Custom ESS System for Multiplus

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alferz asked May 14, '23

Custom ESS System for Multiplus

Hi all, looking for some advice on how to setup an energy storage system with my Multiplus-II 2x120v. I've read extensively on the ESS assistant, which seems to be pretty close to what I'm looking for, but lacks PowerAssist which in my case would be an issue. Basically I am looking for a way to control my MP-II to do the following. I have used Raspberry Pi in multiple automation systems so a library, script or community tool would work for this.

Installation Details:

- 12.9 KWh 8s2p LiFePO4

- 20a single phase AC-In grid circuit for passthru/charging

- Critical loads subpanel on AC-Out sized to run up to 45a of loads (20a grid + 25a inverter)

- Not grid tied, no backfeed into grid should be possible.

- No solar or generator

Requirements:

1. Ability to set a charge window of 12am-6am to take advantage of favorable rates from grid

2. NO FEED back into the grid.

3. Able to connect to grid instantly if loads exceed 2000w and switch back to off-grid when below 1500w

4. Able to connect to grid if SOC or voltage drops below a certain threshold (but ideally, NOT charge batteries until 12am).

5. Able to continue using Power Assist when load is > 2000w and connected to grid

I have been able to do number 2 through 5 without the ESS assistant at all, but #1 is a challenge due to lack of scheduled charging in the base firmware. What other options for more customized control can I explore?

Multiplus-II ESS

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alferz commented · May 17, 2023 at 06:04 AM

It looks like either option would meet 90% of my requirements. The way ESS seems to implement rhe function of PowerAssist, is that once you set a grid setpoint, the inverter will always kick on to support a higher load than the set point, supplying its maximum available DC energy to add to the available AC current which is effectively all that Power Assist is. In secton 4.2 of the ESS Design and Installation manual, Victron says that “The PowerAssist setting in VEConfigure3 will be disabled and ignored“ when the ESS assistant is installed. This is strangely worded to me because it makes me think the function of PowerAssist wouldn’t work as long as you’re using ESS, however as others have said and I was able to test it appears it actually does work.

I like the simplicity of using a 5V relay to schedule charge times as @JohnC suggested. Ie, trigger a programmable relay assistant monitoring aux1, which then flips the general flag, which is then assigned to ignore ac input 1 in a general flag user assistant. This lets the firmware entirely do the job without the nuances of ESS and the possible risks it exposes (lack of US cert, possibility of unintended grid feed-in, etc). You would actually not need any GX device in this case, you could use a PLC or even a simple timer relay like the BAOMAIN on Amazon to trigger the start and stop times by simply sending a 5v signal.

When I decide the best way to go here I will report back!

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Modifications Space

Node Red Space

Answer 1 · 2023-05-14T02:18:38Z

derrick thomas answered · May 14, 2023 at 02:18 AM

You still have power assist with ESS. It is unchecked in configuration because it is controlled by the ESS assistant.

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klim8skeptic ♦ commented · May 14, 2023 at 03:23 AM

Power assist is not available in split phase mode.

Dunno if ESS works in spilt phase mode.

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derrick thomas klim8skeptic ♦ commented · May 14, 2023 at 03:29 AM

OP mentions nothing about split phase. He has single phase input, which will be single phase output on the mp2 2x120. (L1 and L2 outputs will be tied together during passthrough or inverter mode) ESS will absolutely work in this situation, with power assist on both L1 and L2 outputs.

If OP decides to connect split phase input to the mp2 2x120, then L1 and L2 outputs will remain separate and on opposite phases. ESS can still be used in this scenario but it will only apply to L1. That goes for power assist as well.

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Answer 2 · 2023-05-14T10:10:20Z

thanar answered · May 14, 2023 at 10:10 AM

When set up with ESS assistant, a Victron system always runs in parallel with the grid, no way to disconnect, unless there is no input on the AC-in side, in which case the system runs as an off-grid one. You can set up the system to target zero feed-in, but there will always be short bursts going outwards when some large load shuts off.

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alferz commented · May 17, 2023 at 06:52 AM

Thank you Thanar. This is well stated and matches my testing with ESS in Mode 3. I wish Victron would copy and paste that into their manual because I dont think that was ever super well explained. There are a lot of powerful things about ESS the more I explore it, especially with the node-red building blocks that have been done that allow for an impressive amount of customization. I wonder if Victron will ever obtain US compliance, in the meantime Im a bit wary of using ESS knowing how it works and the risk of unintended grid feed.

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Answer 3 · 2023-05-14T12:44:14Z

JohnC answered · May 14, 2023 at 12:44 PM

Hi @alferz

Just thoughts..

Presumably you've used Assistants in the Multi to achieve "2 through 5". And as you've found, the Multi can't deal with anything time based.

You could look at bringing in your time needs from an external source via an Aux port, and adding in to existing logic that way.

Or via a GX (or RPi with VenusOS), using this.. https://www.victronenergy.com/media/pg/Cerbo_GX/en/gx---generator-auto-start-stop.html Most of the existing logic you've already set up could be done from there too. You could just retain the IgnoreAC functionality in the Multi.

In both cases a signal wire pair to the Multi would be required. No ESS.

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alferz commented · May 14, 2023 at 03:28 PM

Thanks @JohnC — so far I actually have used no assistants to achieve 2-5, just the basic settings I can configure in Victron Connect using the mk3 usb adapter primarily in the AC input control section. Which assistants would accomplish what I need, something like programmable relay I take it? I think I understand the suggestion for generator start/stop to be able to trigger charge start/stop times - since Im using a raspberry pi I think i would need to use the gpio pins or an external relay, but on the MP-II side, how do I configure it to enable/disable charger based on the signal wire pair input? Would that be a programmable relay assistant or something similar?

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JohnC ♦ alferz commented · May 15, 2023 at 11:12 AM

@alferz

Ok. Starting afresh, I'd use the Generator thing in the GX (RPi). Link already provided. It has some time based things like Quiet Hours you could use, along with the other parameters.

I'm a bit rusty on the Multi's Aux port, but all it should need is an open/closed signal, like a contact across the 2 terminals.

For Assistants, see the links here.. https://www.victronenergy.com/live/assistants:start

Easier for me to do it than describe it..

This should come close. Adjust the time delays as needed. Also consider your 'logic polarity', you may need to change off/on and open/closed to suit.

You'll learn as you go along, so have fun. Come back as you need.

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Answer 4 · 2023-05-15T12:02:55Z

Rob Fijn answered · May 15, 2023 at 12:02 PM

Hi Alferz, I think this is very easy to do.
In the ESS set the batterylife to "Keep Battery Charged", then set the GridSet point to what you max want/can get from the Grid. Set no feedback allowed.. This should work.
It will charge the battery if your load is below your GridSetpoint and it will Assist when more power is needed by to load

Rob

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alferz commented · May 15, 2023 at 02:53 PM

Only problem is, I dont want to keep the batteries charged all the time. I am trying to offset my energy use by time shifting and only charging batteries from 12-6am when I can buy electrons at bargain basement prices, using that stored power throughout the day to power loads that would otherwise be burning through more expensive peak hour electrons.

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