Design Confirmation/help for a NOOB

[Jusbechillin]

Been watching videos, read Mobile Solar Power Made Easy, etc. mostly took recommendations from Wills DIY solar website.

installing solar on my travel trailer. Mostly designed for higher amp hours as I’ll probably be mostly going on 2-4 day off the grid trips. System isn’t being designed to be able to run constantly and stay topped off, more just to get me through long weekend trips and then use the solar to charge back up until next use. So I went higher battery capacity and lower solar power. I have a couple questions.

• I’m a little confused on if I need an ATS (automatic transfer switch) or not. I will sometimes end up camping where there’s shore power, or might plug into my house power on rare occasion. I also will need to run a generator sometimes to power my AC. I’m thinking I need one, but have seen a lot of systems people have installed and they never mention using one. And, how would I wire one into the system that can decide between shore/generator/solar?
• For the diy LIFEPO4 battery, are the bars they provide with the cells to connect them together sufficient or should I be concerned with upgrading them to a higher quality?
• My Trailer has a curved roof. What is the reason it’s not recommended to mount directly to a curved roof?

here’s what I already purchased:

4 100 watt Rich Solar 12volt poly panels. Wiring in series & parallel to provide 24v to the battery. Using 10 gauge wire. Depending on performance I want to be able to add two more panels in the future if my needs change.

Building a DIY Lifepo4 battery With cells supplied from Alibaba. They should be here next week! 8 x 280AH, 3.2v cells prismatic grade a cells. Going to wire them in series to end up 24v 280AH. Overkill solar 24v Bms.

Victron MPPT 100/30 smartsolar charge controller.

Giandel pure sine 3000 watt 24v inverter.

300amp main fuse.

40amp circuit breaker.

4 guage wire to the inventor.

Thanks!

 

[svetz]

...I have a couple questions.

1. [do I] ... need an ATS?...
2. For the diy LIFEPO4 battery, are the bars they provide .. together sufficient...?
3. What is the reason it’s not recommended to mount directly to a curved roof?

1. You don't need one, just plug the generator or the shore power into the trailer input. An example of why to have one might be that shore-power is flakey and you want the system to automatically cut over to generator/battery when it goes out. As to wiring it, the schematic will be in the instructions.
2. Busbar quality depends on the kit. If the busbars are getting warm/hot you'll want to double them up or replace them. Will is fond of hammering 1/2" copper pipe flat into busbars. ;-)
3. Linking HRTKD and @tictag as they might have ideas on this.

 

[Jusbechillin]

1) I now understand that when I use the generator it connects to the plug I refer to as “shore power”. But don’t I need an ATS to choose between the solar and the shore power? When you say “plug it into the trailer input” what do you mean?

2) I’ll do the copper pipe trick, that sounds fun and practical.


3) Since this original post I’ve discovered most people arent comfortable mounting via VHB tape to epdm/rubber roofs. As far as the curve is concerned, I put my panels in place with the z brackets to see how they fit and there is still plenty of room for air to get underneath it and the brackets sit flat. My plan is to use the VHB tape, then screw the brackets as well, and finally self leveling Dicor at the seams and over screw heads.

 

[tictag]

Mostly designed for higher amp hours as I’ll probably be mostly going on 2-4 day off the grid trips.

That's fine but you still need to consider your consumption. A 280AH battery (6,720Wh) will only last 2 days if you're consuming 3360Wh per day! Just kidding, but you get my point? You can either measure your consumption using something like this:



... or calculate it with something like this:

Device	Rating (W)	Time (h)	Energy (Wh)
Fridge	120W	12h (at 50/50 on/off)	1,440Wh
Inverter Losses	15W	24h	360Wh
		TOTAL	1,800Wh

I’m a little confused on if I need an ATS .....
And, how would I wire one into the system that can decide between shore/generator/solar?

I have to disagree with @svetz on this, I believe you do need an ATS.

Generally speaking most people (mobile application) either power everything from an inverter or everything from shore/genset, so everything is supplied from one point (usually a consumer box of some description). You cannot connect multiple AC sources together because the frequency, phase and voltage of the supplies will be different and change over time. You must only connect one at a time, and that's why you need an ATS.

You would wire it up something like this:

For the diy LIFEPO4 battery, are the bars they provide with the cells to connect them together sufficient or should I be concerned with upgrading them to a higher quality?

Invariably, the busbar you will get will be sub-standard, just enough to get the job done, but as cheap as possible. I personally would recommend you buy new. Just google 'battery busbars'. Try to ensure they a tinned pure copper, at least 2mm thick, preferably pre-wrapped in heatshrink.

My Trailer has a curved roof. What is the reason it’s not recommended to mount directly to a curved roof?

I'm not sure why this would not be recommended, except to say that it is harder to mount rigid panels on a curved surface ... mounting systems are available, though. Personally, I'd go with flexible panels ... just don't expect them to last as long. A damn-sight lighter, though!

300amp main fuse.

No! I am assuming that your inverter will be your biggest load, at its rated power this will draw 125A from a 24V battery. You should specify your battery cable at this +25% and make sure your fuse is lower than the ampacity rating of your cable. For example, 2AWG cable with a 150A fuse.

Other considerations:

1. You might want to consider adding a battery monitor to your system e.g. Victron, AiLi.
2. You should have a means to manually isolate all supplies. Simple battery isolator switches are usually used for this purpose.

Once you've got your system down on paper, send it in and we can take a further look.

Good luck with your project!

Edit: Added image of energy meter.

 

[Jusbechillin]

I started another post in the general forum with more detail because I wasn’t getting responses in the beginners corner. Not trying to duplicate, I was just hoping to start wiring things up this weekend and needed help. Thanks for helping!

 

[tictag]

OK, I'm sure my advice will be consistent with your other thread. Be sure to avoid your inverter ending up charging your batteries.

 

[Jusbechillin]

I’ve calculated my needs per day conservatively at 2000watts. And count on the solar to provide about 700 watts a day taking the draw off the battery bank down to 1300 +/-. With this math I figure I could go 5 days which is longer than my normal trip. And, I’ll generally run the generator during the day to run AC so If need be I’ll get a little power topped off in that process OR I might add two more panels.

 

[tictag]

Sounds good.

For your own sanity, keep in your mind that power (instantaneous) is measured in Watts and energy (over time) is measured in Watt-Hours. This will definitely help you when it comes to figuring out what Wattage (W) of panels are required to replenish your Watt-Hours (Wh) of energy you consume.

I noticed Ohms Law noted in your diagram, Ohm's and Kirchoff's Laws are better represented like this:



...simply hold your thumb over the value you want e.g. I = P / V, V = I x R etc

You can also re-arrange for finding power without knowing voltage:



Note: I am only telling you this because you posted in Beginners Corner, so thought this might be useful to you.

 

[Jusbechillin]

Yes it is thank you. And I am a beginner for sure

 

[svetz]

...1) I now understand that when I use the generator it connects to the plug I refer to as “shore power”. But don’t I need an ATS to choose between the solar and the shore power? When you say “plug it into the trailer input” what do you mean?

The trailer should have a socket on it something like this:

The generator should have a cable that plugs into it while you're out camping. While at home, you should have a power cable that plugs into the house on one end, and plugs into the trailer on the end.

So, you can choose manually by which one you plug into the trailer socket.

An ATS on the other hand has two inputs and one output. The inputs being the house cable or the generator cable, the output being the electrical equivalent of plugging into the socket on the trailer.

Now for solar rather than a generator... an ATS will make it more convenient than a manual switch... Here's the real expert...

Hope that helps!