My first off-grid system design, how am I doing?

[TheWanderingJackalopes]

My wife and I are converting a 30' school bus into an RV that will be our traveling retirement home once we downsize. I'm almost done with the plumbing, and soon it will be time to focus on the electric. The heart of the system is a Growatt off-grid solar converter. The battery bank is over-sized for the number of panels we have, and I'm okay with that. I think I have figured out the components and wire gauges, but I sure would appreciate having some folks with more knowledge and experience than myself take a look at it and tell me where I might have mis-stepped. Also, new member on the forum, so I hope this is a good way to start interacting. - Tim

EDIT: Ignore the drawing of the Battery wiring. I was trying to figure out how to draw in bus bars and equal length wire and forgot to wire the schematic for 24v.

 

[Bobert]

Here is a video you might want to watch about limitations of a all in one inverter. https://www.bing.com/videos/search?...D15AA54B267DFA14BFD0D15AA54&FORM=VIRE&PC=APPL
Your incoming power is below the recommended amps for this unit and if you use a standard rv generator you may have additional problems because of the collapsing sine wave issue. I use a 3500w all in one unit so I have dealt with all these problems only more so. I set the charge parameters back a bit in order to avoid tripping the 30a breaker and I use a inverter generator to avoid the sine wave issues and lower the charge parameters modifications so I don’t overload the generator. Don’t get me wrong I love the all in one setup but it is not possible for it to be a set it and forget it system if you want to use it’s full potential. I wanted to make sure you were aware of these limitations before making the plunge. 8 gauge is called for by the manufacturer but in a 30a rv situation you can’t safely supply more than 30amps so a 10 gauge supply from generator and shore power to the inverter is all you need and 30a is all you can get

 

[acdoctor]

I converted a utility trailer 22ft x 8.5f. I have a Growatt 3k. LFP 280 ah, 11 cf 115 volt refrigerator 1 ton mini split. 24 to 12 converter need fuse before it otherwise it has 400 amps if it shorts internally. I have 2 kw of panels they don’t preform very well horizontally. Half of them tilt. I have a Westinghouse igen 2500 I can charge at 60 amps so long as there are no larger loads. When growatt sees grid it passes it through if charging is needed it does it at the same time. That gen should handle pretty good though. Growatt does have a high self consumption. If you have inverter running and no load at all it will consume 1.6 kw in 24 hours. And about half of that from batteries in pass through grid mode.

 

[TheWanderingJackalopes]

Thank you for sharing that link. There's a lot of good info there. I was planning to wire my solar panels as either parallel or series/parallel, and since the open circuit voltage is 39.9v I could possibly go either way, but to be safe perhaps I should stick to series/parallel.

I am going with the 0 AWG wire instead of the 1 AWG per his recommendation.

I think the idea of a 50 amp circuit on the AC side is simply not realistic. We will rarely be plugged into shore power and if we are, it will most likely be 30 amp. I understand what he's saying, but it appears that he's assuming maximum utilization, which is never going to be our case. Looking at the configuration capabilities, I think all of the concerns he goes over regarding minimum power requirements can be ameliorated with a proper setup.

 

[TheWanderingJackalopes]

I converted a utility trailer 22ft x 8.5f. I have a Growatt 3k. LFP 280 ah, 11 cf 115 volt refrigerator 1 ton mini split. 24 to 12 converter need fuse before it otherwise it has 400 amps if it shorts internally. I have 2 kw of panels they don’t preform very well horizontally. Half of them tilt. I have a Westinghouse igen 2500 I can charge at 60 amps so long as there are no larger loads. When growatt sees grid it passes it through if charging is needed it does it at the same time. That gen should handle pretty good though. Growatt does have a high self consumption. If you have inverter running and no load at all it will consume 1.6 kw in 24 hours. And about half of that from batteries in pass through grid mode.

It sounds like your setup is not far from ours. We don't have much that needs to run 120v all night, so unless we're running the mini-split I believe we can power down the Growatt at night and just run everything 12v until we need AC for something. I'm not sure if that's good for the Growatt, though. What do you think? Would you move that 70 amp fuse, or run a second fuse before the Victron 24-12 step-down converter?

 

[TheWanderingJackalopes]

Here's a question: If you were going to swap out the Growatt with Victron, what would your setup look like? I am pondering this just in case we cook the Growatt and want to go a different way.

 

[acdoctor]

I started with a 10 awg cord and RV30 amp plug but at home during the winter at times I would need to plug in and would just use a 50 ft 12 awg cord. So got to thinking why bother with the 30 amp. So now I just have a 12/3 extension cord 25 ft. And a spare if I need the length. We are currently on day 5 of a 8 day stay at a state park with shore power. Last night was stormy so I unplugged and remained for about 20 hours. Used about half the battery. I have the charge lowered to 40 amps. Took about 3 hours to recharge.

If that’s 70 amps output input would be a tiny over half.

 

[TheWanderingJackalopes]

Right, 70 out at 12v, 35 in at 24v. So I should go with a 40amp fuse on the input side and stick with the breaker on the output side.

 

[acdoctor]

I am not familiar with victron other than people on here discussing it. I have Schneider stuff in my home.

Typically a layout other than a all in one is
Panels, possibly combiner box, breaker, solar charge controller, breaker, buss bars, from there you would go in three directions. Direction 1 inverter, direction 2 breaker to batteries then batteries. Direction 3 breaker 12 volt converter.
A inverter with charging capability usually has a transfer switch built in to feed through shore power seamlessly.


I would stay with a 30 or 35. I would rather have a nuisance trip than burn up. I have seen some on here toasted.
There are some on here that have all victron stuff and really like it.

Are those lead acid batteries. If so that’s a lot of weight. You show them 12 volt parallel 412 ah ( should say 824ah ) but feeding 24 volt growatt. So you would need series parallel for 24 volt 412 ah. Groups of two series then parallel the groups.
The great thing about LFP is you can charge them at high amps to full capacity. Lead acid you may need 3 to 4 hours from 80% to 100%. I have lead acid at home. 48 volt 860 ah.

 

[Bobert]

It sounds like your setup is not far from ours. We don't have much that needs to run 120v all night, so unless we're running the mini-split I believe we can power down the Growatt at night and just run everything 12v until we need AC for something. I'm not sure if that's good for the Growatt, though. What do you think? Would you move that 70 amp fuse, or run a second fuse before the Victron 24-12 step-down converter?

We boondocked for almost 2 months last fall and initially used fla batteries. Because our battery bank is small we would shut down the inverter every night to conserve energy. Our all in one unit is a cheaper powmr and we had no trouble. I would expect growatt to be better quality than the powmr. One thing you might want to consider is a dc to dc charger so that you can add power to the batteries while driving. This would be especially helpful if you have lead acid batteries.

 

[TheWanderingJackalopes]

I am not familiar with victron other than people on here discussing it. I have Schneider stuff in my home.

Typically a layout other than a all in one is
Panels, possibly combiner box, breaker, solar charge controller, breaker, buss bars, from there you would go in three directions. Direction 1 inverter, direction 2 breaker to batteries then batteries. Direction 3 breaker 12 volt converter.
A inverter with charging capability usually has a transfer switch built in to feed through shore power seamlessly.


I would stay with a 30 or 35. I would rather have a nuisance trip than burn up. I have seen some on here toasted.
There are some on here that have all victron stuff and really like it.

Are those lead acid batteries. If so that’s a lot of weight. You show them 12 volt parallel 412 ah ( should say 824ah ) but feeding 24 volt growatt. So you would need series parallel for 24 volt 412 ah. Groups of two series then parallel the groups.
The great thing about LFP is you can charge them at high amps to full capacity. Lead acid you may need 3 to 4 hours from 80% to 100%. I have lead acid at home. 48 volt 860 ah.

The batteries are LiFePo4, and yeah, I was redrawing the battery layout and forgot to series-parallel The system is 24v at 414a. I updated the drawing.

 

[TheWanderingJackalopes]

We boondocked for almost 2 months last fall and initially used fla batteries. Because our battery bank is small we would shut down the inverter every night to conserve energy. Our all in one unit is a cheaper powmr and we had no trouble. I would expect growatt to be better quality than the powmr. One thing you might want to consider is a dc to dc charger so that you can add power to the batteries while driving. This would be especially helpful if you have lead acid batteries.

I do plan to add a dc to dc for charging while driving, but I figured I would wait until after I get all of this working. With almost 10kw of battery, it'll probably take 2 good days of sun to charge from 10% to 90%.

 

[TheWanderingJackalopes]

I appreciate all of the insight being shared on this forum! It doesn't always work out that way. ;-)

 

[LywWyr]

I would move the 400 amp fuse as close to the busbar as possible.

 

[TheWanderingJackalopes]

I would move the 400 amp fuse as close to the busbar as possible.

Do you think 400a is the correct size for this setup?

 

[Bobert]

Do you think 400a is the correct size for this setup?

I am interested in what other have to say but it seems to me that at 24v the most continuous draw you should se would be less than 150 amps it seems to me that 200 amp would be plenty for the draws you would have.

 

[acdoctor]

I agree with @Bobert on fuse size. A breaker I would use 150A but fuse probably a 200A.

 

[TheWanderingJackalopes]

Thanks guys. I was not clear on the full purpose of the fuse, was I protecting the batteries, the inverter, the dc to dc converter, the wires, or what combination? I will change to a 200a fuse unless I arrive at a different understanding.

Another question: Would you go with a 30a Main Breaker? Since the output of my inverter is 3kw and my shore power and generator are also 30a, this is what makes the most sense to me. I have no expectation of exceeding 30a at any time, as our only dedicated 120v appliances are a high efficiency mini-split and a uv sanitizer that only operates when the shower is running. Other than that, it will be a few things used occasionally like toaster, coffee maker, blender, maybe blow-dryer.

 

[Bobert]

Thanks guys. I was not clear on the full purpose of the fuse, was I protecting the batteries, the inverter, the dc to dc converter, the wires, or what combination? I will change to a 200a fuse unless I arrive at a different understanding.

Another question: Would you go with a 30a Main Breaker? Since the output of my inverter is 3kw and my shore power and generator are also 30a, this is what makes the most sense to me. I have no expectation of exceeding 30a at any time, as our only dedicated 120v appliances are a high efficiency mini-split and a uv sanitizer that only operates when the shower is running. Other than that, it will be a few things used occasionally like toaster, coffee maker, blender, maybe blow-dryer.

I would use a 30 amp breaker for the ac because you will max out at 30 amps you only need 10 gauge wire but bigger wire won’t hurt anything. The breaker is different if you were to pull into a campsite and find that all you have working is a 50 amp outlet and you connect with a dog one to your rv an overload situation could smoke your cord and or shore power connection if you have more than a 30 amp breaker.

 

[TheWanderingJackalopes]

I would use a 30 amp breaker for the ac because you will max out at 30 amps you only need 10 gauge wire but bigger wire won’t hurt anything. The breaker is different if you were to pull into a campsite and find that all you have working is a 50 amp outlet and you connect with a dog one to your rv an overload situation could smoke your cord and or shore power connection if you have more than a 30 amp breaker.

Thank you for that clarity. I feel like I'm getting closer to having my parts list nailed down.