RichardVowles 12 Posted December 30, 2012 Share Posted December 30, 2012 Looking for advice as software is my thing, I'm still pretty much new to hardware. It would seem that DC-DC Converters (Boost and Buck) would always be the preferred method to get the voltage you require as they are very low loss. Aren't regulators going to burn off a lot of wasted battery current? How do you guys deal with powering your battery operated projects for a long time at 3.3v? A project I'm wanting to work on is that I wanted to create a mesh network of cc2500's with attached water controlling solenoids and soil probes. Most solenoids are 9v or 12v, but i don't think a battery will last very long given the current required to keep it open. But when I look at DC-DC converters, they are pretty expensive - Adafruit (who are always more expensive I know) sell a drop-in regulator replacement for $US15. Are there other parts that do as good a job? Or is this something one would just design into a board? Any advice appreciated! Richard sirri 1 Quote Link to post Share on other sites
oPossum 1,083 Posted December 30, 2012 Share Posted December 30, 2012 How do you guys deal with powering your battery operated projects for a long time at 3.3v? Lithium (CR2, CR123A), Li-Ion, or Lithium thionyl chloride batteries and carefully selected components that will tolerate the voltage range of the battery so no regulator is required. As a practical matter a LDO voltage regulator is typically required with Li-Ion because the max cell voltage is 4.2V and most 3.3V components won't tolerate that. Sometimes a carefully selected diode can be used instead of an LDO. Switching regulators have various concerns such as cost, quiescent current, and actual efficiency (spec sheets promote the max not the typical). Quote Link to post Share on other sites
RichardVowles 12 Posted December 30, 2012 Author Share Posted December 30, 2012 And if you need to drive something at a higher voltage e.g solenoid, is it best to drive that with a different battery and an optoisolator/fet combination? Quote Link to post Share on other sites
abecedarian 330 Posted December 30, 2012 Share Posted December 30, 2012 Options would include: multiple battery packs, able to be routed in serial for high-voltage needs, and in parallel for low-voltage needs or multiple battery packs wired in serial for high voltage, then down-convert to low volt for the MCU. *disclaimer- I'm a noob and quite often, an idiot. Ignore me if I'm off base. Quote Link to post Share on other sites
SirPatrick 35 Posted December 30, 2012 Share Posted December 30, 2012 I am a big fan of using solid state relays when switching bigger loads from my MCU. Besides that though you can use FETS or just some heavy duty transistors Quote Link to post Share on other sites
GeekDoc 226 Posted December 30, 2012 Share Posted December 30, 2012 Options would include: multiple battery packs, able to be routed in serial for high-voltage needs, and in parallel for low-voltage needs or multiple battery packs wired in serial for high voltage, then down-convert to low volt for the MCU. *disclaimer- I'm a noob and quite often, an idiot. Ignore me if I'm off base. Also from a noob, but: I think tapping a subset of a series of batteries is discouraged. You end up draining cells at different rates, which causes problems. (EEs could explain much better.) Quote Link to post Share on other sites
abecedarian 330 Posted December 30, 2012 Share Posted December 30, 2012 My logic was based on the MCU and charging being provided for in parallel with the cells, but the "high voltage" system drawing power from the cells in series. Yes, it would be a logic/switching nightmare.... Quote Link to post Share on other sites
Lgbeno 189 Posted December 30, 2012 Share Posted December 30, 2012 Are you going to spin a board(s) for this? I've used small buck regs from alpha & omega and a boost from semtech. The efficiently is much better than a LDO or a diode and allows you to increase voltage without more batteries. Some also disable themselves when there is a very light load. Depending, sometimes the internal discharge of the battery is the biggest drain on power. For driving actuators like solenoids, hopefully the state that they will be in most of the time is undriven. So if there is a water valve to say water plants, it is on 1% of the time and off the rest. Then I would just use the uc to enable the boost reg when this actuator needs to be on. Quote Link to post Share on other sites
cde 334 Posted December 30, 2012 Share Posted December 30, 2012 You could always just give the mcu it's own batteries. The msp430 is just fine on a single cr2032 for a long time, and then use a real battery pack for the heavy solenoids. Quote Link to post Share on other sites
Lgbeno 189 Posted December 31, 2012 Share Posted December 31, 2012 Check this out https://www.sparkfun.com/products/10255 And http://www.digikey.com/product-detail/en/SC4503TSKTRT/SC4503TSKCT-ND/1249536 Regs should be $5 if implemented board level Quote Link to post Share on other sites
chibiace 46 Posted December 31, 2012 Share Posted December 31, 2012 lm317 Quote Link to post Share on other sites
RobG 1,892 Posted December 31, 2012 Share Posted December 31, 2012 There are switchers you can buy for under $3, see below http://www.ebay.com/itm/160816822389 http://www.ebay.com/itm/221087978222 Quote Link to post Share on other sites
username 198 Posted December 31, 2012 Share Posted December 31, 2012 If its a small battery application, generally a SMPS isn't worth it. What ya gotta worry about is quiescent current usage such that you don't drain the battery over time. For general purpose, the MCP1702 is a nice, easy, flexible, low quiescent current LDO for battery applications. SMPS are super handy for 12-24V battery systems where you need more than 1A draw at a low voltage rail. It always depends on the application. oPossum 1 Quote Link to post Share on other sites
Lgbeno 189 Posted December 31, 2012 Share Posted December 31, 2012 I agree with username for the most part. Only caveat is the comment about a freshly charged lipo being 4.2 volts then to fully discharge, take it down to 2.5 volts, this is where the tps61200 comes in handy. I'd just be careful about the drop across the LDO after it falls out of regulation which it will over the discharge of the battery. So many solutions, hard to choose. I think they all have merit. Quote Link to post Share on other sites
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