Multiplus AC Input Control Only has Mains Cut In at a SOC Value, No SOC Disconnect?

DIY
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1

The question:

Why does the Multiplus only have a setting for AC Input control to be able to use SOC for AC mains connect, but only VOLTAGE for disconnect?

Why no disconnect SOC?

Configuration:

Multiplus 3/6kW 120vac 24v inverter/charger, Cerbo-GX (just added,) 500 amp Smart Shunt, 2.7kW solar, a non Victron 2800 watt MPPT controller, (100 amp at ~27v,) an external 120vac to 40amp ‘28’ vdc charger, a 12kWh LiPoFe battery pack made up of 100aH 12v individual batteries in series/parallel. (Yes, each string has both a breaker AND a terminal top 100amp fuse.)

System is always plugged into 120v power, and AC input is limited to ~16 amps until I get a dedicated 30a wall socket installed.

The Multiplus has the UPS flag set, I have Solar priority enabled, and AC Input Control is active.

The system function is to basically look like a generator plugged into the Gen Tran panel and be a ‘partial house’ UPS for some medical gear, fridge/freezer, some lights, etc. It has an added benefit of reducing the overall power bill because the solar power is actually supporting that part of the house load via the Gen Tran panel for at least part of the day and most of the night. On a good day during the summer, I’m seeing about 14kWh from the solar system.

Multiplus Assist will occasionally kick in on a fridge / freezer compressor starting, but I expect that with the input current limited.

Pre-Cerbo, I was stuck using ‘best guess’ voltage points to control the AC mains connection. (Worked after a fashion with a bit of fooling around with voltage / time delays, but not what I really wanted, nor very accurate in terms of SOC, as expected.)

With the addition of the Cerbo, I can now use the LOW SOC function as measured by the Smart Shunt and communicated to the Multiplus via the Cerbo.

The LOW SOC value for reconnecting the mains works perfectly, so in the early pre-dawn time, the batteries hit the 30% SOC, the Multiplus connects back to the main and switches into Sustain Mode. (BTW, 30% SOC leaves me about 6 hours of run time, which is more than enough time to get a generator up and connected to both charge the batteries and support that partial house load.)

When the sun comes up, I want the batteries to charge up a bit, (say to 50%,) and then drop the AC main and go to strictly DC for the rest of the day and evening. (Yes, I’m compensating for not enough battery / solar, but that $$ is needed elsewhere for a bit..)

Using only voltage to tell the Smart Switch to disconnect the main is far from ideal, but surprisingly, there is no selection for using SOC for that disconnect function.

I’m guessing it would be a firmware update to add that to the Multiplus, which is something I’d be willing to bet isn’t exactly on the future features map, but I thought I’d throw this out and see if anyone has any ideas.*

Thanks,

Steve

(*Well, other than using Node Red, which I have never messed with before, but I did snag the large firmware download and have installed it on the Cerbo to the point I can open a console…)

2

Why not set it up as ess? That will do what you want, use as much pv as possible

Switching on and off ac in will wear the relays

3

Can be done with node red with soc

Or a clever wiring set up that uses the generator start stop control on the gx.

Or using the generator start stop in the assistant on the inverter to ac ignore.

These are all well discussed over this forum

4

I suspected Node Red would be the answer for implementing disconnect on SOC, but as I indicated to Marc, I cannot let the inverter back feed the grid.

Time to put on the learning hat…

Thank you for your reply.

Steve

5

It wasn’t an option until now, but with the recent addition of the Cerbo…

It >cannot< be allowed to back feed the grid, however.

(Dang, why didn’t I think of that!!)

I’ll do some more digging.

THANKS!!

6

There are actually a few copy paste flows for it knocking around on the forum; easy to copy paste edit to values you want.

7

Again, thank you.

I’ll do some digging!

Steve