Solar panel fuse - voltage exceeded AHH

[Silvester]

Hey guys,

trying to figure out a way to fuse my solar panels safely. I only have 4 panels wired in series+parallel the are 275w panels and put out 9.27A max and 31.3 volts max for a total without loss of 18.52A 62.6V as wired (pretty sure that's the math).

does anyone know were I can get a fuse rated to support that kind of voltage so I don't have the current jump the air gap as bolts tend to do? It seems that most automotive fuses are 32VDC. I have a breaker box I could use but those my breaker size I have are only AC rated and that doesn't solve my air gap problem as I know you shouldn't use AC breakers for DC application due to the air gap jump concern.

thanks.

[Silvester]

I think I found my answer; use square d QO series breakers as they are DC approved woot woot! A dollar saved!

[littleharbor]

QOU breakers are the higher DC rated version. Approved for 48 volt systems.

https://www.schneider-electric.us/en/faqs/FA119735/

[Sunking]

You do know fuses or breaks are NOT required or needed right?

[Silvester]

You do know fuses or breaks are NOT required or needed right?

I wasn't aware, that's the best news I have heard all week! Dilemma solved.!.

Do you mind elaborating a bit if just for my curiosity and learning purposes?

thanks in advance man!

[Mike90250]

2 parallel strings of panels do not need fusing. 3 strings do. So you are under the 3 string limit. However, you will be in a bind if you ever have to do any troubleshooting on your system, or even powering it up and down, because the battery power to the Controller gets turned on first, and after it boots up, the solar PV can be applied. Without a breaker or a DC rated switch, you can't do that. A Midnight Solar box, DIN rail, and 3 din rail 150VDC breakers would be about $100 bucks, and simplify your life.

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[Sunking]

Do you mind elaborating a bit if just for my curiosity and learning purposes?

thanks in advance man!

I will try to explain. Solar Panels are Current Sources, NOT voltage.

If you look at any solar panel specs you will see one labeled Isc or Current Short Circuit. That is the maximum current the panel could ever produce under extreme conditions. You would be hard pressed to find a panel with more than 10-amps Isc. Say you had a string of 10 panels in series and Isc = 10 amps on 12AWG wire. Short the panels out right at the controller input and at most you have 10 amps at high noon with crystal clear skies and no humidity. No problem a 12 AWG is good to 25 amps before it even gets warm. Wire up a second string of 10 panels and put it in parallel with th efirst string. Short the panels out and you have as much as 20 amps on a 12 AWG. No problem, wire might get a little warm but there is no safety or fire issue.

Add the 3rd string now you have a possibility for too much current of 30 amps. So you can use a Breaker or Fuse on 2-strings if you want, but there is no requirement for any. As for me I just put a Shorting Switch at the Input of my Controller to short the panels out when I want to turn the panels off.

[Silvester]

Much appreciated Mike and Sunking! Great explanations as always!