Alistair Warburton avatar image
Alistair Warburton asked

DVCC for DC charge current control from node red - Unintended effects?

Hi Folks,

I currently have a Multiplus and Smart Shunt hooked up, standard fission, to a Cerbo GX.
My batteries do not communicate, although they do have internal BMS's. The need to be handled like any other dumb battery, settings not withstanding.

For, non standard / unsupported, reasons I need to be able to control Charge current without limiting AC input. I am using the charge current control assistant, right now, which works well.
The above is set to disable the charger when I set 0 current and that results in a Passthru state leaving Assist enabled and ready... Which is great.

The analogue input associated with the CC assistant is currently physically connected to a voltage reference circuit, just a few diodes essentially, which in turn is driven by the Cerbo GX relays.

It works but is admittedly a messy solution. So...

Dose anyone know...

If enabling DVCC, which I should probably do anyway, will allow me to control charge current, with the Node Red node, and still have the Multi go into Passthrough, as opposed to Bulk/Float with 0 current?

Are there any red flags or DVCC setup, particularly when manipulating it that I should be aware of for my simple setup? Still reading the manual but so far all the complication seem to be around ESS and/or more complicated integrated stuff.

Will DVCC and the charge current assistant conflict with each other or is the current setpoint common? (Mainly asking so I know which order to do/test things)

lastly, if I haven't asked something I should have when considering this stuff.

Any and all comments welcome,

Cheers folks.

cerbo gxNode-REDDVCC
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4 Answers
Jeremy Albrecht avatar image
Jeremy Albrecht answered ·

I'm not using the charge current assistant, but I am using DVCC with my MultiPlus-II (2x120), a SmartSolar, and a pair of "dumb" LiFePO4 batteries to implement what I like to call storage mode, setting the DVCC current to 0 if I've clicked the "Storage Mode On" button and the SOC is above 60%. When the DVCC is set to 0 both the SmartSolar and Multi remain in Bulk mode (the Multi does *not* go into Passthru) with a 0A output. I actually consider then better (for my case) than going into full passthru, as the Multi and/or SmartSolar will output power on the DC side to match whatever draws there are on the DC system.

Not directly related, but may be useful info for you: I also have a 60A DC-DC charger (my setup in in an RV) that is enabled (using the Cerbo Relay) via NodeRed when the Multi is not charging, the tow vehicle is hooked up and running (determined via SmartShunt seeing the voltage of the tow vehicle's battery is above 13v), the trailer battery bank SOC is below 90%, or if there's high AC draw (the trailer air conditioner is running). When NodeRed enables the DCDC charger is sets the DVCC current to my battery bank max charge current - 60A. The charge from the DCDC shows up as a negative current on "DC System" in Venus. Unfortunately, even though the battery shows a positive (charging) current on the Cerbo, DVCC doesn't take that DC charging current into account when controlling the Multi and SmartSolar.

I've done quite a bit of work with this so I'm happy to share any information and NodeRed flows if you'd like.

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Alistair Warburton avatar image Alistair Warburton commented ·
Thanks, that's helpful... I was wondering about DC-DC, but that is another story.

I have two Multiplus 5000 units, a 24 and a 48.

My solar and primary BYD battery are hooked up to the 48 and configured absolutely standard for a BYD connected system.

The 24, which I only installed a week or so ago, has a 300Ah pack assembled from 6 100AH 12V Ultramax LiFePo4's, which thus far look good.

I cant parallel the two because the Multi's are not identical and don't share a battery or GX device, even if they were.

The output of the 48 feeds the input of the 24 so with appropriate AC current limits I get circa 8 kW with the 48 inverting and the 24 assisting or 12kW with 4kW from the generator and both assisting... Cool (At least I think so)

The node red flow needs to manage SOC of both, throttling AC input to the 24 if I want to discharge from it whilst keeping the 48 hot as it were. I will arrange the limit so that there is always 2kW of headroom that way if my better half turns on a third hob, or makes toast whilst boiling eggs and frying bacon, sufficient load will already have been shifted back to the 48 for the 24 to assist and hold everything up.

Of course when doing that, or distributing Solar or generator input I also need to manage charge current on the 24.

I have wondered about 48-24V charging but I don't know if that is a thing and anyway it would only be worth while if it was far more efficient than DC-AC-DC as it is now.

I have had a fiddle and it looks like the 0 current setting isn't quite 0...

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Alistair Warburton avatar image Alistair Warburton Alistair Warburton commented ·
Maybe it is... I think I am just looking at noise on the current readings. I mistakenly put the negative for the Cerbo Power directly on the battery, rather than the shunt where it should be which is perhaps upsetting things and I guess a few tens of watts noise is to be expected.
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Jeremy Albrecht avatar image Jeremy Albrecht Alistair Warburton commented ·
I see a few W plus or minus usually too. I expect it would be too difficult to control it that finely.

I’m not sure what BYD means.

Out of curiosity, why the two different voltage battery banks and different inverters?

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Alistair Warburton avatar image Alistair Warburton Jeremy Albrecht commented ·
BYD is a battery manufacturer, very well respected in the industry, as I understand it, and Victron partners with both companies cooperating to produce integrated solutions.

I wanted resilience, being totally off grid.
I could have gone with another, identical 48 and more BYD batteries but lacked the finance to do that, even if it had been my preferred choice.

Installing a second, essentially separate, system means that should one of them fail, for any reason, I can simply switch to the other.
They cant be in parallel, but although unsupported feeding one from the other, in either direction, gives a good result.
Power Assist, and the 100A transfer capability, allows aggregation of all three devices in the chain... Generator, 48 & 24 can all easily contribute 4kW to my total output, if needs be. In reality we rarely hit 4kW let alone 8.

And 24V as opposed to 48... Well the 25 inverter is slightly more expensive than the 48, probably due to the high current requirement but it gives me the freedom to buy/add batteries in sets of two as opposed to the 4 mandated by a 48V setup.

There is space on top of the 48V battery cabinet to place 6 100Ah 12V batteries, which is what I have done, giving me an additional 300Ah@24V.

That equates to approximately 50% additional usable capacity.

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liam-tuvey avatar image liam-tuvey commented ·
This sounds like just the sort of "storage mode" I've been looking at implementing. Be really interested to see your flows / schematics.
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Jeremy Albrecht avatar image Jeremy Albrecht liam-tuvey commented ·

My RV is at the storage lot right now so I don’t have access to it to pull the flow, but I’ll try to go over and pull it down in the next few days. Feel free to remind me if I don’t post them by next week.

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Jeremy Albrecht avatar image Jeremy Albrecht liam-tuvey commented ·

I've attached my flows as discussed. They're a bit messy, and I'm not completely satisfied with the DCDC control, as occasionally I get some flip-flopping. Also, when the DCDC kicks in it sets the DVCC current to ensure that DVCC+DCDC is less than my max charge rate, when I'd prefer to not enable the DCDC if DVCC+DCDC would exceed my max charge rate. I've struggled to get that to work though.

My "default" DVCC current is set in an inject node at the top left of the "Charge Control" flow.

To use these you'll also need to install node-red-contrib-bool-gate, node-red-contrib-edge-trigger, and node-red-contrib-unit-converter (though the last one isn't vital to functionality, just the system info display).

Something not previously discussed is I have a slider to control the MultiPlus "switch" position, and then a button to confirm the requested change.


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Alistair Warburton avatar image
Alistair Warburton answered ·

I can absolutely control charge current using the assistant, which sets CC based on an analogue input. To keep this GX based, I am/was using the relays to set a charge rate in 4 steps, 0 and 3 levels above that. Solid but clunky.

Folk with that know more than I do, about Victron nuance, have said that ESS can do this without the relay/analogue hack/fix and provided that the result is the same, or at least broadly similar, it would be a cleaner solution.

I am not 100% convinced yet... Basically the first paragraph of the ESS manual states that off grid installations should not use ESS and as it is potentially varying voltage, and frequency, to do what it dose, I can see why that would be a thing.

I also have to contend with...

My CCGX cant do much other than stock firmware, so no Node Red.
My Cerbo GX is still a GX, despite enhancements, and will only play as it should when it is the controller/interface for, a single 'system'.

I want/need a single local dashboard that displays both Victron systems as a single cogent system for my home and neither GX can do that natively. In fact looking at documentation/questions/comments I think installing Node Red dashboard nodes on a GX is likely to be hard and difficult to support.

The ESS setpoints for the charge current control may well make sense. I can use Modbus to allow the flows on the Cerbo, 24V system, to access data, and control points, made available on the 48 by the CCGX.~
This should allow me to build up a 'system' that is essentially autonomous and, aware/in control of, the 24 and 48, hosted on the 24's Cerbo.

However this 'system' will still have to communicate with another external node red instance to show its status and accept high level commands telling it what its current goals are... Like ESS basically, but with two separate, yet interconnected, systems with a common UI.

I expect it sounds worse than it is... Assuming adequate control of the Multi's, the logic is fairly simple with just a few modes of operation, as a system making, sense.

I am more than happy to share flows, but you need to be aware that I am not an expert, yet, and everything I am doing/proposing is either skirting supported or simply isn't supported.
That said it isn't a hack either... I will only be setting parameters, not messing with sub-systems or hardware so although I could, and probably will, make a mistake, logically, hardware damage shouldn't occur. feeding one inverter with another isn't supported, so far as I know, anyway so in that respect, and with a healthy dose of caution, I guess I don't have much to loose.

I will play with ESS tomorrow but from Sun, I am away working and will not be back in the saddle until Fri next week at the earliest.

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Jeremy Albrecht avatar image Jeremy Albrecht commented ·
It’s actually shockingly easy to do dashboards nodes on NodeRed.

I think I understand what you’re saying, I’d have the CCGX control one Multi and run MQTT and have it be essentially “slave” to the Cerbo. Run NodeRed on the Cerbo and have it control the multi on the CCGX via MQTT. You should (I think) be able to control DVCC current on the CCGX that way, or directly set current on the Multi if you don’t what to use DVCC.

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Alistair Warburton avatar image
Alistair Warburton answered ·

I don't think I can, or want to, mess with DVCC on the 48 as the BYD BMS is using that to manage the battery. Anyway if I need to limit charge from AC I can easily use the AC limit, although I cant see a need to do that right now. AC limit, yes obviously to manage the generator load but the charging can just do its thing. On the 24, I need to manage charge current without impacting the AC limit so I can effectively choose where any available charge current ends up. Loads will always take priority but assuming I have the input available, AC or DC, it will charge the 24 first, because that is a load on the 48, unless I restrict that behaviour.

To force the 24 to discharge, I just need to shut down or limit the 48, or the 24's AC input.
I will of course need a loop that lifts the limit if the house load go's up, maintaining headroom in terms of output capability.

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Jeremy Albrecht avatar image Jeremy Albrecht commented ·
Is there any reason the 24v system has to be fed by the 48v system instead of hooking both directly to the generator output?
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Alistair Warburton avatar image
Alistair Warburton answered ·

DVCC current control is working just fine on the 48.
When set to 0 the battery go's idle but the unit is not going into Passthru, like it dose when the Charge Current assistant is controlling things and has disable charger at 0 current checked.

I tried running both, thinking that DVCC would override the assistant setpoint, in the hope that I could use the assistant to disable charging all together whilst still using the DVCC setpoint when charging was enabled but it seemed unstable/unresponsive so I took the assistant out again.

I have read through the documentation for ESS again and I am concerned that adding LOM protection will cause problems with the generator whilst removing it an enabling ESS, even with export disabled could potentially back-feed the 48 and as I do not know what that may do I decided not to go there without further advice.

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