# 18650 Battery Pack Feedback



## Ziggythewiz (May 16, 2010)

Apparently the real photo from this thread  has been removed, so I'll just link another similar one. 



Most of Tesla's IP is tied up in how to keep this from happening when you use thousands of laptop batteries to power a car. DIYing such a setup is risky business.


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## BigCity (Aug 20, 2013)

Well thanks for the positive feedback, I'll keep doing my research. Definitely don't want any fires, my pack will be much smaller. I do already have a Tesla Model S in the garage so plenty of lithium ion under the roof already.


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## Karter2 (Nov 17, 2011)

Rather than use an inverter etc, It may be simpler and easier to convert your aquarium equipment be be all DC....if it is not already.!


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## BigCity (Aug 20, 2013)

Karter2 said:


> Rather than use an inverter etc, It may be simpler and easier to convert your aquarium equipment be be all DC....if it is not already.!


That's an idea though I know the main pump is AC and was just bought, had I been thinking many of the newer pumps are DC.


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## Ziggythewiz (May 16, 2010)

Basically what you need is a charge controller and a Battery Management System (BMS) that ensures each cell doesn't go over or under voltage. 

The inverter will likely have some kind of low battery warning and possibly cutoff but unless it is specifically designed for your ur18650f cells it won't do those functions at the proper voltages.


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## electro wrks (Mar 5, 2012)

Ziggythewiz said:


> Apparently the real photo from this thread  has been removed, so I'll just link another similar one.
> 
> 
> 
> Most of Tesla's IP is tied up in how to keep this from happening when you use thousands of laptop batteries to power a car. DIYing such a setup is risky business.


Here's the recent fire I think you're referring to: https://endless-sphere.com/forums/viewtopic.php?f=1&t=82403&p=1209923&hilit=tesla+modules#p1209923

If you listen carefully on the video, I think you can hear individual cells cooking off! And, apparently some of them landed ~100 feet away!


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## BigCity (Aug 20, 2013)

I appreciate all the warnings and heads up about the dangers, so how about we turn that into a discussion on limiting and engineering solutions to those limitations? 

I had tossed around the idea of using the plastic tab holders to allow for some space between the cells that I would then fill with fire stop caulk or possibly foam depending. Maybe create a couple of small test cells to see how if that creates a separate heat issue with the packs possibly. Figure it can't be much worse that those that hot glue the cells together and then shrink wrap them.

I figure the cells could then be mounted in a metal cabinet of sorts to further limit any heat/fire related problems. Like a filing cabinet, minus the flimsy shet metal lol. Or possibly a plywood enclosure lined with cement board or other fire rated type material.

Any feedback on the voltage question for this type of application, is there an advantage to a higher voltage when running an inverter? Higher voltage lower current to the inverter smaller cables for the packs?


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## BigCity (Aug 20, 2013)

I'm thinking the pack will be 24V at least right now, will know better when I take the time to calculate the total load for all the items I would like to run. From there I will be able to calculate the capacity and start more detailed planning.

I've gone both ways on BMS, but seems like the safe bet is to have it than to try to manage it properly without. Not that expensive to begin with any way. Anyone have any recommendations for a high quality BMS system?


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## Ziggythewiz (May 16, 2010)

A lot of your decisions will depend on whether you're optimizing for your aquarium usage or future EV usage. The two use cases are very different.

You probably don't want foam in between them for cooling purposes and potential maintenance.


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## BigCity (Aug 20, 2013)

Ziggythewiz said:


> A lot of your decisions will depend on whether you're optimizing for your aquarium usage or future EV usage. The two use cases are very different.
> 
> You probably don't want foam in between them for cooling purposes and potential maintenance.


Very true, at the moment I am leaning toward building a unit with the same specs as one tesla module, will it be oversized for what I plan on using it for initially, absolutely, but then again having many hours or days of run time when it comes to an aquarium investment isn't necessarily a bad thing. 

Got the first batch of Sanyo's last night, tested very well with right at 2500mA capacities. So that is encouraging. Another question should I test all of the cells just to be sure there isn't a dead one, guessing that would be a prudent thing to do to avoid potential problems in the future.

I may also further reduce risks by getting a BMS that I can set different set points so maybe discharge less than the 3.0V and only charge to the 4.0-4.1V point. Plus it will give the added benefit of longer life as well.

Currently researching the Manzanita Micro Mk3 BMS controller, seems to have some nice features and goes beyond just a dumb unit with lights.


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## Ziggythewiz (May 16, 2010)

With the little cells it's best to test everything individually and monitor every series connection and investigate any anomaly immediately.


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## electro wrks (Mar 5, 2012)

From what I've been able to glean, Tesla and Panasonic do multiple aging and testing on their cells before they match them in the 74s, 6p configuration in their modules. If it hasn't been done, somebody really needs to hack the BMS they put on each module to make them safe to use up to Tesla's standards.

BC, you might research the safety protocols and standards Tesla uses for their Power Walls.


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## Karter2 (Nov 17, 2011)

Videos of the Tesla pack assembly line show no suggestion of individual cell testing equipment or processes
Im sure Panasonic have comprehensive testing protocols in place for ensuring every cell shipped to Tesla is performing to spec, and possibly even graded into matched batches.
But, if Tesla is like any modern organisation , they wont invest the resources, money , or time, into retesting individual cells, they will have set specs and tolerances which a supplier like Panasonic must match 100% components to, with enormous penalty clauses to ensure compliance. Random quality checks would be in place to monitor .
Tesla would most likely do performance checks at module level before final pack assembly.
My concern is that Tesla and other commercial customers get the "cream" of the production cells , and any that dont meet the "A grade" customer specs are redirected to "B" grade supplier channels, like the numerous wholesale/retail outlets we use.
So, yes, i would test all your cells at least for matched capacity, IR, etc, just incase !


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## electro wrks (Mar 5, 2012)

By "Tesla and Panasonic" I meant as a partnership, not as individual battery makers.


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## piotrsko (Dec 9, 2007)

With all the volt packs out there you'd think the bms is hacked by now. THAT would be ideal for pack monitoring, and cheap as dirt.


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## SirNick (Jun 14, 2015)

As for voltage, the advantage of higher voltage is lower current draw for the same output power. That is, 48W is 2A at 24V or 4A at 12V. As the power requirements increase, it gets more difficult to meet the current demands without losses. At low power, it's less important. At <1000W, take your pick based on the inverters you find that meet other criteria.

I wouldn't count on finding an inverter that is built for Li-Ion battery packs. Most that handle charging (like a repurposed UPS) are designed for lead-acid and CAN be used if you're really careful, but probably shouldn't be.

The biggest thing with 18650s is going to be ensuring the series groups are kept within their tolerances and not abused. If you can do that, they're plenty safe. Source: All the portable electronics around you that use them or similar cells of the same chemistries. It's not rocket science, but some people get in trouble with excessive BMS features or bad wiring. Keep it as simple as possible but not simpler and you'll be OK.

Don't worry about heat unless you're planning to drive the cells into high-C charge or discharge. Also, don't do that. ;-) It takes more finesse to push the cells to their limits. You're much better off avoiding the extreme stuff.


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## BigCity (Aug 20, 2013)

Built a charger out of the TP4056 chip so I can bulk charger batteries and then use the Opus to do the discharge tests. So far the Sanyo's are consistently producing right around 2450-2550mAH. I also got a bulk lot of Dell batteries that were new, tear down resulted in cells with only 1.5V charge but a quick trickle charge and they rebounded quickly. They test out consistently around 2250mAH of capacity and seem to hold charge as well. Cells did not have any markings on them, they were a red with a bit of a metallic sheen.

Now that I have the battery testing rolling I'm going to continue to research the size of the pack and charging options. Right now it looks like the best option would be to get a smart BMS and standalone charger for pack management and then just have a standalone inverter. As mentioned above I think the pack will be so large that I won't have to worry about current draw issues, unless I convert it to a whole house solution down the road. At that point I could reevaluate and just add more capacity.

I've seen some circuits online for voltage monitoring that triggers relays to cut pack connections. That may be another good option to implement for even further protection if I'm feeling really geeky on creating additional circuitry. Initially though I think having a low current draw and proper monitoring I should be plenty fine and operate well within the packs capabilities.


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## Hollie Maea (Dec 9, 2009)

Karter2 said:


> Videos of the Tesla pack assembly line show no suggestion of individual cell testing equipment or processes


I've assembled more than 100,000 18650s, and have never encountered a bad cell. When they leave the factory, they are perfect.

Needless to say, this only applies to the big companies that also sell you TVs: Panasonic, Samsung SDI, LG Chem, Sanyo, Sony...


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## palmer_md (Jul 22, 2011)

Karter2 said:


> Videos of the Tesla pack assembly line show no suggestion of individual cell testing equipment or processes....


Link? I've not seen any videos of the pack construction process. Plenty of the car building, but nothing of pack building. I'd love to watch a few videos of it.


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## dain254 (Oct 8, 2015)

I'm currently running a battery pack in my small EV made of 720 18650 cells salvaged from laptop batteries - they are Panasonic cells. Bonding the cells together is the bit where I cheated as they were bonded in groups of 3, so I simply soldered wire across the tops to create 36P "cells", which there are 10 cells/module. I run 2 modules in series for 20S36P, and I balance it with 4 hobbyking cell medics. Only have to balance every 10 cycles or so, but I assume that is due to my slow charge rate at 10A, takes about 8hrs! Using the cell medics and charging slowly is by far the easiest and cheapest way to safely use a lithium battery I've come across so far! Good luck!


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## BigCity (Aug 20, 2013)

Cool, did you have a build thread by chance to reference?

Right now I'm planning to build 2 modules each being 24V, 7S80P based on the Sanyo batteries and the ones I'm salvaging from some new laptop batteries. So far they are consistently testing around 2300mAH each on average. I figure 2 modules will give me the flexibility to step up to 48V if needed. Will be way more capacity than is needed but it's kind of snowballed with getting good deals on the batteries lol. More time to keep the aquarium running is never a bad thing either. More details to come soon hopefully, got a bunch of parts and connectors, but still testing all the cells as well as breaking down the laptop batteries. I'm about half way through on both right now.



dain254 said:


> I'm currently running a battery pack in my small EV made of 720 18650 cells salvaged from laptop batteries - they are Panasonic cells. Bonding the cells together is the bit where I cheated as they were bonded in groups of 3, so I simply soldered wire across the tops to create 36P "cells", which there are 10 cells/module. I run 2 modules in series for 20S36P, and I balance it with 4 hobbyking cell medics. Only have to balance every 10 cycles or so, but I assume that is due to my slow charge rate at 10A, takes about 8hrs! Using the cell medics and charging slowly is by far the easiest and cheapest way to safely use a lithium battery I've come across so far! Good luck!


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## BigCity (Aug 20, 2013)

Ok, been awhile but have begun the module assembly. Ended up with 7S68P and I'll run 2 in parallel for 24V or possibly just switch to 14S68P for a 48V system. Still looking at PV controllers, that appears to be best bet for finding something that can switch sources plus charge all in one unit, plus have the added benefit to add solar panels for power generation in the future!

So if my math is right (correct me please if I miss something) each 24V pack will have a capacity of (25 cells at 2400mA, 43 cells at 2200mA) giving a total capacity of 154AH at 24V or double that in parallel. Now I don't plan on fully charging so I won't have the full capacity but theoretically that is the total capacity.

Conservative current draw allowable would be 1.5-2A per cell so that would be 102-136A per 24V module with max the cell is capable of being 4-5A so 272-340A. I have 1/4"x1/2" busbars for to connect 34 of cells to for each pack, then plan on using 4/0 to do the interconnections for the parallel packs and connection to the inverter. 

All is way overkill for what I originally intended to do, but this will allow for a large scale whole house partial solution as well.


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## dougingraham (Jul 26, 2011)

electro wrks said:


> From what I've been able to glean, Tesla and Panasonic do multiple aging and testing on their cells before they match them in the 74s, 6p configuration in their modules.


I think you meant 6S 74P. Module voltage is a nominal 22.2. If it was 74S the voltage would be 273.8.


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## BigCity (Aug 20, 2013)

dougingraham said:


> I think you meant 6S 74P. Module voltage is a nominal 22.2. If it was 74S the voltage would be 273.8.


Lol yes indeed good catch.


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