Boost or buck converter for Li-Po/Li-Fe? - Page 1
Forum section: electronics / projects

author: lufihengr
author_rank: Contributor
timestamp: June 14, 2015, 01:11:15 pm
content: So I want to make a usb power bank with a 5 volt output and was wondering which would be the best optionOption A: Have a single cell Lipo or Life battery with a boost converter to 5 volts, orPros: easy charging with only one cellCons: Slightly less efficientOption B: 2 or more cells in series and a buck converter down to 5v?Pros: Higher efficiencyCons: Cell balancing required when chargingPlease correct if my info is incorrect.Also if someone can point me to a boost or buck converter board from a reputable source that I can just pop in to a case with a battery, that would be great. Found one on dealextreme but I don't trust them very much.

author: con-f-use
author_rank: Unknown
timestamp: June 14, 2015, 02:15:17 pm
content: In the 1Amp range the efficiency difference between the most efficient buck and boost are not that great. I'd opt for a larger single cell and boost, which also means greater capacity.

author: lufihengr
author_rank: Contributor
timestamp: June 14, 2015, 03:12:11 pm
content: Quote from: con-f-use on June 14, 2015, 02:15:17 pmOk, thanks!

author: djQUAN
author_rank: Frequent Contributor
timestamp: June 14, 2015, 03:32:45 pm
content: There are lots of off the shelf power bank PCBs available in fasttech.com for very cheap, I have bought some a while back.Most already have built in chargers, boost converters and control uC, others have LED/LCD battery charge indicators etc.You'd just need a box to put it in. Not as fun as building your own from scratch though unless you want an easy way out

author: lufihengr
author_rank: Contributor
timestamp: June 14, 2015, 03:54:59 pm
content: Quote from: djQUAN on June 14, 2015, 03:32:45 pmWhich exact ones have you got?I would prefer to have a pre soldered board, as I don't believe I can solder such small components as reliably as a machine can :p And of course it is easier.

author: djQUAN
author_rank: Frequent Contributor
timestamp: June 14, 2015, 04:09:39 pm
content: I usedthis onewith six 18650 cells in parallel but when those failed, replaced them with four Li-poly cells. worked fine until the uC suddenly stopped working for some reason. Hard wired a flip flop and used it as a dummy charger/boost converter. The uC only does battery indication using the RGB led.I also have these but haven't made use of them. Wired them to a single cell and it works fine. Never had the chance to make a case for it.https://www.fasttech.com/products/0/10004229/1323101-sc-0202-0-8a-diy-mobile-power-bank-pcb-moduleThis I made a couple with a three 18650 battery holder and mounted the PCB in the middle slot using hot melt glue and cut holes for the LED and connectors. My dad still uses one to this day with two Samsung 18650 cells.https://www.fasttech.com/products/0/10004229/1323200-hp-123-1a-diy-single-usb-mobile-power-supply-pcbIf you want a different type, just search for "5v diy power supply" and there are lots more to choose from.https://www.fasttech.com/search?5v%20diy%20power%20supply

author: lufihengr
author_rank: Contributor
timestamp: June 14, 2015, 07:43:48 pm
content: Quote from: djQUAN on June 14, 2015, 04:09:39 pmThank you very much!E: What lips are you using right now? On fast tech there are some cheap LG 18650's but I don't know are they actually LG. Hobby king has some 1 cell flat lipos I thought would work?

author: djQUAN
author_rank: Frequent Contributor
timestamp: June 15, 2015, 12:34:30 am
content: I just used salvaged turnigy nano techs from a friend. I haven't tried other brands of 18650 cells from fasttech but have used many of their Panasonic 3400 cells and appear to be legit and works fine for all my uses (high power handheld lasers and flashlights)For Lipo cells, I don't think you can beat the selection and price that Hobbyking offers. Though I prefer original branded round 18650 cells for power banks as they are more robust and safer with the metal case especially for something that you'd carry around.

author: alank2
author_rank: Super Contributor
timestamp: June 15, 2015, 03:42:09 pm
content: What about a DC DC module like this:http://www.mouser.com/ProductDetail/Murata/LXDC44AAAC-169/?qs=%2fha2pyFaduheAo%2f7xQlv7Saft%252bbITEnw6TvqBuLakK4swUJeoIoRqw%3d%3d

author: lufihengr
author_rank: Contributor
timestamp: June 17, 2015, 01:38:42 pm
content: Quote from: djQUAN on June 15, 2015, 12:34:30 amOk so 18650 might be the way to go. Aren't they a bit lighter than flat Lipo's too?Quote from: DiligentMinds.com on June 15, 2015, 02:52:31 pmThe battery would be just used in the power bank. You don't need to do balancing if you have cells in parallel, right?Quote from: alank2 on June 15, 2015, 03:42:09 pmThat would work I guess. Do I need to worry about any other pins than GND, Vin, Vout, and EN? Will it just work if I put a switch from Vin to EN for on/off? Are the caps and resistor necessary? Sorry if the answer is obvious.

author: sacherjj
author_rank: Frequent Contributor
timestamp: June 18, 2015, 02:04:00 am
content: If you use LiFePO4, you don't have to worry about cell balancing for a dual cell setup. If they are both manufactured in the same run, they are fine. We are running a primary battery that is two LiFePO4 cells. You get a 6-7.2V battery that bucks down to 5V very well.The advantage is you get something that lasts for a decade of use, rather than a couple years.

author: eas
author_rank: Frequent Contributor
timestamp: June 18, 2015, 07:17:49 am
content: Quote from: sacherjj on June 18, 2015, 02:04:00 amIf you treat higher capacity lithium ion cells as if they have the capacity of a LiFeP04 you can get a lot longer life too.Moreover, LiFePO4s have a mixed track record on meeting their longevity promises.

author: lufihengr
author_rank: Contributor
timestamp: June 18, 2015, 08:00:28 am
content: Quote from: sacherjj on June 18, 2015, 02:04:00 amWhat brand batteries do you use? A123?Quote from: eas on June 18, 2015, 07:17:49 amIs it an issue with no name brands only, or is it a problem in the chemistry itself?

author: eas
author_rank: Frequent Contributor
timestamp: June 20, 2015, 10:49:45 pm
content: Quote from: lufihengr on June 18, 2015, 08:00:28 amIs it an issue with no name brands only, or is it a problem in the chemistry itself?Overall maturity of the cells and their application, I think. As of a couple years ago, cells of reputable manufacture experienced severly accelerated aging at elevated, but not unreasonable, charging, storage and operating temps. Things may have improved since then, but that wasn't so long ago. I'm not convinced the growing pains are in the past yet. They have their place, but people recommend them like they are good for all things.Meanwhile, its not like the other LiIon chemistries are standing still.

author: lufihengr
author_rank: Contributor
timestamp: June 22, 2015, 10:42:34 am
content: Quote from: eas on June 20, 2015, 10:49:45 pmOverall maturity of the cells and their application, I think. As of a couple years ago, cells of reputable manufacture experienced severly accelerated aging at elevated, but not unreasonable, charging, storage and operating temps. Things may have improved since then, but that wasn't so long ago. I'm not convinced the growing pains are in the past yet. They have their place, but people recommend them like they are good for all things.Meanwhile, its not like the other LiIon chemistries are standing still.That's interesting. I know that some Li-Ion chemistries are more sensitive to their operating temperatures than others, but I didn't know this about Li-Fe batteries. Good to know. I think it might be best to hunt down some Li-Co batteries, I believe those are the ones Tesla use in their cars and seem to work best under a wide range of temperatures. Thanks