diy solar

diy solar

Solar Panel Fusing

Missileman Tom

New Member
Joined
Apr 26, 2021
Messages
22
I am building the 24V 2000/4000W Off Grid System. I have everything but the batteries but I see most systems seem to have fuses for the solar panels which Will does not show in his schematics or photos. All of my solar cables are 10 AWG, 26Ft. to and from the panels which are two 410W bi-facials in series. Do I just need one fuse and of what amperage? I see many different amp fuses listed with MC4 in-line fuse holders. Also I can't find a source to sell me TWO SOK 100AH batteries. They are limiting me to one only.
 
Panels are typically 10awg wire and MC4 connectors are speced for a max of 30a. A typical panel (and string in series) will be around 9-10a. If you parallel 2 strings - its 20a. If you parallel 3 string it's really exceeding the intent of mc4 / 10awg wiring - so you combine at a combiner box and go on with higher gauge wire as appropriate.

If you have 1 string with MC4 / 10awg wiring - then you need at least as much as the panels produce - but you can go a bit higher. For example you might use 15a instead of 10a - its perfectly OK. If you have 2 strings in parallel - then likely 25a or 30a.

If you have alot of panels - Will just did a 'combiner box' youtube that might apply for your situation :)
 
Last edited:
I recommend a circuit breaker if you do not have some sort of solar disconnect. Fusing or circuit breakers may not be mandatory for a single series of panels or two series in parallel, but if you ever need to power down the system in the day, it beats climbing on the roof and covering the solar panels.

I have an RV and store the batteries shut off and every time I return, I shut the circuit breakers to the panels off, and then shut the battery switch off, and it is ready to be stored.
 
All of my solar cables are 10 AWG, 26Ft. to and from the panels which are two 410W bi-facials in series. Do I just need one fuse and of what amperage?

Two panels in series, any number in series as a single string, no PV fuses needed.
If you have 3 or more strings in parallel, the each string needs one fuse or breaker to protect against backfeed from the other strings, in case of a fault.

There are some exception (transformerless grid-tie inverters) which need both ends of a single PV string fused.
But not your off-grid setup.

Lithium batteries, now those should have fuses. Class T are recommended because they can interrupt the 20,000 amps we expect the battery to dump into a short circuit.

Amazon shows 20 SOK 100 Ah in stock.


Have you considered DIY?
I think you can make 280 Ah 24V for about 2/3 the price.
 
My batteries are fused on the board for my system (The large type Will Prowse recommends). I saw schematics on-line that showed PVs in series with fuses between each. I knew that would be best in a parallel PV setup. So many different ways! I do have XT-60 connectors in place from the MPPT controller to the PVs that I can disconnect. This system will probably just be used in emergency situations anyway and my PVs will be on mounts in my driveway. Think I'll mount wheels on one edge to roll them in and out of the garage. I built many electronic units for NASA over the years but never worked with solar. I have been retired about ten years now. I can build just about anything but think I'd prefer two of the SOK batteries with warranties. Thanks for your input. So I may or may not add an MC4 15A in-line fuse. Probably not. I will check with Jeff Bazos, I mean Amazon on the SOKs.
 
Back
Top