Difference in reading between BMS and Victron Battery Monitor?

[chrisclifford]

Hi all, I've installed a solar system in my van and so far it has been working well. I have a Victron charge controller and battery monitor, and a Renogy 200ah Lithium Iron Phosphate battery (I am aware that Renogy is not the most reputable manufacturer). I installed the system about 3 weeks ago, and the battery's BMS said it was at 95% charge after I charged it for the first time. I manually set the Victron battery monitor at 95% to sync the two. After using the system for a few weeks, the Victron monitor still says it's around 93% after some discharge and recharging. However, the BMS in the battery says it's only at 73% charge. No settings have been changed on the charge controller. Any idea what is causing this discrepancy? I assume that the BMS is more accurate? Any advice is appreciated. Thanks

 

[Crowz]

Well they will never be truly in sync because all of that fancy bluetooth wireless stuff + the bms's native draw to operate + balancing the cells will eat power that never goes across the shunt though 93 vs 73 seems a bit much for being off. I couldn't see anything in the specs googling that battery to see if it had internal heating. If the model you have has internal heating and its cold there that would easily account for it.

 

[Q-Dog]

I would assume the Victron is more accurate, but not before a couple of complete discharge/charge cycles.

 

[DIYrich]

Have you done a full charge (100%) recently. If not, SOC can drift.

 

[mikefitz]

The default settings in the Victron may cause it to sync to 100% early.
It's possible the settings in the Victron monitor are not quite correct for lithium and solar charging.
Set charged voltage to 0.2 lower than your absorbtion voltage set in the charger and charge efficiency to 99%.
It's possible some of the other settings will need slight adjustment.

Once the Victron monitor is optimally set up regard this as near correct.

Mike

 

[chrisclifford]

Thanks everyone. I've incorporated this advice and will see what results it yields in the coming days

 

[Tomthumb62]

Thanks everyone. I've incorporated this advice and will see what results it yields in the coming days

I look forward to your findings. The Powerurus 200Ah battery we recently got has a Bluetooth BMS as well. It does show remaining capacity in amp hours. I’m guessing that while it won’t be as accurate as a true columb shunt, it will be in the ball park enough to know if we have 60% remaining capacity or only 15%, +/- 5-10%. Would be nice to know if that +/- is 10% or 3%. In any case, I don’t think we actually need to added expense or complexity of adding a shunt, even if the data hound in me would love it.

I know you and I have different batteries/BMS, but I imagine the tech involved for a BMS to estimate capacity (without an actual shunt) are probably fairly similar.

 

[chrisclifford]

So here's the update: this morning the Victron monitor read 100% and the internal Renogy BMS told me through the app it was at 19.8%. I disconnected the charge controller at the solar panel and the battery master switch, disconnecting it from the fuse box. After an hour, I turned both back on and now the Renogy app reads at 100%. I think the Renogy battery BMS is just very inaccurate, my only fear is that it will read too low and shut the battery off when it is actually fully charged. I think for now I will just monitor it and see if the discrepancy continues

 

[Rickey]

I have a junctek KH140F, I use it on my three-wheeled electric car, it is very convenient to use it to check the battery level, it may be the reason why I am often fully charged, the remaining battery percentage is accurate.