Eric M. avatar image
Eric M. asked

Consumed Ah trending down over weeks

A few months ago I swapped out my AGM batteries for LiFePO4, and set the initial battery settings to those recommended by the manufacturer and Victron. After a couple weeks, I left on a trip that got extended for a couple months. My rig was parked in the sun, with minimal loads, so the solar was hitting float quickly every day. But checking VRM, I noticed a trend where the Ah consumed (and therefore SOC calculations) were trending down never showing a full recharge.


My assumption is that this is an issue with calibration and SmartShunt settings, because the low voltage was not also trending down - never dropping below ~13.28V daily.


Would the community agree this is a SmartShunt settings "issue," and if so, which values would you recommend I try adjusting?


Thank you for any suggestions!

Follow up question for bonus points... :) What do most people do with LiFePO4 batteries when leaving for some time, while small loads will still need to access the power? I assume I'll hear some people concerned about keeping these batteries so close to 100% all the time?

Lithium BatterySmartShuntbattery capacity
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2 Answers
nickdb avatar image
nickdb answered ·

For one thing your charged voltage is high and from the readings it is never getting there so will never sync, which will help the soc drift.

Here is a good tutorial:

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Eric M. avatar image Eric M. commented ·
I have gone through that video a few times.. Sorry, maybe I wasn't clear, I'm hoping to avoid using the crutch of the "sync to 100%" feature, so I have my ChargedVoltage and DetectionTime set to very difficult to reach values. Hoping to really dial in settings so I can rely fully on amps in/out to have a fully correct reading. This makes me wonder if its something to do with efficiency factor and peukert values...
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JohnC avatar image
JohnC answered ·

Hi @Eric M.

You're talking quite a low drift here, like 0.8Ah/day average. Yet you've left the Current Threshold at 0.1A (default?), so it won't count A below that. You could try setting that to 0A, and also do a Zero Current Calibration.

The Ah reported isn't absolute, it's corrected. You could lift Charge Efficiency, but that's only adjustable by 1%, so 100% might be unrealistic. Or raise Peukert a little so that it gives more credit for your very low loads (if they don't happen all at once).

It's all very noble to want to never need to sync, but the only real check that SOC is accurate is when the batts are at 100%. And you have the means to define that to do it automagically. Sure you don't want it to happen every day, but batts are well-up-there in our imperfect world, and they can behave strangely, especially with temp variations and how they're treated. By all means tune it, but that Sync is the ultimate failsafe.

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kevgermany avatar image kevgermany ♦♦ commented ·
@Eric M.

Daily consumption actually increased. The amp hours consumed is the difference between the high and low points on a day. The range increases but is fairly stable on the later parts of the graph. Downward drift is inevitable due to lack of sync.If you follow the excellent advice already given, the graph will be more useful.

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