expected normal voltage drop from load?
Is there a rule of thumb or guidance for an expected voltage drop based on amp load on a pair of 6V GC batteries? I was tinkering in my trailer this weekend and ran a 750 watt AC electric heater off ...
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6v GC have higher signficantly internal resistance and hence voltage drop than do 12V starting or marine or for that matter deep cycle batteries. 750W load is around 60-70A, a pretty good load for a pair of GC.
Here is what I and some others have found with GC batteries. Once they get below about 80%SOC, a load in the 750-1000W range WILL very often trigger the low voltage alarm on a inverter and have a voltage in the 10.5ish range. The fact that it rose to 12.5 volts w/o a load is IMHO a good indicator that the batteries are probably around the 75-80% SOC and you just found the reason that those who draw 75+ Amps from a battery bank either go with mutiple 12V or a bank of 4 GC. It also doesn't help that you were around freezing. AH capacity of a battery decreases at low temps, and internal resistance rises. All going in the WRONG direction if your trying to get a big draw from GC batteries.
So.... before you get real worried, get the batteries FULLY charged with a good charger, measure the SG on each cell. Good chance what you will find is that you know the main drawback to GC batteries.
4 GC with 550AH capacity won't give the cranking amps that I get out of a puny 70AH 12V starting battery for my diesel.
Here is what I and some others have found with GC batteries. Once they get below about 80%SOC, a load in the 750-1000W range WILL very often trigger the low voltage alarm on a inverter and have a voltage in the 10.5ish range. The fact that it rose to 12.5 volts w/o a load is IMHO a good indicator that the batteries are probably around the 75-80% SOC and you just found the reason that those who draw 75+ Amps from a battery bank either go with mutiple 12V or a bank of 4 GC. It also doesn't help that you were around freezing. AH capacity of a battery decreases at low temps, and internal resistance rises. All going in the WRONG direction if your trying to get a big draw from GC batteries.
So.... before you get real worried, get the batteries FULLY charged with a good charger, measure the SG on each cell. Good chance what you will find is that you know the main drawback to GC batteries.
4 GC with 550AH capacity won't give the cranking amps that I get out of a puny 70AH 12V starting battery for my diesel.
