First build plans and questions

[offgridaaron]

Hi all,

I'm planning out the 12v system to upgrade my travel trailer's power. My trailer is sitting on a perm spot without utilities. I had thought about going 48v right off the hop, but I wound up getting a sungoldpower 12v 4000w inverter for near free so kind of moving along with this plan.

From what I understand the inverter being large and 12v will need a 500A fuse, and 0/4 wire. I'm still researching the other wire and what would be appropriate sizes, but since I'm a couple days into my research I figured it was time to share here, and see if I'm going in a totally wrong direction.

The questions I have on the todo list are:
1. I read that 1000W solar array is kind of the max you'd want to put into a 12v system, is that accurate? Right now I'm looking at 3x 300w panels in series, but down the road if it'd allow it I'd add 3 more and do 2p3s for 1800w.
2. What sort of battery disconnect would I need? I had originally planned on a Blue Sea switch, but if the inverter is looking at 500A fuse, I imagine the Blue Sea 300A battery disconnect would not cut it.
3. Battery cables should probably be 0/4 to match the inverters?
4. Sizing of cables to the travel trailer, to the always on 12v box, from the charge controller to the lynx, and from the panels to the 2p breaker to the victron

I picked the Victron Lynx Distro 1000 because it was the only bus bar I could find that was 500A or above. In my head its nice because all loads are fused.

I think I should get the Victron 1000A shunt, not the 500A, I don't know if the inverter will actually pull 500, but with the other 12v loads it seems like the 500A may be underpowered.

In the lynx distro i was thinking a 70a fuse for the charge controller, 2x 80's for the trailer and 12v panel, and a 500a for the inverter.

The batteries are TBD

I'm sorry for the bad drawing, but this is what I've started to put together.

The big question, is, am I on the right track or do I need to stop and re-assess what I'm doing?

thanks!

 

[MichaelK]

Forget about trying to get 4000W out of that inverter. They are lying to you. Ask one simple question. Is this inverter UL listed? If it isn't, then it ain't 4000W. Whatever battery you are likely to have in your RV is not large enough to ever get close to supplying that much power. I'd plan on 2000W and you'd be good to go.

You should be talking about your battery size in terms of determining how much solar to have. Let's say you have 250Ah golf-carts wired in series for 12V. Generally, a lot of batteries like charging at 1/8th of C. So, that works out to be 250Ah X 1/8th = 31.25A. To get 31.25A you need that amperage times the charging voltage, or 31.25A X 12.5V = 390W.

Panels almost never put out their rated power, so I always incorporate a fudgefactor to compensate. For panels pointed directly at the sun, I use 85%. For panels laying flat on a RV roof, I'd use 60%. So, 390W/60% = 650W of panels. So, maybe two of your panels is OK to start out with. Use the formula given if you have a different sized battery.

Those are Li batteries in the pic? They are 200Ah each? C is 200Ah. Li likes a higher charging rate, 1/4th C is good, so the math for 2 200Ah batteries in series would be (400Ah/4) X 12.5V =1250W.

But, since you only have a 70A controller, anything over 70A is just wasted. With a 60% fudgefactor that's (70A X 12.5V)/60% = 1458W, so maybe 4 or 5 of those panels. With an odd number like 5, you can only wire them in parallel, as 1S5P.

 

[offgridaaron]

Hi Michael, thanks for the reply! Good point on the inverter, I doubt its UL listed. The 4000k is way more than I'd need, I just want to be able to use a laptop, charge a drill, or turn on the TV here are there (the point is getting away from city stuff so all 3 would be rare use, just nice to have the option), and like I say I got it for next to nothing.

Batteries I really want to go Li, thats why they're TBD, its really "what can I afford at the end?". I'd like to get 2x 400AH but we'll see, that is probably going to be more than i can stomach cost wise. I kind of want to setup the core of it right, so even if I have to do something temporary for batteries i'm positioned to upgrade down the road.

Do you think I should go bigger on the controller? That component is starting to get uncomfortably expensive hah

thanks!

 

[chrisski]

1. I read that 1000W solar array is kind of the max you'd want to put into a 12v system, is that accurate? Right now I'm looking at 3x 300w panels in series, but down the road if it'd allow it I'd add 3 more and do 2p3s for 1800w.

I would say 100 amps is the max continuous charging or discharging you want, which is about 1000 watts on a 12 volt system. I do agree that you need to ditch the 4000 watt inverter and get a UL478 inverter. When I was 12 volts, I had a 2000 watt inverter, which I used at a max of 1000 watts except for a couple three or four times a day use an inverter that pulled around 1850 watts for a couple minutes to warm, not cook in a microwave.

There is an art to that though with overpaneling and limiting an SCC to so many amps output. Also as mentioned not to charge more than 1/8 C. Four 6 volt batteries limited me to 60 amps, so to reach the 100 amp limit I talk about, that’s abut 8 batteries.

2. What sort of battery disconnect would I need? I had originally planned on a Blue Sea switch, but if the inverter is looking at 500A fuse, I imagine the Blue Sea 300A battery disconnect would not cut it.

Please don’t even consider 500 amps. I had a 350 amp Blue Sea switch for my 12 volt 2000 watt inverter.

3. Battery cables should probably be 0/4 to match the inverters?

Really need to look at ampacity of the wire. I doubt your 4/0 wires are rated to 500 amps. The 4/0 wire I used was for 250 amps max, and I never expected to go near it. ==============
You really need a realistic power requirement of what you want to build your system for.

In normal Boondocking season for me when the weather is comfortable, I will barely use any power, perhaps 1 kWh, but when the cold happens and my propane heater runs, This can go to 3.5 kWh. When I have run a single Air conditioning for six hours, used the electric water heatrer for one shower run the electric/gas fridge on electric, I have used 18 kwh.

Huge difference in the build requirements. Mine kind of grew from a 1000 watt 12 volt system, to 1450 watts of panels at 12 volts, to 2100 watts of panels at 24 volts, to 2550 watts of panels at 24 volts.