Dry camping with furnace on
I was dry camping this weekend and had to put the furnace on for the first time. I was worried that I would kill the battery if I ran the furnace overnight. I was right :(. The house battery was ...
Forum Discussion
So you got misled by the voltage method of estimating state of charge. Me, too! I killed my house batteries on our first long trip.
The voltage on the batteries is artificially high for at least 8 hours after all charging is stopped. With the voltage method you can't tell how much charge you have until it is too late to be useful - the batteries will already be damaged. To see the problem charge your batteries, then with no significant load measure the voltage every hour or so for at least 8 hours. This is what I found:
Note that the battery is 100% charged for the whole time and all those different voltages. It seems it takes hours for the "surface charge" to be absorbed. So you see, the fully charged voltage is well over 12.6 volts for the first hour or three and a 12.6 reading could mean half discharged, where damage begins. I have to wait about 12 hours for the voltage chart (12.6 is 100%, 12.0 is 50%) to be accurate. But do check out your own batteries for yourself. An expert here posted that this effect varies with the type and age of the batteries.
The only easy way to know the state of charge is to install a battery monitor. If money is no object go for an American made name brand such as Trimetric. If you would rather get a bargain from China, this is a higher current version of the one I have (looks like it is improved with the shunt separate): Ebay item
Mine is the 30 amp version with shunt built into the monitor
The trouble with it is that the monitor needs to be located near the batteries and the terminals are too small for heavy wires.
The voltage on the batteries is artificially high for at least 8 hours after all charging is stopped. With the voltage method you can't tell how much charge you have until it is too late to be useful - the batteries will already be damaged. To see the problem charge your batteries, then with no significant load measure the voltage every hour or so for at least 8 hours. This is what I found:
Note that the battery is 100% charged for the whole time and all those different voltages. It seems it takes hours for the "surface charge" to be absorbed. So you see, the fully charged voltage is well over 12.6 volts for the first hour or three and a 12.6 reading could mean half discharged, where damage begins. I have to wait about 12 hours for the voltage chart (12.6 is 100%, 12.0 is 50%) to be accurate. But do check out your own batteries for yourself. An expert here posted that this effect varies with the type and age of the batteries.
The only easy way to know the state of charge is to install a battery monitor. If money is no object go for an American made name brand such as Trimetric. If you would rather get a bargain from China, this is a higher current version of the one I have (looks like it is improved with the shunt separate): Ebay item
Mine is the 30 amp version with shunt built into the monitor
The trouble with it is that the monitor needs to be located near the batteries and the terminals are too small for heavy wires.
