<div dir="ltr"><div><div>The subject of Lipo batteries and battery fuel guage were discussed at a previous TriEmbed meeting. For your application, I think it is overkill as what you are doing is constant - wake up, take a measurement, log it, and go back to sleep - so you should be able to determine the length of time a charge will last without it.<br><br></div>The issue with Lipos is that you should not overuse them so they go undervoltage, but why not go with one with builtin overcharge, overcurrent and undervoltage circuitry built in, like this one from Sparfun:<br><br><a href="https://www.sparkfun.com/products/341">https://www.sparkfun.com/products/341</a><br><br></div>They have a variety of sizes from from 40mah to several thousand mah, so you could first test your circuit with the smaller unit, determine how long it will last, and be able to better extrapolate out how big of a battery you would need to last for the amount of time you would need between charges.<br><br></div><div class="gmail_extra"><br><div class="gmail_quote">On Thu, Sep 18, 2014 at 1:11 PM, Charles 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">Michael, <div><br></div><div>Thanks for taking a look at the power supply thread, as my projects run on batteries, I have put some time into this.</div><div><br></div><div>Here are a few thoughts:</div><div><span style="white-space:pre-wrap"> </span>- Like you, my circuits draw a relatively small amount of current. I developed these tests at a higher current so they would not take a month to run</div><div><span style="white-space:pre-wrap"> </span>- your current regulator (<a href="http://ww1.microchip.com/downloads/en/DeviceDoc/20001826C.pdf" target="_blank">MCP1700-3302E</a>) is Linear so it will dissipate - read waste - power equal to the product of the difference between Vin and Vout time current (Eqn 6-1 in data sheet)</div><div><span style="white-space:pre-wrap"> </span>- This is where I started but I decided to move to a switched power supply for three reasons:</div><div><span style="white-space:pre-wrap"> </span>- They are battery omnivores - since the <a href="http://www.ti.com/lit/ds/symlink/tps63030.pdf" target="_blank">TPS63031</a> is both boost and buck and is over 90% efficient over a large range (1.8-5.5Vin) - I can throw all sorts of batteries at it</div><div><span style="white-space:pre-wrap"> </span>- As they are more efficient, they should throw off less heat - potentially a big deal since I put them in a box and bury them</div><div><span style="white-space:pre-wrap"> </span>- This supply can handle from very small 25uA to 800mA currents</div><div><br></div><div>As with all things in Engineering, there are some trade-offs I had to accept:</div><div><span style="white-space:pre-wrap"> </span>- more expensive</div><div><span style="white-space:pre-wrap"> </span>- QFN packaging - ugh</div><div><span style="white-space:pre-wrap"> </span>- weird and exotic new component required - an inductor - no really! There are a bewildering number of choices here!</div><div><br></div><div>Some suggestions:</div><div><span style="white-space:pre-wrap"> </span>- I would be happy to loan you my test rig which you could use to test your current power supply and compare it to the three I made. </div><div><span style="white-space:pre-wrap"> </span>- I added the Excel spreadsheet with the full set of tests and results to the posting on the <a href="http://triembed.org/blog/?page_id=234" target="_blank">Triembed.org</a> site</div><div><span style="white-space:pre-wrap"> </span>- I could give you a TPS63031 breakout board so you could test the supply in your circuit without the pain of soldering - I have some extras</div><div><span style="white-space:pre-wrap"> </span>- You could look at commercial options such as the little breakout boards from Pololu - I have <a href="http://www.pololu.com/product/2122" target="_blank">one of these you could borrow</a> if you like</div><div><br></div><div>Hope this helps. </div><div><br></div><div>BTW, my next step in my power supply obsession is to add a battery fuel gauge to the circuit so my Arduino can check it and so I could use LiPO batteries with more confidence.</div><div><br></div><div><br></div><div>Chip</div><div><br></div><div><br></div><div><br><div><div>On Sep 16, 2014, at 5:00 PM, <a href="mailto:triembed-request@triembed.org" target="_blank">triembed-request@triembed.org</a> wrote:</div><br><blockquote type="cite"><span style="font-family:Helvetica;font-size:12px;font-style:normal;font-variant:normal;font-weight:normal;letter-spacing:normal;line-height:normal;text-align:start;text-indent:0px;text-transform:none;white-space:normal;word-spacing:0px;float:none;display:inline!important">MCP1700-3302E</span></blockquote></div><br></div></div><br>_______________________________________________<br>
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