Question about offgrid inverters/chargers
As an example, I have specs for the EG4 3000W all-in-one inverter (data sheet PDF). My question is about the input PV voltage range, and what some of their numbers mean. See page 6, but details here:
For solar input, they list these values:
- Max PV input: 5000W
- Max Voc: 500V
- PV MPPT voltage range: 120-450Vdc
- Start up voltage: 42V
I'm thinking about getting this unit for a small project, an off-grid shed. There is room for four panels (1000-1200W). Let's say the panels have a Voc=37V, and Vmp=32.
So with this Vmp, four panels in series is 4*32 = 128V. With hazy skies, clouds, etc, the panel voltage would be less, and less than the MPPT lower range of 120V. What happens in this case? If the device starts up at 42V but the panels are producing somewhere in the 42-120 range, is the charger working?
Does the "MPPT voltage range" just describe the optimal range for max charging?
I'm really surprised this EG4 3kW unit has such as high range, because the LV6548 clones have an MPPT range of 90-230Vdc, but I don't need a 6500W inverter, and it costs at least twice as much.
Posted Nov 12, 2022, 2:21 AM UTC
My gut feeling: it starts as in showing something on the screen/LEDs as soon as it gets 42V from somewhere. Somewhere might be the battery. Charging starts at 120V.
The MPPT range is a question of circuit design. The more traditional design cannot do huge ranges, but the current design can. Older models will have a more narrow window.
The usual setup puts the solar Voc as close as possible to the upper end of the charger input voltage. That's not strictly needed with the newer designs: the max amps and wattage also limit input. 18A at 450V would be 8kW, but the system can only do 5kW overall. You already reach 5kW at 280V.
Thanks for explaining that.
I found something interesting in the manual, on page 14. While the maximum PV voltage the unit can handle is 500V, the MPPT has a range of 120-450V. This page also says that the Vmp of the panels must be more than the startup voltage of 42V.
What I read in that is that MPPT works in the 120-450V range, but charging can still occur outside that range. Perhaps they fall back to PWM in these outer ranges, IDK, but that's what I'm curious about.
This page also shows some recommendations using an example panel with Voc=40.35 and Vmp=33.25. They recommend at least 5 panels in series. So my system with 4 may not be big enough.
I just want to know definitively what happens between 42-120V, lol.