Is a fuse a fuse?

[Vintage465]

I'm fusing my solar panels individually in the combiner box before they are combined. Initially, I purchased the 15a MC-4 fuse holder and the connectors. This came out to about 6-1/2" long. Too long for my combiner box with all the other hardware in there. So, can I use any automotive inline type fuse and fuse holder so long as the the fuse size is right and the wire size(10ga) is the same? The reason I ask is the conductor/fuse is real small on an automotive 15a and I always concern my self with not carrying as much juice cause of the small fuse link compared to the 10ga wire? Meaning, is there a "special" solar fuse that carries more juice?

Thanks,

[CA_Traveler]

Solar cells fail and short, doesn't take a tree branch or wires shorting.

[time2roll]

BFL13 wrote:
Need a scenario. Say a tree branch falls on one of your RV roof panels and smashes it all to heck. Perhaps somehow a cell gets shorted.

Cells are all in series with each other, so hard to figure how a short can occur with pos and neg touching. But even if a cell is shorted, what will happen? Shorting the whole panel is harmless. That is how you measure Isc and Voc.

If the panel shorts the other two panels feed current through. If the panel fuse rating is 15 amps and you push 20 amps through the short (10 amps x2 panels) they you might get some heat.

[BFL13]

Need a scenario. Say a tree branch falls on one of your RV roof panels and smashes it all to heck. Perhaps somehow a cell gets shorted.

Cells are all in series with each other, so hard to figure how a short can occur with pos and neg touching. But even if a cell is shorted, what will happen? Shorting the whole panel is harmless. That is how you measure Isc and Voc.

[time2roll]

Ed_Gee wrote:
Has anyone heard of a solar panel short circuiting in its internal power connections? I have not.... just seems like a lit of work for nothing.

Not on an RV. Tesla did recently battle Walmart due to some Solar City installations that caught fire. Lawsuit was resolved and withdrawn.

Doubt the risk is significant at these low voltages. Residential/commercial systems often run 400 to 800+ volts. Big difference.

[Ed_Gee]

Has anyone heard of a solar panel short circuiting in its internal power connections? I have not.... just seems like a lit of work for nothing.

[TechWriter]

Vintage465 wrote:
I'm fusing my solar panels individually in the combiner box before they are combined . . .

OP, I suggest checking out the MidNite Solar Forum. These are the guys who manufacture, test, and install solar equipment . . . actual experts.

The advice you get on this forum may be well-meaning, but it can be mixed, and even outright dangerous . . . for example, one of the current posters suggested that using a piece of wire was just as good as a fuse.

[time2roll]

Yes with three panels the array (-1) may exceed the individual panel rating.
MC4 is designed to use outside of a box. If you have them and the panels still have the connectors you can certainly use them snapped on the end of the panel connector.

3 to 1 MC4 connector.

Of course to really clean things up you may need to cut the cables and attach your own MC4 at the proper length. At that point you only need a basic box to seal the cable entry on the roof.

Can also get MC4 with #8 wire if you prefer for the run down to the controller. Just cut the cable in half with the MC4 attached to the 3 to 1 adapter and the cut end on the controller.

Just an additional option to consider.

[pianotuna]

Hi,

There is no need to fuse the panels at the combiner box. In fact it is undesirable to do so.

A switch after the combiner box close to the charge controller is a good plan.

If using MPPT controller, wire for highest input voltage and use a DC rated switch or circuit breaker.

Vintage465 wrote:
I'm fusing my solar panels individually in the combiner box before they are combined. Initially, I purchased the 15a MC-4 fuse holder and the connectors. This came out to about 6-1/2" long. Too long for my combiner box with all the other hardware in there. So, can I use any automotive inline type fuse and fuse holder so long as the the fuse size is right and the wire size(10ga) is the same? The reason I ask is the conductor/fuse is real small on an automotive 15a and I always concern my self with not carrying as much juice cause of the small fuse link compared to the 10ga wire? Meaning, is there a "special" solar fuse that carries more juice?

Thanks,

[BFL13]

It is all here as to when you need fuses or not depending on your solar set-up. Scroll down to the discussion page 6 and on.

http://www.cooperindustries.com/content/dam/public/bussmann/Electrical/Resources/technical-literatur...

[CA_Traveler]

Vintage465 wrote:
Some people recommend fusing them. Some don't. Renogy recommends(or shall I say I saw in of their solar "101" info write-ups) fusing each panel. Samlex doesn't mention fusing at the panels. I don't have any issue from a technical perspective about fusing, whether or not it should be. Only from a "does it still charge as well" perspective.

Good plan and no effect on charging.

Many don't understand the possible hazard of a parallel panel catching on fire.

[CA_Traveler]

wa8yxm wrote:
The only other thing would be the "inline resistance) of the fuse (The resistance pin to pin not blown) likely too low for your meter to measure but I'm not sure how the "Solar rated" fuses compare to standard automotive/house fuses in this aspect.

Fuse resistance and even wiring to the combiner is normally a non issue for for parallel 12V panels. Normally rated 18-20V for 14.8V battery charging. Doubtful that even a MPPT controller with parallel panels would have any practical loss due to fuses.

My 3 serial panels are NOT fused due to limited Isc from the other panels so no need for a fuse since it wold never blow. Not to mention the 9 bypass diodes that also protect the panels and add shade tolerance.

[Vintage465]

Ed_Gee wrote:
Not sure I understand why one would fuse a solar panel. What rating fuse would you use? ...the solar panel is simply incapable of sourcing higher current than its maximum output.....a fuse could never blow. The other end is not a current source assuming it is a charge controller, so nothing that could provide current to blow a fuse there, either..... am I missing something?

Some people recommend fusing them. Some don't. Renogy recommends(or shall I say I saw in of their solar "101" info write-ups) fusing each panel. Samlex doesn't mention fusing at the panels. I don't have any issue from a technical perspective about fusing, whether or not it should be. Only from a "does it still charge as well" perspective.

[CA_Traveler]

ktmrfs wrote:

Ed_Gee wrote:
Not sure I understand why one would fuse a solar panel. What rating fuse would you use? ...the solar panel is simply incapable of sourcing higher current than its maximum output.....a fuse could never blow. The other end is not a current source assuming it is a charge controller, so nothing that could provide current to blow a fuse there, either..... am I missing something?

single panel I agree. Multiple panels another story. Let's assume you have 6 panels in parallel. One panel develops an internal short positive to negative, each panel can supply 15A, Now all the sudden you have 5 panels suppling up to a total of 60A through the wiring on the shorted panel. not a good idea. The fuse serves as a isolation device.

Fusing requirements for solar panels are more focused on house grid tie applications where you could have a dozen or more panels in parallel.

Correct answer and the reason for fusing 3 or more parallel panels.

[ktmrfs]

Ed_Gee wrote:
Not sure I understand why one would fuse a solar panel. What rating fuse would you use? ...the solar panel is simply incapable of sourcing higher current than its maximum output.....a fuse could never blow. The other end is not a current source assuming it is a charge controller, so nothing that could provide current to blow a fuse there, either..... am I missing something?

single panel I agree. Multiple panels another story. Let's assume you have 6 panels in parallel. One panel develops an internal short positive to negative, each panel can supply 15A, Now all the sudden you have 5 panels suppling up to a total of 60A through the wiring on the shorted panel. not a good idea. The fuse serves as a isolation device.

Fusing requirements for solar panels are more focused on house grid tie applications where you could have a dozen or more panels in parallel.