vicky avatar image

Multigrid - stop discharging battery based on external signal ?

I still want to stop my Multigrid from discharging the LG battery, when charging my car during the day. Firstly it is not efficient to use battery power to charge another battery, but main thing is to preserve battery energy for night time when PV isn't available, to the grid suppliers either. During daytime there is plenty of PV power fed in the grid, so I am OK to use this whilst during nighttime sources are different - not PV for sure.
So is there an input (sensor) I could use for that? E.g. stop discharging by applying a certain voltage somewhere, make a short or connect a switch or whatsoever. Txs for any help

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4 Answers
vicky avatar image
vicky answered ·

..or maybe by a specific command ?

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Matthias Lange - DE avatar image
Matthias Lange - DE answered ·

Maybe you can use the "Two-signal BMS support" assistant with the option "The BMS has one contact which switches only on a low-cell condition". Then you can connect a switch to one of the AUX or Temp.sens input. If you close that switch the Multi should switch into "charger-only" mode and stop discharging the battery.

For an automatic switch you maybe could use the "generator start and stop" assistant to switch one of the build-in relays if load is higher than X watt and connect that relay to the AUX you used above.

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I'll give this a try, thanks

VE Config states:
The two signal BMS support assistant should/need not be used with ESS
Will I run into problems or damage if I ignore the warning ?

This is because you set the BMS type in the ESS assistant, and not in a separate assistant.

The LG battery has a CAN-bus BMS, right? I think this shouldn't be a problem or damage. I would give it a try.

I can't test it by myself at the moment, maybe tomorrow.

vicky avatar image vicky Matthias Lange - DE ♦ ·

You are right. LG has a CAN-bus BMS, would be great if you could test ;o) txs

I tested it with a BYD Battery (also CAN-bus BMS) and you are right, if you use the ESS assistant you can't use the "Two-signal BMS support" assistant at the same time.

Do you have a Venus device? If so you can use that to switch the Multi into charger-only mode that worked at our test bench.

vicky avatar image vicky Matthias Lange - DE ♦ ·

Txs for testing. Yes I do have a Venus. Is there another way to change the mode, else than through the menue ? I wasn't able to figure out how to assign switching to "charging only" to any of the inputs.

I think there is no option to switch into charger-only with an external signal at the venus.

You have to make this via remote console.

Daniël Boekel (Victron Energy Staff) avatar image
Daniël Boekel (Victron Energy Staff) answered ·

Hi @Vicky

Let's look at this differently: you don't want to send battery power to the car-charger.

Why not just wire the charger before the Victron system? if you have a grid-meter, before the grid meter.

Safe's you a lot of trouble and systems not doing what they're made for...

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Hi @Daniël Boekel (Victron Energy Staff) this would be a good solution indeed, however wiring the charger before the grid meter and Victron would mean to run approx 30meter of heavy wire across the house and three floors. Charger sits at the very end of the house / shop, opposite side of supplier feed..

If you have AC coupled PV (PV inverter), then the only thing I can think of is to limit inverter power, but I don't know if you can somehow do that dynamically

But....doesn't the charger have it's own supply / breaker anyway?

vicky avatar image vicky Daniël Boekel (Victron Energy Staff) ♦♦ ·

Yes it does have its own breaker, but wired into a sub distribution panel. The main distribution panel with grid meter is far away.

I am currently looking into setting up an iobroker as this has tons of adapters to all kind of devices, there is a Modbus adapter too. Maybe I can make my Victron speaking to the iobroker which then talks to my homeautomation where the car charger is controlled.
Seems to become a topic for "long winter nights..." If I make progress I'll share it

That's a cool project!

If you have questions / updates about it, make sure to post it in the 'modifications' area, as there is a lot of knowledge about the inner workings of the systems:

vicky avatar image
vicky answered ·

@Daniël Boekel (Victron Energy Staff)
Just to let you know.. I made it :). ioBroker is a fantastic thing.
As soon as the wallbox of my EV is activated, I tell the Multigrid, to stop discharging the battery.
To do so I read the status of the wallbox switch from the homematic device. If it is activated (true) I write "0" to register 2704 ESS_max_discharge_current. So I can avoid my battery being drained by my EV :o)

If the wallbox switch it is deactivated (false) I write "4000" to the register, so inverter kicks in.

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