question

You have to calculate, how much Current is flowing when you use the mp2 as charger ... And maybe es inverter at the same time ... I Think it would be easier to charge the batteries direct ...

Okay, the nominal max. 35A charging power of the Multiplus seem to result in max. 1800 Watts charging power. The Multiplus shows max. 1800 Watts and approx 32A DC max. when charging.

I assume a 1800W continous power specified inverter will be the min requirement. It might get hot when running at max power for a few hours of charging.

If there is an easier way to charge a 48V battery bank from a 12 V car alternator, I will be happy to use it.

Although this should be easier and more efficient, the 12V -> 48 V DC/DC converters in that power range seem to be uncommon and more expensive than the usual 12V -> 230V DC/AC car power inverters.

Daniel

Hi Daniel,

The Multiplus-II 48/3000 has a mínimum shore current input limit of 3A, or 690W at 230V.

That means you need an inverter which is able to produce at least 690W permanently - that would be the 12/1200 Phoenix Inverter, or a bigger model.

The 12V DC input current of the 12/1200 inverter for 690W might be around 55A (690W / 14V / 91% inverter efficiency).

The "regulation" of the input power could be done with AC Input current limit in the Multiplus, but as mentioned above, you cannot go below 3A limit. Additionally you can reduce the 48V charge current in the Multiplus, but if you have an AC consumption at the same time that will sum up with the AC Input power needed to charge the batteries, till the AC Input limit.

You would have to set a car battery voltage above 13V to stop "charging" with the inverter (=turn the inverter off, or disconnect the Multiplus from AC Input, in case there are other DC consumers in the car and the alternator cannot supply the additional 55A or more.

Also you have to make sure to connect the 12V inverter only when the engine is running.

An alternative to a 12V inverter which I would recommend might be to use DC/DC converters. Unfortunately Victron does not (yet?) have any 12V to 48V Orion DC/DC converters. You may use a 2-stage approach, a 12V to 24V converter, and at its output a 24 to 48V converter with slightly less power than the 12/24V unit. With this you have the option to implement a lower power charger than the 690W inverter solution.

Question: Is this installation in a vehicle? Or do you just want to use a vehicle to backup a house installation?

For a vehicle installation you might consider a 12V Multiplus installation, to avoid change of voltage levels. 24V is also easier than 48V, as there are Smart Orion 12/24V units. Also it might be easier to integrate PV panels with a lower system battery voltage, because do you not have to generate a high PV voltage (48V requires 2 PV panels in series which might complicate to find the space on the roof, especially if you want to add PV power later on and need to fit panels into the remaining spaces.