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DIY Powerwall with 18650 batteries


PurePower

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I got the cells from a pile of solar lanterns I was asked to scrap. I'm busy putting together abother pack which I expect to have a useable capacity of about 18 to 20 Kwh from laptop packs. The batteries, plus holders and a BMS and the steel cabinet with internal calbing, basically a 48v 350Ah Li-ion pack for about R20k.

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21 hours ago, seant said:

You don't want to know

Did you consider Spot Welding ? Some guys was claming soldering is over heating battery.

What are your charging voltage , current etc settings ?

What BMS’s you are considering ?

If you use very low power ( charge discharge ) and very low energy (%40 DOD ) ; is it still dangerous to not use BMS at all ? ( Because you have big but cheap batteries )

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I didn't consider spot welding at the time. I haven't had a failure due to the soldering yet. As for charging I set the float voltage to 57v to give me a little less than 4.1v  per pack and I've set the absorb time to 0. The low voltage disconnect is at 46v ,  I've then told the outback controler to switch the ups to Eskom via a set of solid state relays and disconnect from Eskom at 48v. As for charge current , it will happily take what ever it gets from the controller (peaks at about 45A for now until I can add on more pannels. ) I'm not too concerned about the bottom voltages but I would like a BMS for the top balancing of the voltages. The nice thing about a large battery pack of 180 odd cells is that even with my 5kva inverter maxed out there is only about 0.03A being drawn front an individual cell which should give me a long battery life (provided I can keep the max and min voltages in check) . The cells all came from the same application so their capacities are nearly all the same and the age of the cell are similar too, and thus the packs are quite well balanced as a whole . I keep a close eye on the battery pack and there is a variation of less than 0.08v between all the packs. So for the price the steel box,  the holders ,  wiring and a whole lot of time I certainly complain about the way it came together.  To be honest I'm surprised more people haven't done this here in SA .

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55 minutes ago, seant said:

To be honest I'm surprised more people haven't done this here in SA .

I was very keen on a DIY Lithium project but here in the Karoo I was singularly unsuccessful in trying to get a source of cells. After some research I decided I would be better off with LiFePO4 anyway.

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20 hours ago, Chris Hobson said:

I was very keen on a DIY Lithium project but here in the Karoo I was singularly unsuccessful in trying to get a source of cells. After some research I decided I would be better off with LiFePO4 anyway.

If you live elsewhere in the world, you have way better access to this sort of thing. There is this guy in Youtube, Jehu Garcia, who occasionally does group buys and they get these cells at 1USD a piece or thereabouts. But we live in Africa... en sulke dinge is ons eenvoudig nie beskore nie.

So a friend of a friend, who lives in Italy, says things aren't necessarily much better there. You also have trouble getting supplies of many electronic things.

21 hours ago, seant said:

Has anyone had a look inside the fredomwon battery packs? What makes them worth the price compared to a diy powerwall?

I'm told they use LFP cells made by Sinopoly and an Orion BMS.

I'd say you'd first look at chemistry and what that means. 18650 batteries are usually LMO or NMC. The main battery pack makers use LFP though.

The advantage to the NMC side would be higher charge/discharge currents, but usually shorter cycle life. They have a higher energy density, but are more susceptible to thermal runaway. I think they also cost more.

(Eg, NMC batteries in cars are often liquid cooled).

LFP on the other side has slightly lower charge/discharge currents (depending on construction though, the better batteries do 0.5C!), lower energy density (not a big deal in a house), but they are less susceptible to thermal runaway and a better cycle life.

A new 18650 is around R20 a cell, maybe R15 if you can get a good cheap supplier :-) So your talking around 40k worth of cells, before labour, with no BMS. For 64k I can get 4 x pylontech racks, with a BMS, support, and less risk of a fire :-)

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On 25 February 2018 at 4:50 PM, plonkster said:

If you live elsewhere in the world, you have way better access to this sort of thing. There is this guy in Youtube, Jehu Garcia, who occasionally does group buys and they get these cells at 1USD a piece or thereabouts. But we live in Africa... en sulke dinge is ons eenvoudig nie beskore nie.

 

Somehow people in SA can not reach to scrap batteries. In Europe , USA or Australia it is easier. For sure there is not logic to use NCA or NCM 18650 if you can buy LFP of Pylon or even LTO. But the cost of used laptop batteries is extremely cheap. If you can find reliable and logical price BMS lots of people can find those cells in SA as well. Current situation for 300USD DIY powerwall from laptop batteries we need 500USD BMS of Batrium. Then it makes no sense to do it. Pylons are the way to go.

But I am still searching ways to do DIY powerwall with old laptop batteries safe and cheap because i found out that in lots of countries it is not still possible to Recycle 18650 , AA , AAA with Lithium , Nicad or NiMH. In stead of recyclying they collect and store in underground safe place for leakage. It hurts me. If we can not recycle it is not sustainable. At least i want to give those 18650`s a second life. 

Sorry for the emotions in message.

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  • 2 weeks later...
27 minutes ago, Mars said:

r30 is a lot of money. guess people will be curious of the quantity of batteries?

Sorry R30 for a pack that yields between 4 and 8 useable 18650 that is about on average R6 a cell , I don't see that being expensive . Let's do the sum, you'd need give or take 500 packs to have enough good cells to build an approximate  300Ah 48v battery.  That's about R15k a good BMS like a Batrium about R8k . A steel box to put it into and the holders and wiring to go with it give or take R7k. that works out to about R30k all in. And then you time of course . But if you take what other similar spec batteries cost well you make up your mind what expensive  is.

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2 hours ago, seant said:

Sorry R30 for a pack that yields between 4 and 8 useable 18650 that is about on average R6 a cell 

You know Testers for 18650 like Opus takes a lot of time and money for end users. ( If you only use for your own project , what you will do with 10 Opus later ? )

Do you have testers ? Can you test and sort 18650 in large amounts ? So maybe you can offer Tested batteries sorted and delivered in South Africa ?

Like 2000-2100mah 500 batteries each R5

...

Like 2400-2500mah 500 batteries each R9

 

I guess not everybody can reach 18650 , so you can deliver those people.

Even Lithium Loving Chris Hobson said he could not find good source.

On 24 Feb 2018 at 6:21 PM, Chris Hobson said:

I was very keen on a DIY Lithium project but here in the Karoo I was singularly unsuccessful in trying to get a source of cells. 

At the end of the day you will give 18650 another chance in a powerwall for solar or 12V battery for peoples car or ebike etc etc.

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I think 18650 is the wrong chemistry for a house battery. Make no mistake, it is neat, clever, I love what people are doing with it, but it makes no financial sense unless it is actually a hobby of some kind.

Reminds me (for some reason) about the old joke of the Linux guy who complained that he has sex about as often as he reboots his computer, to which the Windows guy said it is about the same for him and he doesn't understand what the problem is... :-)

It really depends on what you'd rather spend time on.

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Easy to source laptop battery's .. . just do gumtree search for people recycling pc's etc.   Otherwise contact recycling centers, they sell by weight.   I found about 800 packs within few days and just got it couriered.

Busy doing my powerwall now, at  900 cells soldered now, probably another week or 10 to do the reset (1500 in total) .  its a slow and very boring process to test 1500 battery's and then solder them all up.  so be warned.  Been busy about ~9 months already.

So far +-R 5000 invested for packs/chargers/testers/wires etc ,   +- 520 ah (tested) capacity (~2kwh ).    Lot cheaper than any other method of doing it.

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9 hours ago, plonkster said:

 

Reminds me (for some reason) about the old joke of the Linux guy who complained that he has sex about as often as he reboots his computer, to which the Windows guy said it is about the same for him and he doesn't understand what the problem is... :-)

Hahaha! This is the best analogy I've ever heard of Windows VS Linux problems ;)

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12 hours ago, SilverNodashi said:

Hahaha! This is the best analogy I've ever heard of Windows VS Linux problems ;)

That was back in the day when it took a lot of time to install Linux and get everything working. You know, recompiling your kernel to get your sound blaster card working and things like that. It literally came down in many cases whether I even had time for that kind of thing... that whole "I just want it to work" thing.

Today I use Ubuntu. I literally just want it to work :-)

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On 3/8/2018 at 10:21 AM, plonkster said:

That was back in the day when it took a lot of time to install Linux and get everything working. You know, recompiling your kernel to get your sound blaster card working and things like that. It literally came down in many cases whether I even had time for that kind of thing... that whole "I just want it to work" thing.

Today I use Ubuntu. I literally just want it to work :-)

I remember those days very well. My first, decent, OS was Redhat 4.2, then Slackware 4 and FreeBSD 3.6. Man, those were the days.... sounds cards were a luxury, even network cards was a luxury sometimes. Recompiling, or rather, compiling the kernel just to get the VGA to look good was the norm ;)

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  • 2 weeks later...

Good evening Gents, i see some good chatter here and decided to chime in, seems that the local price of laptop battery cells is fairly cheap and building is the only issue with these power walls, i have vast experience and knowledge on the topic and willing to lend a hand if any one wants give me a shout send me a pm, im based in JHB and can give advice on rating, testing, sorting and choosing the correct cells if necessary, i do also have cells in stock but not at the prices you mention, to add some controversy i see that most stores around sell new 18650s for 75rand to 120 rand .....To mention a few fire hazard stories, if the pack is built with cell level fuses does it still pose a fire risk ? most cells will only ever become a fire hazard when over charged and when discharged into the ground and then 1 cell bank goes into reversal a very weird but common problem with Li ion cells in a string of series .... once the cell is in reversal if you have no way of preventing charge from entering the pack you will have a exploding fireworks show... follow the guidelines seek advice and if ever in doubt about some ones advice do the research it wont take long . I do believe Pylon tech warranty sheet needs a few re reads, they presumably warrant their packs to a end of life at 70% of original capacity ????? this doesnt sound right and most will warranty to 80% of original or 20% reduction ... secondly they will only warrant the portion of remaining 7 year life span ... use the battery for 6 years and you will end up paying for another 6 years through a complex calculation at then in the future prices which eeerrrmmm would mean buying a new battery pack from them effectively a they will only cover 2% of the cost of the battery ? interesting read ......

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  • 2 months later...

Seeing that eksdom forced my hand, Had to install my pack this weekend ..   Its about 180ah usable capacity at 1C and easily handles our 500w continues load and I ran the  aircon few times , 1800w 80A at battery level, to check cable tempts etc.  

What the nice part is … after power came back on, took 40 minutes to fully recharge at 0.1c .  I increased the charge level to 0.25 and we had  a ~3 hour power failure last night and recharged fully in 1hr  when power came up.  The  Pack is set to charge to 4.05v per cell (Lithiums don't like being charged to full capacity). Float at 4v.

I also ordered a Batrium battery management system (cost double the price of the battery bank, but need a balancer that plug and play with inverters , no time to build own now) so will see how goes then.  Then its to solder the other 500 cells to get pack to final size.

Will also try do a full discharge to see what true capacity of the pack is , should be about 30% more than the 1A discharge tests as each cell now only see a load off about 0.05c at normal load ..

so in total its should be about  ~R 11k  with management for a usable(not total) 10Kwah bank. So thats same as about 30Kwah lead acid bank (if my calcs are right ).

 

 

 

 

 

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44 minutes ago, Karman de Lange said:

Then its to solder the other 500 cells to get pack to final size.

Great to see someone getting a DIY pack up and running, well done.

My only issue with laptop batteries (and please correct me if I am wrong) is that you are using Li-Ion (3.7/4.2V) and not Li-Iron (LiFePO4 - 3.2/3.7V) - My problem with Li-ion is that the average life expectancy is 300-500cyc when the battery is new. The laptop batteries that you are using are used, and although I assume that you are testing them and discarding the dodgy ones, the ones being used are probably 1/2 life by now.

So have you allowed for the fact that the pack may die within 150-250 days, or am I getting this all wrong?

Edited by pilotfish
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11 minutes ago, pilotfish said:

Great to see someone getting a DIY pack up and running, well done.

My only issue with laptop batteries (and please correct me if I am wrong) is that you are using Li-Ion (3.7/4.2V) and not Li-Iron (LiFePO4 - 3.2/3.7V) - My problem with Li-ion is that the average life expectancy is 300-500cyc when the battery is new. The laptop batteries that you are using are used, and although I assume that you are testing them and discarding the dodgy ones, the ones being used are probably 1/2 life by now.

So have you allowed for the fact that the pack may die within 150-250 days, or am I getting this all wrong?

Hi, 

Ok, some info re "life expectancy".   A manufacture regard 80% capacity as end of life.  Most lithium packs do about 500 - 3000 cycles (2-10 years) if you partial cycle them (50-80%), then after those cycles you have 80% capacity left..  Now also, remember lithium gets damaged when fully charged , the opposite of lead acid that get damaged when not 100% charged

Now we go buy "dead" laptop battery with "80%" capacity left and they have  not seen any charge for years (so no extra damage really occurred).   You test each cell by charging/discharging them and then sit them one side to see if they self discharge.  Any cell below 4.0v after month go to the use for something else pile.  If they get hot on charge, they go in bin immediately.

Now the cell might have been 2500mah  when new. Now its a 2000mah after 5-10 years of use (80%).   That is still a lot for what we need, we don't care about weight etc, so can simply add more cells.  Even 1000mah is perfectly fine if they don't self discharge and don't get hot on use.  Its just double the amount of work (or triple of new cells).  I used anything above 1300mah tested capacity .

So our cells should give us  another 5-10 years of use with only a reduction of 20-30% of capacity (of course, will only know that in 5-10 years). So in theory we will then still have 70% of our current capacity, which is still more than what we need.

 If I can get 5-8 years out of this pack, its same or more than  Lead acid in real world  and at 2% of the price with no worry making sure water levels are right, room is ventilated its a no brainer.   

There article somewhere about Tesla cars (same battery tech) and there battery life expectancy is 25 years with daily use, or more than the life of the car. 

 

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1 hour ago, Karman de Lange said:

There article somewhere about Tesla cars (same battery tech) and there battery life expectancy is 25 years with daily use, or more than the life of the car. 

Tesla is rated for 2000 cycles, but real life shows about 3000. At that point they aren't dead, just reduced capacity.

Jehu Garcia explains the whole thing here.

I still don't think the cells used in laptops is necessarily made to the same level as that for cars, but it illustrates the idea.

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Oh, and for goodness sake... don't burn your house down. I've heard of two cases now via the grapevine of people playing with batteries getting into serious trouble.

Also, no hackery with BMSes. You can't use a Raspberry Pi running Linux to implement a makeshift BMS. Linux is pretty stable and all but not certified to never hang or crash. You probably know this, but I have to say it again for anyone reading this.

Don't burn down your friggin house!

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