question

If you have a Multiplus unit then you have to select the max power setting that you want from the grid, the multi plus will then reduce the charge rate down and up so that they max load is NOT exceeded. IT WILL also supply extra power from the batteries if the max load fidure is exceeded.

I don’t think it will automatically change from 15 to 32 to 64 though you would have to adjust that yourself.

NOW if you purchased a Quattro this has 2 AC inputs so you could set AC 1 IN to 15 amps and then AC 2 IN to 32amps so then if you had two inputs and you use the correct input then this would be sort of automatic. JUST a Idea if thats of help

The main difference between a Multiplus unit and a Quattro is the Quattro has 2 AC Inputs

My Multiplus Compact 80A charger seems to do that "dial down" automatically to some extent at least. I have it set at 30A 120V (the size of my shorepower cable), but the boat is presently out of the water and I plugged the shore power cable via an adapter to a 20A 120 outlet (whose circuit is shared with other outlets). When charging the batteries, it seems to just reduced the max charge to what is available, so I'm getting about 40-55A of charge at any particular time. This is on a lithium setting, so it is pretty much charging max when it charges.

There's no way for the multi to know how many amps are available on the power source it's plugged in to. I can think of two caveats to this, which maybe victron staff would know more about:

1) 50A shore power is actually split phase, so if you had your system set up to ingest both "regular" 120 service and 240v split phase, it could know that had more to work with on 240 and act accordingly. I think this type of system would either require a quattro or some interesting external switchgear digitally connected to a multi.

2) Voltage drop. If you had your multi current limit set to a very high number of amps, but plugged in to a house with a 100ft extension cord or were at a campground with dodgy hookups, the multi might notice that long before it reached it's current limit the voltage sagged significantly and it might throttle it's charging. but this wouldn't help you if you plugged into a 15A circuit where you were close to a panel and there was not much voltage drop. The voltage wouldn't sag and the multi would trip the breaker. and I don't know what a multi's exact behaviour is when voltage sags like this.

But the short answer is no, the multi has no real way to detect how much current is available on a given source for it to charge with until you tell it.

When a shore power current limit is set the MultiPlus can never take more than that current limit from shore.

If a lot of AC load are connected to the multi the first thing to be reduced is the charge current. Of all available shore power, first the loads are supplied and if there is power left, this will go towards battery charging. This is called PowerControl.

If even more AC loads are turned on, eventually the battery charging will stop.

And if the AC loads are increased even more, the Multi will start inverting to supplement the missing power. This is called PowerAssist.

This process is explained in our marine brochure, on page 112. See this screenshot: