What do you use/recommend for battery powering 3.3V or 5V projects... - Page 1
Forum section: electronics / projects

author: alank2
author_rank: Super Contributor
timestamp: January 15, 2016, 09:51:37 pm
content: I've done a SMPS with a higher voltage than I needed with an 8xAA type battery pack before, but there are so many batteries you can choose from.A solution that uses power from USB when plugged in and charges an internal battery would be pretty cool.What do you guys use/recommend?

author: Fungus
author_rank: Super Contributor
timestamp: January 15, 2016, 10:06:01 pm
content: This+ a 18650 battery + a DC buck/boost to the voltage you require (egthis).nb. eBay sellers picked at random. Lots of sellers have those items.PS: Don't buy a 18650 battery with the word "fire" anywhere in the name. Just don't. Good 18650 batteries cost $10 or more, each.

author: mariush
author_rank: Super Contributor
timestamp: January 15, 2016, 10:18:26 pm
content: Microchip has a bunch of chips that can take power from USB and charge a lithium battery:http://www.microchip.com/pagehandler/en-us/technology/batterymanagement/See for exampleMCP73811orMCP74831or see a whole bunch of chips in various packageshere.From there, I guess it depends... if your product uses 3.3v and low current consumption, i may be tempted to use a linear regulator, for 5v or anything high current it would be worthwhile investing in a buck or a boost circuit - plenty of good high efficiency switcher ICs out there.Browse the regular stores, Digikey, Mouser, Farnell/Newark , TME etc

author: alank2
author_rank: Super Contributor
timestamp: February 04, 2016, 03:40:02 pm
content: Does anyone have any comments on 2xAA vs a single 18650. Could be for 3.3V or 5V. I'm looking for simplicity so perhaps the 2xAA where you could just use alkaline or some LSD nimh would be better.

author: Fungus
author_rank: Super Contributor
timestamp: February 04, 2016, 04:24:43 pm
content: Quote from: alank2 on February 04, 2016, 03:40:02 pmThat works too, although I'd use 3xAA for 5V. You'll need a suitable DC buck/booster.The advantage of the 18650 setup is that you can recharge it using a USB cable.

author: rob77
author_rank: Super Contributor
timestamp: February 04, 2016, 05:00:08 pm
content: i use MCP1624 or MCP1640 for single or 2 alkaline batteries to power 3V3 or 5V stuff. it's a small footprint sot23-6 boost converter (and goes down to 0.6V input - sorry bateriser, no room for you here either)

author: Fungus
author_rank: Super Contributor
timestamp: February 04, 2016, 05:29:07 pm
content: Do you build your own boost converters? They're seriously cheap to buy.

author: uncle_bob
author_rank: Unknown
timestamp: February 04, 2016, 05:47:02 pm
content: HiOne thing to take a look at:Do you even *need* a regulator in your project?Supply voltage ranges on some parts have been getting wider and wider over the years. You can find chips that are quite happy running on anything from 3.6V down to < 1.8V. That pretty much covers the whole range from "brand new pair of AA's from Walmart" right down to dead battery, time for more.Bob

author: alank2
author_rank: Super Contributor
timestamp: February 04, 2016, 05:59:18 pm
content: Bob - Good idea - I was pondering that too. You could use 3xAA for a 5V project and it could run down to 3V or so and still work fine, no boost required.

author: uncle_bob
author_rank: Unknown
timestamp: February 04, 2016, 06:14:05 pm
content: Quote from: alank2 on February 04, 2016, 05:59:18 pmHiBe sure to take a look at the *max* voltage for your battery chemistry. I spend so much time looking at nearly dead batteries that I often forget just how much they put out when brand new. That said, 2 for 3.3V and three for 5V is not likely to get you in major trouble. You only need to stay under the very big print "max allowed voltage" for the time small amount of time the battery still puts out it's full voltage. I seem to remember 1.56 volts per cell as being a pretty good number to use. I'm sure others will yell at me if that's wrongBob

author: alank2
author_rank: Super Contributor
timestamp: February 04, 2016, 06:19:15 pm
content: I've seen some alkalines put out 1.64V when very fresh.

author: rob77
author_rank: Super Contributor
timestamp: February 04, 2016, 07:15:56 pm
content: Quote from: uncle_bob on February 04, 2016, 05:47:02 pmif you don't mind the much lower max clock frequency for many MCUs at lower voltages, then it's a way to go.

author: Fungus
author_rank: Super Contributor
timestamp: February 04, 2016, 08:07:48 pm
content: Quote from: alank2 on February 04, 2016, 06:19:15 pm2x1.64 = 3.283x1.64 = 4.92No problem!

author: mariush
author_rank: Super Contributor
timestamp: February 04, 2016, 08:22:11 pm
content: Quote from: Fungus on February 04, 2016, 08:07:48 pmDepends on the mcu he uses. Some are 20+ Mhz from 3.6v and up, 12+ Mhz from 2.5v and up or something like that, less Mhz for lower voltages.If he needs fast mcu, he may need 5v. He may also need more than 3.3v for some i2c or spi devices that are designed for 5v and consider a digital 1 anything above a threshold, which could be as high as 3.7-4v

author: uncle_bob
author_rank: Unknown
timestamp: February 04, 2016, 11:56:52 pm
content: Quote from: rob77 on February 04, 2016, 07:15:56 pmHiThere are indeed some families of parts that claim the same frequency range (say 48 MHz or 120) at 1.7V as they do at 3.6V. I suspect that I would pick one of them if I was really worried about max CPU horsepower at zero voltage. Fortunately they also have nice things like sub 1ua current drain in low power modes so they are ok in that respect as well.Bob