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Rooker23
Member
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# Posted: 18 Nov 2017 11:18am
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My charge controller will show 12.4V for example when I'm charging my laptop through a small inverter but as soon as I turn it off it jumps back to 13V. Which is the true state of battery charge?
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Mike 870
Member
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# Posted: 18 Nov 2017 11:33am
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Neither one actually. Under load the voltage will drop. During charge it will rise and read higher than it is. At rest, it takes some time to get a true reading. For most purposes, you can go about a half hour with no charge or discharge to get a decent reading. Then there’s the whole thing where voltage itself isn’t the best indicator of battery charge, but we won’t get into that.
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Rooker23
Member
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# Posted: 18 Nov 2017 10:29pm
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Also have a difference between controller and a monitor plugged into a 12v outlet.
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creeky
Member
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# Posted: 19 Nov 2017 01:41pm
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Good old lead. Voltage drop. Ha ha ha.
With lithium the voltage pretty much tells you where your charge level is at. Neat eh!
Of course resistance in wires, shunts, bus bars, meters, lugs will alter the reading on any system. Lead or lithium. If you see large voltage drops take your voltmeter and double check before and after connection points. You may have a bad lug, or ...
By example: Measured an install: .5v drop across the shunt. No idea why it was so high. The shunt was 12 years old. Maybe corrosion from lead acid fumes/humidity?
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