4x100w panels in parallel - to fuse or not to fuse

[12VoltInstalls]

at 48.6Voc,

A decent DC breaker is rated for the volts you need, albeit at lesser amps than the blue sea. But fine for your panels.
The switch posted is intended as a battery disconnect.

 

[dsaint1884]

A decent DC breaker is rated for the volts you need, albeit at lesser amps than the blue sea. But fine for your panels.
The switch posted is intended as a battery disconnect.

Do you have a suggestion of a disconnect I should be installing in this system? When I've searched for them I continue to get ones rated for 48v and are seemingly for battery disconnects.

Alternatively, I can just stick to parallel and stay in the 12v range (24.3voc) and most of these switches seem like they would then be fine.

 

[12VoltInstalls]

You need to search for DC breakers

Outback is a “safe” brand. A few Chinese breakers- very few- are acceptable. I have bought chaitaxi DC breakers to use as disconnects that appear to be properly designed as breakers. I still use fuses for the panels, just have the breakers for disconnects .

 

[PVorBust]

In my head I was thinking of the scenario where the positive and negative wires both have a short touching the van.

If both the positive and negative become shorted:

• Something has gone seriously wrong
• You can't get a shock (it's shorted)

Put an over rated Double-Pole switch on the feed and worry about the important things.

 

[Zil]

I have the Renogy 400w solar kit. The panels have:

15a max series fuse rating
Short Circuit Current (ISC) 5.21a

If I run the 4 panels in parallel I'd be up to 20.84a (5.21x4). If one of the panels shorts and the other three panels decide to take the path into that panel they would only be pushing 15.63a (5.21x3 good panels) right? So that 15.63 is right inline with the 15a max series fuse rating.

Their website seems a bit contradictory to me. It shows a diagram of the panels in parallel with a 10a fuse on just one panel (not sure what that does) but then also says 'if you choose to connect in parallel, you can use three pairs of Solar Y Branch Connectors to connect four panels in two by two, and then parallel again; do not use an in-line fuse in parallel circuits."

New 400 Watt 12 Volt Solar Premium Kit W/MPPT or REGO Solar Charge Controller

4* 100W Eclipse Monocrystalline Solar Panels totaling 400 Watt, 1* 40 Amp MPPT Charge Controller, 2* 20' Solar Extension Cables, 1* Solar Adapter Kit 9'' in length, and 4 Sets of Z brackets for Mounting

renogy.com

I suppose I could add in a 10a fuse on each positive line from the panel, beyond the short circuit current but enough to catch the 15.63 short circuit ratings, but is adding a fuse on each panel positive wire, 4 in total, really necessary?

With three or more panels in parallel each panel needs be fused at the labeled max fuse rating. For my Renogy 100W panels that is 15 amperes. I used a 4 space fuse panel from Blue Sea. https://www.bluesea.com/products/5045/ST_Blade_Compact_Fuse_Blocks_-_4_Circuits Parts available a reasonable discounts than MSRP.

 

[Zil]

If both the positive and negative become shorted:

• Something has gone seriously wrong
• You can't get a shock (it's shorted)

Put an over rated Double-Pole switch on the feed and worry about the important things.

Could have a fire.

 

[PVorBust]

With three or more panels in parallel each panel needs be fused at the labeled max fuse rating. For my Renogy 100W panels that is 15 amperes.

Under what circumstances would a 15A fuse blow while "protecting" a 100W panel?
[making an assumption your 100W panel is 21Voc, that's about 5A]
So I repeat the question: When will a 5A panel blow a 15A fuse?

Fuses are one of the simplest electronic components, but still poorly understood.
A 15A fuse is rated to "operate" up to 15A, not blow at 15A. So even if one of your panels goes short-circuit and the other two feed their full current (10A) into the short, your 15A fuse still won't blow.

Have a look at this data sheet from Littlefuse: https://www.littelfuse.com/media?re...d73-a6c8-aca6d27b9a37&filename=spfi-datasheet
Is clearly shows a 15A fuse will carry 19A for 1000 seconds (16 min) before blowing (see the graph below).
Even with 30A going through it, a 15A will take 1 minute before it blows.

Could have a fire.

Possibly, but a fuse won't save you.

 

[12VoltInstalls]

15A fuse is rated to "operate" up to 15A, not blow at 15A. So even if one of your panels goes short-circuit and the other two feed their full current (10A) into the short, your 15A fuse still won't blow

That is why I fuse stuff for the load even if the wire is 20A. (Not to say anyone should under wire something and rely on a fuse, either, fwiw)
It’s always been a mystery to me- and how common it is- that in small systems people use a 1500-2500W inverter and then feed a breaker box with a a 30, 40, or 50A main breaker. Might as well skip the ocp altogether!