Elimac avatar image
Elimac asked

DVCC not compensating voltage drop


I have been trying for a while now, and I never managed to make my system compensate the voltage drop in the DC part of my system.

System is composed of:

2x MPPT 250/60 ver. 1.37

Venus device, ver. 2.23

Multiplus 3000/24/70 ver. 423

Battery bank 24V 14kwh OPzS

Section cables of 35 and 50mm2, lenghts of around 5m on MPPT to battery, 2m between battery and Inverter.

2 fuses involved along the way

Voltage drop needed to compensate in high currents: around 0.3 to 0.7V, at most.

Without DVCC, I see correct voltages monitored in both the MPPTs and the Multiplus. The Multiplus is closer to battery and with the Voltage Sensor correctly connected (confimed with multimeter).

In absorption stage, there is some voltage missing to be optimal value, and slowly rises when current drops. Only in final moments before going to float I see the voltage reach the expected 28.8V + temperature compensation.

So, I enabled DVCC + SVS, and what I see is that instead of the MPPTs rising a little the output voltage, nothing changes on system, and he only difference is that now the Multiplus reports the voltage of the MPPT instead of its own!!! Battery monitor selected is the Multiplus!

Yesterday, I switched off DVCC and added temporarily the Smart Battery Sensor, just to test. The system started to respond as expected and the MPPT immediately raised their output voltage in order to have true 28.8 + temperature compensation on the battery terminals. But I would rather use DVCC, since I have Venus device.

Any ideas of what is going on?

Thanks and regards

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5 Answers
Mark avatar image
Mark answered ·

Do you also have a battery monitor (BMV) in the system?

Normally / ideally the voltage as measured by a BMV or BMS should be used as the master voltage source for SVS.

In your situation it seems like it is automatically prioritising & selecting the MPPT voltage for SVS over the VE.Bus voltage as measured by the Multi.

You could try selecting the Multi from the list as the active battery monitor & see if anything chages.

I am not sure if you can manually select the SVS voltage source with the current firmware, but also have a hunt around the SVS related menus to see what you can find.

Another point to consider is that if the use the VE.Bus voltage from the Multi for SVS, the Multi will STOP transmitting this data IF it is switched off. There is no way around this apart from maybe leaving the Multi in 'charger only' mode (with NO AC in connected) when not in use - or just leave it always on.

Lastly, it would also be a good idea to update your Multi & MPPT firmware to the latest revisions.

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Thanks for replying!

1. Yes, I got the same impression that it selected the MPPT voltage as the SVS source, but I never read it could be like this on the DVCC documentation. I was expecting the Multiplus to be used. Maybe someone from Victron staff could clarify?

2. I don't have BMV or BMS. In the source list I can select automatic - which if used selects the Multiplus - or manually force to use Multiplus. I tested both options already, it did not change anything. Untill now this seems the only option that could be related to SVS, couldn't find anything else. Again, if someone from victron could clarify if the battery monitor selection is also used for SVS source.

3. I couln't understand the last part of your answer. What do you mean exactly? My Multiplus is in inverter mode >90% of the time, only change to charger in winter on bad weather, to save battery life. Since it was installed, only switched off once to install different fuse and cable on battery bank.

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No problem.

Well it seems like the fix for your situation is to allow the user to maually select the source for SVS. I'm not sure if it is already coming in the upcoming Venus firmware update (2.30) or not. Someone from Victron or a tester of the Beta version would have to confirm...

PS. I have just asked on your behalf - see link below;

Alternatively you could purchase a BMV - which would be useful for much more than just getting SVS to work. (Particularly with future planned updates such as MPPT absorption phase end based on BMV measured charge current)

My last point was stating the fact that if you ever decide to turn your Multiplus OFF (by the rocker switch on the front) then it will loose communication with the Venus device & stop sending voltage information to use for SVS. This may or may not be an issue for you... (I like to turn my Multi off when I am not around to save the ~25w of stand-by power draw). The idea to put it into 'charger only' mode was a work around suggestion, as in this mode the inverter turns off but it seems that communication is still active.

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Thanks Mark!

I considered for a moment to install this Beta version, but my wife won't allow for glitches in our home, or I will become forbidden to continue to invest time and money on this system again if something happens :)

I also considered to update other devices firmware, but I can't see any relevant additions on the release notes. I avoid firmware upgrades as a professional habit. Wait for maturity, etc... also, I don't have MK3 to upgrade the Multi, it is on its original factory firmware. But this version should make DVCC work ok, according to documentation.

The BMV may be an option later on, if this system is stable and I continue with Victron brand for a 2nd system, with bigger inverter and battery bank.

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Elimac avatar image
Elimac answered ·

I repeated the tests, with just one 250/60 MPPT at a time. The results are the same: with DVCC + SVS enabled it seems the Multi gets the voltage reference from the MPPT instead of being the MPPT to get the measurement from the Multi, which has it's own VSense connected directly to battery. In menus, it is selected Multiplus as battery monitor.

In DVCC documentation we can read:

Shared voltage sense (SVS) for VE.Bus devices and VE.Direct Solar Chargers.

  • The system automatically selects the best available voltage measurement. It will use the voltage from the BMS or a BMV battery monitor, if possible, otherwise it will use the battery voltage reported by the VE.Bus system.

Since my only VE.Bus device is the Multiplus (besides the Venus) I was expecting the measurement to come from it, namely the Vsense measured value....

Can anyone shed some light please?

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Elimac avatar image
Elimac answered ·

Latest news:

- Increased cross section of copper conductor of the Multiplus Vsense -> no change (is ignored)

- Upgraded both MPPT 250/ 60 from 1.37 to 1.39 -> no change, but got error "dup-95" while upgrading, still don't know what this means

- Upgraded Venus device from 2.23 to 2.30 beta 40 -> no change in the DVCC + SVS compensation but started working admirably for the DVCC + Temp compensation, obtaining data from Multiplus right away.

I still don't know why DVCC + SVS is not compensating cable voltage drop. I can't believe I am the first one to try this, am I?

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Elimac avatar image
Elimac answered ·

With DVCC, SVS, STS and current limit set to ON, is the following normal?

Shouldn't the Solar Charger Voltage control be also ON ?

DVCC section as below:

1554887060145.png (60.6 KiB)
1554887139766.png (44.5 KiB)
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Can't you click on that line & change it independently to the DVCC toggle switches?

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Hi Mark,

No, they are just information/ monitor lines. The action is somewhere else. Namely, the "Solar Charger Current Control" changes to "ON" if I enable DVCC + Limit Charge current.

I was expecting the same for voltage control when I enable DVCC + SVS... but nothing happens.

Information is scarce about DVCC and I can't find anyone on this forum with some explanation.

I am already using Venus 2.30 beta 4

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Hi Elimac,

I know/recall that you can click on the battery monitor line & then select an alternative option or automatic from the pop up menu, so thought it might/should be the same logic for the other few lines.

Sorry I couldn't check myself as I'm not at the location where my setup is. Hopefully I can load up the beta 2.30 firmware this weekend & give it a whirl myself...

Yes all these features are still quite new & still maturing so info is a little scarse at the moment.

Maybe try posting in the Venus 2.30~40 post within the 'modifications' section to get some more answers/support.

PS. I also see that 2.30~42 is now available, but don't know what the updates are.

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I'm going to test 2.30 b 4.2 today

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Mark avatar image
Mark answered ·

Hi @Elimac,

It seems like you may be in luck soon with regards to resolving your issue. By chance I just saw that a GitHub ticket has just been raised;

The text seems to also provide some info/direction to possibly get it working before this update. Is the Multi battery monitor function turned on in VE Configure? Do you have the DC loads option turned off?

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Thanks Mark for the info, the text/ ticket seems to point exactly to my case. Yes, the Mulit has the battery monitor function enabled. I reckon is not as precise as BMV but is better than nothing and certainly better than the MPPT.

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FYI - That ticket has just been actioned & closed. So with some luck you may see the update in the next beta release.

Yes the Multi SOC calculation is definitely not as accurate as a proper BMV with a shunt. But better than nothing & should be fairly accurate as long as the batteries are fully charged often so that it can sync. Just ensure that the 'Use solar charger current to improve VE.Bus SOC' is automatically enabled on the CCGX.

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