[TriEmbed] Sealed Lead Acid Batteries - how low will they go?

[Shane Trent]

Chip,

The end point voltage of a sealed lead acid battery is a little arbitrary.
The point is that you are reaching the point that there is little usable
energy left in the battery. At very light load you could keep running
longer but  you will be reducing the number of cycles you can get out of
the battery in it's operating life.

At moderate to heavy loads the battery voltage will generally recover once
you reach your cut-off voltage and remove the load. But when the voltage
recovers, the battery still contains very little energy and will quickly
drop the voltage under load.

The East Penn Manufacturing (I love their batteries, sold under many names
including Energizer at Sam's Club) documents below show the battery
capacity remaining at specific open circuit voltages. They show 0% at 11.80
volts. A table in the other document shows that stopping 12:00 volts would
extended your AGM battery expected life by over 33% (450 cycle at 100%
depth of discharge to 650 cycles at 80% depth of discharge.

Another issue often missed is that battery terminal voltage, charging
voltage and capacity all vary with temperature. So lab measured battery
operating time will probably not be matched in the field. Be conservative.
But it sounds like your solar cell is going to be giving your battery much
more power that you will be needing. If you hit only 50% depth of
discharge, your battery should last for 1000 cycles or around 3 years. Cut
it to only 25% depth of charge an you stretch the battery life to 6 years.

Great technical reference about AGM and Gel batteries
http://www.soligent.net/uploads/products/32669_3.pdf
http://www.eastpennmanufacturing.com/wp-content/uploads/Guide-to-Commercial-VRLA-Batteries-2007.pdf

I hope the information is helpful!

Shane

On Fri, May 29, 2015 at 8:04 PM, Chip McClelland via TriEmbed <
triembed at triembed.org> wrote:

> To all,
>
> Taking your collective advice, I have been testing a sealed lead acid
> battery with my cellular data logger.  It has been dutifully sending
> updates to Ubidots hourly for almost three weeks now.  Here is a link to
> the current voltage
> <http://app.ubidots.com/ubi/getchart/page/fwweXqpV5QlRbiZ8nzEvou4nNi8> of
> the 12V battery
> <http://www.amazon.com/UPG-UB1280I-Sealed-Lead-Batteries/dp/B0009GIKNE/ref=sr_1_1?ie=UTF8&qid=1432943993&sr=8-1&keywords=UPG+UB1280I+Sealed+Lead+Acid+Batteries> that
> has been running things.
>
> The question is, when do I stop the test?  I have read different articles
> stating that these batteries should be discharged only to 11.9V (but, this
> is a 12V battery - albeit one that started at 13.1V at full charge) and
> others that say that a full discharge is OK as long as you recharge the
> battery quickly.
>
> Any advice would be appreciated.
>
> Thanks,
>
> Chip
>
> P.S. - the LiPo Solar version
> <https://twitter.com/chipmc86/status/604435703653658625> s now ready to
> make it’s public debut on the Greenway trails.
>
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>


-- 
A blog about some of my projects.  http://fettricks.blogspot.com/
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