battery voltage
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battery voltage
is it true that you can't accurately read battery voltage with a meter? i got new batteries today and the guy said the only way to really measure charge is to measure the specific gravity of the water. if this is true, i am not so sure i understand why.
Lead Driver
Joined: May 2007
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From: Belair md
ask him how to do that on my gell batteries...... or even standard service sealed battereis. read it with a meter, load testing is the best way to check a battery though. you can have a battery that reads 12.4 volts but fail a load test
Cross-Country
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[quote=Eric_F250;7071166]
Yes, you can read battery voltage with a meter but it is just a snapshot. Voltage on a battery will vary if under charging, load or at rest.
Electrolyte is the liquid in a battery, most often sulfuric acid. Specific gravity is also just a snapshot of the batteries state of charge. Lower state of charge has lower SG. A battery that has been on the shelf a long time may have less than optimum SG and voltage reading.
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What Joe said is true - the only true indicator of how much energy a battery will give up is thru a load test. To add to that, a partially charged battery with good cells will do better on a load test that a fully charged battery with a weak cell. Often new batteries will do better on a load test after cycled several times.
Most of the off grid power systems we do for homes have large battery banks - 2000 to 5000 #. We use a lot of deep cycle 2 volt industrial cells with various series configurations to achieve 12, 24, and 48 volt nominal DC voltages. An inverter converts the stored power in batteries to AC during night and cloudy conditions. In addition, you can parallel series strings to achieve a desired capacity. The two batteries in your PSD are in parallel. You can check them individually with a multimeter to get an indication of what is happening. The voltage at rest should be nearly identical. If when cranking, the voltage on one battery drops more than another there is most likely a weak cell. There is no way to check the voltage on an individual two volt cell on a car battery - no external connections. THe SG will show lower on a weak cell. Believe it or not, a weak or bad cell will charge rapidly, will not store energy, and discharge rapidly.
We utilize a multimeter, hydrometer (measures SG) and load testing to diagnose battery problems. First we remove all charging to the battery bank and place the entire bank of batteries under load. Checking voltage on each cell can be done quickly with a multimeter so we do that first. There is no need to remove any series/parallel connections. A weak cell will show up with a reduced or no voltage under load. If all cells are close in voltage, we then check SG. There is a correlation between voltage and SG. You can have a good voltage but low SG from sulfation on the cellls plates. Sulfated plates reduces the battery's ability to store and give up energy. So, there is a place/time/use for a meter, hydrometer and load test. The above is most pertinent to deep cycle batteries but the basics also apply to automotive batteries.
Perhaps more than you really wanted to know??
Ron Stauffer
Montrose CO
PHP Code:
is it true that you can't accurately read battery voltage with a meter?
PHP Code:
i got new batteries today and the guy said the only way to really measure charge is to measure the specific gravity of the water.
PHP Code:
if this is true, i am not so sure i understand why
What Joe said is true - the only true indicator of how much energy a battery will give up is thru a load test. To add to that, a partially charged battery with good cells will do better on a load test that a fully charged battery with a weak cell. Often new batteries will do better on a load test after cycled several times.
Most of the off grid power systems we do for homes have large battery banks - 2000 to 5000 #. We use a lot of deep cycle 2 volt industrial cells with various series configurations to achieve 12, 24, and 48 volt nominal DC voltages. An inverter converts the stored power in batteries to AC during night and cloudy conditions. In addition, you can parallel series strings to achieve a desired capacity. The two batteries in your PSD are in parallel. You can check them individually with a multimeter to get an indication of what is happening. The voltage at rest should be nearly identical. If when cranking, the voltage on one battery drops more than another there is most likely a weak cell. There is no way to check the voltage on an individual two volt cell on a car battery - no external connections. THe SG will show lower on a weak cell. Believe it or not, a weak or bad cell will charge rapidly, will not store energy, and discharge rapidly.
We utilize a multimeter, hydrometer (measures SG) and load testing to diagnose battery problems. First we remove all charging to the battery bank and place the entire bank of batteries under load. Checking voltage on each cell can be done quickly with a multimeter so we do that first. There is no need to remove any series/parallel connections. A weak cell will show up with a reduced or no voltage under load. If all cells are close in voltage, we then check SG. There is a correlation between voltage and SG. You can have a good voltage but low SG from sulfation on the cellls plates. Sulfated plates reduces the battery's ability to store and give up energy. So, there is a place/time/use for a meter, hydrometer and load test. The above is most pertinent to deep cycle batteries but the basics also apply to automotive batteries.
Perhaps more than you really wanted to know??
Ron Stauffer
Montrose CO
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