Hi all,
I have a few concerns with my Victron system, fully set up and configured by me. I have some experience with solar over the past 15 years or so and felt confident with the equipment selection I made for our off-grid cabin.
I have the following installed:
Cerbo-GX
MultiPlus-II 48/3000/35-50 120V
SmartSolar Charger MPPT 150/45 rev3
SmartShunt 500A
Battery temperature monitor
8 Rolls Surrette S6 L16-HC Lead Acid batteries wired to 48 volts
4 Canada Solar 320Watt Solar Panels wired 2S2P giving 1320 Watts
My first issue is regarding SOC and voltage levels. As I type this, my SOC is 86.8 and my voltage is 48.3v. I realize that voltage is not a solid way of identifying SOC, but I’m not quite understanding where my system stands and am curious to know if I am worried about nothing. I have the battery voltage vs. depth of discharge chart below and would love to have a little guidance to help me to understand how to read this for my system. During the off-season (winter basically) the only draw on the system is a StarlInk system and a few Wyze cameras. This hangs around the 60 watt mark 24/7.
My second concern is again related to the SOC and the way it jumps from some random figure in the 90s, straight to 100%. This happes with every single solar charge of the system, for example on 11/10/2024 the system jumped to 100% from 95.2% at 55.45 volts and on 11/11/2024 it did so from 97.8% at 52.55 volts. Again, I get that voltage is not a great way to know the SOC, but why would the SOC make such large, random jumps straight to 100%?
Thanks for any advice you all may be able to provide.
Have a read of this FAQ in the DIY section, linked from the FAQ sticky post at the top of DIY.
This explains why it jumps randomly and how to set your synchronisation voltage. The FAQ is based on 12V systems recommending setting the SmartShunt charged voltage 0.1 to 0.2V below absorption, fpr 48V something like 0.5V below would be a good starting point.
It often jumps if the charged voltage is set too low.
If you still get jumps then you need to slightly alter charged efficiency and/or Peukert coefficient.
I changed my charged voltage (on the SmartShunt) from 54V to 59.2V. I used the information from the link you provided and removed .2 of a Volt per 12 Volts from the absorption voltage. 60V - (4 x .2V) = 59.2V.
I’ll use this as a starting point and update as time goes on.
I don’t think I need a Battery Balancer as I only have one series of batteries.
I did follow some documentation, and have the settings mostly correct as far as I could tell.
I have now adjusted the charged voltage as indicated in the FAQ and will update as necessary. We have a dark and wet forecast over the next week so may not see any real charge for a while unless I visit my cabin and run the generator for several hours.
Can you send your multiplus parameters ?
Did you change the disconnect voltage ?
It’s highly recommanded to preserve the power bank against big discharge.
Exactly as expected, the Charged voltage is too low, a setting of 59.0 or 59.5V should stop the solar synchronising too early.
The charged efficiency may be too low for good quality batteries like Rolls, if you still see the SOC jumping from say 95% to 100% despite the change in charged voltage then I would increase the charged efficiency factor to 90% and see if that helps. This factor sets how efficient the charging is and if it is set too low it under predicts the SOC as the batteries recharge.
Hi Rene.
For the Smartshunt I ran those batts through the Victron Peukert calculator and it bobbed with 1.10 between C20 and C72 discharge rates. The 1.25 default is too high and will result in an overestimated SOC (less discharge shown than actual). Then adjust your Charge Efficiency as needed when charging, the aim there is to bring the SOC back to 100% naturally at the same time as the shunt syncs. It’s also possible to sync under Float conditions. A little trickier to set up, but under Absorb conditions you must make sure it syncs before it returns to Float. There’s maybe 1% SOC or more SOC to be gained under Float, but you could test this. Consider increasing Charge Detection Time to 5 min to help prevent passing cloud causing false syncs (if you decide to sync in Float).
For the mppt you’ve chosen 60.0V, but Rolls give a range, the lower one is 58.8V. Aggression won’t make them last longer. Check with Rolls what Temp Comp figure to use, that default is likely too low.
Take a lot of care with how you set up the length of Absorb time. At those V’s there’s damage to be had if you regularly overdo it.
I’ve adjusted the Peukert to 1.10 based on what you wrote above.
Regarding to 60.0V MPPT setting, that is based on a daily discharge/recharge recommendation from the Rolls manual as shown in the attached screen capture. I am using the values for a 48V system in the top table as our system discharges to some degree each and every night and typically gets a fully charge each day (…if the sun ever shines again). I also have the temperature sensor installed with the batteries.
@ReneJ
Your spec sheet found the Temp Comp figure, -120mV/degC (don’t forget the minus). That’s upper end, and means that for every 10 degC below the 25 it will add 1.2V to the charge target. It’s why your T reading is important. Set that in both mppt and Multi.
In the Multi…
Set Absorb 0.1V below the mppt’s. That will give the mppt priority over the genset if both reach Abs. Float V works the same, but you probably shouldn’t be running genset in Float anyway
Tick Dynamic Current limiter, that’s to help genset adjust to load changes.
If you don’t have Grid, untick Storage mode.
Charge Current you could open up a lot. Then use Input Current Limit to match the genset sweetspot.
Take a look at DVCC (in the GX), all functions will be of use for achieving a smooth system. You can limit total battery charge there.
But mostly watch that Absorb Time. Once you see Charge A getting near ~15A at Abs V, start wondering. There’s Tail Amps in the mppt that can override the Adaptive algorithm.
Set Absorb 0.1V below the mppt’s. That will give the mppt priority over the genset if both reach Abs. Float V works the same, but you probably shouldn’t be running genset in Float anyway
Tick Dynamic Current limiter, that’s to help genset adjust to load changes.
If you don’t have Grid, untick Storage mode.
Done.
Why not run float from the genset?
Charge Current you could open up a lot. Then use Input Current Limit to match the genset sweetspot.
I’m limited to 35A in VEConnect. My generator barely comes off eco mode when charging but this seem to be a hard limit and gets a little over 2000 watts of charge power indicated on the Cerbo screen.
Take a look at DVCC (in the GX), all functions will be of use for achieving a smooth system. You can limit total battery charge there.
I had a quick read on DVCC since you pointed it out. Does this trump all the settings on all the units and allow for management in one place? If I enable DVCC, will I have to work through the settings as we have been doing here, or will it pick them up from the various units and give me that to start from? Is it just a dumb display as I am now using it?
But mostly watch that Absorb Time. Once you see Charge A getting near ~15A at Abs V, start wondering. There’s Tail Amps in the mppt that can override the Adaptive algorithm.
I guess this is my next bit of education!
Thanks for all the help here. Your suggestions along with explanations behind each suggestion is helping me to better understand the system I have in place. Hopefully these settings will help to ensure I am charging the batteries properly, and as efficiently as possible.
The past two weeks have been wet and dark and the next week and a half looks to be about the same. I’m barely getting any solar power and will soon head up and run the generator for a few hours or overnight just to get some charge back in the batteries (remote gen start discussion may be in my future! lol)
Sorry, I overlooked the 35A charge limit of your Multi. I don’t like running gensets, they’re noisy, smoky, and cost for fuel and maintenance. So when I run it I load it up with anything I need to run that day and charge only when batts can accept full current. Float for you might be just the last 1% of SOC, so it’s just not worth it.
It’s why I never use auto-start, sometimes you can get better value early in the day, then shut it down and let solar finish it. Remote start if you’re not there would be useful though.
Maybe you could schedule visits to fit with that scheduled Equalize. Once that’s done, no need for more Float.
DVCC lets all your gear see the same info and work in unison. The battery Current from the shunt can also be used to terminate Absorb, because the mppt’s own will include loads too.
@JohnC I also hate running the genset. I don’t think I’ll use auto-start myself, but being able to run it remotely would work well for me and the weather we have been having lately.
As you can see in this screenshot of my SOC, if I hadn’t run the generator a little over a week ago (the large increase in SOC near the middle of the image), the SOC would likely be way down closer to the 60% mark (using the current settings). The blip right after I ran the generator was due to an incorrect adjustment I made and then corrected.
