[Elecraft] SLA Battery charge level

[G3VVT at aol.com]

In a message dated 11/12/04 23:24:04 GMT Standard Time,  
johnlon at sbcglobal.net writes:

According to the PowerSonic instruction sheet, after "bulk" charging  (< 
1.6 Amps for my 8 Amp Hr SLA), you are supposed to switch to about  14.2 
volts for "absorption" charging.  Once the current gets down to  80 ma, 
you can switch to a 13.8 volt "float" charge indefinitely if you  wish.  
Since you are drawing 80 ma at just 13.8 volts, my guess is  the battery 
is still charging.  It should slowly drop to quite a bit  less than that, 
maybe 30 ma or less when totally  charged.


The "absorption" charging or otherwise called "equalise charge" after the  
main charging cycle is complete is to equalise the voltages across the  
individual cells and get the maximum possible energy into the battery. With  solar 
power systems we found that this period was better restricted to about 15  
minutes when done daily to save overheating of the battery and consequently  loosing 
electrolyte. Extended overcharging with SLA's greatly reduces their  service 
life.
 
When the battery is on "float" which for a small 12V SLA is commonly done  at 
13.8V, the current will come out at usually 25 to 50mA depending on the  
battery. This can be left on indefinitely as is common with fire alarm panel  use, 
though will eventually reduce the capacity of the battery by a  degree.
 
Bob, G3VVT