Help/Critique of RV System, Wire/Connectors

childcarepro

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I'm attaching my latest draft of my solar system for my Winnebago Via 25' Sprinter chassis class A motorhome. I've been researching and buying for a few months, and I have all the major components (Victron gear, solar panels, battery cells), have yet to purchase the little stuff (connectors, bus bars, wire, lugs, etc). I want to thank @WillProwse and this community for all the help so far. I'm excited and nervous about heading down the home stretch finally!

This design is based on two Victron diagrams (Victron Van project and a Victron MultiPlus 24/3000 diagram). My priority is to strike a balance between functionality and simplicity, hence my decision to wire into my RV's existing distribution panels rather than gutting those.

For mounting solar panels, I am planning on using Eternabond and strut channels:
This plan is to maximize adhesive contact to the roof, and for the mounts to actually be screwed down to something, the strut channels. I will also follow @WillProwse's advice to also have a safety cable attached to each panel.

In the diagram I have a solar breaker/isolator on the input side to the SmartSolar as well as closer to the battery; I don't think both are necessary, but any thoughts one way or the other is welcome.

I would appreciate help with suggestions on design changes, simplifications/deletions, and recommendations on the nitty-gritty stuff (switches, breakers, bus bars, wiring, lugs, crimpers, etc.).

Thank you in advance! Here's a link to the PDF: https://www.dropbox.com/s/rxs6hdhux...Wiring Diagram Simplified 10-20-2020.pdf?dl=0

Winnebago Via Electrical Solar Wiring Diagram Simplified 10-20-2020-4.jpg
 

BiduleOhm

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As you already have disconnect switches, fuses would be a better choice than breakers (less expensive, available for currents > 250 A, more reliable). If you still want to use breakers then don't buy the cheap chinese ones (at best they will trip before their rating, at worst they will start a fire), use Bussmann (or other good brand) ones.

You're missing a fuse close to the battery positive terminal. MRBF fuses are very nice for that application ;)

You cannot use the battery protect to power the inverter directly, you can use it to control it however if the inverter has a remote input (it should as it's a Victron one) or doing a bit of DIY on its power switch.

Nice diagram BTW ;)

Edit: you're missing small fuses on the two small positives feeding the Cerbo and the shunt.
 
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childcarepro

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As you already have disconnect switches, fuses would be a better choice than breakers (less expensive, available for currents > 250 A, more reliable). If you still want to use breakers then don't buy the cheap chinese ones (at best they will trip before their rating, at worst they will start a fire), use Bussmann (or other good brand) ones.

You're missing a fuse close to the battery positive terminal. MRBF fuses are very nice for that application ;)

You cannot use the battery protect to power the inverter directly, you can use it to control it however if the inverter has a remote input (it should as it's a Victron one) or doing a bit of DIY on its power switch.

Nice diagram BTW ;)

Edit: you're missing small fuses on the two small positives feeding the Cerbo and the shunt.
Thanks for the pointers, @BiduleOhm!

That MRBF fuse does look great. Would you recommend putting it right on the main positive terminal, or just off the terminal before the main positive bus bar?

Call me lazy [crazy?], but I prefer the idea of resetting breakers to replacing fuses. :) I'll be sure to get quality ones; I'll look into Bussmann. I know they should be somewhat oversized, but my 24V system will never go past 200A in either the charge or discharge direction:

Charging. It will almost never charge from solar and shore, but even if it did:
- 70A shore power charging
- 42A solar charging (200W 24V panels x 6)

Loads. RV heat pump for now, will replace with 24VDC heat pump:
- 112A max inverter load at 3000W (MW + A/C, only short bursts)
- 30A peak for 24VDC heat pump, 2.6A for 24VDC fridge

Yeah, I learned the Victron Smart Battery Protects are one-direction. I was reworking the diagram to replace it. But yes am using a Victron MultiPlus 24|3000. I checked out that thread you referenced, it sounds like a lot of work! I'm leaning toward replacing my 100A and 220A Smart Battery Protects with two 65A's to control my DC loads for efficiency and more control (one for essential loads, one for nonessential).

I have a question out to 123Smart and GWL, one of their distributors, and if the 123SmartBMS doesn't directly disable the inverter load or charge current, I will probably add a 200A DC contactor. Kind of a bummer, as I hear the contactor constantly consumes current (nice alliteration), though I don't know how much.

Any pointers on bus bars? Blue Sea?
 

BiduleOhm

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That MRBF fuse does look great. Would you recommend putting it right on the main positive terminal, or just off the terminal before the main positive bus bar?

The closer to the battery the better. But given you're in a mobile setup be careful about stress on the terminals, it's highly recommended to attach the wire going to the MRBF fuse and not let it move (because of the leverage of the fuse holder it puts a lot of stress on the battery terminal otherwise) or to use a short wire/flexible busbar section between the battery terminal and the fuse.

Call me lazy [crazy?], but I prefer the idea of resetting breakers to replacing fuses. :) I'll be sure to get quality ones; I'll look into Bussmann. I know they should be somewhat oversized, but my 24V system will never go past 200A in either the charge or discharge direction:

Charging. It will almost never charge from solar and shore, but even if it did:
- 70A shore power charging
- 42A solar charging (200W 24V panels x 6)

Loads. RV heat pump for now, will replace with 24VDC heat pump:
- 112A max inverter load at 3000W (MW + A/C, only short bursts)
- 30A peak for 24VDC heat pump, 2.6A for 24VDC fridge

Well, it's a personal choice ;) the thing to remember is just to not cheap out on the over current protections, whether it's a fuse or a breaker.

Yeah, I learned the Victron Smart Battery Protects are one-direction. I was reworking the diagram to replace it. But yes am using a Victron MultiPlus 24|3000. I checked out that thread you referenced, it sounds like a lot of work! I'm leaning toward replacing my 100A and 220A Smart Battery Protects with two 65A's to control my DC loads for efficiency and more control (one for essential loads, one for nonessential).

It was one of the first thread in my search results but probably not the best to explain how to do it. You may want to search clearer explainations or ask your own questions but given the inverter has a proper remote input it shouldn't be complicated. NB: a simpler and cheaper battery protection board is a option; something like that, or like that, or that too (NB: didn't check those have appropriate specs for your use case, it's just examples).

I have a question out to 123Smart and GWL, one of their distributors, and if the 123SmartBMS doesn't directly disable the inverter load or charge current, I will probably add a 200A DC contactor. Kind of a bummer, as I hear the contactor constantly consumes current (nice alliteration), though I don't know how much.

You can use a SSR, there's a great thread about them here.

Any pointers on bus bars? Blue Sea?

Anything decent (i.e. not the cheapest chinese ones you can find...) ;)
 

childcarepro

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The closer to the battery the better. But given you're in a mobile setup be careful about stress on the terminals, it's highly recommended to attach the wire going to the MRBF fuse and not let it move (because of the leverage of the fuse holder it puts a lot of stress on the battery terminal otherwise) or to use a short wire/flexible busbar section between the battery terminal and the fuse.
Sounds good. Oversize but flexible wire. Seems the least amount of strain on the terminals possible would require the fuse holder be mounted to the cells? As long as that mount is firm, it would transfer the strain from the terminal to the fuse holder. I do have misgivings about these M6 battery posts on the 280Ah cells.

My battery bay is open on the bottom, so I plan to fully enclose it, waterproof it, and install high density foam as a shock mount/insulation as well as foam spacers between cells, and add a heating element underneath and wire it to the tank heater circuit.

Well, it's a personal choice ;) the thing to remember is just to not cheap out on the over current protections, whether it's a fuse or a breaker.

It was one of the first thread in my search results but probably not the best to explain how to do it. You may want to search clearer explainations or ask your own questions but given the inverter has a proper remote input it shouldn't be complicated. NB: a simpler and cheaper battery protection board is a option; something like that, or like that, or that too.

You can use a SSR, there's a great thread about them here.

Anything decent (i.e. not the cheapest chinese ones you can find...) ;)
Easy there, that's a lot of warnings about cheap goods... I'm getting the feeling you've pegged me as a cheapskate. Not so! I'm value-conscious. With all my Victron gear and choice of 123SmartBMS over $20-200 Chinese alternatives, I think I've shown I'm willing to pay more for objectively better quality (but not orders of magnitude more for perceived premium products). IOW, I buy Teslas, not Bentleys. :) The only thing I cheaped out on was my LiFePO4 cells, but come on, they're commodity cells companies sell the same or similar cells with BMS, box, brand sticker, and charge 5-10X. I bought McMaster-Carr hardware to replace the cheap hardware the cells came with. Not cheap!
 

BiduleOhm

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Sounds good. Oversize but flexible wire. Seems the least amount of strain on the terminals possible would require the fuse holder be mounted to the cells? As long as that mount is firm, it would transfer the strain from the terminal to the fuse holder. I do have misgivings about these M6 battery posts on the 280Ah cells.

Yes but then you need a flexible connection between the cell terminal and the fuse holder, else you'll have an over-constrained system which will put stress on the components.

Simplest and best solution is to put the fuse holder on the terminal, attach the wire 6-8" to the cell or something else that doesn't move relative to the cells, and then bend the wire into place and bolt it on the fuse holder (don't bolt it and then bend and attach it as you'll put stress on the terminal).

My battery bay is open on the bottom, so I plan to fully enclose it, waterproof it, and install high density foam as a shock mount/insulation as well as foam spacers between cells, and add a heating element underneath and wire it to the tank heater circuit.

Basically you want your battery to be one solid block mounted via compliant mounts to absorb shocks and vibrations (exactly like the engine and the exhaust are mounted in a car for example; they're both rigid assemblies attached via rubber mounts).

So foam around it is a good idea, but foam between the cells is a bad idea (unless you have really flexible busbars between them I guess), doubly because it's recommended to clamp them to prevent expansion and associated internal delamination (although it's not critical if you don't do that, but you can gain more cycles out of the battery if you do and it's just the cost of some planks and threaded rods so well worth it IMHO...)

Easy there, that's a lot of warnings about cheap goods... I'm getting the feeling you've pegged me as a cheapskate. Not so! I'm value-conscious. With all my Victron gear and choice of 123SmartBMS over $20-200 Chinese alternatives, I think I've shown I'm willing to pay more for objectively better quality (but not orders of magnitude more for perceived premium products). IOW, I buy Teslas, not Bentleys. :) The only thing I cheaped out on was my LiFePO4 cells, but come on, they're commodity cells companies sell the same or similar cells with BMS, box, brand sticker, and charge 5-10X. I bought McMaster-Carr hardware to replace the cheap hardware the cells came with. Not cheap!

No, no, don't worry, I saw you use basically all Victron stuff so clearly not trying to cut costs. I was just warning about cheap stuff because it's really important and can lead to a very unsafe system. You can actually cheap out on a lot of things without really bad consequences (you'll just get a less efficient/reliable system most of the time) but OCPDs are the one thing you don't want to do that and also the one mistake we see the most often here, countless stories of "my system doesn't work well" ending with a cheap breaker being the problem...

But yeah, not a likely problem with your choices so far ;)
 
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childcarepro

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Yes but then you need a flexible connection between the cell terminal and the fuse holder, else you'll have an over-constrained system which will put stress on the components.

Simplest and best solution is to put the fuse holder on the terminal, attach the wire 6-8" to the cell or something else that doesn't move relative to the cells, and then bend the wire into place and bolt it on the fuse holder (don't bolt it and then bend and attach it as you'll put stress on the terminal).
Great, thanks for the tips!

Basically you want your battery to be one solid block mounted via compliant mounts to absorb shocks and vibrations (exactly like the engine and the exhaust are mounted in a car for example; they're both rigid assemblies attached via rubber mounts).

So foam around it is a good idea, but foam between the cells is a bad idea (unless you have really flexible busbars between them I guess), doubly because it's recommended to clamp them to prevent expansion and associated internal delamination (although it's not critical if you don't do that, but you can gain more cycles out of the battery if you do and it's just the cost of some planks and threaded rods so well worth it IMHO...)

Re: spacers between cells, I was thinking of heat dissipation, but I suppose heat shouldn't be a real issue unless I exceed 1C discharge rate.

@Will Prowse recommends breaking an 8S bank into two 4S banks for manageability... These 280Ah cells are pretty heavy! I'm thinking of clamping 4 cells together x 2, once I load the two 4S bricks in the battery bay, clamp them together with draw toggle latches once they're in the bay.
 

BiduleOhm

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Yep, usually heat isn't a problem for solar applications as we are well below 1C ;)

You can totally split your pack into two smallers packs, just use a flexible wire/busbar to connect them and it'll be fine ;)
 

cinergi

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A fuse between battery and Battery Disconnect Switch for sure. I wouldn't use MRBF for that - use Class T. MRBF isn't rated for the high interrupt currents that LiFePO4 can have under short-circuit conditions. If you go with MRBF, I personally would not mount it directly to the cell terminal; you don't want that stress on the terminal, it generates heat, and I wouldn't want the fuse blowing that close to the cell under short-circuit conditions.

Smart shunt comes with an inline fuse for its positive lead. Not sure what Cerbo comes with yet.

Add fuse to DC Load 150A switch. Move battery protect after that switch.

All fuses (if you switch from breakers) should be before the cutoff switches (basically at the beginning of the run of the wire in question).

How will you connect Cerbo to your network?

Will you have the Cerbo doing auto-start on the generator?

You'll have 3 electrical systems grounded (12vdc, 24vdc, 120vac) ... I wonder if anyone can comment on that. I would have recommended floating your 24vdc batteries but you'll be using 24vdc appliances.

+1 on using fuses generally everywhere instead of breakers (except PV isolator - and it's good that that's double-pole). I saw too many bogus trips on breakers and it's another failure point within the system. If you go with breakers, go with good ones as has been said. Midnite solar is another vendor option for breakers.
 

childcarepro

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A fuse between battery and Battery Disconnect Switch for sure. I wouldn't use MRBF for that - use Class T. MRBF isn't rated for the high interrupt currents that LiFePO4 can have under short-circuit conditions. If you go with MRBF, I personally would not mount it directly to the cell terminal; you don't want that stress on the terminal, it generates heat, and I wouldn't want the fuse blowing that close to the cell under short-circuit conditions.
That sounds reasonable. I'll plan a short flexible wire to the fuse holder on the board before the main positive bus bar.
Smart shunt comes with an inline fuse for its positive lead. Not sure what Cerbo comes with yet.
I have both of these already; the Smart Shunt comes with two positive leads w/ inline fuses (1 for accessory, I'll use it to monitor the chassis battery), and the Cerbo GX also comes with an inline fuse for its positive power lead.
Add fuse to DC Load 150A switch. Move battery protect after that switch.

All fuses (if you switch from breakers) should be before the cutoff switches (basically at the beginning of the run of the wire in question).
Thanks, let me look into that.
How will you connect Cerbo to your network?

Will you have the Cerbo doing auto-start on the generator?
I am looking at a Verizon hotspot, most likely. I'll run a Cat 6 cable to it if feasible.

I was going to use the MultiPlus's auto gen start; seems like a more direct approach without a middle man (Cerbo).
You'll have 3 electrical systems grounded (12vdc, 24vdc, 120vac) ... I wonder if anyone can comment on that. I would have recommended floating your 24vdc batteries but you'll be using 24vdc appliances.
I was just wondering about this myself as I was fleshing out my system diagram, how the negative 12 and 24V will work together. I wasn't even thinking about the 120V system.

In my head, my solution was to return all 12V negative back to the negative terminal of the 24-12V converter, thereby having just one set of 24V negative wires to return to the battery terminal. But the Orion 24/12-70A only has one negative terminal, and the manual says, "First, connect the 'minus' cables to the minus terminal of the Orion." To me, that sounds like both 12V minus from loads and 24V minus to battery are joined there. Am I reading that right?

+1 on using fuses generally everywhere instead of breakers (except PV isolator - and it's good that that's double-pole). I saw too many bogus trips on breakers and it's another failure point within the system. If you go with breakers, go with good ones as has been said. Midnite solar is another vendor option for breakers.
All right, your vote for fuses (+2 votes now) and rationale (I'm going for as set-and-forget as possible) has convinced me. I do not want to deal with false trips. I guess fuses it is!
 

BiduleOhm

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In my head, my solution was to return all 12V negative back to the negative terminal of the 24-12V converter, thereby having just one set of 24V negative wires to return to the battery terminal. But the Orion 24/12-70A only has one negative terminal, and the manual says, "First, connect the 'minus' cables to the minus terminal of the Orion." To me, that sounds like both 12V minus from loads and 24V minus to battery are joined there. Am I reading that right?

That's correct ;)
 

childcarepro

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Good evening, friends! I'm back. My solar gear has been sitting in the garage for far too long, so I'm getting serious. I'm also trying to simplify, because I won't actually finish it unless it's manageable. To that end, I've uploaded a simplified diagram for your help:

1. Rather than a 123Smart BMS (which is an amazing setup, BTW), I'm going with Overkill's 8S 24V 100A BMS
2. Trying to remove any components that aren't completely necessary.
3. Hiring an RV technician rather than DIY'ing it (if I'm honest, I'll never finish it)
4. I will assemble batteries and BMS (I can do that much, probably beyond the RV technician's abilities

Please ruthlessly suggest things to cut out, or things I should add back in.

Other questions:
1. Should I remove my generator? Between shore power and solar (1200W + 7.2kWh battery) I should be good, right? I could use that generator bay for storage.
2. If I remove my generator, I no longer need the ATS, right?
3. I could not find a battery box big enough for my 8S 280Ah cells (22.68 long, 6.85 wide, 7.87 tall), so I ordered two of these from AliExpress: https://www.aliexpress.com/snapshot...d=8131759461112114&productId=1005002026770701, so I would connect them like two 12V batteries in series.

Thank you in advance.
 

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HRTKD

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I considered ditching my on-board generator. Gaining storage space and losing 300+ lbs (generator and fuel tank) would be a nice diet to put my trailer on.

But in the end, I'm keeping the generator. There have been times in very cold weather that the generator has come in handy.

I think the fuse and switch between your positive bus bar and the solar charge controller are overkill. A Blue Sea Systems Series 187 circuit breaker is a simpler and less expensive solution. The same could be said for the other two fuse/switch circuits. The setup you have works, it's just more than is necessary and likely costs more.

I think your connection to your 12v chassis battery is incorrect. There is a port on the Multiplus specifically for starter battery charging. The 12v battery needs to be connected directly to that port. The 12v battery negative can't be connected to the 24v shunt. Hopefully the 24v Multiplus can be configured to charge a 12v starter battery.

It's been pointed out in another thread that if you have each parallel string fused (you're using circuit breakers) then a circuit breaker is not necessary downstream. I can see the point, but having a single, central cutoff with the dual pole breaker is handy. If it was me I would go 3s2p with the panels so I could avoid using a fuse in each parallel string, and then use a larger solar charge controller.

I'm not a fan of your battery box idea. These batteries don't need to be in a box, but they do need to be compressed.
 

childcarepro

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But in the end, I'm keeping the generator. There have been times in very cold weather that the generator has come in handy.
Yeah, my wife loves that generator. But of course we NEED that generator now because we have 100W solar and 744 Wh of battery. Question is will we still with 1200W and 7168 Wh. I know I can't charge when the cells are sub-zero, but my battery compartment can be insulated (it's under the top step of the entry).
I think the fuse and switch between your positive bus bar and the solar charge controller are overkill. A Blue Sea Systems Series 187 circuit breaker is a simpler and less expensive solution. The same could be said for the other two fuse/switch circuits. The setup you have works, it's just more than is necessary and likely costs more.
Thanks, I am trying to minimize the complexity. I like the circuit breaker idea for simplicity, but several members here whose knowledge I respect prefer fuses to breakers.
I think your connection to your 12v chassis battery is incorrect. There is a port on the Multiplus specifically for starter battery charging. The 12v battery needs to be connected directly to that port. The 12v battery negative can't be connected to the 24v shunt. Hopefully the 24v Multiplus can be configured to charge a 12v starter battery.
You're right; I was trying to keep the chassis battery charged, but I need some sort of charger on it, not just a passive circuit. Plus the -12V return won't work with the -24V circuit.
It's been pointed out in another thread that if you have each parallel string fused (you're using circuit breakers) then a circuit breaker is not necessary downstream. I can see the point, but having a single, central cutoff with the dual pole breaker is handy. If it was me I would go 3s2p with the panels so I could avoid using a fuse in each parallel string, and then use a larger solar charge controller.
I think I'm using 3 strings to increase shade tolerance (plus I have 3 ports in my roof cap), but I learned panels with bypass diodes are already pretty shade tolerant.
I'm not a fan of your battery box idea. These batteries don't need to be in a box, but they do need to be compressed.
I'm definitely going to band the cells together. The boxes are for:
1. Structural rigidity (hard shell);
2. Shock absorption (add foam);
3. Additional layer of insulation (foam);
4. Hopefully beefier lugs than the cells' M6 hardware;
5. More finished look than cells strapped together with spaghetti wire all over (though no one will see them unless there's a problem!)

The battery bay is currently open to the street on the bottom. I want to enclose the battery bay and insulate it w/ high density foam for both insulation and shock absorption, plus have the battery cases surrounded with high density foam for thermal isolation.
 

childcarepro

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OK I think I have this figured out, mostly. Please let me know if there are any glaring problems or opportunities for further simpilfication.

Another question: is my Orion DC-DC Converter 24/12-70 may be too much converter for my 25' Sprinter chassis motorhome, especially since the specs show only 92% efficiency, compared to the 24/12-25 rated at 96% and 24/12-40 at 95% efficiency. I should look at my load center and see what the max current draw is, but I have it in storage.

Thank you in advance.
Winnebago Via Electrical Solar Wiring Diagram Simplified 2021-05-16.png
 

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childcarepro

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It was helpful for my own mental clarity to clean up my diagram, grouped by logical flows of current (e.g., A/C input, solar input, battery storage, control/monitoring, positive and negative wiring), with fewer intersecting wires.

One more thing I'm puzzling over is whether it's OK to connect both the 12V chassis batter and the 24V house battery to the same chassis ground. I'm leaning toward NOT OK, but I don't know what the solution is.

Thank you.
Winnebago Via Electrical Solar Wiring Diagram Simplified 2021-05-16-2.png
 

Boondock Saint

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The 12v in the Winnebago has dependencies and can't be totally lifted. It seems there should be some isolation between the other systems. The 24v system and it's dependencies can be "isolated 2-wire runs to the 24v appliances" and never shall the two meet the 12v except for the Orion 24|12-30 charging the 12v battery. It's non isolated and only has IN, GND, and OUT to 12v batt.

Kill the chassis GND on the "Central Negative Busbar" and what no longer works in the schematic? Everything that needs to be in common will still be in common on a metal bar on a block of wood.

The Orion 24|12-30 DC-DC Charger works because of the path from the Existing 120v/12v Load Ctr to the 24|12 converter.
 

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cinergi

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You should ground both systems especially if the 24v system goes physically beyond the boundaries of the battery & inverter. It's safe to ground both. This is necessary so that a fault (short to chassis) can trip a breaker/fuse instead of leaving +24v live on the chassis. It's also a good idea from a static electricity perspective (so that a floating 24v system doesn't present a static shock hazard). It's OK to have multiple systems reference the same ground; ground is meant for fault interruption, not carrying current (although it's unfortunately been used otherwise - but that still doesn't present a problem in this case).
 

childcarepro

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Thanks, @cinergi. That makes sense. I think I was overthinking it. The chassis ground isn't something that's in play (drawing current) except when there is excess voltage somewhere, right?

Attached hopefully close to final diagram with specific hardware including busbars and wire gauges. I started with a diagram from Victron, but couldn't find the exact terminal blocks or busbars shown. So I replaced them with two 600A Blue Sea busbars and two 150A common busbars to aggregate smaller loads.Winnebago Via Electrical Solar Wiring Diagram Simplified 2021-05-17.png
 

Boondock Saint

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Hey I'm fine w it too, that was my original answer. HOWEVER at 3 in the morning I then saw a post by an admin saying otherwise so I did some rethinking and big long edit. I want my sleep back now!

What is this, rev 3 of your drawing I've downloaded? If I can ever finally get a system designed I'm gonna plagiarize the hell out of it. : D
 
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