Hi, I have an issue with a smart shunt SOC and battery voltage not corresponding.
This is the 3rd shunt now, last one just replaced by Victron dealer, however I was not confident I had 2 bad shunt’s before they wanted to replace the last one.
So 1 change the batteries full with a Victron IP22 charger.
They are lead acid 12v 100Aah each.
I have the charger set right and the shunt set right but the voltage drops way faster than the SOC to the point I can be 85%SOC but barely 12v on batteries.
This is a continuous problem I’ve had since the 1st shunt.
This in a truck camper that we boondock a lot and not very good to not have a component not telling you the proper information.
The last couple times I charged fully, then made sure there was no load on the batteries and left them sit not charging or loaded before I synchronized to 100%.
Been dealing with this since last year and dealer can’t resolve the issue and Victron has no customer service.
Any help would be appreciated
Highly doubtful you have 3 bad devices. Is the displayed voltage wrong or just the SOC?
If the Smart Shunt shows proper voltage and current, but disagrees on the state of charge, your batteries might not actually be 100Ah. OR the shunt is wired incorrectly and load current is bypassing the shunt.
Would you please post the settings of the charger and the shunt…
Voltage was 12.22.
I’ve had a load on for a couple hours now hoping I would see some change but I am thinking not
The shunt is wired properly.
All cables on the load side and single cable to the battery negative
Would you please post the settings of the charger and the shunt…
The photshot of the Victron app shows 90SOC but only 12.18 V I think.
Definitely not right
Your charger is set to 14.4 volt absorption voltage, so the shunt should be set to 14.2v, it is 13.2
And the Tailcurrent works better at 1 instead of 4%.
Battery SoC on reset should be " keep SoC", not set to 100.
Try these values and see if your system works better.
I will try these settings and see what happens.
I do believe I had the last shunt set to 14.2, and that made no difference.
Thanks
How old are the batteries?
If the battery actual capacity is reduced e.g. by sulphation, then the Voltage will drop sharply as soon as the charge is removed.
Batteries are two years old.
Voltage doesn’t drop quickly
The issue is the voltage drops normally, but SOC does not follow the rate of voltage drop.
For instance today testing it dropped to 12.2 v but was still showing 92%
How much load did you apply?
Lead acid has a lot of voltage sag. Have you checked your specific gravity and capacity tested?
Only had Max air fan on drawing about 1.75 amps.
Haven’t did specific gravity tests but I had 2 brand new AGM GC batteries and had same issue, so hard to believe it is the shunt after 3, and second set of batteries
two years is more than old enough for sulphation to have taken place. If the batteries are not fully charged at least once a month or preferably every week, then sulphation can take place.
If you are placing a heavy load on the batteries, then make sure that the pukhert coefficient is correctly set in the shunt. Also ‘New’ batteries from a distributor can have been sitting on a shelf for 6 months or more, typically without being charged, and are likewise reduced in life.
One cannot measure SG on AGM batteries, as these are sealed and also the electrolyte is semi-solid.
Minimum charge rate needs to be c/10 ,
1.75A load should be very light for ?2 x 100Ah batteries, so you should not get that level of voltage drop from a good battery. See if you can get an automotive battery tester that can put a 100A load on the battery, and see what happens.
I guess my confusion is if even if there was bad batteries and they were fully charged but drop quickly with load, why does the SOC not follow the drop in voltage?
My brand new Rolls batteries were fully charged and I kept an eye on voltage till we went Ted, y morning with the furnace running on and off, and fridge, the SOC was 83% in morning, but my voltage was 11v!
The soc is based on AH consumed not voltage.
How is your shunt wired?
Battery connects to the batter negative of the shunt.
EVERYTHING else goes to system side of shunt.
( chargers, loads etc)
As mentioned above, the SOC is calculated from the consumed Ah, and the GIVEN capacity of the battery, not the actual capacity. This is not a physical measurement like voltage or current.
Hence, if a sulphated battery of 100Ah (plate) has only 20% of its capacity available, i.e.20Ah, and you discharge this at 2A for 5 hours, The actual SOC will be 50%, as indicated by a 12V terminal voltage, but the predicted soc will be 90%, as in 10Ah out of a 100Ah battery.
Testing battery: Charge to 14.4V until charge current <1-2A. Leave disconnected for 1 - 4 hours, measure terminal voltage. This should be 13.2 - 13.8V. discharge on 5 - 10A load , measure voltage at terminals, till V= 12V. This would give ~ 50% soc, so you can use the time taken to do this as an indicator of available capacity. Recharge to 14.4, not max charge current in CC (Bulk) charge condition, this should be ~30A until V>= 13.5V, then start to tail off with your above charger settings.