Multiplus AC ignore and overload situation

DIY
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1

Hi all,

I currently have a MPII in AC ignore mode, works great!

It’s configured to connect AC-in as soon as it’s using >3500W for 20s.

I notice that when this happens, the full power is taken from AC-in (up to the current limit, it swithces off when higher current).

Is it possble to have the MPII deliver up to 3500W and when it is >3500W for x seconds have AC-in supply the rest (up to the set current limit)?

As soon as power <3500 for x seconds it should break AC-in again, back ot ignoring AC-in…

Thanks!

2

@basco Which MPII? 3 or 5kVA and why only 3500W as the latter can do 4000W? Is it because of a battery limitation? ESS is the easiest way to have the grid make up for the shortfall once the set limit for the inverter output has been reached. Check the certifications for your region and local regulations to ensure you remain “legal” as connecting power generators to the grid in this way. It will sync and run parallel with the grid and the connection to the grid will be “permanently” enabled as long as the safety test have been passed to allow closing the two relays. Also note the output circuits should be adequate to accommodate this e.g. if the transfer rating is 32A AC, then the inverter output power should be added to this for the cable sizing.

3

Hi!

5kVA. But that 4000W drops with temperature. In my setup 3500 is the sweet spot + a little margin to not go into temperature shut down. In my setup the grid is only used for “emergency” situations. ESS is not the way to go for me. 99% of the time AC-in is disconnected. But when to much power is drawn for too long (set by me: 3500W) then i would like the MPII to connect to the grid and supply remaining power above 3500W… I think the hardware to do this is there, but havent found a way to configure it (i.e. the software does not allow me to configure this). Thanks!

4

Unless you are running ESS, the logic is to use grid power over battery power for the AC load.

The AC input is probably also charging the battery in addition to supplying the load power. Even if the battery is at 100% SOC, I’ll see a high battery charge current for a few seconds if the battery is below float voltage.

You might be able to set the AC input current limit to just what you need to supply the load over the 3,500 watt limit you’ve set, and the Multi’s Dc/0/MaxChargeCurrent to 0. If you need the values to change, then you could probably do that via node red or over Modbus or MQTT.

5

I could probably use node red to do this, thanks.

Maybe it would be nice to add an extra feature in the “ignore ac-in” settings to connect ac-in on an ac1-out current condition, so that all current above this AC1-out current condition is supplied by AC-in.. And as soon as the current drops below this threshold for x seconds AC-in opens.

Thanks!

6

When grid reconnects, the inverter will pull everything mains and then ramp down. The speed can be affected by the grid code in use.

It will always transition like this, so if it switches often , then it will be less efficient.

Using ESS might work better when you can control the inverter output limit, and then apply additional automations.

The ESS setpoint does use power, you will have to do the maths to see what is the most efficient for your setup.

7

I’m not seeing a ramp down. I’m using my MPII in ignore AC-in mode. When it connects AC-in it pulls all current from the grid, but no ramp down (so the inverter does not kick in to minimize grid usage). Cannot use ESS, i’m wired to be off-grid. Could this be because i have no grid code selected? In my setup “grid” is not the publc utility grid, so i did not select a grid code. Should i select a grid code to make it ramp down from ac-in?

8

What is your grid exactly? A genset?

Without ESS, you would need to look at power assist.