Link in the description, I purchased two of the $35 packs. it comes to about $1.75/ea LG cell
Check eBay for solar panels. If this is a “travel” item, you might look for panels embedded in plastic or buy a ready made panel that folds up neatly and clips onto your batteries when you want to charge the. There are some very nice “fold out” solar panels that are really compact when folded. It is that money question. How much do would want to spend?
Be careful about buying Li batteries on ebay that seem to be a great deal. You will probably get what you pay for. "Genuine’ may just mean they are fakes. I bought an expensive little charger discharger that cycles the battery and determines the charge and discharge capacity. It’s totally programmable from the target voltages to the charge and discharge rate. I bought a few of the ‘cheap’ ebay deals and found they were often 10 to 15% of stated capacity and about a third of the lowest capacity 18650 and often advertised as up to 5000 mah. I opened some of them and they had used some sort of mini lithium battery wired into the shell and filled the battery with either sand or stuff that looked like ground dry wall dust - in order to feel heavy enough.
At least he is only saying they are 2200 mah and not 5000. There is not an 18650 > 3500 or so mah in the first place - always a fake if advertised as 5000 mah for ex.
Also realize that a truly valuable Li battery pack is one with excellent battery management circuitry. If you just series and parallel them they will get into a positive feedback failure mode that will kill off come cells then lead to failure of the whole pack. That is what leads to Tesla’s success is the uniform thermal environment of it’s cells an individual cell monitoring and equalization thru a massively complex system to keep the cells equal and alive.
You can buy the chips to create a battery management system for your battery packs. It’s fascinating but would take a lot of work but would be worth it if you want a long lived system. If you could get a sample of the cells from the guy then it would be worth paying way more for a couple before buying a bunch of fakes.
thanks dejswa,
the yt channel, jehugarcia, has done more with li-ion batteries than I can ever imagine, I’ll take his word on this one.
I already ordered my bms boards for the specific packs i’m building. 2S and 3S packs.
I already bought two packs from the ebay link, $70 shipped for 40 cells. The included BMS looks high quality, but I don’t have the need for a 36v battery pack.
Because they are only stating 2200 mah, I suspect you are in luck and will get the real deal! The scammers seem to boast about impossible mah on their batteries.
If anyone has any experience in building a robust Li battery management system, let me know. I’d love to go buy a bunch and build my own powerwall but I realize you have to be able to identify a single cell that might be going bad and keep it equalized or else your entire pack may go bad. Of course, you may group cells and sort of hedge your bets to reduce the amount of circuitry but increase the risk of a single faulty cell causing a problem.
I was reselling Lithium 18650. I got burned so many different ways.
4000 mAh, 5000 mAh. Wow, wonderful, FAKE.
I searched for some way to validate what might be legitimate. Panasonic was selling batteries with 3400 mAh. That became my bench mark. Any offer below that MAY be legitimate. Anything above that is in all probability fake.
I also use eBay as they are US based. The Chinese are culturally vendor looking for any financial advantage.
Best of luck.
Paul,
How did this deal ever work out? Did you get the 18650’s? Were they good quality? I have a project coming up that may need a battery pack or two and I may be looking for a source of these cells. And I’ll need to do some BMS research.
I’ve been busy with other projects and put this one on hold. But I did remove the cells from the pack and started using the dms battery spot welder, works as it should. The few times I was able to charge and discharge them, it seemed to be performing ok. I’ll be taking more notes pretty soon.
I’ve built a few packs and about to build a 4S10P pretty soon for a all around laptop/phone charger on steroids. What voltage, load, and capacity were you looking to make?
The link below is where i bought them from. They come 10s2p already and a bms on board, but i ended just tossing the included bms.
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Pau, thanks for the reply. I have a few things I would consider. Most I’ll never get to. I’m studying BMS a bit first. Here are some of the ideas I have.
- Battery pack for E-bike
- DIY power wall
- Battery pack substitute for expensive pack used for LED studio lighting ($500 each!)
- Plug in electric hybrid car conversion
I need to study a bit more on BMS as I’d like to do a really good job with that. It’s worth another thread so I won’t get into it right now.
BTW, so sad that folks sell this stuff. But the guy seems to have a good ebay rating. Probably because the buyers know what they are getting and they are just reselling the same junk. No such thing as a 5AH 18650
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I was selling 18650 batteries for several years. And had to learn this the hard way.
There is a fog around mAh. Meaning deception and theft.
Panasonic brand batteries largest size is 3400 mAh. I trust Panasonic to make the largest battery possible therefore anything above 3400 mAh is a lie.
Buy a trusted brand from a trusted source otherwise know they are lying to you and you are getting less. Then the question is how much less?
Li-ion batteries are not real tolerant of deep discharge or charging outside the recommended charge curve. And if you take the time to actually read the data sheets, you will find that recommended charge rate is based on the percentage of charge the battery currently has. This has lead to making some custom chips that are called smart charger ICs or battery fuel gauge ICs. If you don’t want to buy a high end product like you gave a link to, another alternative to buying an IC and building something from scratch is to buy an engineers evaluation board. Both Maxim and Linear Technology make charger/fuel gauge ics and corresponding demo boards.
Both Digi-key and Mouser tend to stock (or drop ship what they don’t stock) on IC demo boards.
Another point is that charge rate is derated by temperature, and these smart charger ics either incorporate a temperature sensor or provide an input pins for temp. sense.
If you want to keep costs down, then you can just pick a lower charge rate and use that all the time.
The downside is that it will take significantly longer to charge to full.
There is more than an order of magnitude between the fastest and slowest charge rates.
The best low cost DIY build I have seen was on the Dangerous Prototypes website using a quad op amp to make a current mirror. That meant the the charge rate for battery A was duplicated for battery B,C, and D in a four battery pack.
Good points. Yes, after I posted that ad for the 5AH batteries I went back to look at the feedback. Those that really tested them found them to test out at around 1AH. You are absolutely correct!! The more they are rated over 3400 mAH, the lower the capacity. I have experimentally found the same thing with a few I ordered and a really nice tester / charger / coulomb counter I have. You see the same thing on Amazon. As soon as they get too many bad reviews on Amazon, they simply re-list the ad with a different made up battery name and post a bunch of made up reviews. They are simply cut and paste and the seller doesn’t even bother to create new reviews or new photos, just a new company name.
They really need a policy against any claim for more than 3400 mAH on an 18650.
Electron_pusher - your points are really good ones. Yes, de-rate your Li batteries with regard to full and empty charge as well as charge and discharge rate (and temp) for more life.
I also have looked at the LiFePO4 which apparently have longevity advantages at the expense of having about half of the gravimetric and volumetric energy density. (plus safety advantages) But I have also seen arguments that with a good BMS, one can derate the standard Li ion battery (18650) and get most of the same advantages of the LiFePO4.
I would love to have a Li battery BMS ‘development board’ so-to-speak, that had all these components plus a coulomb counter plus a controller (Arduino, for ex) interface that would report each cell ‘health’ and allow me to change parameters on the fly, such as min / max cell voltage, max charge / discharge current. In addition, I would like active, like charge pump cell equalization rather than a resistive equalization although this might be overkill on a small pack.
This plus a few other things:
That is, while it is essential to have a BMS on an sort of Li battery, I don’t like the fact that it’s a black box and I can neither monitor nor change the parameters.
OK, sorry I said I wasn’t going to turn this into a BMS thread . . . BTW someone wanted ideas for a class - a great DMS class or project . . . built teach / develop the ultimate Li BMS!
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I bought some prebuilt 2s, 3s, 4s BMS boards on amazon and haven’t tested it to the max just yet. But if your device is smart enough to have a cutoff signal for low voltage, you could just add a balance connector and use an external charger. I have the hobby charger below that has a lot of charging features. It’ll even tell me how much Ah its putting into the battery.
This would be a great class to teach since LiPo batteries are everywhere these days, especially in RC electrilfly aircraft.
Maybe the class could build the smart charger you describe. What would the cost of sourced components? Any idea?
I own a nice LiPo charger. https://www.amazon.com/Combo-Special-Tenergy-Balance-Charger/dp/B00466PKE0/ref=sr_1_3?ie=UTF8&qid=1500561674&sr=8-3&keywords=turnigy+lipo+charger but I’d be interested in a class none the less.
Agree. It teaches so many things:
Embedded processor programming and interface - Arduino or other
Possibly PCB design if we build our own although that might be beyond what we have time for
Concepts of battery management - why it’s needed, methods of equalization (resistive, capacitive, charge pump)
Use of power control semiconductors such as FET or IGBT (the former for individual cells and the latter for high power switching.
Temp monitoring techniques.
Current measurement thru shunts or other mechanisms.
Galvanic signal isolation (might be needed for some parts of this)
Plus, as you mention. The use of Li batteries grows unlimited as the cost is reduced. IF you can take extreme care with their maintenance, I think the high cost justifies their use in so many application. I would be happy to never buy another Pb battery again. In fact, why the heck to we even put them in ICE vehicles?? Just put a GOOD / small Li battery in the vehicle. Give it EXCELLENT conservative management and possibly use LiFePO4 (I’m not totally up on the different technology but the LiFe seems to be more robust for the long haul and under more brutal environmental conditions.
BTW, your ‘charger’ has BMS. I have noted that generally the term ‘charger’ in battery forums, refers to mostly a power supply at a particular voltage with a rated current. They tend to separate the charger from the BMS. Although most BMS do not limit charge rate and leave it up to the user to limit this thru the charger (either program it for a suitable charge rate with a programmable charger or use a suitable ‘dumb’ charger (power supply) that won’t kill your non-current-regulated BMS.
BTW, I’ll throw out this recommendation for a general purpose do-everything charger - looks like a great option . . .
This guy’s website is excellent as his instructions page on DIY 18650 battery pack. One tip I would add, however is the addition of a tiny fuse to each 18650 if you are considering building a mega paralleled pack. That is what Tesla does. Not sure how often an individual cell has a melt down (short) but that would be a disaster in a hugely paralleled system like a powerwall or EV.
Yea my charger has the BMS setup built in, but I like to build my battery packs with a BMS board because my devices connecting to it will drain it below dangers levels.
3s5p pack. Toss the onboard bms, add your own, and its soldered/tack welded for the most part.
What do you think?
2x18650’s in each of those “cells”?
Not too horrible of a deal but be aware - you are buying used cells. I recognize those battery packs from hospital mobile workstations. They fast charge them and they run pretty hot in the bulk charger. Might be a little concern about what’s left in them.
That’s around $200 per KWH
This is where i got the link from and information on those packs.
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Good video review on those cells. I’ve seen this guy’s DIY powerwall videos. I guess I’d have to really think about used cells vs bulk new ones if I was doing a hugely paralleled battery like a powerwall. I’ve never really priced new cells in bulk.I’d just hate to put in a ton of work and have problems with it but those look like pretty good cells. And if you run them conservatively then they probably have pretty good life left in them.
But I just did a quick search and I’m not finding any great deals on bulk new cells - some are $6 each. That makes a new powerwall from Tesla sound like a good deal at $350 per KWH.
I use 10 WH per cell in my calculations. So the powerwall is around $3.50 per cell. Plus it’s already built and includes power management and battery management.
However, I’d probably take a chance on a DIY one myself some day.