I am operating three SmartShunts 300A (one per battery). Despite identical settings and firmware, Shunt A does not synchronize to 100% when the target voltage is reached and when the tail current falls below the threshold.
Have I overlooked something? Or is the shunt simply defective?
The little jump up on the end of the others means the settings aren’t quite right for your batteries.
Also notice the shunt with the ‘issue’ is drawing less current - or at least is appears so with the graphing scaling. I guess you would be able to compare better with a mouse hover.
In short (ignoring settings) it could be current sharing, it could be resistance in connection. Or the battery is a little less happy than the others.
the threshold value in A is not reached when I look at the graph. Either less voltage due to losses or the MPPT regulates beforehand because the other shunts return fully
So the jump in synchronisation on the other graphs means the same thing.
The shunt synchronised on the other two.
Check the peukerts. Is is possible it is 1.03
This would suggest poor current share or poor connection as mentioned. Especially if it is sharing a bus bar.
Its a bit hard to see but it looks like battery A does discharge with less current compared to the others. It gets close to -20A as max discharge while B provides close to -40A and C well over -20A, but to be honest the scaling is not so great for the current. How does it look when you overlay the three currents over each other in a single diagram?
Bat A also discharges much less than the other two when it comes to Ah.
How exactly are they put in parallel?
Edit: Also, does the charger/power source in any way react to the first battery reaching 100% SOC, since it looks to me like at the same time as batteries B and C reach 100% the voltage jumps up quite a bit
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Huge cell/ battery imbalance?
Hi @n-e-w-solar
Can you, please, post here the config of the three shunts?
VictronConnect - Settings - three dots - save settings to file.
You many need to rename it as txt for the forum to allow you to upload them.
I also have - but still not installed - a 300A shunt and I am curious of the issue before installing.
And who knows, maybe we can find some discrepancies.
Battery A delivers less than B and C. This is despite the fact that all batteries are connected to a busbar with identical cable lengths and cross-sections.
But that is another issue that I do not want to go into further here. In my opinion, it has no influence on the behavior of the shunts discussed here.
As I understand it, all shunts should synchronize to 100% SOC when the following three conditions are met:
- Target voltage: > 54.2V
- Current: < 4% of capacity (280AH * 4% = 11.2A)
- Time: after 3 minutes
.
Since these conditions are met for all three batteries, I cannot explain the behavior of shunt A.
I am not clear on the role that the Peukert exponent should play in this. Nor am I clear on the role of cell balance, which, incidentally, is below 10mV for all batteries.
The configuration of the shunts is absolutely identical. I have attached the configuration files (renamed .bin to .txt).
SmartShunt300A-C.vcsf.txt (20,8 KB)
SmartShunt300A-B.vcsf.txt (20,8 KB)
SmartShunt300A-A.vcsf.txt (21,0 KB)
It would mean that the battery that discharges at a lower rate, bat A, will in theory have a higher total amount of usable energy compared to the other two
I assume the voltages above in the graphs are taken from the shunts directly, via VE.direct/bluetooth? If thats the case, then i would also expect the sync to happen at the same time, regardless of the previous charge/discharge rate.
Have you tried exchanging shunts between batteries, to see if the issue stays with the battery or with the shunt?
Indeed, according with your files:
- all settings are the same.
- A has 0 automatic syncs, while B and C have 3 automatic syncs.
- A has 0 charge cycles, while B and C have 2 charge cycles.
- A has 50.5 hours since last full charge, while B and C have only 4.5 hours since last full charge.
Another thing…
A has an average discharge energy of 0 (zero), while B and C have around 102…
But it could be related to the fact that it doesn’t have several cycles/syncs in order to make the average.
All of these confirms what you are saying…
But also something strange…
According with the Shunt A trends data, it also recorded SOC 100% between:
- 2026-02-24 21:05:51 UTC <---------> 2026-02-25 00:35:52 UTC
- 2026-02-25 22:05:57 UTC <---------> 2026-02-26 00:05:57 UTC
- 2026-02-26 21:36:03 UTC <---------> 2026-02-27 00:36:03 UTC
- 2026-03-01 23:06:20 UTC <---------> 2026-03-02 01:06:21 UTC
- 2026-03-02 20:06:25 UTC <---------> 2026-03-03 16:56:30 UTC
A simple elimination test would be to switch/swap its position to another battery changing nothing else.
All data comes via VE-direct. So the sync times should also be identical.
The discussion so far has not revealed any compelling evidence of an error in the configuration of the shunt. As a final step in troubleshooting, it certainly makes sense to replace the shunts/batteries.
I will probably do this in the next few days when the fourth shunt arrives, which I had already complained about to the dealer because it was not working at all.
I will report on the result here.
I now have data covering several days and can report that Shunt A is not defective. What happened?
Three batteries are connected in parallel to a busbar via their own shunts. In this configuration,
interaction apparently occurs when the end-of-charge voltage is reached. One or two shunts meet the sync condition
for resetting to 100% SOC and synchronize to 100%. However, the third battery is still charging with a current
above the limit of 4% of capacity (280AH * 4% = 11.2A) and does not yet meet the conditions for synchronization.
Next, the control reduces the charging voltage to the absorption value of 54.0V, which is below the synchronization voltage
of 54.2V. As a result, the shunt on the third battery can no longer meet the conditions and remains at the
SOC value achieved up to that point.
This effect has now occurred in all three batteries, regardless of the degree of discharge. This effect can be avoided by
increasing the current value to a suitable value > 4% of the battery capacity.
Who would have thought of that?..
Why one would set the absorption lower than sync voltage?
Usually one sets the sync voltage a tad lower than the constant voltage of the absorption, in order for one of the two conditions of the sync (voltage) to be true and to wait for the other one (current) to become true.
You are absolutely right. The sentence in my last post should read: “Next, the control reduces the charging voltage to the float value of 54.0V, which is below the synchronization voltage of 54.2V.” Absorption voltage is 54.4V.
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Then, besides voltage tinkering, you have another choice of setting the absorption time long enough in order to allow, up until float, for the current to drop below sync current. I believe it’s better this way, instead of raising the sync current, because a longer time and a lower current means the balance will be better.
Anyhow, good that’s sorted.
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This may be the preferred alternative.
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