wire sizing for off grid cabin

wren

New Member
Joined
Oct 7, 2021
Messages
8
Hi everybody, I am a bit over my head with installing a solar array of 2 400 w, 24 v modules. I am hooking them up in parallel and don't kno wthe cable size from there on, to my 4 12 volt 200Ah AGM Renogy battery bank. Will a 6 gauge wire do?
And do Ineed n inline fuse between the array and the 80amp charge controller?
The inverter is a 2500W 24 v.
Inverter and charge controller are an All in One unit that was recommended by Will Prose. The batteries are in series and parallel, to meet the 24v. Are the automotive battery cables of 4 gauge enough?
And again, do I need to put an inline fuse between charge controller and batteries? What size?
And what size cable will feed from the batteries to the inverter? Fuse there as well?
It would be awesome to figure this out, so I can finally mount my modules on my cabin and have sufficient power to hopefully run a 110 v, 4amp convection heater for a few hrs in the early morning and a 1500w, 110v vitamix for a min every morning, as well as have a booster plugged in for wifi, when needed, possibly 2 hrs a day.
Are these loads too much?
Thanks for listening.
wren
 

rmaddy

Full-time Solar-powered Trailer Life
Joined
Nov 16, 2019
Messages
1,650
Location
USA
Post the full specs for your solar panels. Those numbers will determine the wire size needed. Also include the wire length needed to go from the panels to the charge controller. The length also helps determine the wire size.

With just 2 panels in parallel you do not need a fuse between the panels and SCC. But you should have a disconnect switch. A breaker is a common choice for such a disconnect. Though the breaker is only acting as a disconnect, it will not be protecting the wire.

2400W inverter / 24V system / 0.85 efficiency factor is about 120A. You want at least 2AWG for that level of amps. 4AWG is too small. And you would need a 150A fuse between the inverter and battery.

There should be a fuse or breaker between the SCC and batteries. If the SCC has a max output current of 80A then you want 4AWG wire and a 100A fuse.

But, since this is an all-in-one I would think there is only one set of wires between the all-in-one and the battery. Or are there actually separate wires needed for the inverter portion and the SCC portion? Assuming it's one set of wires then use the higher values I posted for the inverter.

Your heater will only be about 480W so it will run fine on its own.

The vitamix might be a problem, even on its own. It may have a large startup surge that might be too much for a 2400W inverter. Once running it will be fine at 1500W.

You have 4 12V 200Ah batteries. That's 4 x 12.8V x 200Ah = 10240Wh. But you only get 50% with AGM. So you have 5120Wh usable.

The heater is 2 hours at 480W. That's 960Wh.
The vitamix is 1/60 hour at 1500W. That's 25Wh.
The WiFi booster might be 40W (I don't know) for 2 hours. Let's just call it 100Wh.

So you need 960+25+100 = 1085Wh per day. You have 5120Wh in your battery. So you can run your stuff for nearly 5 days before needing to recharge.

Your 800W of solar might give you 700W in good sun and angled well. If your power usage is 1085Wh per day, your solar can keep that running and the battery full in 90 minutes. Of course it will take longer on cloudy days.

In short, you seem to have a good setup. The big question is whether the inverter can handle the startup surge of the vitamix.
 

time2roll

Photon Sorcerer
Joined
Mar 20, 2021
Messages
2,400
Careful with automotive wire as SAE is smaller than AWG.

The 400w panels I see are close to 40 volts and 10 amps. I would use standard #10 MC4 solar extension wire and a pair of parallel connectors. Cut the extension in half and use the connectors to plug and play to the panels and the cut end on the controller/inverter. No fuse needed.

Inverter instructions will cover the wire size.
 

newbostonconst

Solar Addict
Joined
Sep 24, 2019
Messages
660
time2roll, I agree it will likely 10 amps each so 20 amps in parallel, so before the solar cables are joined to be parallel the wire can 14 awg for most runs and 12or10 awg after they are put in parallel going to SCC. But you always need a fuse or breaker, some get away not doing it when the components are really close like a few feet apart. Fuses/breakers protect the wire from burning down your house.

35 amps appear to be going from the SCC to the batteries so 8 awg. The 2400 watt inverter can pull 100 amps so 4 awg wire.
 
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