Over the > 5 years of having an LFP battery in my travel trailer, I have found the SOC “out of sync” problem to be a real nuisance and found that re-synching it is not worth the effort most times. Fortunately, it is pretty easy to just go by the battery voltage which ranges from 13.3 to 13V from over 90-40% SOC as the battery discharges. When I see I’m getting below 13V, I start thinking about recharging. It could be there is a problem with my SOC meter or an intermittent connection but I haven’t been able to track down the cause of my chronic “out of sync” issue. Anyone else have this problem or insights as to why it happens? The only device in my setup that bypasses the shunt is my SOC meter.
Most SOC indicators use a shunt to measure current in and current out. They work pretty well but can get out of sync over time. Also, something like a smoke or CO detector may bypass the shunt which would cause the SOC meter to get out of sync much faster. As Mentioned, there is a process to resync these meters which normally involves fully charging or fully discharging the batteries. The other possibility is that the meter is configured for a much larger battery bank than you actually have.
Hello Mike, Please note that AGM voltage vs. state-of-charge varies significantly with the temperature of the electrolyte. Temperature compensated AGM voltage vs. state-of-charge charts are widely available. Examples: At 100 degrees F, 12.9 VDC corresponds to 100% S.O.C. At 30 degrees F, 12.2 VDC corresponds to 100% S.O.C. Other key voltage vs. S.O.C. are those for 20% S.O.C., the minimum S.O.C. recommended by AGM battery manufacturers, and voltage vs. S.O.C. for 50% S.O.C., the minimum S.O.C. for electrolyte for temperatures below 32 degrees F. Also note that the voltage vs. state-of-charge varies depending upon the present load on the battery and upon the recent (past few hours) load. An AGM battery must settle between 2 hours and 24 hours with no load in order to obtain a reasonably accurate, temperature compensated indication of the S.O.C. for a given battery voltage.
The Victron shunt does drift around, mine has drifted positive and over a couple months showed my battery fully charged from 50% when I put it away even though there was nothing connected charge wise or usage wise, it has also drifted negative. I don't bother to sync it any more, what I do is just charge it up all the way before a trip then the monitor will be at 100% anyway and I can keep track of usage very accurately for the duration of the trip. (It may hit 100% at any point in charging but if it is not fully charged it will continue to charge till full, or it may be fully charged but showing a lower SOC in which case I would have to sync it but so far a long charge such as the first day of travel gets me to 100% on both, then I have accuracy for the entire trip)
As mentioned any load or charge that bypasses the shunt will make the readings inaccurate. Folks need to understand that a shunt is basically a bean counter, it doesn't actually look at the battery voltage in determining SOC, it just keeps track of usage and charging mathematically although it does use SOC voltage in it's watt calculations. If it doesn't receive accurate info it will not be accurate, just like plugging the wrong numbers into a calculator.
A Coulomb counting battery monitor, such as those sold by Victron, is a much more reliable means of determining the state of charge of an RV house battery bank. As indicated in other posts, it is necessary to keep the battery monitor in sync with the state of charge of the batteries by charging the batteries to 100% S.O.C.
Battery voltage is not a very reliable manner in which to determine S.O.C. for an RV house battery bank. Factors that contribute to inaccuracy include the following: 1. Electrolyte temperature (requires knowing the temperature of the electrolyte and the use of a temperature corrected voltage vs. S.O.C. chart). 2. Present load on the battery and recent history of loads. (Requires battery to settle with no load for 2 hours up to 24 hours for a meaningful voltage measurement.) 3. Accuracy and resolution of the voltmeter. (Consumer grade (non-laboratory grade) digital voltmeters can be off by as much as 0.2 VDC at 12 VDC.)
Over the > 5 years of having an LFP battery in my travel trailer, I have found the SOC “out of sync” problem to be a real nuisance and found that re-synching it is not worth the effort most times. Fortunately, it is pretty easy to just go by the battery voltage which ranges from 13.3 to 13V from over 90-40% SOC as the battery discharges. When I see I’m getting below 13V, I start thinking about recharging. It could be there is a problem with my SOC meter or an intermittent connection but I haven’t been able to track down the cause of my chronic “out of sync” issue. Anyone else have this problem or insights as to why it happens? The only device in my setup that bypasses the shunt is my SOC meter.
Most SOC indicators use a shunt to measure current in and current out. They work pretty well but can get out of sync over time. Also, something like a smoke or CO detector may bypass the shunt which would cause the SOC meter to get out of sync much faster. As Mentioned, there is a process to resync these meters which normally involves fully charging or fully discharging the batteries. The other possibility is that the meter is configured for a much larger battery bank than you actually have.
Hello Mike, Please note that AGM voltage vs. state-of-charge varies significantly with the temperature of the electrolyte. Temperature compensated AGM voltage vs. state-of-charge charts are widely available. Examples: At 100 degrees F, 12.9 VDC corresponds to 100% S.O.C. At 30 degrees F, 12.2 VDC corresponds to 100% S.O.C. Other key voltage vs. S.O.C. are those for 20% S.O.C., the minimum S.O.C. recommended by AGM battery manufacturers, and voltage vs. S.O.C. for 50% S.O.C., the minimum S.O.C. for electrolyte for temperatures below 32 degrees F. Also note that the voltage vs. state-of-charge varies depending upon the present load on the battery and upon the recent (past few hours) load. An AGM battery must settle between 2 hours and 24 hours with no load in order to obtain a reasonably accurate, temperature compensated indication of the S.O.C. for a given battery voltage.
The Victron shunt does drift around, mine has drifted positive and over a couple months showed my battery fully charged from 50% when I put it away even though there was nothing connected charge wise or usage wise, it has also drifted negative. I don't bother to sync it any more, what I do is just charge it up all the way before a trip then the monitor will be at 100% anyway and I can keep track of usage very accurately for the duration of the trip. (It may hit 100% at any point in charging but if it is not fully charged it will continue to charge till full, or it may be fully charged but showing a lower SOC in which case I would have to sync it but so far a long charge such as the first day of travel gets me to 100% on both, then I have accuracy for the entire trip)
As mentioned any load or charge that bypasses the shunt will make the readings inaccurate. Folks need to understand that a shunt is basically a bean counter, it doesn't actually look at the battery voltage in determining SOC, it just keeps track of usage and charging mathematically although it does use SOC voltage in it's watt calculations. If it doesn't receive accurate info it will not be accurate, just like plugging the wrong numbers into a calculator.
A Coulomb counting battery monitor, such as those sold by Victron, is a much more reliable means of determining the state of charge of an RV house battery bank. As indicated in other posts, it is necessary to keep the battery monitor in sync with the state of charge of the batteries by charging the batteries to 100% S.O.C.
Battery voltage is not a very reliable manner in which to determine S.O.C. for an RV house battery bank. Factors that contribute to inaccuracy include the following: 1. Electrolyte temperature (requires knowing the temperature of the electrolyte and the use of a temperature corrected voltage vs. S.O.C. chart). 2. Present load on the battery and recent history of loads. (Requires battery to settle with no load for 2 hours up to 24 hours for a meaningful voltage measurement.) 3. Accuracy and resolution of the voltmeter. (Consumer grade (non-laboratory grade) digital voltmeters can be off by as much as 0.2 VDC at 12 VDC.)