[TriEmbed] Sealed Lead Acid Batteries - how low will they go?
Shane Trent
shanedtrent at gmail.com
Sat May 30 10:03:47 CDT 2015
Chip,
Finding a good charger is a challenge. Most well designed controllers are
build for large systems and are not a good size or budge match for your
project. One issue with most small controllers/chargers is they do not
adjust for battery temperature. Not a big problem for a charger in your
office but guaranteed to compromise a battery mounted in an outdoor
enclosure (over-charged on hot days and under-charged on cold days). I do
not know of an off-the-shelf charger/controller that is a good fit.
Depending on the resources left on the Arduino, you could add the charge
controller to your code. It should be pretty simple (your system has power
to spare so MPPT would be overkill), just set the output voltage based on
battery temperature and cut back to the float voltage once you hit the
desired maximum charge voltage. You only need the charge controller when
the panel is powered so power consumption should not be an issue. I would
enjoy working with you on the charging aspects if you want to go that way.
It might be fun to adapt a Pololu DC-DC converter to serve as boost
converter/controller that would even let you keep your existing solar
panel, just use the Arduino PWM to set the output voltage of the boost
converter (temperature adjusted of course). I have used the Pololu boost
converters on a couple of projects and have been very please with their
performance. Pololu rocks.
Here is are a few notes from East Penn Manufacturing on charge voltage vs
temperature for SLA batteries.
Gel Charge and Float Voltages at Various Temperature Ranges
Temp. Charge Float Temp.
°F Optimum Maximum Optimum Maximum °C
≥ 120 13.00 13.30 12.80 13.00 ≥ 49
110–120 13.20 13.50 12.90 13.20 44 – 48
100–109 13.30 13.60 13.00 13.30 38 – 43
90 – 99 13.40 13.70 13.10 13.40 32 – 37
80 – 89 13.50 13.80 13.20 13.50 27 – 31
70 – 79 13.70 14.00 13.40 13.70 21 – 26
60 – 69 13.85 14.15 13.55 13.85 16 – 20
50 – 59 14.00 14.30 13.70 14.00 10 – 15
40 – 49 14.20 14.50 13.90 14.20 5 – 9
≤ 39 14.50 14.80 14.20 14.50 ≤ 4
To compensate for battery temperature not at 20°C, subtract 0.005 V/cell
for each 1°C above 20°C; add
0.005 V/cell for each 1°C under 20°C.
Shane
On Sat, May 30, 2015 at 12:06 AM, Chip McClelland <chip at mcclellands.org>
wrote:
> Shane,
>
> Thank you for the great information. Based on this, and my desire to see
> how long this run-down test will last, I will program the Arduino to shut
> down the test at 11.9V. Going forward, to extend the life and account for
> temperature effects, I will need to be more conservative.
>
> One of the advantages of the Adafruit Solar option was I could use their
> charge controller and all I had to do was regulate the voltage and measure
> the battery’s % charge. In this setup, I will need a 12V panel and a new
> charge controller circuit. I found one here
> <http://www.electroschematics.com/6899/12v-ldo-solar-charge-control/> but
> please let me know if you can recommend anything better.
>
> Thanks again,
>
> Chip
>
>
> On May 29, 2015, at 8:25 PM, Shane Trent <shanedtrent at gmail.com> wrote:
>
> 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/
>
>
>
--
A blog about some of my projects. http://fettricks.blogspot.com/
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