question

b-champ avatar image
b-champ asked

Setting up 2 Multiplus units with a Cerbo GX

I just purchased a system from my battery and Victron supplier. The system includes two Multiplus units and one Cerbo GX. Now, after taking delivery of the system, my supplier tells me I cannot use a Cerbo GX with the 2 Multis. This is very frustrating, since I went to great expense to have all critical components communicate via a Cerbo.
I have the two Multis in order to supply 6000 total watts to both 50 amp AC lines of my RV.

So, the question is: How can I use the Cerbo GX with the 2 Multis? Is there a workaround?

cerbo gx
2 |3000
Toggle Comment visibility. Current Visibility: Viewable by all users

Up to 8 attachments (including images) can be used with a maximum of 190.8 MiB each and 286.6 MiB total.

4 Answers
Kevin Windrem avatar image
Kevin Windrem answered ·

You need to configure the two units to work in split phase mode. This is covered in Victron training but your supplier should have done this for you. I’d try to get them involved.

4 comments
2 |3000
Toggle Comment visibility. Current Visibility: Viewable by all users

Up to 8 attachments (including images) can be used with a maximum of 190.8 MiB each and 286.6 MiB total.

Matthias Lange - DE avatar image Matthias Lange - DE ♦ commented ·

Or parallel mode.

https://www.victronenergy.com/live/ve.bus:manual_parallel_and_three_phase_systems

@B. Champ I moved that question to the normal Q&A space.

0 Likes 0 ·
b-champ avatar image b-champ commented ·
Thanks, Kevin! The problem for me is: The two Multiplus units were supposedly programmed by my Victron distributor to work in split phase (3000 watts continuous on each leg). They even drew up a simple schematic which showed both Multis connected to the Cerbo. But now, after taking delivery they are telling me it can’t be done, and that the Cerbo will only ever function with one. This is NOT what I expected when I ordered and paid handsomely for this system though.

Can someone at Victron reach out to the distributor (a very well known and respected battery manufacturer in the US) and inform them as to how this can be done?

0 Likes 0 ·
klim8skeptic avatar image klim8skeptic ♦ b-champ commented ·
Note that both multi's have to be the same model # and the same hardware revision.

There should be a sticker on both units with that info.

0 Likes 0 ·
b-champ avatar image b-champ klim8skeptic ♦ commented ·

The only number that is different on the white sticker on the outside of the shipping container box is a number beginning with the letters HQ.18565b0a-9ec5-481a-ae9a-c1c833bb801e.jpegImage Caption

71cbb89a-ba60-4287-95bc-153fb3a79850.jpeg
0 Likes 0 ·
18565b0a-9ec5-481a-ae9a-c1c833bb801e.jpeg (1011.2 KiB)
71cbb89a-ba60-4287-95bc-153fb3a79850.jpeg (1.9 MiB)
Kevin Windrem avatar image
Kevin Windrem answered ·

There are notes in Victron documentation that indicate a GX device can only control one Multi, BUT when properly configured as multi-phase and/or parallel operation all the Multis appear as a single unit to the GX. This certainly IS possible and they should know this and done the programming. They sold you a system. They need to be responsible to make it work!

If you can’t get anywhere with your dealer, you can do the programming yourself using VictronConnect on a Mac or PC. An Mk3 USB cable is needed. But you really should have some guidance.

Training is available on professional.victronenergy.com

11 comments
2 |3000
Toggle Comment visibility. Current Visibility: Viewable by all users

Up to 8 attachments (including images) can be used with a maximum of 190.8 MiB each and 286.6 MiB total.

b-champ avatar image b-champ commented ·
Thanks, Kevin. I really do wish Victron would have made their Multiplus II 5000 for the U.S. market. That would have solved several problems for me. But wishing doesn’t make it so.


The configuration for my 50 amp RV service is simple though—each Multi is on one leg. So, one Multi supplies 120AC inverter power to line 1, and the other to line 2.

Now, I’m left wondering whether I should have gone with some other solution, or whether the supplier should have even sold me the Cerbo to begin with.
They also insisted that I design my system as a 12 volt system, but I have not thought that to be wise, since I have 2400 watts of solar and 12,996 watt hours worth of batteries. The amps are off the chart; and I’ve also had to buy bigger MPPTs and 4/0 cable for most everything!

0 Likes 0 ·
Show more comments
b-champ avatar image b-champ commented ·
Since Victron does not offer a 60 Hz Multiplus II 5kv model, should I have purchased a 12 or 24 volt Quattro instead of the two Multis? I think the Quattro does work with a Cerbo GX… right?
0 Likes 0 ·
Show more comments
Kevin Windrem avatar image
Kevin Windrem answered ·

You should carefully look at all the Victron products at their web site: victronenergy.com

The ONLY single unit that will support split phase power is the Multiplus II 3000 VA 120x2. It has a single inverter that will feed both legs when shore power isn’t available.

ALL other systems will require TWO Multis or Quattros to produce 120/240 volt split phase. 3000 VA is as much as you can get from a single Multi. So you’d get 6000 VA when you combine both legs of your split phase service. As mentioned previously, the maximum power from theses units is 2400 watts ad 25 degrees C, not 3000 watts. If you need more power than 2400 watts per leg, you’d need two Quatros. Plus, if you go over 3000 VA per leg, you’d need a 24 or 48 volt battery system.

12 volts will be marginal to provide 6000 VA to a pair of inverters but can be done with careful attention to wire sizes and keeping wire runs short.

The stock flow overview screen WILL list L1 and L2 power plus the total of both legs. Obviously, the individual leg power is the most important. I also have some enhanced pages that deliver additional information including power gauges so you can see your power relative to limits graphically, but get the system running before playing with enhancements.

https://github.com/kwindrem/GuiMods


1 comment
2 |3000
Toggle Comment visibility. Current Visibility: Viewable by all users

Up to 8 attachments (including images) can be used with a maximum of 190.8 MiB each and 286.6 MiB total.

b-champ avatar image b-champ commented ·
Kevin, thanks for taking the time to explain this, and for the link!

So, the bottom line is: it appears I will need to keep what I already have—2, 120v 3000VA Multis, if I go ahead with a 12v system.
Would an autotransformer help with what I am trying to do?

I’m not sure if I’ll keep the Cerbo GX if it cannot monitor each leg of each Multi separately, and will only see both Multis as one unit.
If there is a workaround for this, I’d like to know about it.

I’m seriously thinking of returning my 2, 12v Multiplus units for 2 24v ones, and setting my entire system up for 24 volts. That would not only cut the amperage in half and allow for smaller cable gauges, but it would also give me more solar room to grow with my 2, 150/100 MPPTs.

0 Likes 0 ·
Kevin Windrem avatar image
Kevin Windrem answered ·

Keep the Cerbo. It will show you all the information you’ll need. Read through the training on Multi-phase and parallel inverter/chargers for more information on how this works and how it is configured.

I’d highly recommend speaking out a new dealer who is interested in providing you the technical support you’ll need to get this system working.

6 comments
2 |3000
Toggle Comment visibility. Current Visibility: Viewable by all users

Up to 8 attachments (including images) can be used with a maximum of 190.8 MiB each and 286.6 MiB total.

b-champ avatar image b-champ commented ·
Thanks, I’ll keep the Cerbo, but I do wish it would provide information on each leg individually.


I’ll have to stick with the dealer though, since I have already purchased the system from them—2400 solar watts and 12,996 watt hours of battery storage, 3 MPPTs, etc—and they are geographically very far away.

The dealer has been fairly responsive, but my main point of disagreement with them right now is their insistence that I configure the system as 12v.

Question: If I use 2 Multiplus II units in parallel instead, would they do a better job of regulating the 3,000 watts over each leg?
And would the Cerbo recognize both legs or just see them as one unit and one leg?

0 Likes 0 ·
Kevin Windrem avatar image Kevin Windrem b-champ commented ·
Cerbo WILL show you power on both legs on the flow overview and in the menu for the Multi.


If you configure the Multis in parallel you would need to limit your RV power to 6000 watts and not be able to use the second leg at all. This is not the way to go!

Switching to 24 volts will require additional components so you can provide 12 volts to your RV’s DC loads.

You need help from someone who understands Victron components and RV systems.

0 Likes 0 ·
b-champ avatar image b-champ Kevin Windrem commented ·
Thanks, I’m now settled on configuring it as a 24v system; and I’m returning the 12v Multis for two standard Multiplus 24v models.


Thankfully, I only have two 12v accessories which draw their power directly from the battery and not the 120AC to 12v DC converter. So, I will purchase an appropriately sized Orion for those loads.
0 Likes 0 ·
b-champ avatar image b-champ b-champ commented ·
One multi will be on one leg and the other on the second leg. And yes, I will have to be constantly aware of my watt usage on each leg. But, I’m sort of used tot that when I’m connected to a 30amp shore power source of generator anyway.
0 Likes 0 ·
mvas avatar image mvas b-champ commented ·

Did you consider the MultiPlus-II 3000va 2x120v? It is specifically designed for the 30A / 50A RV application. I believe they can be connected in parallel. The Cerbo would then always show the Amps in L1 and L2.

12 volt and 24 volt !

Multiple LiFePO4 batteries in parallel will reduce amps per batt. All Batteries combined at Bat Bus Bar. Then double wires from Batt Bus Bar to each Victron terminal.

0 Likes 0 ·
derrick thomas avatar image derrick thomas mvas commented ·

Yes they can be connected in parallel. When operating on single phase shore power, both L1 and L2 loads are aggregated on L1 input.

0 Likes 0 ·