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Old 09-02-2015, 11:55   #16
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Re: battery experts

Originally Posted by btrayfors View Post
Not quite, Stu. If the voltage is too high, the battery will take too much current and boil over and possibly do some serious damage to the battery.

I know you know this.

Don't exceed the recommended voltages when equalizing.

And, don't equalize unless you are there to monitor the process, including voltage and battery temp.

Thanks, Bill, I tried the "shortcut" and failed!

Thanks for the clarification for the OP.

Stu Jackson
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Old 11-02-2015, 11:31   #17
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Re: battery experts

Just FYI, the above statements that for a fixed charging voltage the current will be governed only by the battery resistance is not correct. The current does not reduce due to change in resistance.

The overall battery resistance is very nearly constant and does not necessarily increase with charge, in fact it is more likely to decrease.

Looking at it in closer detail, what you have is a charging source, say 15.5 volts. You have a circuit resistance (cables, battery resistance and charger source resistance) that is nearly constant. And you have a battery that is charging.

If the battery has a charge of 12.5 volts you only have 15.5 minus 12.5 = 3 volts pushing charge current into the battery so the current is 3 / resistance, not 15.5 / resistance.

In this formula the battery voltage increases as the battery charges so 15.5 - 14 volts for example, means only 1.5 volts is available to force charge in. THIS is the reason for charging current dropping off.

What is confusing is since you can only measure the voltage on the battery terminals, you can't measure the actual charge level. This terminal voltage measurement shows the total of the actual charge voltage PLUS the voltage drop across the internal resistance. The actual charge level is what you would see on the terminals after the battery has been off charge for 24 hours.

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