Multiplus charge current control? assistant/ESS

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Alistair Warburton asked Jun 27, '22

Multiplus charge current control? assistant/ESS

Hi Folks... This is going to raise a few eyebrows I expect but none the less...

I have two Multi's 5000/48/70-100 and 5000/24/70-100.

They are connected in series, as in, the output of the 48 feeds the input of the 24. I have done this to take advantage of the assist feature, giving me more overall output whilst retaining the ability to use either system independently, external manual changeover switch, in the event that either system has an issue or needs to be switched off for maintenance/modification.

My solar is DC coupled to the 48 system and managed by the BYD battery ( Standard config :-) )

We are completely off grid so my system needs to be as fault tolerant as possible.

The configuration works well, AC input limit on the 24 protects 48 and can be used to determine which battery is actually supplying my loads, assuming that the load is les than 4kW at the time and I anticipate using charge current limit, dynamically, on the 24 to determine the balance of available charge current between the batteries.

However...
I discovered that I cant directly connect both Multi's to the same VE.Bus as they immediately try to go parallel which isn't the goal and as far as I know would not work anyway.
I have connected the 24 to my CCGX via an MK3, which seems to work locally and within VRM.I
(I cant access the registers on the 24 via Modbus but that is a different question.)

I need to control the charge current limit and am aware that there is an assistant which I think will allow me to do so with an analogue input or potentially 1 or more digital in's

I am also aware that ESS is replacing this kind of functionality and was wondering if treating the 48 as a grid and running ESS on the 24 is possible and if it is weather it would be a better, more integrated, approach.

Questions In summery...

1) What options do I have for managing charge current limit remotely/externally?

2) Is ESS an option?

3) Is it possible to handle the second Multi, 24, as an AC coupled charger for the first Multi, 48, like AC solar?
In an ideal scenario it would be good to be able to cross feed energy in either direction and manage where available charge is going, as a system.

4) Is there a GX variant that will allow both Multis to be directly connected, so I have full access to parameters and remote config, whilst keeping the two systems from trying to parallel up?

Sorry this is a bit long, I wanted to provide an accurate context.

Cheers,
Al

MultiPlus Quattro Inverter Charger remote console

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Modifications Space

Node Red Space

Answer 1 · 2022-07-01T09:23:57Z

Jason - UK answered · Jul 01, 2022 at 09:23 AM

Hi @Alistair Warburton I would love to see a schematic of your system.

In answer to your questions as best i can within my level of understanding....

1. You can limit the charge current within the VE confure and using an assistant to do that in conjection with using one of the Aux connections.

2. In a normal settig, the answer is no as ESS is for grid connection systems only but you may be able to run the 2nd Multi in a ESS arrangement making the first Multi as the 'grid'. I've not tried this or explored this as an option my self.

3. Ideally I would need to see an schematic to make comment. Yes it should be possible but I think you are over complicating it.

4. No. A GX device, as far as I am aware can only control one type and size of Victron multiplus unit.

1

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Alistair Warburton commented · Jul 02, 2022 at 12:36 AM

Thanks for that...

I am learning as I go here, It hadnt occured to me to post a schematic butit is a good idea, I will see what I can knock up tomorow.

0 ·

Answer 2 · 2022-07-02T01:01:53Z

Just a bit of an update... Leasons...

"The configuration works well..." There appear to be caviats, which isnt unexpected.

With borh batteries at a reasonable voltage or better all is well for the most part.
Enabling ground relays causes issues as the self test gets confused, occasionally, if the 48 is shut down.

Charge current control definatly isnt available via Modbus but as Jason states should be managable from Aux In. Given that the Aux ports have an internal pullup it should be possible to use 1 or two relays and the forward voltage drop of a few diodes to set some charge rates. Trying that tomorow.

I did note that shutting off the charger, as opposed to setting 0 charge current, disables passthrough.

Modbus to Node Red is working well, once I figured out what was available from where. 24 via a MK3 included!

Remote config of the 24 also works, which previous posts I found said wouldnt work due to limitations of the MK device,

I also have some issues which will have to be explored...

Currently my 48 is off, having stopped on low battery a short while ago.
the 24 is at 90% SOC but with the MK3 connected to the CCGX it too is shutting off on low battery despite being well above that threshold.

My suspision here is that there must be a VE.Bus alarm, probably asociated with the BYD BMS that is forcing a system wide battery low condition but I do not understand the mechanisme right now.

If anyone has insight there I would be very greatful of a leg up so to speak.

I am positive the 24 voltage is fine, it is on now with the MK disconnected, and even when connected and it shuts down the reported voltage is still fine,
Odly the 24 is reporting a low state od charge on the CCGX/VRM despite having SOC monitoring disabled/enabled, I tried both.

SOC shutdown is not enabled for either system within the multi's

Looks like tomorow willbe interesting!

Answer 3 · 2022-07-02T04:45:08Z

Alistair Warburton answered · Jul 02, 2022 at 04:45 AM

Schematic as requested...Layout.pdf

layout.pdf (395.0 KiB)

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Answer 4 · 2022-07-03T21:41:55Z

Alistair Warburton answered · Jul 03, 2022 at 09:41 PM

There is only so much messing about that makes any sense...
Fitted new Cerbo GX this afternoon and reconfigured, all looks well now.
See updated layout below.

Modbus connectivity coming along nicely, and I was taught a neat way to handle signed integer data if anyone is interested.

I know this is not a supported solution, stacking inverters like this, but it works great now the GX system confusion has been alleviated.

New Layout.pdf

new-layout.pdf (395.1 KiB)

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