Do any of you know of a power supply that you can insert your own charged 18650s for emergency/power supplies out there? I’ve got several new old battery packs from before (thanks to those who alerted on this forum!) that could easily work together for a short period. I think they would be preferable to those old lead acid/AC battery units. It would be great to have a reasonable AC/USB/DC power supply from 18650s.
Worst case (if there are no good options for direct 3-4.5v to AC) you could look into pairing a 3-4.5v to 12v boost module with a common 12v AC power inverter.
The main problem is the massively inefficient conversion process. You would lose a lot of energy in the process. Your stock of 18650s wouldn't last long powering things like a fridge for instance.
There have been a few discussions along these lines in various threads over the years. Perhaps you could give us a clue what devices you have that need AC mains voltage?
For things like laptops for instance, where you are simply wanting to power an AC brick that drops the output down to a lower DC voltage for charging purpose, you would be better with a dedicated DC-DC converter. Perhaps you can consider using alternative equipment designed for 12V DC instead. There are several USB power banks out there that take 6 cells and offer a 12V DC output as well as the usual 5V USB. Also various DC-DC boost modules on Ebay if you are up for a little DIY.
If you are wanting to use 18650s as a base for AC inversion, then we can assume that you are planning to be away from mains supply for some time? How would you recharge them? Or perhaps you aren't planning to.
Mostly it would be an emergency power, and short term car camping power source. Yes, inefficient, but significantly less efficient as to save enough to buy a lead acid battery unit to use this way and recharge a few times/rarely? Devices like laptop, small fridge, etc. is what I would be planning to use it for.
Sure you could build a battery from multiple cells…but the charge pattern and vulnerability of Li Ion vs lead acid is a thing for concern
A. matched cells
B. proper charge pattern
C. current draw ability
I mean 3 Li Ion in series gives you approx 12vdc, a bunch of those in parallel could easily make a rather high mAh battery, but charging those cells properly and safely become and issue, and quickly counteract the cost effectiveness of lead acid vs multiple and properly charge Li Ion
Is it doable…sure…is it advisable in a DIY situation…probably not…unless you are aware of the dangers involved and have taken precautions to minimize the risk
Plus many electric motors DO NOT operate properly with cheap modified sine wave inverters, in order to prevent overheat and damage to electric motors a true sine wave has to be produced , on start up they draw MASSIVE current temporarily, but once going quickly drop back down to a much lower amp draw, for other solid state devices the modified sine wave is “ok” but only because that sine wave is rectified back to DC for the most part
Here…check out what some have done
Research, educate, then if you feel it necessary go for it…just remember Li Ion is VERY sensitive to misuse unlike lead acid that is very forgiving, but even those go kablooey if treated improperly
In case you haven’t notice…many here err on the side of caution…it’s safer that way 
I have an idea to replace UPS battery (12V 7Ah SLA) with 18650 pack. Never tried yet because I have not enough good cells.
most ups working battery mode in till 10.5V. charging voltage is CV/CC 13.8V
4 battery series. 16V CC/CV charge 4V each.
charging circuit can easily modified to 16V. some ups have preset to adjust CV
problem is cell balance.
when PC powered, UPS battery current range between 8A-12A for entry level pc.
Internal voltages from a computer are DC, the powersupply converts AC back to DC 3.3vdc, 5vdc, 12vdc, I wonder if it would be more efficient to either make or get a DC to DC regulator at those voltages…in fact you can already get them
But, they ain’t cheap (well not at “useable” watt levels anyway)
http://carnetix.com/P2140/CNXP2140.htm
12v Power Supply <-more info
Oh snap….DC-DC converter UPS 18650! OpenUPS2
OP, focus on getting a “safe” 12-14vdc high mAh power box (safe chemistry, protected, balancing of charge of the cells), once you get that a 100~400 watt inverter (for camping and other light duty use) is easy to find
Just get a Powersonic 12volt AGM battery of appropriate size for your needs and a suitable 120Volt inverter. Simple, safe, cheap, reliable and done.
( I have one of these at 6+ years old and still tests close to original capacity, only needs topping up every 3-4 months when not used)
Its good idea. But little complex. most motherboards need –5V/-12V supply too. some need only –5V. however this way more efficient.
Once I saw compaq computer that powered by Atom processor with external power supply like laptop. these are very easy to mod
Those carputer links I provided provide the correct voltages and have the ATX plug on them…plug and play more or less
I use one of the 12v PicoPSUs from mini-box for a little server and it works great. I’ve been thinking of making a little UPS for it that would fit in the case. If I were to do so, I’d swap out the 12v version for one of the models that support a wider voltage range so I wouldn’t need to regulate the voltage coming off the battery pack separately.
Personally, feeding an inverter to feed a standard AC PC PSU offends my sensibilities. Rather than going that route, I’d just buy a standard UPS and be done with it.
I have about the same problem. I have a ton of salvaged 18650 cells of varying quality but same chemistry. I am a beginner in electronics. The only good use I can see is to put them in a balancing-charger setup and use it as a power supply for a computer server a.k.a. UPS. DC-DC is enough. I don’t mind basic soldering but designing circuits is way over my head. What would you do with 70x 18650 in “ok” condition?
EDIT: I am thinking of individual cell charging+18650 holder for easy swapping. Any reccommendations on the PCB side? Do some have temperature controls? Miller ML102 looks nice but it but it will be quite expensive this way.
mixed cells in “ok” condition are best used in non demanding single cell devices.
to work well in series they need to be matched AND have a bms whose cost would negate any gains in reuse of your cheap or free cells.
getting 3 parallel groups matched from this mixed lot would be an exercise in futility.i have however opened used but still good packs and bundled all the cell groups in parallel for long runtime.like for a camp lamp.
I like this idea but the safe way to do it would be individually controlled cell banks that have a maximum draw and is designed for mismatched cells and for the chemistry the cells belong to, and i’m willing to bet no one has designed such a bank. So frankly i would not pursue this. The best thing to do is buy cheaper lead acid deep cycle batteries or a Tesla powerwall which is designed for this and has new matched cells with a proper control system.
Oh yes the wonderful PowerWall. Fun fact: I registered because there’s “budget” in the address
Ok, you guys make sense. I am recondsidering it, and now thinking of a 5-6 cell box for camping / laptop DC use. I only know of 2-cell boxes that use individual charge control (i.e. allow mix-and-match batteries). Are there any any larger boxes that offer what I am looking for? Doesn’t need to be dirt-cheap.
EDIT: So far I have found 2 boxes that have independent 4 cell charging: 1) Tomo V8-4 (Soshine E3) and 2) Huamen/Evertones ET-406. BUT both have only 10W max output via USB and that is not useful.
The problem with battery powered refrigeration in in rush current at motor start up. Lead Cid batteries excel at providing hundreds of amps for this purpose.
If it is for camping, the best solution is a gasoline mini generator or a solar panel system with a lead acid storage cell.
Thats why i mentioned lead acid, li ion storage is more then double the cost of lead acid storage, and half the price is always more budget
What would be great is nickel iron or large capacity nimh, unfortunately no one sees fit to build them, the train left them at the station and went to li ion.
Recently saw where some ‘solar’ folks are using re-purposed Tesla car battery packs for their DC power storage. No details for you, but as long as the cells have some life left in them at least they would be matched, the capacity large, and the proper charging circuitry is apparently known and do-able.
There’s two good approaches to remote power. One is to skip the fuss and get a generator; the other is to reduce the electrical needs first and then use some form of renewable battery power. Propane-powered fridges are made in many sizes, a small tablet or smartphone can handle the computing by itself for awhile, and most other things can be had or already are DC powered. If you’ve got the space, an old car battery gives decent low-draw service or you can get a new deep-cycle one (or several). AGM’s and SLA’s handle mobility issues well; used but not over-used wheelchair batteries are a cheap (sometimes free) source for these. New prices are OK too. And charging with these is simple and non-critical- they can handle some abuse.
As good as LIon is, it isn’t the best for every purpose and I’d prefer something which can’t be damaged by some mild over-discharging. Protected cells ain’t cheap either. Kind of nice to be able to use what you’ve got but it’s not always the best solution or even a good one.
Phil
There is at least one company making and selling NiFe cells. I have only ever seen large cells for solar people to use. I also think they are a bit pricey.
https://ironedison.com/iron-edison-usa-series-nickel-iron-nife-battery
12 V @ 100 AH $1,270.00 + hazmat shipping