<div dir="ltr">Chip,<div><br></div><div>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.</div><div><br></div><div>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. </div><div><br></div><div>Here is are a few notes from East Penn Manufacturing on charge voltage vs temperature for SLA batteries. </div><div><br></div><div>Gel Charge and Float Voltages at Various Temperature Ranges<br></div><div><div><br></div><div>Temp. Charge Float Temp.</div><div>°F Optimum Maximum Optimum Maximum °C</div><div>≥ 120 13.00 13.30 12.80 13.00 ≥ 49</div><div>110–120 13.20 13.50 12.90 13.20 44 – 48</div><div>100–109 13.30 13.60 13.00 13.30 38 – 43</div><div>90 – 99 13.40 13.70 13.10 13.40 32 – 37</div><div>80 – 89 13.50 13.80 13.20 13.50 27 – 31</div><div>70 – 79 13.70 14.00 13.40 13.70 21 – 26</div><div>60 – 69 13.85 14.15 13.55 13.85 16 – 20</div><div>50 – 59 14.00 14.30 13.70 14.00 10 – 15</div><div>40 – 49 14.20 14.50 13.90 14.20 5 – 9</div><div> ≤ 39 14.50 14.80 14.20 14.50 ≤ 4</div></div><div><br></div><div><div>To compensate for battery temperature not at 20°C, subtract 0.005 V/cell for each 1°C above 20°C; add</div><div>0.005 V/cell for each 1°C under 20°C.</div></div><div><br></div><div>Shane</div></div><div class="gmail_extra"><br><div class="gmail_quote">On Sat, May 30, 2015 at 12:06 AM, Chip McClelland <span dir="ltr"><<a href="mailto:chip@mcclellands.org" target="_blank">chip@mcclellands.org</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div style="word-wrap:break-word">Shane, <div><br></div><div>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. </div><div><br></div><div>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 <a href="http://www.electroschematics.com/6899/12v-ldo-solar-charge-control/" target="_blank">here</a> but please let me know if you can recommend anything better.</div><div><br></div><div>Thanks again,</div><div><br></div><div>Chip</div><div><div class="h5"><div><br></div><div><br></div><div><div><blockquote type="cite"><div>On May 29, 2015, at 8:25 PM, Shane Trent <<a href="mailto:shanedtrent@gmail.com" target="_blank">shanedtrent@gmail.com</a>> wrote:</div><br><div><div dir="ltr">Chip,<div><br></div><div>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. </div><div><br></div><div>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.</div><div><br></div><div>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. </div><div><br></div><div>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. </div><div><br></div><div>Great technical reference about AGM and Gel batteries</div><div><a href="http://www.soligent.net/uploads/products/32669_3.pdf" target="_blank">http://www.soligent.net/uploads/products/32669_3.pdf</a><br></div><div><a href="http://www.eastpennmanufacturing.com/wp-content/uploads/Guide-to-Commercial-VRLA-Batteries-2007.pdf" target="_blank">http://www.eastpennmanufacturing.com/wp-content/uploads/Guide-to-Commercial-VRLA-Batteries-2007.pdf</a><br></div><div><br></div><div>I hope the information is helpful!</div><div><br></div><div>Shane</div></div><div class="gmail_extra"><br><div class="gmail_quote">On Fri, May 29, 2015 at 8:04 PM, Chip McClelland via TriEmbed <span dir="ltr"><<a href="mailto:triembed@triembed.org" target="_blank">triembed@triembed.org</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div style="word-wrap:break-word">To all, <div><br></div><div>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 <a href="http://app.ubidots.com/ubi/getchart/page/fwweXqpV5QlRbiZ8nzEvou4nNi8" target="_blank">link to the current voltage</a> of the <a href="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" target="_blank">12V battery</a> that has been running things.</div><div><br></div><div>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. </div><div><br></div><div>Any advice would be appreciated.</div><div><br></div><div>Thanks, </div><span><font color="#888888"><div><br></div><div>Chip</div></font></span><div><br></div><div>P.S. - the <a href="https://twitter.com/chipmc86/status/604435703653658625" target="_blank">LiPo Solar version </a> s now ready to make it’s public debut on the Greenway trails. </div></div><br>_______________________________________________<br>
Triangle, NC Embedded Computing mailing list<br>
<a href="mailto:TriEmbed@triembed.org" target="_blank">TriEmbed@triembed.org</a><br>
<a href="http://mail.triembed.org/mailman/listinfo/triembed_triembed.org" target="_blank">http://mail.triembed.org/mailman/listinfo/triembed_triembed.org</a><br>
TriEmbed web site: <a href="http://triembed.org/" target="_blank">http://TriEmbed.org</a><br>
<br></blockquote></div><br><br clear="all"><div><br></div>-- <br><div><div dir="ltr"><span style="font-family:HelveticaNeue-Light,'Helvetica Neue Light','Helvetica Neue',Helvetica,Arial,'Lucida Grande',sans-serif;font-size:16px">A blog about some of my projects. <a href="http://fettricks.blogspot.com/" target="_blank">http://fettricks.blogspot.com/</a></span><br></div></div>
</div>
</div></blockquote></div><br></div></div></div></div></blockquote></div><br><br clear="all"><div><br></div>-- <br><div class="gmail_signature"><div dir="ltr"><span style="color:rgb(0,0,0);font-family:HelveticaNeue-Light,'Helvetica Neue Light','Helvetica Neue',Helvetica,Arial,'Lucida Grande',sans-serif;font-size:16px">A blog about some of my projects. <a href="http://fettricks.blogspot.com/" target="_blank">http://fettricks.blogspot.com/</a></span><br></div></div>
</div>