Comments on: Power Craft https://blog.nearfuturelaboratory.com/2007/08/05/flavonoid-power/ Clarify Today, Design Tomorrow Fri, 18 Aug 2017 18:02:59 +0000 hourly 1 https://wordpress.org/?v=5.5.1 By: Julian https://blog.nearfuturelaboratory.com/2007/08/05/flavonoid-power/#comment-217 Thu, 06 Sep 2007 23:17:26 +0000 http://www.nearfuturelaboratory.com/2007/08/05/flavonoid-power/#comment-217 That’s a good idea. I actually ended up knuckling under and adding a 12mm coin cell battery holder to the design so that the RTC would continue to keep time even if the battery went flat. I also went a bit bonkers and added a bunch of things to the power management part of the design — easily over design in hind sight, but I wanted to button the thing up.

Details are here:

http://www.nearfuturelaboratory.com/2007/09/06/the-benefits-of-zealous-design/

]]> By: Steve https://blog.nearfuturelaboratory.com/2007/08/05/flavonoid-power/#comment-216 Thu, 06 Sep 2007 05:55:29 +0000 http://www.nearfuturelaboratory.com/2007/08/05/flavonoid-power/#comment-216 Have you considered using smaller batteries of the same total volume and flip-flop the batteries? In this arrangement, one of the batteries is always charging while the other is powering the RTC and the rest of the board. I use LiPo cells (flat pack Union batteries) ranging from 100mAh to 2000 mAh for most of my battery operated projects. I was putting together a project one day and didn’t have one of the 2000 mAh batteries that I needed, so I decided to use 2 1000 mAh batteries in parallel. The project wasn’t a big power user (120 mA peak), but I like the fact that the larger capacity batteries give me very long run times between charges. While hooking everything up and trying to figure out what the discharge/charge cycle was going to have to be, I realized that charge time for one cell (using a MAX1555 and USB power) was less than discharge time. I was also in trouble at that point because the MAX1555 is designed to charge a single LiPo cell and I’ve learned that with LiPo cells you follow the rules or you risk your project (and possibly your work bench). So with a couple of changs to how I use the battery monitor in my code and a bit of rewiring, I was able to reduce the power requirements when the operating battery reached a low threshold, switch in the fresh battery (still in parallel as far as the project was concerned) and switch the now depleted battery over to charge. I still have some problems with this setup if the project runs at peak for too long. The discharge time is less than the charge time and it switches to a not fully charged battery. The whole project then goes into what I call battery pendulum mode. The maximum voltage in both batteries will eventually get to the low voltage tthreshold and the only thing going on is battery swithcing. I’ve partially solved the problem by utilizing the small LED on the breakout board of the MAX1555, The LED goes out when the battery is fully charged. I placed a photodetector on the board and when the LED goes out, I log the date/time (project has a GPS receiver that provides date/time data). When I detect a battery low threshold and go into the battery switch routine, I compare the current date/time with the stored charge end date/time and log the difference. If the discharge time gets too close to the charge time (time representing “too close” still being determined). I have to make a decision to reduce power or call for help (alarm to indicate that the system needs to be plugged into a proper wall wart for a while to top off both batteries.

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