FW BMS and Smartshunt SOC not synchronized

Batteries Battery Management Systems (BMS)
1

Morning guys, Stalker here…

I installed 2 FW eTowers almost 2 years ago and have had only the best experience with them, no issues at all. Only thing I would like to see on VRM, but couldn’t, was the “time to go” data. After some very mild research, I acquired a Smartshunt (yes everything else is Victron) and installed it as close to the battery as possible, also adding that there’s around 300mm of cable (equal length on + & -) between the batteries and the busbars, where the Smartshunt is connected and then another 500mm (again equal lengths) to the 2 x 48/3000/35 Multiplus inverters.
The battery BMS and Smartshunt SOC keeps going out of sync by about 2% after a few day though. I fiddled with settings on the Smartshunt, without any luck but do not want to change anything on the eTower parameters (yes i have Pbmstools, cables and password to do so) seeing that it will probably screw with the FW warranty. Both batteries have a 100SOH after around 490 full cycles (last time I checked)
Again, as I said, I have absolutely no issues with the system or batteries, the Smartshunt was installed purely for the “time to go” function.
Can anyone give me some pointers at what settings I can try and adjust on the Smartshunt? Tailcurrent maybe? The Smartshunt SOC starts to go around 2% higher than the FW BMS after about 5 days. If I cannot get the issue fixed there might be a Smartshunt up for grabs soon :wink:

2

On my DIY Lifepo4 bank, the BMV matches the BMS SOC damn close.

Yes, it is a wee bit out when BMS uses volts to determine the SOC, but at the bottom/top, most of the time in sync, or as close to as one can.

These are the BMV settings I use:
NOTE: Check the Ah and Charged Voltage … divide volts by 18 (cells) to get volt per cell, then times your cells.

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3

Dankie Jaco. Ek gaan maar nog so bietjie peuter en kyk of ek die 2 nader aanmekaar kry.

4

Settings wat direk invloed het:
BMV Charge Efficiency: 99% or 98%
BMV Charged Voltage: 0.2v below Absorption
Discharge Floor: 90%
BMV Tail Current: 4% Will Prowse: 2%
BMV Charged Detection Time: 4min Will Prowse: 3min
BMV Peukerts Exponent: 1.05

Moet maar aanpas by jou spesifieke bank, ek het Will Prowse en Andy, Off-Grid Garage, Victron settings se goed gevolg.

Hier is Andy se settings. Sien die Smartshunt deel.

5

SOC drift is normal. I would ignore it, especially if just a few percent.

6

As I read this I checked mine. Also have E-Towers. Difference of about 3%

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Not enough to bother my OCD. :laughing:

7

When discharging/charging, there will be a difference. BMS factors the volts in too.

The AH in/out, if one can tune that, best one can do, will result in a comfortable reading overall. 3% is “comfortable”.

The not-so-obvious benefit: … that I discovered accidently. :slight_smile:
If the BMS and BMV have been in sync for a long time, regularly synced and all that, and suddenly one day one sees they differ vastly, that could indicate a potential brewing problem on the batt.

Saw that with my first BMS. BMS said 100%, and Smartshunt showed 55% SOC. Checked and found cells totally out of whack. DIY bank, cheap cells (compared), and even cheaper-ass crap BMS.

8

I’ve changed some settings and synchronized SOC with the eTower BMS so will wait a few days again to see If I can get it closer. ESS uses the eTower BMS to control the system so this is purely out of interest and boredness. My system has been working flawlessly for more than 2 years now so I don’t want to scratch where it’s not itching. I will revert back as soon as I can see any results. Thanks for your input okes