# SLA (Sealed Lead Acid) battery charging specifications



## alvin (Jul 26, 2008)

There is a charge control IC for sealed lead acid batteries called UC3906.

In the application notes the bulk charge is held at the Overcharge rate until the amps have dropped to 10%. It also compesates for temp.

It will adapt to larger strings of cells and can control a low voltage cut-off.


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## PStechPaul (May 1, 2012)

OK, I appreciate that. I found a link to the app note:
http://asmith.id.au/files/uc3906-battery-charger.pdf

I also found discussions:
http://e2e.ti.com/support/power_management/battery_management/f/179/t/177944.aspx
http://www.microchip.com/forums/m639754-print.aspx

And other ICs from TI:
http://www.ti.com/product/uc3909
http://www.ti.com/lit/ds/slus929c/slus929c.pdf
http://www.ti.com/lit/ug/sluu464/sluu464.pdf

So I guess now I need to incorporate this information into my SLA BMS. Or maybe just get one of these ICs.

Thanks.


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## onegreenev (May 18, 2012)

Have a look here:

http://www.evdl.org/lib/index.html


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## PStechPaul (May 1, 2012)

That's some good information. I took a bit from here and there, and came up with the following specification:


```
[FONT=Courier New]Initial charge at 0.2C for 5 hour nominal charge time[/FONT]
[FONT=Courier New]12V 12Ah initial charge at 2.4A[/FONT]
[FONT=Courier New]Maintain charging until voltage reaches 2.4-2.5 Vpc = 14.4-15 VDC[/FONT]
[FONT=Courier New]At 14.4V battery is 70-80% charged[/FONT]
[FONT=Courier New]Keep at 14.4 volt until current = 0.02C (240 mA for 12 Ah)[/FONT]
[FONT=Courier New]Float charge at 12.8-13.2V (or initiate new charging cycle at 12.5 volts (90%)[/FONT]
[FONT=Courier New]Voltages are based on 25C. Voltage changes by -0.003 Vpc/DegC. So 14.31V at 30C and 14.49V at 20C[/FONT]
[FONT=Courier New]SOC chart for open circuit voltage after 3 hours rest:[/FONT]
[FONT=Courier New]SOC   Vpc    V12[/FONT]
[FONT=Courier New]100%  2.116  12.700[/FONT]
[FONT=Courier New]90%   2.083  12.500[/FONT]
[FONT=Courier New]80%   2.070  12.420[/FONT]
[FONT=Courier New]70%   2.053  12.320[/FONT]
[FONT=Courier New]60%   2.033  12.200[/FONT]
[FONT=Courier New]50%   2.010  12.060[/FONT]
[FONT=Courier New]40%   1.983  11.900[/FONT]
[FONT=Courier New]30%   1.958  11.750[/FONT]
[FONT=Courier New]20%   1.930  11.580[/FONT]
[FONT=Courier New]10%   1.890  11.340[/FONT]
[FONT=Courier New]0%    1.750  10.500[/FONT]
```


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