01-17-2016, 12:56 AM
(01-16-2016, 12:15 AM)paulieg Wrote: I was not commenting on your setup as a whole, although there are comments to be made - balancing may be desirable or mandatory for safety depending on the exact chemistry your 18650 uses (18650 is a form factor, not a chemistry specification), likewise with protection - protection is hard to do properly if you don't have the discharge curves and with cheap no-name batteries you never do. I was simply stating that buying el-cheapo batteries is invariably a bad idea for high discharge applications. Depending on the exact chemistry used, it may not be a fire risk but you might have brownouts or considerably shorter lifespan that makes these batteries more expensive than higher quality, well-branded ones. There's a huge amount of information online about this subject, so it's a bit pointless to rewrite it here. Suffice to say that certain communities like vapers (batteries powering atomizers) and flashlighters have done a huge amount of extensive testing on this, the upshot being that you have every opportunity to use their data to select appropriate batteries.
As a matter of simple math, generic chinese 18650s sold as 3000mAh usually turn out to be in the region of 1000mAh. Since they're usually only capable of 1-1.5C and the curve stops delivering much earlier, you're starting to butt up against it if you place a 2+A load on them. Since you're now running them harder and out of balance as well, chances are you're killing the lifespan and total capacity, screwing the curve even more (although I'm not sure if reduced capacity affects C rating for all chemistries - you need to check datasheets).
This isn't a dig at you and I think people posting their DIY projects and results is awesome. I'm sure people will find yours useful. I'm just pointing out that, in the case of batteries for high discharge applications, paying for quality ends up being cheaper in the medium to long term, safer and considerably more hassle-free.
-p
yes, i know, i did that research before i bought these from ebay. these aren't exactly "cheap" batteries. they aren't a "major" brand. i saw how many knockoffs there were and what brands to stay away from. in this specific application that i am using, there already is a protection circuit in play with the part that connects directly to the 18650's, which is the third part i listed.
your concerns about the 18650's with chemistry, voltage, amperage discharge, capacity, pretty much all of that, i have checked before i ever bought these in the first place. because there were a lot of batteries out there and the amount of batteries that people have been labeling as something else (like you are stating that they have different capacities than stated and what not, all of your concerns) i basically found a brand that looked solid. i tested it already to great lengths, and thats why i listed these for you guys.
the reason i do not usually buy from say, bestbuy, walmart, or amazon, is because they usually list products at 3 times the price they bought them for or with amazon they buy it from ebay and resell them for a hefty markup and they are the same thing you find on ebay.
each person i listed also has many transactions on record with a 98.5+ rating (given the amount of sales done already and knowing how some people will just leave negative feedback when it was their own fault) i listed those and bought those because i also know i am dealing with a piece of hardware that needed voltage/amperage protection and a steady stream of juice.
if im willing to use these on a 250$ almost irreplaceable tablet (due to the things i have on it and the funds available) i think it would be okay to hook it up to a 35$ mini computer through a very well put together protection circuit with a battery readout.
the chemistry of the batteries are lithium ion. if you do a quick search on ebay for toosell 18650, you will see the number of sellers that have them listed. if you do a search on google regarding them you will also see what im talking about there.
but aside from the batteries i listed, lets move onto the protection circuit i have posted here. that is for both usb charging for the 18650 lithium ion batteries and will protect the pine64 from overvoltage and overamperage. the circuit board there will allow you to use the same usb cable that you are using to plug into the pine64 to power it as you do to charge the batteries by simply using a regular tablet charger.
other similar batteries as the flat wide long batteries with built in circuit for this will cost about 20$ for about 7000mah give or take 5 or 6$. if you just want to buy a battery that's all in one that will just plug into it and charge it without having to go and build this like i am, you can buy it for about 25-30$ already put together, and it's also going to have about 4 of these 18650's in it, with basically the same circuit, in a case, you can also use it for a tablet/phone with i think about 10000mah give or take about 4000mah depending on who you buy it from and the brand of battery pack.
considering this is an SoC that we are all building and having fun putting together as well as making things to use for it, i decided to give you an idea on how to put together a battery pack that will be a bit fun to put together, no matter what batteries you use ( i do believe you can put an elongated flat battery hooked up to this if you really want to, although its made for the 18650 style batteries)
if you have a different suggestion regarding a battery pack, i'ld like to know your setup you plan on utilizing, with a parts list you plan to use, if you do plan on using one instead of a tablet charger (which provides 2.1a at 5v and is suitable to charge expensive tablets and phones).
