What's a good battery level monitor?
What's a good monitor that I can install in my Casita to see the battery level throughout the day? Ideally a monitor that draws minimal power since we boondock frequently. When we're camping in an...
Forum Discussion
Regarding the drifts and possible inaccuracies due to a variety of behavioristics of charging and/or the batteries themselves....
I can see how IN THEORY you could have an issue if every time you charged your batteries you immediately STOPPED charging once your monitor said you are at 100%. If you were in fact not 100% full (...let's say the true SOC is only 95% even though your monitor incorrectly says 100%) and then you used your battery down to 50% as stated on your monitor, you would in actuality only be at 45% SOC. Then if you charged back up to what you thought was 100% and immediately stopped charging once your battery monitor says you are at 100% but in fact if it once again fell short you might only be at 90% true SOC. If you repeated this many times in a row, then I can see you'd have a problem. (drift)
Perhaps a good rule of thumb would be to make it a habit to continue to charge your batteries for a little while beyond the time when your monitor says you just reached 100%. Or, if your monitor shows amps going into your battery while charging, you can get a sense that way as to how much "charging" is still happening once your monitor reaches 100%.
This "drift" problem gets fixed/reset anytime you do have a situation where your charger stays on/active for a long enough time after your battery monitor says you are at 100%. For example, if you do find yourself plugged in at a campsite and your monitor reaches 100% (even if your true SOC is less then 100% because it has been drifting) while you are sleeping and then continues getting you to true 100% until you unplug. Or, if you are driving from one destination to another and your alternator is charging the battery...if your monitor gets to 100% (when your batteries are actually at less than 100%) the batteries will continue to get closer to 100% as long as you are driving. This "erases" any of the drift delta that might have built up.
Also: Most battery monitors tell you the Voltage it sees on the batteries. From most 12v SOC charts you can see that 12.06v resting voltage corresponds to 50% SOC. So if you ever see your battery resting voltage at 12.06v REGARDLESS OF WHAT YOUR BATTERY MONITOR SAYS percentage-wise, you should charge your batteries. Likewise, when your batteries are truly fully charged to 100% they will likely read ~12.7v at rest. If your monitor says it is 100% full but your batteries are only at 12.4v or 12.5v then you should continue charging until you get all the way up to 12.6-12.7v at rest. If your batteries never get there, then there is likely a problem with your monitor voltage reading (you can test by putting a voltmeter directly on the batteries) or a problem with your batteries.
-Chris
I can see how IN THEORY you could have an issue if every time you charged your batteries you immediately STOPPED charging once your monitor said you are at 100%. If you were in fact not 100% full (...let's say the true SOC is only 95% even though your monitor incorrectly says 100%) and then you used your battery down to 50% as stated on your monitor, you would in actuality only be at 45% SOC. Then if you charged back up to what you thought was 100% and immediately stopped charging once your battery monitor says you are at 100% but in fact if it once again fell short you might only be at 90% true SOC. If you repeated this many times in a row, then I can see you'd have a problem. (drift)
Perhaps a good rule of thumb would be to make it a habit to continue to charge your batteries for a little while beyond the time when your monitor says you just reached 100%. Or, if your monitor shows amps going into your battery while charging, you can get a sense that way as to how much "charging" is still happening once your monitor reaches 100%.
This "drift" problem gets fixed/reset anytime you do have a situation where your charger stays on/active for a long enough time after your battery monitor says you are at 100%. For example, if you do find yourself plugged in at a campsite and your monitor reaches 100% (even if your true SOC is less then 100% because it has been drifting) while you are sleeping and then continues getting you to true 100% until you unplug. Or, if you are driving from one destination to another and your alternator is charging the battery...if your monitor gets to 100% (when your batteries are actually at less than 100%) the batteries will continue to get closer to 100% as long as you are driving. This "erases" any of the drift delta that might have built up.
Also: Most battery monitors tell you the Voltage it sees on the batteries. From most 12v SOC charts you can see that 12.06v resting voltage corresponds to 50% SOC. So if you ever see your battery resting voltage at 12.06v REGARDLESS OF WHAT YOUR BATTERY MONITOR SAYS percentage-wise, you should charge your batteries. Likewise, when your batteries are truly fully charged to 100% they will likely read ~12.7v at rest. If your monitor says it is 100% full but your batteries are only at 12.4v or 12.5v then you should continue charging until you get all the way up to 12.6-12.7v at rest. If your batteries never get there, then there is likely a problem with your monitor voltage reading (you can test by putting a voltmeter directly on the batteries) or a problem with your batteries.
-Chris
