I am a Robotics Engineer so I’m familiar with the concepts and systems but I lack experience with solar and inverter system configuring.
I have an off grid working system with a Multiplus II connected to a Cerbo GX, a 48V 200Ah Dyness battery, two solar panels with MPPTs, and an 8KW generator as well. I have occasional 2-3 hour loads of 5.5kW connected to the AC OUT 1 and AC OUT 2 is not in use.
It works well for more common uses but in my case, the system is off-grid, and the AC LOADS need to be the priority.
What is happening right now is: The battery + solar supplies 5.5kW to AC LOADS until the battery reaches its lower SOC value and the Generator Auto Start feature kicks in to start the generator. Then the generator supplies 8kW, 4.5kW of it being used to charge the battery and only 3kW for AC LOADS.
I understand I could limit the charge current to indirectly supply only 2kW to the batteries, but when I’m not using the AC LOADS that would more than halve my charge time.
I couldn’t find anything in the manuals, or the community and it is not recommended to use ESS in a OFF Grid system.
Hi Yves,
The Multi will already be prioritizing the loads from the generator and charging with the remainder of it’s Input Limit. Note the Multi cannot charge and invert at the same time.
You may be seeing distortion in the figures from what you expect to see, perhaps due to Power Factor issues with the load? Always a source of wonderment for me too…
Could you suggest how I could verify this? My AC Loads are 8 Victron Phoenix Chargers each drawing max 740W. But the load vary depending if they are in Bulk or ABS mode.
I have attached two screenshot pictures taken from the moment the generator powers off.
Certainly a good example of the ‘distortion’ of figures I was meaning. I see it on my own offgrid system, just not that bad. Eg. I might have a 200W AC load showing, but when I run the genset it drops to near Zero. Can’t be right because the loads are still running.
I can’t explain it, but I suspect a poor sinewave output from the gen (they’re notorious for that) has much to do with it. And maybe the Victron measurement, RMS or not, doesn’t cope well with it.
The battery DC is probably ok, and I’ve learnt to trust the ACIn to a larger degree than the ACOut. But I’d only be guessing if I tried to offer you more than that.
Maybe your AC loads are actually changing with the different quality input??
The AC loads don’t seem to change with different types of inputs, as I can measure them pretty well. They have standard power draw stages, so it’s easy to identify how much power they should be drawing, and I have double-checked in the Victron app with the live readings of the devices.
I’m doing some more testing but one thing is that I have something in the range of 1400W being used and not shown in the VRM Portal. I know the Multi draws around 700W when outputting higher loads, but I’m still not sure where the rest is.
I tested this by using only my buffer battery and measuring the AC OUT devices multiple times for a couple of hours. And also looking at the battery SOC.
