Solar panel fusing

[grahampa]

https://www.windynation.com/jzv/inf/how-properly-fuse-solar-pv-system

Windy nation tells me to fuse each solar panel at 30a plus a 60a fuse before the charge controller if wiring in parallel. (Well, I only have 3 solar panels at 100w instead of four but I'm still not sure of the need for the higher amp fuse). 

https://www.renogy.com/blog/how-to-fuse-your-solar-system/

Renogy tells me to use one 20a fuse (based on my calculations for my 3 100w panels) on my system if wiring in parallel.


So I came to the conclusion that I should use 30a fuses on each solar panel plus sticking with the 20a fuse just to be safe.. I know it's fairly pointless to have both but I dont trust some of these cheaper fuse companies I will end up using. Basically I'm wondering what the advantage of having a higher (60)amp fuse leading to my 40 amp charge controller. Any thoughts?

 

[Trebor English]

Every wire needs to be protected from too much current at every point where power is applied.  This protection can be either a fuse or a current limited source.  For example, there is a black wire from a head light bulb to ground.  The head light bulb limits the current that can be applied to that wire.  That wire must be big enough to carry the full current from the bulb.  Since the wire is big enough to carry the maximum possible current the bulb can deliver a fuse isn't necessary.  The other side of the bulb is different.  Presume for a moment this is a '57 Chevy.  There is a wire from the battery to the bulb.  There is a switch to turn the light on and a high beam low beam switch.  All that wiring is not fat enough to take the full battery current.  If the wire chafes and shorts there will be a problem.  This requires a fuse to protect those bits of wire and switches from the full wrath of the battery.  The fuse needs to be small enough to protect the wire.  The wire needs to be big enough to carry the necessary load.  Now with that fuse in place, if the headlight bulb shorts the black wire on the far side of the bulb is also protected.

With 3 solar panels each capable of producing 5 amps, 8 amps into a short circuit, you have a possibility of 24 amps.  The panels don't store energy so they are limited to the amount of current they can generate from the sun.  The circuit runs from the panels through the charge controller to the battery.  Although AWG #12 (20 amp) would be sufficient you probably want at least AWG #10 (30 amp) wire. You probably want even bigger to have good voltage drop performance.  Since AWG #10 wire can tolerate 30 amps you could put a 30 amp fuse at the battery.  That way any short to ground will cause that fuse to blow protecting the wire.  Since the wire is fat enough to take the full solar panel current there is no need to protect the wire from too much current from the panels.  That source is limited.

The solar panels come with leads attached.  Those are probably AWG #10.  From the battery all the way to the solar panel if the smallest piece of wire is AWG #10 then a 30 amp fuse is sufficient.  Normally you think of current going from solar panels to battery.  Put a short in the circuit now you have current from the battery back to the short.  The short could be in a panel.

If you put a 30 amp fuse at each solar panel how could an 8 amp panel blow the fuse?  If the fuse can't blow what is it protecting?  If you got ten panels with AWG #10 wire leads on each panel then it's different.  If a wire shorts 80 amps could flow and all those AWG #10 wires would need to be protected.  There the Windy Nation advice of a 30 amp fuse for each panel located at the point where all the panel wires come together would make sense.  From that point to the battery you would have much bigger wire with 10 panels.  The fuse at the battery would need to be sized to protect that much bigger wire.  Rather than 10 fuses with 10 panels you could connect 2 or 3 panels to shared 30 amp fuses and still not have too much current in those skinny panel leads.  

Bottom line, you need a fuse to protect everything from the battery.  It must be close to the battery.  With 3 100 watt panels there is no need for individual per panel fuses.  Sprinkling in some more fuses only provides more potential points of failure.

 

[Weight]

My expertise. Free on the internet. Worth twice what you have paid. Each connection and each fuse adds to the voltage drop in the system. More drop across a fuse. Four 100 watt panels, each with maximum short circuit current of 6.75 amperes. Wired in series, all four would be maximum 6.75 amperes. Wired in parallel, each panel 6.75 amps, total four panels could be 27 amps to a short. The 10 awg that comes with the panel can easily handle the amps to a short, so no fuse needed. The 10 awg can easily handle the combined 27 amps. No fuse needed. The panels are self limiting. If, Wired to a combiner box in parallel connection. It is possible for a short in a panel to drain all the power from the other three panels. So I use a 15 amp fuse on each panel. Three panels shorting into one would be 20 amps. The bad panel drops out with a blown fuse. The other panels keep producing power. After the box, I use 10 feet of 4 awg to the controller. 1.27% voltage drop. No fuse needed. I do recommend a disconnect switch. A switch, not a breaker. A switch will have lower voltage drop than a breaker. From the 45 amp controller to the battery positive buss-bar I use 5 feet of the 4awg left from the other end. Less than 1% voltage drop. The 4awg can handle well over 130 amps. I fuse at the battery positive buss bar with a 100 amp fuse. The battery has unlimited amperes available. The 100 amp fuse protects the wire with the least voltage drop. I wouldn't be opposed to using a larger fuse, maybe 125 amp.
There are limited amounts of sun power available and house batteries are hungry devils. It is good practice to limit voltage drop in a charging circuit. That means proper crimped wire ends. Quality wire with a large enough size to carry the expected current. Fuse only where needed and sized to protect the wire, not the device. Switches should be the best you can afford. I use BlueSea battery disconnect switches. I also would not use anything but marine grade wire and cable. Not welding cable. Not Home Depot household wire. Not automotive wire. The marine grade wire is consistent good quality. The stuff in auto parts and hardware stores is sometimes of questionable quality. Household wire is stiff, hard to work with, and not designed for movement. Welding cable also comes in many different qualities and you don't know what you have until the insulation splits and sparks fly. I also realise this is Cheap RV Living. If you have access to the wire, use what you have for yourself. Don't use cost cutting if you are building for someone else. Buy yourself a good set of crimpers or use one of the custom wire and cable suppliers, Genuine Dealz or Bay Marine. dot coms I tried to edit and hope there are no mistakes. But I am up to argue my method.

 

[MrNoodly]

For what it’s worth, I don't have a fuse between my 270W solar panel and the charge controller. It has been like that for six years. I figure there isn't going to be a sudden excessive spike in sunlight (and if there ever is, we’ve all got bigger problems than my solar setup). I also figure if there's ever any kind of short in the current path between the panel and controller, it’ll be one that breaks the flow to the controller.

But if you want to put a fuse between the panels and controller, why not connect the panels to a bus then just use one fuse between the bus and the controller?

 

[brahmon]

now that i'm learning that a fuse is not necessary, i'm kind of pissed that i spent $100 on inline fuses.    why would renogy advise to fuse each panel other than to generate unethical revenue?

 

[Seminole Wind]

every panel can be different, follow the specs and recommendations from the panel manufacturer 9often printed right on the panel) for fusing panels.

as for fusing the wires to the controller or from controller to battery. look up the spec for the wire gauge and type and fuse to protect the wire.

you should have a fuse (or breaker) located very close to and current source. in some cases 1 wire may need 2 fuses, one on each end.

 

[Weight]

Solar panels are self limiting energy sources. If the wire is properly sized, no fuse is needed between the panel and controller. See my above post about fuses on parallel panels. $100 on inline fuses?

 

[Spaceman Spiff]

If a manufacturer recommends a fuse it is prudent to use a fuse.  Morningstar recommended a 60A fuse on the solar panel side for my 45A controller.

Good quality 12V fuses are expensive.  The 60A ANL fuses I use are ~ $20 each for fuse and holder.  Mainesail has a good writeup on fuses; what fuses to use in mobile applications and why you don't want to use cheap fuses:  https://marinehowto.com/fusing-termination-voltage-drop/

 

[MrNoodly]

Morningstar recommended a 60A fuse on the solar panel side for my 45A controller.

But if the total output of someone's panel(s) can never be that high, then the fuse is pointless.

 

[Spaceman Spiff]

Think Morningstar knows a little more about it than we do?

 

[grahampa]

Had to look into this for myself spiff. What I see is Morningstar referring to the connection between the battery and the charge controller at a maximum of 70 amps, fusing your solar panels at 70 amps seems pointless to me. The 10 gauge wire common on solar only holds up to 30 amps. Potentially even a fire hazard, but only if you have enough solar panels hooked up in your system to break the 30 amp limit. I have a very basic understanding of these systems so I could be wrong

 

[grahampa]

My expertise. Free on the internet. Worth twice what you have paid.

? Damn I'm lucky to have found this site
I wish I could have some of you guys come down and check my stuff out to tell me how bad I ****** it up.. total amateur build that will hopefully be up and running tomorrow

 

[Weight]

If the wire from the solar panel is sized to handle the maximum shorted amperage of the panel, no fuse is needed between the panel and controller. Morningstar legal team doesn't know how many or what size panels you may use. They have to cover their ass. A roof top system can be very large with the potential for high amperes.

 

[Spaceman Spiff]

 . . . What I see is Morningstar referring to the connection between the battery and the charge controller at a maximum of 70 amps, fusing your solar panels at 70 amps seems pointless to me. The 10 gauge wire common on solar only holds up to 30 amps . . .

Morningstar's installation instructions included with the controller recommended a 60A fuse between the solar panel and the controller.  I also have a 60A fuse at the battery positive terminal and at the starter battery connection to the house bank.

I have 4 AWG wire from the roof to the controller.  It amazes me that one would spend a lot of money on solar panels, controller, and batteries and go cheap on wire and fuses.  Solar gives little enough energy without throwing some away with undersized wire.

I looked at Renogy, Windy Nation, and Arizona Wind and Sun; all three recommend fuses between panels and controller.  They should know more about their systems than I do so I am willing to spend the 20 bucks to fuse the connection.

 

[Weight]

If the wires are sufficant to carry the maximum amperes generated by the solar panel output, no fuse is needed. Solar panels are self limiting. Not like shorting a battery.
Solar gives little enough energy without throwing some away with undersized wire., Or adding a resistor, oh, a fuse that is not needed.

 

[Spaceman Spiff]

If the wires are sufficant to carry the maximum amperes generated by the solar panel output, no fuse is needed . . . 

Then why do so many makers and sellers of solar panels and controllers recommend them?

 

[Trebor English]

Then why do so many makers and sellers of solar panels and controllers recommend them?

Every wire needs protection from too much current.  If you have ten 100 watt panels parallel connected there could be 80 amps short circuited and that's too much for an AWG #10 panel lead.  Three 100 watt panels, no problem.  Ten, problem.  

One size fits all, no math, no thinking, cost and performance don't matter, just sprinkle in fuses everywhere.

 

[Weight]

Fuses are resisters. Fuses and the extra connections restrict the power delivered by the solar panels. I need all the power I can collect. I do not have 80 amps of solar on my roof. And, as I stated, IF the wires are sized properly, there is no need for the fuse. If i was collecting 80 amps from solar panels, I would use 6 awg cable. No fuse needed.

 

[Seminole Wind]

Fuses are resisters. Fuses and the extra connections restrict the power delivered by the solar panels. I need all the power I can collect. I do not have 80 amps of solar on my roof. And, as I stated, IF the wires are sized properly, there is no need for the fuse. If i was collecting 80 amps from solar panels,  I would use 6 awg cable. No fuse needed.

there are situations with multiple panels that under certain failure conditions that can cause more current than is safe to flow. with multiple panels it is not just about current through the wire, but the panel and its components as well. melting a wire because you skipped the recommended fuse is one thing, burning up hundreds of dollars worth of panels for the same reason is all together different. all panels have a certain level of protection built in. you can find it in the specs for the panel. 1, 2 and usually 3 panels come in under the built in protection, but when you get into more the odds go up that you should have some external fusing. the only way to know is read the spec and do the math. the old head in the sand and fingers in the ears yelling lalalalal... does not change that

 

[Weight]

Go back and read my first post in this thread. The part where I post about parallel wired panels. Then, I want you to site a true story about solar panels being destroyed by a short, any where.