Using recycled 18650 Li-Ion batteries for "powerwalls"

[Sid Genetry Solar]

This is undoubtedly a very sensitive topic for some, especially those who may have heard about "making yourself a large battery for very cheap."  Please note that we at Genetry Solar do not condone or recommend these types of projects, largely in part due to the severe potential risks that could result in burning your entire house down.

(Sid) I have personally made a "DIY powerwall" myself out of recycled laptop batteries.  14S, 26P or something like that--over 360 cells.  Made a nice 50Ah battery for an eBike.  However, in the process of making the battery bank, I did discover that there are a wide range of cell problems amongst 18650 Li-Ion batteries:

• "Dead" cells (< 2.0v) can sometimes be "rejuvenated" by low charging current.  Sometimes these cells end up with good capacity.  Sometimes they will be a dead short...other times they'll have a significant self-discharge rate.
• "Heaters" are cells with extremely high self-discharge rates, and they are literally ticking time bombs before they overheat and explode burning lithium all over the place, catching any nearby items on fire.  One cell I encountered charged perfectly fine up to 4.1v (2.2Ah capacity, too--it was a good one!) but any attempt to take it above 4.1v resulted in the cell getting hot to the touch.  Unknowingly mixing a cell like this into a bank that is then charged to 4.2v is literally asking for a fire.
• Cells with a lower self-discharge rate are already "sick", and likely will only get worse as time goes on.
• "Cell level fuses" provide absolutely no protection against "heater" cells, as their self-discharge current is often less than the 1C rating (i.e. 2.2A current for a 2.2Ah cell).  They only protect against cells that instantly fail to a dead short...which I have never experienced.

In the end, I ended up "parking" the eBike (got a car, haha!)  Two years later, my DIY "powerwall" bank had 3 completely dead strings resulting from excessive self-discharge of "iffy" cells that had tested >2.0Ah in capacity checks.

A house fire is nothing funny.  Not worth saving a few bucks to "make it yourself."  If you're set on making a DIY 18650 powerwall...all the more power to you, but please note that we will not provide help for projects of this sort.  We're here to try to help people realize their off-grid dreams safely...not lose our shirt due to liability.

Personally, I recommend Lithium Iron Phosphate batteries (also referred to as LiFePo4, LFP).  They are a much safer technology, with somewhat lower energy density...but the safety is worth it.  My DIY 32650 12kwh LiFePo4 bank on my off-grid system has been an absolute dream--zero maintenance, no issues whatsoever.  (Made with new old stock cells.)  It helps to price shop around, as most commercial solutions are prohibitively expensive.  But that's a topic for another thread.

[The Blind Wolf]

Thanks Sid for pointing out these things, I've will be sticking with the lyp4 batteries going forwards.  I iknew about they being a fire hazards, as watched others use Tesla batteries and not knowing what they were doing had a fire bomb.

 

I'm useing these on a low voltage level at 28.4v level, while my others will be at 28.8v and the bms will kick on when it drops to that voltage and use them. 

 

I got plenty of the battery hook up 6ah cells that I'm useing and headway 8ah batteries I built.

 

If I could find some slightly cheaper lyp4 cells, I would go with that. 

[Sean Genetry Solar]

I am keeping an eye on battery hookup to get more of my LG cells, they seem to be hard to find.

[Waterman]

15 minutes ago, Sean Genetry Solar said:

I am keeping an eye on battery hookup to get more of my LG cells, they seem to be hard to find.

You have to be fast on the draw with much of what they get. Otherwise it is gone before you can log in.

[Sean Genetry Solar]

Just now, Waterman said:

You have to be fast on the draw with much of what they get. Otherwise it is gone before you can log in.

Indeed, sid will tell you when I first found them online I called him right away to get his thoughts. They had 10 left. An hour later when I got sids blessing I snagged the last 2. Next time I hope to order 6 more.

[dochubert]

I too recently bought from battery hookup.  My main bank is now (8) BYD lifepo4 24v modules configured for 48v.  Another (6) of the same BYD modules make up my water heater 24v bank.  I'm also waiting to snag 8 more for my 48v bank when battery hookup gets more.  They said they expect to have some in the near future (whatever that means).

I did just buy some Bmw li ion modules from them to use in an electric golf cart.  (When the weather gets warmer....)

[The Blind Wolf]

Just got another flycow charger, and dang, taking forever to charge each cell module to 4.10.  I'm on the fourth one right now, got 3 more to go, and this is the first 18650.  So far, they holding their charge and not heating up.  I got the bms set to only charge up to 4.08 before cutting off.  I don't like fully charging a battery any how, even my new 32650 are only charged up to 3.50.  Its funny, most folks don't know that you can charge a cell moudal even if the whole battery is put together.  Sort of like Sid balancers, I've seen where forklifts were 24v with a hot wire in between to run any 12v, skipping the stepdown transformer idea all together.

 

Only works if your running a charge the whole time you are pulling from between.  Never really tried doing that with these other type of cells, but, I've used my talking voltage meter and measured the voltage between and sure, enough you get 12v reading.

 

[Sid Genetry Solar]

Will have to say that the shunt balancer modules I need to order, are hardwired for 4.15v / 3.55v.  Might need to think of a better solution for folks wanting different voltages.

[The Blind Wolf]

Well, I can still use the balancer, if I want to equalize them to top balance :P.  I'm going to have to do that anyhow to get all the cells to hit at the same time, so still need those balancers when ever I can snag them.  Also be nice if you could use a dim switch to change the voltage instead of soldering, or use the old fashion jumper pin.  Personaly the dim jumper probley would work better with if you can code it to change voltage to what ever the dim switch is switch to.

[Sid Genetry Solar]

Dim switch?  You mean a DIP switch?  Those are pretty large, I'd have to double the size of the balancer to handle something like that--though it is technically feasible.  Just need to find some of those SMT DIP switches like PJ uses on their charger board...

[The Blind Wolf]

Well, you know me Sid, I don't know what it is size wise, and yes Dip Switch.

 

That why I was wondering why not make one long board, 4s and a 8s board, then you can put the dip switch on it and have one long heat sink and a fan on it, that one dip switch could be used to control all the balancers voltage, pluse you can put all the risisters in one location to reduce the size of the heat sink foot print.

 

Just my thought, cuase even with a 8s board, you can leave one of them unwired and use it as a 7s. same for a 4s down one to 3.s  and two 8s would do a 48 bank.

[Sid Genetry Solar]

15 minutes ago, The Blind Wolf said:

That why I was wondering why not make one long board, 4s and a 8s board, then you can put the dip switch on it and have one long heat sink and a fan on it, that one dip switch could be used to control all the balancers voltage, pluse you can put all the risisters in one location to reduce the size of the heat sink foot print.

A single DIP switch for a dozen balancers...well, that would be ideal, but it is not possible due to the balancer design.  It will have to be a separate DIP switch for every single unit--you can see how cost stacks up pretty quickly.

Reducing the size of the heatsink is not the idea--the bigger the heatsink the better.  These things will get HOT at full load!  If you're running 14S (48v Li-Ion), that's a maximum heat output equivalent to 14 small soldering irons all running at full blast.  Even a Pentium 2 (desktop) heatsink will not be adequate, even if there's a fan on it.  Maybe for 1 or 2 balancers...but definitely not for 4...or 14.  Sean was running 6 balancers each on several long Power Jack heatsinks (each about 3x the size of a Pentium 2 heatsink), and they quickly overheated without a fan.

If I make "block boards" of a set size, then customers will end up paying for materials/items that they may not need.  Currently, they're manufactured in "snappable blocks", but that way you only pay for the exact number that you need.

[The Blind Wolf]

Ah, make since, didn't know just was a Idea. as far as the dip switch.

 

Not sure how much more it would cost to include a dip switch.  I would still buy the ones with no display, since I can easly go into the bms of each battery since all of them are bluetooth and change the cell voltage to allow for the balancers to kick on if I need to rebalance the battery.  I'll probley just restrick the solar charger to only go up to 48.4v, and all the batts can have the normal settings 29.2 I think is the max voltage. and all I have to do is change the solar charger to go to that volatage to top balance, then change it back to 28.4

 

hmm why not have the power go to a hmm what they call it, I got one for my wind turbine, it dumps the extra power to it and its like a heater.

[Waterman]

9 hours ago, Sid Genetry Solar said:

A single DIP switch for a dozen balancers...well, that would be ideal, but it is not possible due to the balancer design.  It will have to be a separate DIP switch for every single unit--you can see how cost stacks up pretty quickly.

Reducing the size of the heatsink is not the idea--the bigger the heatsink the better.  These things will get HOT at full load!  If you're running 14S (48v Li-Ion), that's a maximum heat output equivalent to 14 small soldering irons all running at full blast.  Even a Pentium 2 (desktop) heatsink will not be adequate, even if there's a fan on it.  Maybe for 1 or 2 balancers...but definitely not for 4...or 14.  Sean was running 6 balancers each on several long Power Jack heatsinks (each about 3x the size of a Pentium 2 heatsink), and they quickly overheated without a fan.

If I make "block boards" of a set size, then customers will end up paying for materials/items that they may not need.  Currently, they're manufactured in "snappable blocks", but that way you only pay for the exact number that you need.

You would be surprised just what affect just a fan has on things. Back decades ago we used either strings of ( 5 ) 50 Amp or a string of 250 Amp diodes for voltage drops to run four .55HP 24V 22A motors. Just an Aluminum angle for a heatsink. Which without the fan would get hot but with the fan could be run at full load. Now why such high Amperage rated diodes? Well under full loads on the motors we could see 200 Amp draws. Modern extruded heatsinks do a much better job of cooling but a fan can make a big difference.

[Kbeck]

I have major issues with lifepo4 cells. The discharge curve is so flat that you only catch the imbalance of cells at the extremes of the discharge and charge. I've had lifepo4 cells catch fire because the balancing circuits couldn't handle how big the imbalance was as it was charging. Many people built EV's using lifepo4 and ran into destroyed packs in as short as 6 months. Just my 2 cents on it.

[Sid Genetry Solar]

8 hours ago, Kbeck said:

I have major issues with lifepo4 cells. The discharge curve is so flat that you only catch the imbalance of cells at the extremes of the discharge and charge. I've had lifepo4 cells catch fire because the balancing circuits couldn't handle how big the imbalance was as it was charging. Many people built EV's using lifepo4 and ran into destroyed packs in as short as 6 months. Just my 2 cents on it.

I know someone on a somewhat personal basis who burned through several sets of LFP batteries (actually from the same seller as the batteries I have) in about a year with daily 80-100% DOD cycles...and some wimpy 30mA Chinese "balancing BMS" units.  However, with a proper BMS setup (disconnecting charge/load if cells go out of range), the batteries should last a very long time.

Personally, I have a DIY 12kwh LFP bank...it'll have been in full-time service for 4 years here in a few months, and I've had absolutely no issues whatsoever with it.  Worth noting that they were NOS (new old-stock) cells, and I have some 3A balancers of my own design on them.  I've probably only ever ran to 80% DOD on 2 occasions (gloomy cloudy weather for a week).  But my loads never come close to 1C, either.  TBH the balancers hardly do anything.  They got warm/hot the first few days after I put 'em on (in May 2017)...but ever after that, they barely activate at full "absorption voltage" of 3.53vpc.  ("Float" is at 3.50vpc.)

After "tasting" LFP, I'm never going back to lead-acid batteries ever again.  True, balancing and cell protection is critical for any lithium-based battery system...and true again, 90% of the "BMS" setups out there have a balance current of well under 1 amp.  Fine for a little 5A battery...but not for a 300 amp-hour off-grid battery.

[Kbeck]

21 hours ago, Sid Genetry Solar said:

I know someone on a somewhat personal basis who burned through several sets of LFP batteries (actually from the same seller as the batteries I have) in about a year with daily 80-100% DOD cycles...and some wimpy 30mA Chinese "balancing BMS" units.  However, with a proper BMS setup (disconnecting charge/load if cells go out of range), the batteries should last a very long time.

Personally, I have a DIY 12kwh LFP bank...it'll have been in full-time service for 4 years here in a few months, and I've had absolutely no issues whatsoever with it.  Worth noting that they were NOS (new old-stock) cells, and I have some 3A balancers of my own design on them.  I've probably only ever ran to 80% DOD on 2 occasions (gloomy cloudy weather for a week).  But my loads never come close to 1C, either.  TBH the balancers hardly do anything.  They got warm/hot the first few days after I put 'em on (in May 2017)...but ever after that, they barely activate at full "absorption voltage" of 3.53vpc.  ("Float" is at 3.50vpc.)

After "tasting" LFP, I'm never going back to lead-acid batteries ever again.  True, balancing and cell protection is critical for any lithium-based battery system...and true again, 90% of the "BMS" setups out there have a balance current of well under 1 amp.  Fine for a little 5A battery...but not for a 300 amp-hour off-grid battery.

Yea. That was my problem. Most bms systems are super small balancing current compared to the capacity of the cells and charging rates of 1/3-1c. The other issue is a lot of inconsistent manufacturing from most of the lifepo4 producers I know of causing wildly varying cell capacities of batteries even in the same batch. You could buy 100ah cells that are +/-10% capacity. It is super hard to balance large format cells like that within a pack unless you combine them perfectly in parallel assuming you are making a pack large enough. It can still work, just super time consuming. That's why I like automotive ev packs. Volt cells, bmw cells, Nissan leaf, tesla cells. They are perfectly balanced when they come out of those packs and have very little variance. Lately I have been buying model 3 cells for around $120/kwh. Crazy good wh/kg and wh/liter with great cycle life and almost linear in discharge and charge so it is easy to spot the voltage and know what capacity it is sitting at without any coulomb counting.