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  1. #1
    Rolling Along
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    [Discussion] Paralleling (2) MultiPlus II 12v/3000va (2 x 120v) units

    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!Click image for larger version. 

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    Last edited by A.Texas.Yankee; 03-15-2022 at 06:21 PM.

  2. #2
    Site Team Ynot4me2's Avatar
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    WOW, I love it. You really did your research and covered the bases.

    Sent from my SM-P610 using Tapatalk
    Steph & Lise
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  3. #3
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    Quote Originally Posted by A.Texas.Yankee View Post

    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.
    Lots of info here and I’m still unpacking it. But I noticed this.

    If I remember correctly, I did not have a sub panel for the stock inverter on my solitude. My stock inverter was plugged into AC at an outlet running off one of the breakers in the Main panel. The fridge outlet was then wired directly into the inverter. When I installed my multiplus II I just moved the romex coming from the fridge outlet to the box that the stock inverter was plugged into(removing the outlet in the process). If there is another sub panel I have no idea where it would be or even why one would be needed.
    2021 Solitude 375 RES-R
    2024 GMC Denali ultimate DRW

  4. #4
    Rolling Along
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    Quote Originally Posted by JKellerJr View Post
    Lots of info here and I’m still unpacking it. But I noticed this.

    If I remember correctly, I did not have a sub panel for the stock inverter on my solitude. My stock inverter was plugged into AC at an outlet running off one of the breakers in the Main panel. The fridge outlet was then wired directly into the inverter. When I installed my multiplus II I just moved the romex coming from the fridge outlet to the box that the stock inverter was plugged into(removing the outlet in the process). If there is another sub panel I have no idea where it would be or even why one would be needed.
    I plagiarized a photo from another user here, but this is similar to how my inverter is wired, except the AC wire from the inverter does not got to the fridge outlet. It goes off into LaLa land and grand design customer service said there's a subpanel it's tied into. The breaker panel operates the inverter and the fridge line separately from the outlet the inverter is plugged into. I think what you did is exactly what I am doing by leaving the inverter as a pass through... BUT you are right, having a sub panel doesn't make sense. I want to keep that outlet the inverter us plugged into so I might just splice it into that outlet and be done with it. Or butcher an extension cord and go full redneck.Click image for larger version. 

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  5. #5
    Seasoned Camper
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    Quote Originally Posted by A.Texas.Yankee View Post

    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.
    You are right….it’s the nature of the design. L2 switches much slower at 40ms, instead of less than 18ms for L1. Thanks SO MUCH for posting all of this info, I’m researching and planning what I’ll do right now for when our 310 shows up. I’ve been looking at Victrons, came here to search, and you validated what I was thinking.

    One question….do you (or did you ever) use a dc-dc converter for charging from the vehicle when traveling?
    Larry and JoAnna
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  6. #6
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    Quote Originally Posted by LMagelitz View Post
    One question….do you (or did you ever) use a dc-dc converter for charging from the vehicle when traveling?
    I've considered it. I even have an alternator that can handle it (397 amp OEM Ford Dual). But I'm holding off on that for now. Having to run new cables from the batteries on the truck to the bed and then another run if cables via Anderson connectors from the bed to the batteries on the trailer is a bit of a task I don't have the time for, yet. With the solar panels charging while driving, and the ability to run the onboard genset to recharge batteries, I'm not 100% sure I'll need to do it. Only circumstance I can think if is as a back up only when there's no shore power, no sun, and for some reason I can't run the genny. If I REALLY start to boondock more than 1 week at a time... it's on the maybe will do list.

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  7. #7
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    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.)

  8. #8
    Left The Driveway
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    Quote Originally Posted by A.Texas.Yankee View Post
    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
    Texas Yankee, I'm getting ready to do the same thing on my 5th wheel using two of the new 24 volt version MultiPlus-II 24/3000/70 2x120 and I have a question about splitting the big 6/4 AC wires before and after the inverters.

    Question: What did you use to connect and house all those big 6 AWG wire junctions? I'm having trouble figuring out a good way to connect three 6 AWG wires together...

    Skyler

  9. #9
    Site Team Redapple63's Avatar
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    @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
    2019 GMC 3500 SRW Sierra Denali Duramax
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  10. #10
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    Quote Originally Posted by Skyler View Post
    Texas Yankee, I'm getting ready to do the same thing on my 5th wheel using two of the new 24 volt version MultiPlus-II 24/3000/70 2x120 and I have a question about splitting the big 6/4 AC wires before and after the inverters.

    Question: What did you use to connect and house all those big 6 AWG wire junctions? I'm having trouble figuring out a good way to connect three 6 AWG wires together...

    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.

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