48V inverter connected to 12V inverter for RV setup sanity check

[justinm001]

Let me simplify my question. If I have 100amp cables and have red/black/white/ground from my 20k genny.
I then have red/white/ground going to inverter1 in1 then out1 going to an AC unit1 pulling 15amps.
I also have black/white/ground going to inverter2 in1 then out1 going to an AC unit2 pulling 15 amps.
The white/ground wires are shared between the inverters inputs.

Would this work with the genny on, then also with the genny off and it using inverter power?

Because all i'm doing is adding separate inverters on each leg of the 120v.

 

[timselectric]

Let me simplify my question. If I have 100amp cables and have red/black/white/ground from my 20k genny.
I then have red/white/ground going to inverter1 in1 then out1 going to an AC unit1 pulling 15amps.
I also have black/white/ground going to inverter2 in1 then out1 going to an AC unit2 pulling 15 amps.
The white/ground wires are shared between the inverters inputs.

Would this work with the genny on, then also with the genny off and it using inverter power?

Because all i'm doing is adding separate inverters on each leg of the 120v.

Not with those inverters.
You would have to use two identical units. Designed to operate together in a split-phase configuration.

 

[justinm001]

Not with those inverters.
You would have to use two identical units. Designed to operate together in a split-phase configuration.

Why does it need to be split-phase? This is the part i'm not understanding. As I see it either the inverters are bypassing and not doing anything so the generators split-phase system is going through the circuits thus no load on neutrals as long as the AC units are equal. Or the inverters are assuming the load and its separate circuits at the inverter so there's 2 120V loads each 15a so the neutral is passing 30amps which is well under the limitation of the wire.

 

[timselectric]

Why does it need to be split-phase? This is the part i'm not understanding.

Because you want to feed them with split-phase.

 

[timselectric]

Maybe these videos will help you understand split-phase.

 

[justinm001]

Maybe these videos will help you understand split-phase.

I watched those and totally understand how it works but don't understand why I NEED them to be in a split-phase configuration or else itll blow up. I understand if I have them identical as a split phase i'll be able to maximize my wiring and able to utilize all 20kW but i'll never use close to that. At most ill use 12kW and thats for just a few minutes a couple times a year when its been sitting and I want all 6 ACs to cool it down quickly so I can start the genny and turn them all on one by one. Outside of that i'll be using 5kW MAX and just running off solar.

I'm just trying to understand my options and the limitations, not so much best practices. Nothing seems to explain how bypass mode works in inverters and its affect on a split-phase system. Also wanting verification that running them as separate circuits won't cause any issues as long as I'm under the limitation of the neutral.

 

[timselectric]

Nothing seems to explain how bypass mode works in inverters and its affect on a split-phase system.

The inverters don't affect the split-phase system.
The split-phase system affects the inverters.
Those two inverters aren't designed to be used together in a split-phase configuration.
You can not connect them to a 240v circuit.
No matter what loads you connect to them. 240v will be running through the two units.
At best, they will just shut down and save themselves.
At worst, they will release the magic smoke.

 

[jberger]

I'd recommend you first fully document your AS BUILT system.
You mentioned in a post last week that the coach has been re-wired more than once. You cannot depend on anything being standardized at this point and you need an AS BUILT to design any replacement. 3.

Trust nothing and test and trace as much as possible.

It is common on large coaches, to divide the system in to Left side and Right side to make it easier to wire and to connect. I think you are assuming a lot here and the mistakes are very dangerous and expensive.
The comments regarding re-wiring around the ATS make me believe you could end up killing yourself or someone else based on your assumptions.

You need an electrician who understands mobile systems and bonding, that's not going to a regular residential guy who has a pop-up he uses during hunting season.

I am NOT implying you are not capable, but this is not the stuff you want to learn on as these are extremely expensive lessons and life/safety impacting.

 

[justinm001]

I'd recommend you first fully document your AS BUILT system.
You mentioned in a post last week that the coach has been re-wired more than once. You cannot depend on anything being standardized at this point and you need an AS BUILT to design any replacement. 3.

Trust nothing and test and trace as much as possible.

It is common on large coaches, to divide the system in to Left side and Right side to make it easier to wire and to connect. I think you are assuming a lot here and the mistakes are very dangerous and expensive.
The comments regarding re-wiring around the ATS make me believe you could end up killing yourself or someone else based on your assumptions.

You need an electrician who understands mobile systems and bonding, that's not going to a regular residential guy who has a pop-up he uses during hunting season.

I am NOT implying you are not capable, but this is not the stuff you want to learn on as these are extremely expensive lessons and life/safety impacting.

My 12V was rewired to add a firefly integration system only by the coach builder who originally built the coach (Nashville Coach). The 120V systems are original as built by them. I believe I have all the schematics for the 120V system but regardless the 120V is wired and labeled all nice and neat with even the outlets themselves labeled saying which breaker they're on. It was a commercial coach so designed and documented so make their jobs easier when troubleshooting. The 12V is a mess and I've been clearing and identifying items as they come through. I don't have access to the firefly system or controls yet but its a work in progress as I go device by device and map it all out.

Generator and Shore go directly to an ATS built with schematics on the door. I bypassed the genny part of the ATS and ran a new line for genny to my existing Quattro and connected the shore to the quattro directly. It then goes out the inverter using Red and Black as out1 and out (both set always on) thru the Shore ATS relay into breaker panel1 then panel1 goes to breaker panel2. Each outlet has its own 20amp breaker and the AC units have their own 30amp breakers.

There are a couple of lines that have additional relays that the Firefly system controls for 120V. The Coach charge outlet, Air Compressor outlet, Water heater outlet, and a large 12V to 12V gen battery merge relay. These are in a separate panel behind my firefly panel with switches which I believe change the NC to NO option.

This coach is designed differently than production coaches as everything is overbuilt to be reliable and stable as its very important to be working and quickly repaired. All wiring and such is through conduit and properly labelled. Below is my actual coach when I bought it and how it was setup when GTL used the coach (they replaced it with a newer but identical coach).

2008 40 Ft. Dual Slide Prevost

rear lounge with the slide open.

staleycoach.com

Technology in Motion- Bus Picture Gallery | GTL

www.gtl.net

I'm in the process of remodeling it and customizing to fit my needs. I'm a tech guy who runs multiple tech companies including those that house millions of dollars in compute equipment in datacenters so have a full understanding of power requirements, capacity and working with 120V, 230V and even 3 phase power systems. I'm just not well versed inside the electrical cabinets and mainly deal with the N+1 requirements and power limitations at the rack. Its why I'm interested in the how and why not just the yes or no.

 

[justinm001]

The inverters don't affect the split-phase system.
The split-phase system affects the inverters.
Those two inverters aren't designed to be used together in a split-phase configuration.
You can not connect them to a 240v circuit.
No matter what loads you connect to them. 240v will be running through the two units.
At best, they will just shut down and save themselves.
At worst, they will release the magic smoke.

This is what I'm confused about. Below I currently have it setup as #1 with just 1 inverter. Why can't I run it like #2 and how would 240V be running through the 2 units? Compared to running it like #3 where it seems inefficient.

 

[timselectric]

This is what I'm confused about. Below I currently have it setup as #1 with just 1 inverter. Why can't I run it like #2 and how would 240V be running through the 2 units? Compared to running it like #3 where it seems inefficient.

View attachment 151243

There's nothing wrong with any of those options. As they're wired separately to separate loads. (The only common connection is on the input)

But that's not what you described previously.
You were sharing the neutral. (Common connection on the output)

 

[justinm001]

There's nothing wrong with any of those options. As they're wired separately to separate loads. (The only common connection is on the input)

But that's not what you described previously.
You were sharing the neutral. (Common connection on the output)

Ok good thats what I was thinking. But even something like this where the neutral is shared in the breaker panels would work though right?

 

[timselectric]

Ok good thats what I was thinking. But even something like this where the neutral is shared in the breaker panels would work though right?
View attachment 151244

No
These two (different) units cannot be connected to 240v.

 

[justinm001]

No
These two (different) units cannot be connected to 240v.

This is the part i'm confused about as there isnt anything different other than a shared neutral buss bar and the 120v loads should need to return through its correct neutral to complete its circuit. I've watched a couple videos and other things where its been done without issue like the one below as he used 2 120v battery banks to power each leg without issue over a shared neutral buss. He even shows how the 240V shows anywhere from 0 to 240v depending on how out of phase it is at that time.

 

[timselectric]

This is the part i'm confused about as there isnt anything different other than a shared neutral buss bar and the 120v loads should need to return through its correct neutral to complete its circuit. I've watched a couple videos and other things where its been done without issue like the one below as he used 2 120v battery banks to power each leg without issue over a shared neutral buss. He even shows how the 240V shows anywhere from 0 to 240v depending on how out of phase it is at that time.

As I stated before. Which got you on the track of using the two inverters this way. It's completely fine to use the 2 x 120v inverters to feed the two legs of your panel.
What's not safe, is to introduce 240v into the same system.

 

[justinm001]

As I stated before. Which got you on the track of using the two inverters this way. It's completely fine to use the 2 x 120v inverters to feed the two legs of your panel.
What's not safe, is to introduce 240v into the same system.

I agree but I'm not seeing where any 240v is introduced into the system. It's the exact same image as before but using a shared neutral buss. This is the same thar basically every circuit panel is wired up. Can you circle where the 240v is or where the problem lies?

 

[timselectric]

I agree but I'm not seeing where any 240v is introduced into the system. It's the exact same image as before but using a shared neutral buss. This is the same thar basically every circuit panel is wired up. Can you circle where the 240v is or where the problem lies?

Go back to the first video I posted.
When the neutral is disconnected. The loads on either side are operating in series with each other at 240v.

 

[justinm001]

Go back to the first video I posted.
When the neutral is disconnected. The loads on either side are operating in series with each other at 240v.

The neutral would never be disconnected. Look at the image I sent, we'd either have a redundant neutral in a split-phase or 2 separate circuits sharing the neutral bus which my understanding this would be a multi-branch circuit something like the link below.

Multiwire Branch Circuit - Electrical 101

A multi-wire branch circuit in a residential dwelling contains two hot wires of different phases (A and B phase) and share one neutral wire as return current.

www.electrical101.com

 

[timselectric]

The neutral would never be disconnected. Look at the image I sent, we'd either have a redundant neutral in a split-phase or 2 separate circuits sharing the neutral bus which my understanding this would be a multi-branch circuit something like the link below.

Multiwire Branch Circuit - Electrical 101

A multi-wire branch circuit in a residential dwelling contains two hot wires of different phases (A and B phase) and share one neutral wire as return current.

www.electrical101.com

I'm running out of ways to explain it.
It's not safe, for the reasons I explained.
At this point, All that I can do is wish you good luck.

 

[justinm001]

Thanks his video below explains the situation much clearer. The open neutral isn't part of my scenario.

I'll update with a final visio and photos of how everything is installed. I'm thinking it might work better running one inverter into another as I don't think i'll ever have over 100amp load