How to make the most of Victron Multi-Plus Inverter/Charger on SM#387

Dan Carlson

Hello all,  I have been thinking through the best way to install a Victron Multi-Plus Inverter/Charger on SM#387.   I am specifically looking at the 3000w/70a/24v/16a model.   I have seen several previous posts that have discussed aspects of installing Victron Inverter/Chargers.  These previous posts have included discussion of installing switches between sources of supply to the 230v panel, or dividing the 230v panel between the inverter supply and direct supply from shore or inverter…   I am considering the approach diagramed roughly in the attached photo and described below.  Please let me know your feedback, questions or concerns.    


A very brief summary of the he Victron Multi-plus: It will take 230v power from shore or generator (45-65Hz) as well as 24v power from a battery bank to provide 230v power for the boat.   The 16a model is limited to 16a current load.  From this it can provide up to 3000a from the inverter, with or with-out shore power.  Whenever there is excess 230v supply over housed demand for 230v, the inverter will switch to a charger mode to put energy back into the battery bank.   On SM#387 this is great for most of our needs as we are currently restricted to 16a on the Shore power already.   However; we do have one significant conflict for power demand and that is the 230v water-maker which draws approx. 13-14Amps.  


To best solve for this and to minimize the requirement for different switches I would like to connect the output from the Victron directly to the 230v panel to provide consistent ac power for the boat when whether on battery, shore power or generator.    And to solve the current demand needs by removing the water-maker and both of the battery charging breakers from the existing 230 panel.  See notes below for further explanations.


Design notes to accompany attached diagram: 

  1. This approach is based on the current 16a system/limit on Shore Power, the current Onan 7MDKAV generator and the current AMEL switch box that automatically switches between Shore or Generator as AC source.   I think that I will add a 16a breaker on the shore power as a good precaution as I work on my overall wiring.
  2. I will need to add a new breaker box, or perhaps I can use the existing breaker box that was used for the Pro-Sine 1800w inverter that currently supplies power to the boat. This is where I would have the breakers for the water-maker and also for the secondary battery charger (perhaps a Sterling 24v/30a charger).   This will be supplied directly from the AMEL switching relay box.
  3. This would allow me to re-move the wires for the water-maker and the secondary charger from the main 230v panel.  
  4. The breaker the 100a charger will also be removed from the 230v panel, and new wire will be added directly from the Amel switch to the Victron Inverter (with the appropriate fuses/breakers).
  5. The AC output from the Victron Multi-Plus inverter directly to the 230v panel  (I need to consider changing the existing 30a breaker on the main panel to based on the overall limit from the Victron.)
  6. Supply the battery power to the Victron Multi-plus from the existing cable that supplied the 100a charger (This looks like a 50mm2 cable, which is sufficient for up to 5meter run).
  7. Configuration:   The Victron Multi-Plus has a Power Control setting that sets a limit the current that it will draw on the AC input source.   I could set this to a max of 10amps.  The rationale for this is:
    1. When I am running the generator and I turn on the water-maker I have already limited to the Victron current draw to 10amps.  That and the 13-4amps that the water-maker draws will put an appropriate load on the generator.   Note: it is likely that the Victron will regularly be fully utilizing this limit because what ever I am not using for 230a current will be allocated to charge the batteries, up to the 70amp limit for the Victron for charging. 
    2. When I am on Shore power I have set a very conservative 10a limit on the 16amp shore power circuit but I will actually be able to provide more current to the 230 amp panel than I previously would on shore power with out the Victron.   This is achieved through the Victron Power Assist capability.  When the 230v AC demand on the main panel exceeds the 10amp limit on the current input, the inverter will make up the shortage using the Inverter to draw from the battery.   The documented examples from Victron specifically shows an example of a 10a limit on the input current being supplemented with 10amps from the inverter to provide 20amps total AC current out.    This should be sufficient for our needs as most of our higher current draws on the AC side are only for short duration, i.e. hot water kettle for 1-2 minutes, 3-5 minutes to heat water for the washing machine or dishwasher, or short bursts for the micro-wave. 
  8. Operational considerations:
    1. Day in and day out we are already trained to look up at the 230v Current meter before we turn anything on the 230v panel, and shut something off if necessary.  Regarding the water heater, we currently do not leave it on when on Shore Power.  We will turn it on for an hour in the morning and that is sufficient for the whole day.
    2. Regarding the generator operation and water-maker:  I am always in the engine room before and after running the generator / water-make; to set the flush valves prior to the water-maker run and after the water-maker run to flush the membranes and check that everything is ok.  Therefore having the breakers for the watermaker and secondary charger in the engine room do not add any inconvenience to my existing routing for running generator/water-maker.
    3. Important!  The Victron Multi-Plus AC current frequency out will default to 50Hz when on the inverter, but it will switch to match the frequency of any input AC source.  So when running the generator it will be 50Hz, however, when on 60Hz Shore Power then the AC output to the main panel will be 60Hz.



Please let me know your feedback, challenges, questions on this, as I want to get it right the first time and I know I am not the first down this road and there are learnings to be shared.


Thanks and Regards,  Daniel and Lori Carlson on SM#387, sv-BeBe, currently at Shelter Bay Marina, Panama







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