 50w semi flexible panel. it died ironically just after the 1 year warrantee ran out, they werent interested in giving me a discount on a replacement. so i replaced it with a panel from midsummer energy, their own brand panel has a 2 year warrantee. Im using the photonic universe duel battery controller with it and LCD display. I have a quick blow fuse on the wires from the controller to the batteries on the positive side so maybe i need to add them on the negative too. Also the photonic universe panel seemed to stop working after i ran the engine, could that kill a panel? should i put a fuse between the panel and controller? thanks

im also adding another 80w panel on the back of the boat and am using a votronic mppt controller for that

 

[William_H]

I have a 1500w solar PV system at home feeding an inverter to supplement the 20vAC mains. Installed by professionals to required standard. I discovered recently that system was dead. Tracked it down to a fuse on the roof next to the array that had failed. I refuse to believe it was "blown". The fuse was 10 amp 1000v rating and finally found a replacement. Ironically sold as a fuse for digital multimeter for current range. Anyway I am still annoyed that fuses were fitted both pos and negative between the panels and the inverter. The panels into a short circuit can only deliver 5 amps (at 320volts) so why fuses and why did it fail? So definitely to the oP no fuse in line panel to controller unless you want a way to disconnect panels but yes fuse between controller and battery where batter can provide power back into a short circuit to start a fire. ol'will

 

[noelex]

Anyway I am still annoyed that fuses were fitted both pos and negative between the panels and the inverter. The panels into a short circuit can only deliver 5 amps (at 320volts) so why fuses and why did it fail?

William, in some cases fuses are needed on the solar side. The wires inside the solar panel are the concern. The internal wires are kept as small as possible to reduce the shading on the solar cells. Consequently these wires are only rated for just above the output of the panels.

The general rule is that if you have three or more strings, then fuses on the solar side will be needed and these are obviously in addition to a fuse on the battery side in the case of boat DC system. The reason behind this general rule is that a fault in a single string could force the current of the two other strings through the faulted string. The internal wires within the solar panel are not rated for this level of current.

This is especially a concern where solar panels are mounted on flammable materials such as dodger.

We need to dispel the myth that fuses on the solar side are never required. This advice is often repeated in forums. It is incorrect. Fortunately many marine installations are only one or two strings. Fuses on the solar side are not always required, but solar systems on boats are becoming larger and more complex and the lack of correct fusing is becoming a concern.

Without seeing the wiring diagram it is impossible to tell but I suspect your home system does indeed need fuses on the solar side. At first glance the argument that solar cells can only provide a self limited maximium current and therefore fusing the solar side is unnecessary seems sensible, but this is not correct, at least not in all cases.

It is also possible that there is a fault in your sytem and the fuse blowing was not just a nuisance trip (although the later is more likely). If you think about the fault conditions where the current of two or more strings (contributing 5A each) could be directed through the 10A fuse it will give you some idea what to look for.

 

[William_H]

William, in some cases fuses are needed on the solar side. The wires inside the solar panel are the concern. The internal wires are kept as small as possible to reduce the shading on the solar cells. Consequently these wires are only rated for just above the output of the panels.

The general rule is that if you have three or more strings, then fuses on the solar side will be needed and these are obviously in addition to a fuse on the battery side in the case of boat DC system. The reason behind this general rule is that a fault in a single string could force the current of the two other strings through the faulted string. The internal wires within the solar panel are not rated for this level of current.

This is especially a concern where solar panels are mounted on flammable materials such as dodger.

We need to dispel the myth that fuses on the solar side are never required. This advice is often repeated in forums. It is incorrect. Fortunately many marine installations are only one or two strings. Fuses on the solar side are not always required, but solar systems on boats are becoming larger and more complex and the lack of correct fusing is becoming a concern.

Without seeing the wiring diagram it is impossible to tell but I suspect your home system does indeed need fuses on the solar side. At first glance the argument that solar cells can only provide a self limited maximium current and therefore fusing the solar side is unnecessary seems sensible, but this is not correct, at least not in all cases.

It is also possible that there is a fault in your sytem and the fuse blowing was not just a nuisance trip (although the later is more likely). If you think about the fault conditions where the current of two or more strings (contributing 5A each) could be directed through the 10A fuse it will give you some idea what to look for.

Thanks Noelex. Obviously someone in writing the standards believes the fuses are necessary. Perhaps as you say to suit situations where panel strings are in parallel. Certainly in my case all are in series. 8 panels at 40 volts max each giving the 320v to inverter. Anyway the system has worked OK since replacing the fuse. I was intrigued by non availability of the fuse type in all the electrical supply stores I went to. Strange since there are huge numbers of houses around here with solar arrays. (like 25%). ol'will