EEVblog Electronics Community Forum
Electronics => Beginners => Topic started by: Ranger14 on March 15, 2016, 03:57:29 pm
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I have been on the road alot lately with work and I have a nice stash of 18650 cells .. My plan was to make a 2 or more cell power bank with a single 2amp 5v usb in order my phone .. I have a couple power banks already but they can't handle a 2amp output.. But I am not sure whether to use a buck or boost converter ?? Also is it better for the cells to charge in circuit or use a battery holder and replace when dead and use the proper charger ???
Thanks
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If you have to ask this, then my suggestion is to use some off the shelf boards which handle the batteries. Lithium batteries are violent, they have to be handled with proper knowledge and care.
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If you have to ask this, then my suggestion is to use some off the shelf boards which handle the batteries. Lithium batteries are violent, they have to be handled with proper knowledge and care.
It's not that I have to ask but working on hopefully better build instead of tying all batteries together and using a single Cell charging circuit to charge a whole pack like most companies do ..
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Apparently buck converters would be generally more efficient: http://www.eetimes.com/document.asp?doc_id=1273121 (http://www.eetimes.com/document.asp?doc_id=1273121)
But if you were to use multiple cells in series the major disadvantage is that you have to manage charge balancing if you're going to do your own charging.
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These things are nothing like regular batteries, the cell voltage shouldn't drop
below 3.0 volts to avoid damage (better to stop discharging at 3.5 volts or so) and never charge higher then
4.2 volts to avoid explosion and/or blazing fires (better no more then 4.1 volts for a bit better safety margin and a longer life)
To be honest if you want simple go with something like these:
http://www.aliexpress.com/item/5V-2A-Dual-USB-Output-4x-18650-Power-Bank-Batteries-Pack-Case-Holder-USB-External-Mobile/32425962052.html?spm=2114.01010208.3.1.HP9dVh&ws_ab_test=searchweb201556_2,searchweb201602_1_505_506_503_504_10034_10020_502_10001_10002_10017_10010_10005_10006_10011_10003_10021_10004_10022_10009_10008_10018_10019,searchweb201603_9&btsid=ca9a653f-128d-4cdb-b6b2-34c796a363b8 (http://www.aliexpress.com/item/5V-2A-Dual-USB-Output-4x-18650-Power-Bank-Batteries-Pack-Case-Holder-USB-External-Mobile/32425962052.html?spm=2114.01010208.3.1.HP9dVh&ws_ab_test=searchweb201556_2,searchweb201602_1_505_506_503_504_10034_10020_502_10001_10002_10017_10010_10005_10006_10011_10003_10021_10004_10022_10009_10008_10018_10019,searchweb201603_9&btsid=ca9a653f-128d-4cdb-b6b2-34c796a363b8)
Not a fan of the cheap Chinese stuff but hey you could always mod it yourself if you feel like it.
Also note that before you parallel individual cells (that most if not all of these devices do)
the individual cell voltages must be within a couple of millivolts of each other, other wise the "fuller" cells
will charge the "emptier" cells with high currents (could be tens of amps).. :scared: