[Discussion] Paralleling (2) MultiPlus II 12v/3000va (2 x 120v) units

[A.Texas.Yankee]

Excellent write-up on this. I am in precisely the same boat as you, needing power to the L2 leg to run my rooftop AC. I will detail my build below. My question is pertaining to charging. Any issues there? Do both MP-IIs provide charging or only the master?

Solar:
18 x 240W NewPowa panels wires in 3 sets of 3s2p (4320W)
2 x 250/100 Victron Solar Charge Controllers
1 x 150/100 Victron Solar Charge Controller

Inverting/Charging:
1 x Victron Multiplus II 12v/3000va 120x2 (considering second)
Victron Linx Distributor
Victron Linx Power-Up(fused)
Victron SmartShunt
Victron Cerbo GX
Victron Touch 70

Battery Bank:
6 x 200Ah Dakota Lithium battery bank (plans to add 2 more)

And various misc components (4/0 cables, lugs, wire, hardware, communication cables, mounts, etc.)

I never saw this comment so sorry about not replying! If you didn't find and answer it does charge from both units, not just the master.

[A.Texas.Yankee]

@A.Texas.Yankee, Excellent write up. You were certainly thorough and very detailed in your explanations. I am a systems engineer and I am very impressed. You have done an awesome job. Now all we need is some bragging pictures!

Well done young man!

Bill

Thank you. It was a lot of research on my end and even with a Victron Rep telling me I couldn't do it. I figured others would want to know that it is not only possible, but relatively easy vs a standard setup with a single inverter.

As for photos... Well, rig is in process of getting sold! Someone appreciated all my hard work enough to by it, lol.

But I'll try to grab some photos if I can remember.

[Skyler]

Hi Skyler,

My next rig will be with 24v MPII unless they come out with a 48v version by middle of next year.

First, I would not go with the 6/4 unless you wanted a shielded ground for whatever reason. It's stiffer and not necessary. The 6/3 w/ ground (it's actually 4 wires... 2 hot, 1 neutral/common, and 1 bare ground). I went with the Romex 6/3 w/ ground Sim-Pull which I highly recommend. It's far easier to work with (NOT easy, just easier).

As far as for splitting, I went with two methods. For the hot and neutral split in, I went the sticks and bricks route and did a junction box and used wire tires and electrical taped them. After about 5,000 miles on very rough roads, this connection held up great. I would not hesitate to do this again, IF you are comfortable with wire caps and confident on your skills there. I know it's a simple concept, but I've seen plenty of times they were not utilized properly.

For the recombine I went with these little guys (Harris Connectors) and LOVE them, but they are pricey. These worked very well and have also held up great. Cannot use junction boxes with these though as it just won't fit.

The ground I went typical home contractor and left it a mess buy it ties together all in line (I did use one of the Harris connectors).

Hope that helps.

Yes, that helps. Thanks for the tips.

[Trigmish]

I have a similar design that the installer has not done correctly. 2x24v multi-ii. I bought the MP because I wanted to be able to switch from split phase to parallel on the fly. There are merits to both depending on the situation I am in and what I am connected to. My question is how does that need to be wired for the ac inputs. Does it get wired in parallel and the system just ignores ac inputs when in split phase or is it wired in split phase and the inverters do some Magic’s that I don’t understand. Then how do pass ac out to both sides of panel? Right now it is l1 120v inverter 1 And L2 to inverter 2. The. One ac leg to each side of panel.

[A.Texas.Yankee]

I have a similar design that the installer has not done correctly. 2x24v multi-ii. I bought the MP because I wanted to be able to switch from split phase to parallel on the fly. There are merits to both depending on the situation I am in and what I am connected to. My question is how does that need to be wired for the ac inputs. Does it get wired in parallel and the system just ignores ac inputs when in split phase or is it wired in split phase and the inverters do some Magic’s that I don’t understand. Then how do pass ac out to both sides of panel? Right now it is l1 120v inverter 1 And L2 to inverter 2. The. One ac leg to each side of panel.

Without an accurate diagram and knowing the specific use of what you're trying to do, there's wayyyyy too many unknowns to even get an idea of what you're needing. These systems are not really designed to switch back and forth from split to parallel and wiring is usually different between the two.

[houlster]

Do you know if just one of the inverters can be set to inverter only? Or even just off?

I have a similar, dual inverter setup, but I now have the problem if I'm mooching at a friends house, I can't plug into a 15a circuit from the house anymore. You cannot set the input current limit lower than 18.5a with dual inverters. Just wondering if in these cases, if one inverter could be turned off so current limit can be set to < 15a without re-programming everything. ?? (preferable to invert-only so I still get full power to the RV, but even just 'off' would work)

[A.Texas.Yankee]

Do you know if just one of the inverters can be set to inverter only? Or even just off?

I have a similar, dual inverter setup, but I now have the problem if I'm mooching at a friends house, I can't plug into a 15a circuit from the house anymore. You cannot set the input current limit lower than 18.5a with dual inverters. Just wondering if in these cases, if one inverter could be turned off so current limit can be set to < 15a without re-programming everything. ?? (preferable to invert-only so I still get full power to the RV, but even just 'off' would work)

You cannot. But you should be able to plug into a 15amp circuit. You likely wouldn't be able to use power assist and you would blow the 15amp breaker possibly if Exceeding consumption.

[mbmike29]

Thank you for sharing this post. I have a single MP-II 12/3000 2x120V in my 397TH - and I want to add a 2nd one in parallel. I have one question: What size wire did you use on the DC side? Wiring from batteries to lynx / buss bars and wiring from lynx to each individual inverter.

[A.Texas.Yankee]

Thank you for sharing this post. I have a single MP-II 12/3000 2x120V in my 397TH - and I want to add a 2nd one in parallel. I have one question: What size wire did you use on the DC side? Wiring from batteries to lynx / buss bars and wiring from lynx to each individual inverter.

4/0 and I even pondered double 4/0.

[gloaks]

Hello there,

My application is near identical to yours with the exception that I was just researching the install.

If I may ask you some questions?

1. how has the system performed since the install date?
Answer:

2. do you have a wire diagram that you can share?
Answer:

3. Can you please share your Inverter/Charger settings from the:
General Tab
Inverter Tab
Charger Tab

Thank you in advance, I really appreciate any information you provide.

my email address is: [email protected]


Norman

I'm starting this topic as a Q/A and open discussion about my solar and inverter installation that I am in the final stages of completing. It is up an running, but still have a few tweaks and adjustments in the works (mostly cleaning up the install and organizing wires and mounting things properly rather than the "that'll work for now" screws).

It's a continuation of my orig post:

Original Setup Post

Reason for this topic is that I have been asked A LOT of questions and been told numerous times that what I was doing was overly complicated or even not possible. Even a "Victron Ambassador" that was skeptical, lol. So, with that being said I am just an avid DIYer in many things and NOT an EE so please do your own research and take what I say with a grain of salt... I'm just some guy on the interwebs and am still learning as I go and I want to hear others inputs, knowledge, and experiences. This project became more of experiment more than a necessity and there is little information out there in this setup.

First, the basis:

Use our battery bank to power the coach with what isn't a unique idea but was a seemingly difficult goal: power everything on both legs without having to rewire anything on the panel or install a sub panel or anything like that. We wanted to be able to live off battery as we would off shore power (even if only for a shorter period of time). We live, work, and travel full time in our 2021 395MS-R.

Complications:

"50 amp" rv service is two separate legs of 120v x 50amp power that are run split phase. Most current conventional inverters are not designed to easily work with this design. There are several workarounds and paths that can be taken, but I wanted integration and communication those setups did not have. Simply put, we have two lines of power in, and two loads of power out. I need about 4500 watts of power total combined between the two legs (based off months of watching power consumption). That could be 3300 watts on leg 1 and 1200 watts on leg 2, or some combination thereof. So running a 3000va inverter solely on leg 1 and another on leg 2 would cause issues because leg 1 would use over 3000 watts at times so I'd still have the issue if not being able to run everything. Now I could use a 5000va inverter, but then I'm back to a lot of rewiring at the panel and I still wouldn't get the functionality I wanted. I could also wait for the AmSolar SPS to finally come to fruition, but IMHO, that technology is now deprecated. I won't go into detail of why other set up wouldn't work for me.

In comes Victron. Last year Victron released a new model of MultiPlus II 12v/3000va. It is the 2 x 120v model and it is specifically geared towards 50 amp RV service. It has two lines in, two lines out... now you might say all the MP II units have that, but you'd be incorrect. There's AC1 and AC2, but AC1 and AC2 both only have a single load output. The 2 x 120 has TWO lines in AND TWO lines out on AC1. On top of that, it can be set up for multiphase, parallel, etc. So that caught my attention.

I immediately pre-ordered 2 units. I was confident that if my theory didn't work that could sell the second unit and recoup nearly all the investment.

TL&DR

Fast forward months later...

I have installed and paralleled two Victron MultiPlus II 12v/3000va 2 x 120 units and they are 100% functioning as I had theorized. One is master unit and the other is the slave unit.

My FAQ section:

Q:
What did you have to do differently to wire the two units in parallel?
A:
The only difference in wiring setup vs a single unit is that I had to parallel the incoming 6/3 wiring to both units. 4 wires to work with = L1 , PE , L2, N. I started at the power in off the ATS behind my wet bay.
- L1 is split x2 and 1 wire goes to AC1 IN L1 on Master and the other goes to AC1 IN L1 on Slave
- PE is split x2 and 1 wire goes to AC1 IN PE on Master and the other goes to AC1 IN PE on Slave **warning** you have to provide continuous PE so you will have to jumper this split with AC1 OUT on both Master and Slave so ground is not interrupted. Dangerous if you mess this up **
- L2 is split x2 and 1 wire goes to AC1 IN L2 on Master and the other goes to AC1 IN L2 on Slave
- N is split x 2 and 1 wire goes to AC IN N on Master and the other goes to AC1 IN N on Slave **warning** N is NOT continuously ran like in sticks and bricks common/neutral and is something I almost made an error on myself see attachment **
- For AC1 OUT, you do the same as above, but in reverse so you end up with a single 6/3 going to the breaker panel, again keeping PE continuous

Q:
How does it provide power to both legs while on shore power since shore power is split phase?
A:
The units only "pass-through" power while on shorepower. It will not alter the incoming power so whatever is coming in, goes right through to the breaker panel as if they weren't there.

Q:
How does it provide power while on generator power?
A:
In my setup I have a 5500 Onan on the ATS. It functions the same as when on shore power. It is only passing through power so it does not affect it at all (power assist is a different topic)

Q:
How does the inverter power both leg 1 and leg 2 while on battery/inverter mode?
A:
Technically, only line 1 out provides power from batteries, BUT it is split as needed between L1 and L2. So I have 6000va available as needed between the two legs. How it does it... don't know, but it does (see screen shot). Line 1 can show 4500 watts, but line 2 will show nothing and I assure you both lines are getting power in the rig.

Q:
Aren't you worried about overloading your neutral since you are not running splitphase while inverting?
A:
In my case, no. That neutral is designed to carry up to 50 amps and even with 6000va (roughly 4800 watts) I'm rarely going to exceed 50 amps and even if I do, it'll be extremely short and not enough to heat anything up. I've clamp metered the neutral and haven't seen above 42 amps yet.

Q:
How hard was it to program the units for parallel configuration?
A:
Easy. Took about 15 minutes (and this included updates in firmware for both units). I did it from my phone using the Quick Connect app (Android), the MK3 to USB cable, and the V.E. bus ethernet cable going from the Slave to the Master to the MK3 cable to my Samsung Galaxy S22. The app on the phone literally walks you through it and all you do is update firmware and select "parallel" when it asks.

Q:
Any issues with the setup and did you lose any functionality?
A:
I did not lose any functionality. You cannot tell you are running off inverters vs shore power (other than the inverters are loud and you can hear the fans when inverting a heavy draw). So far the only real issue I have is a 4/0 cable running from my main fuse block to my main disconnect gets pretty warm. About 52°C warm. It's well within the 105°C rating on the cable, but no other cables get past slightly warm to the touch under a 350 amp draw, including the cable from battery to the fuse block. The switch is a Blue Sea rated for 900 amps and the fuse block is ANL Blue Sea rated for 600 amps continuous with a Blue Sea 500 amp ANL fuse. I'm thinking a bad wire connection or crimp so I'm going to pull it and redo the lugs with new ones and retorque it all to see if that helps. If not, I'll be forced to upgrade to a Class T sooner than I wanted. I do have some light flickering on the 12v side (like when running the water pump). This may also be cause by my bad connection above.

Q:
How fast is the switch over from shore/gen power to inverting?
A:
This is where the difference between L1 & L2 come into play. Any electronic on L1 you will not notice any change, it's seamless. Sensitive electronics like TVs and PCs won't lose power. Electronics on L2 will see a brief interruption in power. My router is on L2 and reboots. I think this is due to the way it handles power from L1 to L2 internally. I'm still troubleshooting but I think this is nature of the design, not an issue with my setup.

Q:
What did you do with your old converter and OEM inverter with the resi fridge?
A:
I pulled the old converter out completely. No reason to keep it for the measly amps it would add to the system. I can charge over 200 amps from these inverters to my battery which is plenty! Plus 200 amp potential from solar (averaging 1200 watts but it's winter so...)
For the inverter... eh, that's another story, lol. It's installed still as a "pass through" connection on the AC side because I can't locate the stupid sub panel that Grand Design installed to handle the OEM inverter to the fridge... it's somewhere, lol! I even had a dealership tech look for it and we can't find it. It's not in the basement storage, near the fridge, or anywhere behind the panel in the storage bay... so, I am at a loss, lol.

Q:
Why did you stick with a 12v system rather than a 24v or even a 48v?
A:
I really wish I could have to reduce the amperage draw of the batteries. But they don't offer a 24v or 48v MP II with the L1 and L2 pass through capability so I'd be back to square one with rewiring and side by side units, etc.

Q:
Worried about the high amps?
A:
Yes, but I've planned my system accordingly with the proper fuses, and cables to maintain the proper voltages and average draw. I'm within safe and normal operating temperatures and voltages from start to finish.

Q:
Worth it?
A:
Absolutely!Attachment 39444Attachment 39445

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