Mixing 18650's for controlled 12v output

Sorry that this isn't necessarily a flashlight related question (I am quite the Flashlight junkie!), but figured this was a good place due to 18650 experience.

Long story short, I have a low power audio amplifier that runs off of 12volts @ 2amps. I was using a car battery with a 3amp fuse in between to power the stereo which worked quite well! However I want to replace that giant car battery with a set of 18650's. The plan is to run two sets of 4x - 18650 in series, and then use a step down converter to drop the 14.8v or so down to 12volts.



So my question basically is, in this sort of setup, will mixing up two different kinds of 18650's be an issue since I am using a step down converter to regulate the power output?

I have two different sets of 6x 18650 batteries that I'm hoping to use for this.

Link to Amplifier for info: http://www.amazon.com/gp/product/B00721Z1AE/?tag=cpf0b6-20
Link to Step Down Converter for info: http://www.amazon.com/gp/product/B00OZGVL4O/?tag=cpf0b6-20

Conventional wisdom is to just get a 'matched' set of cells of the same make/model/batch/health and run those. You can get quality cells for as little as $5 bucks, from places like FastTech, Illumination dot come, or Mountain Electronics.

That's $40-$50 depending on final price and you don't have to worry about it. You don't even have to buy the better, top of the line models.

If you're going to be mixing various types, do runtime tests for say an hour and then measure your cells to see how they're performing, but the cost for new, fresh and similar cells shouldn't be prohibitive.

Chris

Why not use an 18650 powerbank? e.g. this one (whose price recently dropped from $21 to $14). Populate it with 6 decently matched 18650s (e.g. laptop pulls) and you are good to go. It also can function as a UPS, but it has slow (1s) transfer switch to battery power. This will also take care of protection and balance charging (not clear how you planned to do that for your DIY pack).

Alternatively, you could use a laptop battery as a universal power source, e.g. see here.

Forgot to mention that I'd be used the iMAX B6 to charge the batteries:
http://www.amazon.com/gp/product/B005EF15Q4/?tag=cpf0b6-20

Guess I was shooting for the 2x 4-series array so I could easily get the 12volts, but also have some decent running time.

I'm a bit poor at the moment, so was trying to keep the costs low. Was given a busted laptop, and pulled 6 good 18650 cells out of it (pink cells with "TD18650 2000mAh EI15 EJ13" cells in them), and bought what I was hoping was a matching one off ebay for $11, but that one came with 6 blue cells with "18650 6C20715 505483" and the letters "CJ" on them. The last set of numbers on the blue cells changes so I imagine that's a bit of a serial number. Haven't really found any info on the cells so far in my searches.

Image of the batteries I pulled, 6 of each:

Well, I don't know how old you are, but I remember the 70s show Thrill Seekers with Chuck Connors. It was pretty funny, for the time.

Those cells look to be generics and well...as they say in Vegas, 'all bets are off.'

If you try and match them with your B6, just go in baby steps once you start using them and monitor carefully. Don't start blasting the music at '10' for hours on end.

The only issue would be whether to use 4 pinks in series and then four blues, or to mix and match them.

Don't know, but Google Thrill Seekers.

Chris

FWIW the pinks came out of an original HP battery, the blues out of a ebay generic replacement. The HP was labelled as 10.8v and 4800mAh for the 6 cells (2x 3-in-series), the generic was labelled 10.8v and 5200mAh.

It looks like the blues are CJ brand and seem to be reputable enough:
http://www.candlepowerforums.com/vb/showthread.php?403416-Help-me-identify-these-18650


I was about to just order and try out one of the cheap Power Bank's that Guass163 posted, but in the specs, the 12v output seems to be rated at 0.6Amps? I know the amplifier is going to want to pull 2amps.

pacodeth said:

I was about to just order and try out one of the cheap Power Bank's that Guass163 posted, but in the specs, the 12v output seems to be rated at 0.6Amps? I know the amplifier is going to want to pull 2amps.

Click to expand...

Not true. I linked to the Aili-119, which can output 3.3A, more than enough for your needs. You must have somehow stumbled upon its baby brother Aili-116, which sells for half the price (about $7 on eBay).

In your laptop battery pulls, CJ is Guang Dong ChangJiang Storage Battery Co. They are not a top-tier manufacturer.

Gauss163 said:

Not true. I linked to the Aili-119, which can output 3.3A, more than enough for your needs. You must have somehow stumbled upon its baby brother Aili-116, which sells for half the price (about $7 on eBay).

CJ is Guang Dong ChangJiang Storage Battery Co. They are not a top-tier manufacturer.

Click to expand...

you got that right.
looks like the website is hacked.
this is what i got when i clicked on a product.
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Gonna give the Aili-119 a try, put in an order for one. Man I wish it was available locally (in the states) even for a bit more so I wouldn't have to wait a month on shipping from China. There doesn't seem to be anything comparable in that price range however. I'm hoping that it can do the 3amps when running at 12volts. I know alot of them would kinda say the same thing, about the max amps it could output, but that was when running at 5volts, and the amperage constraints went down as the volts went up.

Also decided to give a OEM Dell 9cell battery a shot, as evidently the Dell's are generally good at providing quality/name brand 18650's. At least then I'll have enough to build my 8 cell array with one type of battery.

If that Aili box works however, I can use it with one of the 6 cell batteries I already have, and then swap it out with the other 6 cell set.

Don't worry, it will do 3A since I have used it at more than that. The eBay seller claimes to use ePacket shipping to USA, which should take only about 10 days.

You can get more capacity by stacking 2 cells in each slot to get a 3s4p pack. This is especially easy if you leave the cells connected when you pull them from laptop batteries. With 12x 2800mAh cells you'd get a 124Wh pack.

Note that the powerbank does not include any cables. Both in/out jacks accept ubiquitous 5.5/2.1(2.5) barrel connectors, so if you don't have a cable at hand you can find them most anywhere. You can even build them quickly without soldering using CCTV jack/plugs that have screw-terminal blocks.

Yeah, finally taking a look at that LiPro charger I got, I realize that it didn't come with any sort of cables, or AC/DC Adapter, heh. So if I do my own block, I'll have to figure all that out. Looking forward to the Aili unit since I can let it do the charging.

I like the idea of saving money, making something with your own hands, and the gratification of it.

Every modern multi cell rechargeable Lithium battery pack I have seen, monitors and in some cases, charges each cell individually in it's own 'channel' as it is referred to. The reason they do this is for safety.

A good example is a cordless power tools battery. Some packs are only as good as it's weakest cell's charge limit, as it charges all the others to it's level. I have had to retire/replace many cordless tool batteries because the charger for them senses a defect in one of it's cells, and won't charge the whole pack. So in essence you throw away(recycle) a battery pack that contains only one or more bad, worn, and susceptible cell(s) within the pack. I mention this because there are a lot more computer battery packs cells that are being re-used, resold, reused and recycled.

Without using matching cells you risk what could be referred to as 'pass through' charging by the stronger cells of the "pack" while it's under load which can be very dangerous. At it's severeness, it can cause a fire and/or serious health concerns from venting fumes. At it's minimum excessive heat and premature cell failure(dead) of one or more of it's batteries within the pack.

One critical piece of information needed to determine if using grouped strings is safe is the individual cells 'C' rating. Each of the cells should all match each other. Example, a fully charged 2000 mAh 1'C' new battery, in 100% condition, should supply 2A at ~3.7V under load and be 100% depleted after ~<60 minutes. A 2000 mAh battery in 100% condition/charged that is rated for 2'C' should put out 4A 3.7V under load for ~<30 min before depletion.

On your amplifier build, check if your amp can be used in an automobile. They run at ~14.2V while the engine is running. If You use a "step converter" that can rob extra power from your pack builds runtime, and possibly inject interference into the amplifiers playback. You may be able to use 4 cell strings as the underload voltage should be less than the at rest string voltage.

I think two matching 3 cell series strings in parallel of matching 18650 =>1800mAh cells totaling 12.6V standing V would work depending upon the amplifiers low end operating voltage. Under a 12V 2A load you may only get ~100 minutes run time without totally depleting the pack's cells. Most unprotected cells suffer irreparable damage when depleted too low.

I would at a minimum be using a battery tester designed for the cells chemistry you use, and get/make multi battery holders for each string. Li-Lions rechargeable's are the easiest to work with and only require a good volt meter to measure the batteries fully charged voltage to determine compatibility of the individual batteries with each other in the string. All other battery chemistry's' require a tester rated for them.

IMO, Why not substitute a used smaller 12V lawn mower, ATV, Motorcycle, or an AGM battery used in computer Uninterruptable Power Supplies? Much easier, safer, and greater runtime? Using unknown batteries that You will only be able to charge individually outside of the pack you build is more difficult and riskier.

Hope You get a smaller solution working soon.
GL

Yeah after reading the messages here, I've decided to not try and mix the batteries. Just got a good condition 9-cell Dell battery pack in, that had 9 Samsung batteries in it. So will prolly try those out. I used the 6 matching batteries from the original HP battery pack (the yet to be ID'ed pink ones), and hooked them to the voltage stepdown to put out 12volts and tested it with the amplifier and seemed to work fine.

I was using a Car Battery, but that was a bit unwieldy. I had thought of picking up a smaller vehicle battery (like lawnmower and the like), but was assuming I could get better runtime/weight ratio from lithium 18650's.

And if I haven't said it already. Thank to everyone who has posted in here giving me help!

pacodeth said:

And if I haven't said it already. Thank to everyone who has posted in here giving me help!

Click to expand...

Please confirm batteries are at least 2000 mAh or greater matching cells in a single string. You may not have a problem, but at least read the post and threads below. They will give you an idea of a battery that has thermal runaway, ones that can get too hot from drawing too much current, and most importantly ones that are unbalanced in series as you're doing.
GL

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Alrighty, so using the batteries pulled from a Dell laptop battery (they were 2600mah Samsungs, all reading the same voltage), I pieced together my lil stereo using a fishing plastic case. Wired up two series of 4 to a molex connector from a computer, then the other end bridged positive and negative connectors into the voltage stepdown converter, out to a 3amp fuse, and finally into the amplifier.

Haven't done any tests to see how long they will run, that will be the next thing to figure out.