valden avatar image
valden asked

Cerbo GX, DVCC and combined charging from Multi, MPPTs and alternator. How measured?

Hello all.

I have some curly questions on using a Cerbo GX and Distributed Voltage and Current Control (DVCC) to manage the system described below.

The yacht installation I’m preparing will have four Victron 12.8V 300Ah Smart LiFePO4 batteries, arranged in parallel. Their overall voltage will be sensed by a SmartShunt, connected to the Cerbo by VE.Direct. The batteries’ 3 Pole Balance Temperature & Voltage (BTV) cables will be daisy-chained to a Smart BMS CL 12-100. This BMS will control a Smart Battery-Protect 220 via its Load Disconnect terminal. The BMS will also control a Cyrix-Li-Charge 120 via its Charge Disconnect terminal. Three Smart MPPT 100/50 solar charge controllers will send current from 1200W of solar panels to the batteries through the Cyrix. The MPPTs will connect to the Cerbo by VE.Direct-to-USB adapters, into a USB hub and then to one of the Cerbo’s USB ports. Another job the BMS will do is regulate battery charging from a 115A alternator.

The system will include a MultiPlus 12/3000/120-50 inverter/charger, connected to the Cerbo by VE.Bus. Current from the MultiPlus will not be routed through either the Smart Battery Protect 220 or the Cyrix-Li-Charge 120, to avoid damaging those with flow in both directions.

I’ve read Victron’s explanations of DVCC, along with relevant discussions here in the Community. I’m satisfied it will work. What I think will happen (and not happen) is:

- the Cerbo will take the battery voltage sensed by the shunt and assess this in terms of what it was told the batteries are, during setup;

- it will look up its program library of how these batteries like to be treated and will instruct the MPPTs and the MultiPlus how they should serve up amps for charging, or draw on them for inverting;

- when the Cerbo assesses that the battery voltage reported by the shunt is getting low, it will tell the MultiPlus to stop inverting;

- the Cerbo will not be able to stop the DC loads from drawing upon the batteries, as it has no data connection to the BMS or the battery-protect. These two will use their load-disconnect linkage to cut the loads when one of the batteries says ‘Stop!’;

- if something goes wrong and the Cerbo doesn’t succeed in stopping the MPPTs from charging, the BMS will step in when the batteries ask it to and stop the charging via its charge-disconnect link to the Cyrix;

- however, if something goes wrong and the Cerbo doesn’t succeed in stopping the MultiPlus from charging, there’s nothing in the system or the setup to cut it off. I assume that the MultiPlus will not stop itself from charging, given it’s been told to be dumb and work under DVCC rules. Perhaps I could add a Cerbo controlled relay as a back-up, to switch off the MultiPlus if it goes feral?

Please set me straight if any of the above is off-beam.


Some aspects I’m less clear on are:

- will the shunt report the overall charging current from the MPPTs, the MultiPlus and the alternator, such that the Cerbo might instruct the MultiPlus and the MPPTs to ease-off or stop?

- if the batteries are full, does the BMS have the ability to throttle the current from the alternator? Checking … . Yes, it does.

- and last but not least …

… the Cerbo GX has a second pair of CAN-bus ports, called BMS.Can. Little is written about these, other than how they can be used to hook up other-brand CAN-bus BMS equipped batteries or BMSs. So how good would it be to have Victron lithium batteries that can talk directly to a Cerbo over CAN-bus? :-D Has Victron said these are on the way, or ruled them out for some reason?

MultiPlus Quattro Inverter Chargercerbo gxBMSDVCCalternator
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bathnm avatar image bathnm commented ·

@Valden, I know you made this post sometime ago. Have you commissioned your system yet. I am surprised by this statement

when the Cerbo assesses that the battery voltage reported by the shunt is getting low, it will tell the MultiPlus to stop inverting;

On my system, I have not found this to be correct or any other information on the Victron site to support this. Did you get it working this way?

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valden avatar image valden bathnm commented ·

@Bathnm Hello Bath. I’ve been having a very interesting time with the Victron system on my new yacht. First I’ll answer your question - no, I have not verified that the Cerbo, when set to operate using DVCC, can/will control the MultiPlus to stop it inverting when the batteries are almost depleted.

I’ve just read through the DVCC section of the Cerbo manual again and I agree with you, it doesn’t specifically state that the Cerbo will protect the batteries from an inverting MultiPlus in this way. Perhaps my statement was based on logical, wishful thinking, because that sure is how I would want the batteries to be protected by DVCC.

I don’t have a way to get into the MultiPlus’ programming, though when I borrowed a laptop and USB interface, I did program the MultiPlus to use LiFePO4 settings. I can’t recall if that included a ‘stop inverting at this low voltage’ setting. It seems like it should - and that this would continue to work under DVCC control. Certainly, the MultiPlus’ charging presets, whether for LiFePO4 or not, remain effective when DVCC is operating with the Cerbo. I know this because I saw how the charging voltages changed when the battery type preset was changed, with both presets under DVCC control.

As you know, the Cerbo is a fantastic piece of kit, especially with the GX Touch 50 display. Unfortunately, there’s a problem with password management for wifi connectivity, messing up the ability to use Remote Console on an iPhone or iPad. I understand it’s being looked into.

To date my system’s lithium batteries have had an easy life. We’ve been on shore power almost all the time, dodging bad weather and the virus, while working on other boat teething problems. Big teeth and big problems. I need to ask a question about what the ‘Charged Voltage’ setting under the SmartShunt’s Battery Settings page means. Mine is showing/set to 13.2V. Is this too low? Curious.

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bathnm avatar image bathnm valden commented ·

@Valden, Which BMS are you using? The VE.Bus BMS or smallBMS. I have just swapped to the smallBMS (with 2-wire BMS assistant) and love the fact that I can shut the inverter down and reduce the parasitic load from the MultiPlus to 0A. With the VE.Bus BMS you could not control it from the Cerbo, and when the MultiPlus was off, it still had the VE.Bus interface powered up, drawing 0.2A!

I have mine set to be 28.2 (as running at 24v). Some might say this is too high and it should be set lower. However I have not found anything definitive on what the BMV setting should be.

I'm current resettling with the VE.Can Smart MPPT, again no definitive information on how it and the Cerbo should work. Little configuration options, but I have no idea if the two units are synchronised and working together. No details on the Cerbo and both showing different system yields! When I get back to the boat it looks like I shall need to go digging around the code and the dBus data to see how it is working and if it is working correctly......

The other day I set the DVCC current limit to 1A, and the two MPPT charge controllers continued charging at >3A, implying that they are not under any form of DVCC control. Only time and effort will tell if things are correct, not what you want when your offshore, miles from anywhere with a problem and not certain how the various parts of the system work with each other.

Maybe we can share more information and help each other. Digging around the python code (dbus-systemcalc) the last few days I do not believe that the DVCC will do anything for the MultiPlus, except possibly reduce the charge current setting. I would check you have a BMS Assistant configured on the MultiPlus.

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valden avatar image valden bathnm commented ·

@Bathnm I’m using the relatively new Smart BMS CL 12 100. I chose it as a good way of protecting my alternator from the lithium batteries, and vice versa. It has no data link to the Cerbo. It simply listens to the batteries and stands ready to intervene if necessary. I’m using two Smart Battery Protects as load and charge police, though these will not stop flows between the batteries and the MultiPlus. Yep, I need a new laptop and the interface to check and tune the programming for the Multi, to make sure it will behave well when the batteries are low.

So far I’m getting good and plausible performance from the Cerbo and DVCC, though my testing has not been exhaustive.

If the sun is up the MPPTs are always prioritised as the charge source ahead of the MultiPlus and shore power. This aligns with Victron’s DVCC guidance.

I will read your comment again to get the most from it. For sure, I’m happy to compare notes; I have some catching up to do though! :-)

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bathnm avatar image bathnm valden commented ·

If you have a windows laptop or MAc with Parallels, you can always use the VRM capability to pull the MultiPlus configuration, edit it with VeConfig and use VRM to push the configuration back

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

Hi @Valden

There's a lot of incorrect assumptions in that text.

Please get an experienced installer / dealer / distributor involved to get your system working as expected and safe.

Also please read the Community guidelines about system design:

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valden avatar image valden commented ·

Hi Daniel. Thanks for your reply. :-)

I am working with an installer, who works for my yacht-builder, but he is in another country on the flip-side of the world and we don't speak each other's language.

The builder wants me to accept products from your competititors; some good, some not. I am insisting that Victron be used throughout, based on quality of products, quality of documentation, breadth of system components and the available knowledge base, including this Community. Attempting to have a discussion on Cerbo GX and DVCC with my installer would be a lost cause. I'm sure you understand. :-)

I can't choose another yacht-builder halfway through construction because an electrician is perhaps less keen on Victron than I am. What I need to do is persist and guide my builder and installer along the path that I want, leading to a fully integrated Victron solution. Expensive, but good.

I was aware of the Community guidelines. I have asked a question about DVCC, which is quite a complex topic. Before asking my question I described my system, to help orientate readers. I didn't ask for help with system design.

I will distill and reiterate the one question I was hoping you might be able to help with. I would appreciate your help. Here goes.

- in the system I described, how does the Cerbo become aware of the total charging current provided by the MPPTs, a MultiPlus and the alternator? It seems to me that only the shunt is in a position to report the total charging current to the Cerbo. Does it?

Thank you.

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Daniël Boekel (Victron Energy Staff) avatar image Daniël Boekel (Victron Energy Staff) ♦♦ valden commented ·

Hi @Valden

did you read this?

I'm sorry about your experience, a distributor should give good guidance, that's what he / she is paid for...

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valden avatar image valden Daniël Boekel (Victron Energy Staff) ♦♦ commented ·

Hi Daniel. Thanks for the link. Yes, I’ve read that DVCC explainer. I've had the document (and others) open on my computer for days as I've been studying this concern. See para 4.4.1 2). It touches on my question about how DVCC manages charging, but it doesn't nail the answer. Nevertheless, it provides a reasonable basis for the conclusion that a GX device with DVCC switched on does not communicate with a shunt to establish the overall charging rate. Certainly, the document states that the contribution from an alternator is ‘unaccounted for’. This is a worry.

Many boats are being fitted with large and efficient solar panel arrays these days and system settings will usually be adjusted to get the most from them. Many boats also have a generator that can contribute, via a charger. The usual practice is to extract the most efficient battery charging outcome that is possible from one or both sources, close to but not exceeding what is optimal for battery health. In this light it is easy to see that when the boat’s engine is started the ‘unaccounted for’ charging contribution from the alternator(s) (which might be fitted with charging optimisers) could result in the battery being blasted with a level of charging current that is well outside of its comfort zone. In other words, the charging from an alternator could damage a lithium battery, even with DVCC operating and even with an ‘alternator safe’ BMS.

It seems strange to me that a GX device with DVCC set to ‘on’ would not take a reading of the overall charging current from a shunt that is connected to it. It could and it should.

Daniel, I’m close to making a decision on whether to spend 30 to 40 thousand Euros on a Victron lithium battery system. It will be used to keep me and my family safe in dangerous places, where there is no Victron distributor walking across the water beside the boat, ready to intervene. Before I make this decision I need to understand the system’s capabilities and vulnerabilities. Accordingly, could I ask you to please consult with your colleagues who are experts on DVCC and charging lithium batteries, to establish whether a Cerbo really is oblivious to a circumstance where batteries are being charged too quickly and therefore being damaged. On a boat, under the equatorial sun and motoring through the doldrums, this could be happening for days on end.

Please come back to me with an explanation as to why I shouldn’t be concerned about this. At this point I have the view that the charging current from alternators being ‘unaccounted for’ is unacceptable.

Thanks for your help with this. :-)

Edit: @klim8skeptic and I were having the same thoughts, although I've been looking at the data sheet for the 12.8V 300Ah Smart Lithium batteries. Please see my next comment - I'm running outa characters!

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klim8skeptic avatar image klim8skeptic ♦ valden commented ·

Have you looked at the SCS text?

You have 1200ah of lithium? That would take a LOT of charge current safely.

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valden avatar image valden klim8skeptic ♦ commented ·

Hi Klim.

As I was writing ...

Edit: @klim8skeptic and I were having the same thoughts, although I've been looking at the data sheet for the 12.8V 300Ah Smart Lithium batteries. The recommended charging current is less than 150A (each), with 600A quoted as the 'Maximum charge current'. Can that 600A figure be accepted as not resulting in damage? If so, then yes, four of these batteries would not be frightened by any normal alternator or two, plus the 90A coming out of the MPPTs. My system should be safe. Folks with minimal lithium would still have reason to be concerned about 'unaccounted for' amps from alternators. Bad things, those unaccounted for amps. :-)

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Daniël Boekel (Victron Energy Staff) avatar image Daniël Boekel (Victron Energy Staff) ♦♦ valden commented ·

Hi @Valden

It is very clearly explained that charging currents other than from the Multi / MPPT's is -not- accounted for (point 4.4.1.) there's no doubt on that.

But it is certainly not worrying,
All this is part of system design: calculate battery (charging) capacity vs. charging capacity.

Lot's of possibilities to overcome this when charging capacity is too high, like:

-disable alternator charging when x (x being SOC, available solar power, voltage, etc)

-disable solar charging when alternator is running

-disable (main engine) alternator when generator is running, etc. etc.

Your proposed system:

12V / 1200 Ah smart lithium, max continuous charge current: 600A, maximum charge current: 2400A

Charge sources:

-Multi 12/3000 = 120A

-Alternator = 115A

-1200Wp of solar = 100A max

total maximum charging power = 335A

So you're safe and no reason to be concerned.

About system design / support, I'd advice you to contact your local Victron Sales Agent to help you with this, he/she can bring you in contact with a local distributor or assist you directly:

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valden avatar image valden Daniël Boekel (Victron Energy Staff) ♦♦ commented ·

Thanks Daniel. It's good to see your expert calculations line up with the ones I've been doing, with data taken from Victron's excellent website.

This is reassuring, given how much I'll be spending and how important the system will be. Much appreciated. :-)

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jasontav avatar image
jasontav answered ·

you don't mention any kind of battery monitoring (other than the BMS, but its job it to protect the expensive lithium batteries, not monitor usage in a complex system)

you might want to read up about the BMV

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valden avatar image valden commented ·

Hi Jason. Thanks for these thoughts. Gee, I thought I did mention that my system will have the new SmartShunt? Let me check - yep, in the second sentence where I'm describing the design, in the second paragraph of the OP. The SmartShunt was only recently announced and it looks like an ideal replacement for a BMV in my system.

It looks like we agree that it's really important to protect the lithium batteries. They cost a bomb and are vulnerable in various ways. I will also be depending on them in a 'Safety Of Life At Sea' sense, including in the Arctic and Antarctic. This is why I'm asking questions about apparent gaps in the protection systems. In a moment I will write a new reply to Daniel, explaining that I am concerned about what appears to be a vulnerability arising from GX devices and their DVCC coding not paying attention to the total charging current. Why can't this be communicated between a shunt and a GX device? It could be and it should be.

What benefit would arise from a coding change in this respect? Well, boats are taking on larger and larger solar arrays. They are also being fitted with larger or dual alternators, sometimes fitted with 'charging optimisers'. It's easy to see that a lithium battery (especially if on the small side) could be blasted with too much charging current, which neither the GX device or the BMS, nor the shunt, nor the Cyrix-Li-Charge pay attention to or do anything about (until the battery is full). That's not good.

The thing about automatic systems like DVCC is that people are told to trust them. They need to be trustworthy, not half-trustworthy. A DVCC system that does not take alternator charging into account is only half-trustworthy. :-|

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justmurph avatar image
justmurph answered ·

Hi @Valden,

I'm in the process of designing a similar setup for my boat. I hadn't noticed DVCC yet, so reading all of this has been a good bit of education. I am now wondering, given that in your case (and in mine), the sum of all the charging sources can't exceed the capability of the batteries, why use DVCC? Wouldn't you be better off letting each component run in stand alone mode, with the Cerbo passively monitoring? What's the advantage to DVCC?



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valden avatar image valden commented ·

Hi Murph.

Hopefully your boat work is going to be more straightforward than mine is right now. Our boat is half built, right in the middle of the Covid-19 pandemic and its flow-on effects. Sheesh! :-/

Thanks for your question. It's made me think again about why I like the idea of DVCC. The best answer from my perspective is that it ensures that the charging from solar panels/MPPTs and from shore-power/MultiPlus is coordinated. This line from the Cerbo manual in the DVCC section got my attention.

8.4.1. Limit charge current

This is a user-configurable maximum charge current setting. It works across the whole system. MPPT Solar Chargers are automatically prioritized over the mains/generator.

There are two aspects I like about this:

- DVCC will allow me to set a maximum charge current that will apply across the collection of chargers (but not including the alternator/s, which shouldn't be a problem given that I don't plan to run the engines in a marina)

- DVCC will select the MPPTs as the priority charge source. The MultiPlus will only be used for charging if there's not enough sun to reach my set charging rate.

Lower charging rates are better for battery health. I will only use high charging rates if we're time-limited.

In many marinas we'll have to pay separately for shore power, so using that only when there isn't enough sun will be advantageous. We'll have 1200W of solar panels, which should cover our power needs in full or partial sun. Scottish winters - doubtful; Arctic winters - not a chance. In these Vitamin D deficient conditions we will plug in once a week or so when visiting civilisation. :-)

I understand your point about the combined maximum charging rate for the battery bank not being exceeded by the three charging sources we'll have; solar, shore-power and alternator/s. In general, I prefer manual control over automatic. However, where an automatic control system brings with it a level of elegant sophistication that's hard to ensure via manual control, it's worth considering. DVCC is all about the batteries determining what kind of charge they receive, rather than having independent chargers dishing up what a human at one point programmed them to deliver, whilst also not talking to each other.

I will add that I would be even happier with the idea of DVCC if Victron's batteries were talking to the Cerbo via CAN-bus, rather than via an imperfectly informed proxy - the SmartShunt. I'll go and have a good look at the third party batteries that presently have CAN-bus connectivity.

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