(01-17-2016, 12:56 AM)Fr0z7y Wrote:(01-16-2016, 12:15 AM)paulieg Wrote: -- snip technical arguments ---
You seem determined to take the technical arguments I am making as a personal affront. Please don't. Firstly, it's not productive. Secondly, it's not congruent with the spirit in which I make them. Thirdly, I've already stated multiple times that I applaud you for taking the time to share your DIY project with the community.
All I've done is made a case for buying quality batteries because they are safer, perform better and end up costing less in the long run when used for demanding applications. I've supported that thesis with technical arguments to a degree which I consider sufficient. It is everyone's prerogative, including your own, to make their own choice based on the arguments presented. I do not intend to restate those arguments; the responses below are simply corrections to (largely technical) inaccuracies.
Quote: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.
This isn't a case of whether a brand is 'major' or not. Kingston is a 'major brand', but their sd cards are A- flash chips and controllers they buy from competitors. With batteries, there are companies that have the technology and manufacturing facilities to produce battery cells, from the high end (eg Pana, Sony, Samsung, LG) to mid-range and cheap (OEMs you're unlikely to have heard of). The more capable or safe chemistries like LiNiMnCoO2 are areas of active research and development and the big boys are the ones doing it - you're simply not going to get INR knockoffs that can compete at this moment in time. Additionally, the problem with no-name batteries is that no-one knows where the cells come from and what their performance is like. Even if you test some batteries from one batch and they're OK, there's every chance the next batch will be different because they've bought cells on the spot market, slapped a case and markings on them and sold them. There's simply no guarantee of consistency, which is why they don't publish datasheets (they don't have the data, they don't care and they wouldn't be able to guarantee conformance over time).
This isn't me making a case for buying Patek Philippe when a Seiko would tell the time just as well; it's me making a case for not buying a cat in a bag, because with batteries unless you know the specs and trust that every battery you buy conforms to them, you're losing money when you think you're saving it (for demanding applications at least). If not on performance and safety, then on lifetime.
Quote: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.
I found no reference to tests done on 'Toosell' 18650s anywhere. The flashlighters don't buy them, nor do the vapers from what I can see. They certainly haven't tested them. You haven't done a capacity test either, otherwise you would've posted the numbers when I brought the question up, therefore the 'testing' you've done is subjective and anecdotal. Even had you done such a test, there's 0 guarantee that the cells in a 'Toosell' battery someone buys today are the same ones as in the ones you bought and tested. There's no incentive to maintain standards - if they sell a catastrophically bad batch that even people who buy these batteries recognize as such (eg because they're now homeless and have soot all over their faces), they can just start selling 'Threesell' batteries tomorrow.
Quote: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.
I haven't bought anything from bestbuy or walmart in years and yes, they mark up their stock to make you pay for the privilege of going to a physical store and having the item in hand immediately. The idea that amazon itself buys anything off of ebay is laughable. Amazon does act as a platform for third party sellers and, yes, they can and do often charge an arm and a leg because plenty of people want to buy off amazon specifically because of prime, convenience etc - it's our responsibility to shop around and determine if we're getting the best deal. Amazon has a great line of Amazon-branded NiMh batteries they buy from an OEM and badge as Amazon Basics or something in that vein at a great price for example. I've just gotten a fantastic deal for genuine coin cell batteries from a third party seller on Amazon as well. As with any e-commerce platform, there are good and bad deals to be had.
Quote: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.
Very few people who have the means to test 18650s properly buy them off of ebay. Very few people who use 18650s for demanding applications buy them from ebay. Issues with many important characteristics such as usable lifetime surface well after the cut-off deadline for leaving feedback has passed. Simply stated, most people just want a rechargeable battery they can stick in a clock or a remote or something of that nature and, as long as it appears to work, they're satisfied. Given this, general feedback ratings in this case are not valid indicators of quality.
Quote: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.
That's certainly your prerogative. In any case, there are few failure modes for batteries that would be likely to result in damage to a tablet. I never said no-name batteries would fry your tablet, I just said that they're very likely a false economy.
Notwithstanding the above, someone's willingness to risk something valuable on the performance of a particular engineering solution has no bearing on the soundness of said solution - technical facts are objective and not an exercise in popularity or a function of confidence. There was once a man who attached a lot of helium balloons to his lawn chair and used this contraption to fly himself like an airship. His willingness to risk his life does not validate his engineering solution.
Quote: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.
Li-ion is a general classification that merely indicates that the charge is carried by lithium ions. Performance and safety considerations vary widely based on the chemistry used, which could be anything from LiCoO2 to LMnO to LiNiMnCoO2 etc. If we are to believe the markings on the batteries you linked, they're ICR which means a cobalt-based chemistry (LiCoO2).
There are plenty of cheap products by Chinese OEMs that are sold widely on the interwebs. Some are good or good enough, some are not. They're not being sold widely because they're good, they're sold widely because they're cheap and people buy them. More people buy Bieber albums than listen to Chopin, their relative merits are not a function of popularity.
Quote: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.
The 'long flat' batteries could be multiple li-ion 18650s (in fact, some laptop batteries can be used to salvage 18650s from) or they could be lipos. Lipos need to be handled differently than most common li-ion chemistries, so be careful there.
Quote: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).
Again, I'm all for this sort of thing - doing stuff yourself, finding deals and putting one over on companies with ridiculous markups on their products. I suspect that's very much the spirit in which most people backed this project. I've merely made the argument that for demanding applications, buying batteries of known quality and fit for purpose *saves money* most of the time. The people whose hobbies center on demanding battery usage, such as flashlighters, vapers and RCers, have long established this to be the case with extensive testing - they love to save money, so they won't buy anything because of a brand - they buy certain brand+models because they deliver the best value.
As for my plans, I have no interest in running pine64 on battery power as of right now. If I did (and I may in future), I'd wait to see what it actually pulls under various conditions before I made any definite plans. My intuition is that lipos are more appropriate in the general case. If I wanted to use 18650s, I'd use IMR (LiMn2O4) or INR (LiNiMnCoO2) and would be prepared to pay the extra money for it.
-p
