Fuse needed between solar panels and charge controller?

Dorothea · Jan 24, 2020

I plan to build a system very similar to https://www.mobile-solarpower.com/simplified-400-watt-fewer-wires-and-alternator-charging.html (awesome page!). The diagrams does not show any fuses between the solar panel and the Renogy charge controller. Yet I have seen other people put in a fuse. Therefore my questions: Do I really need a fuse there? What are the disadvantages/risks of not putting a fuse between charge controller and panels?
Thanks!

MisterSandals · Jan 24, 2020

You absolutely need a fuse. You should also have a cutoff switch. A quality breaker works well to handle both these NEEDS.

Dorothea · Jan 24, 2020

MisterSandals said:
You absolutely need a fuse. You should also have a cutoff switch. A quality breaker works well to handle both these NEEDS.

Thanks! Any recommendation for which breaker? I'll connect two 160W 12V solar panels in parallel.

Craig · Jan 24, 2020

I like these 2P 250V Low-voltage DC Miniature Circuit Breaker For Solar Panels Grid System din rail mount(63A), Breaker DC Circuit Amp Solar Double Pole https://www.amazon.com/dp/B0746DLP7S/ref=cm_sw_r_cp_apa_i_dCYkEbY7D9JW6

They come in different amp ranges you probably need about a 20 amp breaker maybe 30 depending on open circuit voltage.

Dzl · Feb 15, 2020

FilterGuy started a thread on fusing here and in it, someone linked to this article on solar panel fusing

Danny · Feb 16, 2020

I really like Craig's idea but I'm using these. https://www.amazon.com/RKURCK-Water...argid=aud-801381245258:pla-524046089487&psc=1

kenkoh · Feb 17, 2020

MisterSandals said:
You absolutely need a fuse. You should also have a cutoff switch. A quality breaker works well to handle both these NEEDS.

But in single or double string series you don't correct? What r your thoughts on this article? https://www.explorist.life/how-to-fuse-a-solar-panel-array-and-why-you-may-not-need-to/

kenkoh · Feb 17, 2020

Danny said:
I really like Craig's idea but I'm using these. https://www.amazon.com/RKURCK-Water...argid=aud-801381245258:pla-524046089487&psc=1

I don't understand 1P vs. 2P breakers between array & SCC. Does anyone know for sure which is safer?

nosys70 · Feb 17, 2020

1P is to cut device working, 2P is to isolate device (galvanic isolation) , not the same purpose.
for example, if you go to solder on panels frame , you want to isolate (2P) , if you just want panels stop feeding charge controller 1P is ok.
Same for ligthning protection. 1P is useless.
if you got a good ground on Panels, 2P is ok.

kenkoh · Feb 17, 2020

nosys70 said:
it is not the same purpose.
1P is to cut device working, 2P is to isolate device, not the same purpose.
for example, if you go to solder panels on the roof, you want to isolate, if you just want panels stop feeding charge controller 1P is ok.

So which is safer for a novice like myself cutting or isolating?

nosys70 · Feb 17, 2020

isolating 2P.
some device even require 1P (cut) +1P (switch to ground), so you ground one wire (to prevent static electricity for example)

kenkoh · Feb 17, 2020

Craig said:
I like these 2P 250V Low-voltage DC Miniature Circuit Breaker For Solar Panels Grid System din rail mount(63A), Breaker DC Circuit Amp Solar Double Pole https://www.amazon.com/dp/B0746DLP7S/ref=cm_sw_r_cp_apa_i_dCYkEbY7D9JW6

They come in different amp ranges you probably need about a 20 amp breaker maybe 30 depending on open circuit voltage.

Would you recommend the 2P 16A for my 600w build? https://bit.ly/2u1kame

fat_old_sun · Feb 17, 2020

MisterSandals said:
You absolutely need a fuse. You should also have a cutoff switch. A quality breaker works well to handle both these NEEDS.

Why a fuse? I understand the need for a switch for isolating panels from SCC.

A solar panel doe not need a fuse. It does not have the ability to deliver a high current at high enough voltage like a battery does. A fuse on the battery -> SCC line is needed; a fuse on the panel-> SCC is not needed.

Steve_S · Feb 17, 2020

oivey…. seriously, no breakers or fuses ? Cars without brakes... just as sensible.
OK, you hold the wires with 200VDC & 30A running through and tell us how yo make out eh !
Why do Certified Combiners have Breakers in them for each string ?
Why are there Master shutoffs (DISCO) for panels ?
Must be because some regulator somewhere wants to make money, not because of safety & security of the individual or property.

Common Sense dictates Safety First, anyone tells you to ignore safety, RUN ! You only get one life and while some may not give a hoot about theirs, considers yours and your families safety & wellbeing, ignore idiotic "advice".

kenkoh · Feb 17, 2020

kenkoh said:
Would you recommend the 2P 16A for my 600w build? https://bit.ly/2u1kame

I'll update my build.

fat_old_sun · Feb 17, 2020

Steve_S said:
oivey…. seriously, no breakers or fuses ? Cars without brakes... just as sensible.
OK, you hold the wires with 200VDC & 30A running through and tell us how yo make out eh !
Why do Certified Combiners have Breakers in them for each string ?
Why are there Master shutoffs (DISCO) for panels ?
Must be because some regulator somewhere wants to make money, not because of safety & security of the individual or property.

Common Sense dictates Safety First, anyone tells you to ignore safety, RUN ! You only get one life and while some may not give a hoot about theirs, considers yours and your families safety & wellbeing, ignore idiotic "advice".

The OP is putting together a dinky little 400 Watt 12V system & not a high voltage, grid connected installation. Sure, adding a breaker won't hurt, but there's no compelling technical/safety need for one on the solar side. A solar panel is a very peculiar kind of electrical source, quite different from an electro-chemical battery.

If he series connects the four panels, there'll be max 100 V DC at the solar terminals - high enough to electrocute someone. A breaker/fuse on this line will not prevent this. If that 100 V line shorts to ground, a max of 6 Amps will flow to ground, but with very little potential to do any damage.

edited the max current value from 24 Amps to 6 Amps

nosys70 · Feb 17, 2020

the only reason why you would put fuse on solar panel is to protect wiring, so the fuses shoud be put on at the output of solar panels (fused MC4) ?.
if you short circuit a battery you can easily get 1000Amps for a few seconds, so yes, a fuse is mandatory.
if you short-ciruit a 400w solar panel, then well, you got the max amps the panel can provide (33A for a 12v 400W panel)
in that case you can put the fuse at the controller side but if you put a 40a fuse , you are not even sure it will blow, while the wiring can get hot enough to cause problems on the path. If you put lower Amps for the fuse, you will se the risk to blow it up often.

fat_old_sun · Feb 17, 2020

nosys70 said:
the only reason why you would put fuse on solar panel is to protect wiring, so the fuses shoud be put on at the output of solar panels (fused MC4) ?.
if you short circuit a battery you can easily get 1000Amps for a few seconds, so yes, a fuse is mandatory.
if you short-ciruit a 400w solar panel, then well, you got the max amps the panel can provide (33A for a 12v 400W panel)
in that case you can put the fuse at the controller side but if you put a 40a fuse , you are not even sure it will blow, while the wiring can get hot enough to cause problems on the path. If you put lower Amps for the fuse, you will se the risk to blow it up often.

how can a set of panels designed to deliver an absolute max of 33 Amps deliver 40 Amps? Solar panels & their wirings are already rated for their max current & some. It is unlikely that the solar wiring will get hot or even warm. The only way to cause some damage with a set of solar panels is if you go out of your way to select thin wires such that the resistance of the wires is just right that the panels operate near their max power point.

The advice to put fuses on the solar side of low voltage low power systems is like one of those things that get repeated without being questioned - "drink at least 8 cups of water a day" or "don't ever discharge your lead acid batteries below 50%".

fat_old_sun · Feb 17, 2020

Back to the OP's original question (assuming he's still interested in a response): fuses are not needed. switches are recommended. here's a good source - https://www.amazon.com/Waterproof-Marine-Motorcycle-Rocker-Toggle/dp/B01J0PFX3Y

BiduleOhm · Feb 17, 2020

fat_old_sun said:
how can a set of panels designed to deliver an absolute max of 33 Amps deliver 40 Amps?

If you have multiple strings of panels in // it can easily happen. All it needs is a bad cell or a short circuit, then all the others strings backfeed into the faulty one, thus the over current.

Fuse needed between solar panels and charge controller?

New Member

Participation Medalist

New Member

Watts are Watts!

Unofficial Forum Librarian & Perpetual Newbie

Solar Enthusiast

Solar Enthusiast

Solar Enthusiast

Solar Enthusiast

Solar Enthusiast

Solar Enthusiast

Solar Enthusiast

Solar Enthusiast

Offgrid Cabineer, N.E. Ontario, Canada

Solar Enthusiast

Solar Enthusiast

Solar Enthusiast

Solar Enthusiast

Solar Enthusiast

Electronics Sorcerer

Similar threads