18650 Battery bank?

kaipo_boy

I haven't been on for awhile, been too busy at work, sorry!
I am somewhat disenchanted with my 4x 6v GC2 Costco golf cart batteries.  While I understand their limitations and the price point I bought into, I hate the idea of their 5 yearish lifespan and the 200-odd Amp-hours these have given me so far seem dismally inadequate for the larger loads I had planned later.  I have been seeing some videos of some guys who created banks of batteries, using the 18650 high current lithium ion type common in laptops and powerful flashlights, to run their cars... somewhat like what Tesla did for the new S type.  I think the Tesla uses around 7000 individual 18650 cells per car in its battery pack.  Has anyone created such a bank here to use with their home solar system? What about charging systems? Balancing cells? How many years and how deep can you cycle lithium ion cells like these? I know from my flashlights and laptops they have around the same or slightly longer lifespan, I'd say more like 6 to 8 years and can by cycled deeper on average, but that's just my impression since I use them until the light begins to dim, which is probably near 80% used... but I don't use my flashlights daily.   My fridge, on the other hand, doesn't ask for a day off.

aloha,
walt

CALLD

I considered it until I realized how much it would cost to buy all those little cells. However if you can get them cheap enough then buy all means give it a try! It's gonna involve some careful ohm's law calculating taking into account internal resistance, bussbar resistance, connection resistance and wiring resistance. At first I though getting them evenly matched would be impossible but if Tesla could do it then it must be possible!

I may however be tempted to install the newly made DIY battery bank 20ft underground surrounded by thousands of gallons of water "just in case"...

kaipo_boy

Yeah, the 18650 seems to be a rather expensive cell to buy in bulk, but I wasn't thinking of getting 7000 of them... perhaps a few hundred as an exercise would be more realistic initially.  I plan on putting kal-bi and other stuff that needs cooking around mine

Mountain Don

There is at least one person who has bought the battery packs from Tesla wrecks. I don't have the link anymore. The one I am thinking of has several Tesla (model S ?) packs in racks. 

westbranch

Don, was that under owner installed systems?  It was a massive set  of CC's and inverters IIRC...

softdown

You are dis-satisfied with an ~$320 battery bank. Now you are considering a battery bank that may costs thousands of dollars?

Four golf cart batteries is a tiny off grid battery system. That is all there is to it. I would recommend that just to run internet and a couple lights. Why? Because the sun doesn't shine bright every day.

kaipo_boy

Not sure of the cost, haven't really done the math. More like thinking out loud to see what the costs would be vs the run time and useable lifespan. On DX.com the good ones are around $4 each in bulk (more than 10), so a couple hundred of them would be $800 (this site does not charge shipping).  I can see how a wrecked Tesla would become very attractive quickly if you could cannibalize those cells cheaply. Its not a common car to find in a junkyard, though; and items like this bring new meaning to the term 'shelf life.'

Yes, I am a bit dis-satisfied with the 4 GC2 cells I have now.  Nothing wrong with them, but once you connect real demands to them (that's why I only got a small batch, to see how far I'd have to take this concept to go more or less off grid with the rest of my loads) and do the math, it quickly becomes apparent that this gets expensive quickly and then every 5 or 7 years it happens all over again.  I have since come to the conclusion that a used fork lift battery is probably the way to go, but sourcing them in Hawaii might be a bit of a wait and require a bit of opportunistic feeding at a moment's notice so liquid capital helps.  I'm still working on that one as the next step away from GC2's.  Then I saw someone on youtube with the suitcase sized 18650 banks and figured hey, that's a pretty neat idea. I've never really played with lithiums, that's why I posted this; aside from initial cost, how do they run? how far can you discharge and roughly how many cycles to a lifespan?  I know the tesla cells are atypical and not protected, and have some kind of external fire retardant system from the car factory. But none of them have caught fire (yet) unlike the stories I hear about the hyundais.

westbranch

there is the Nissan LEAF too to search for in the wreckers yards.... and maybe a Chevy Volt?

softdown

I can't hardly find trucks newer than 2003 in salvage yards. Tesla's are going to be rebuilt unless they got over by an 18 wheeler. Good luck finding one.

PNjunction

The quick lowdown:

The 18650's you see in typical unsafe amateur one-off hacks, are 3.7v nominal cells, and use a lithium chemistry that far exceeds the performance needs for a solar energy-storage bank.  Laptop cells essentially.  Properly managed, they can be safe(ish).  Amateur-construction - stay away.  

More commonly used for solar storage is a different lithium chemistry, called LiFePo4, and due to the differing chemistry the nominal voltage is only 3.2v per cell.  This is the type of chemistry used in motorcycle powersports batteries (like Shorai, Antigravity etc) where one sits inches away from it.  There are reasons LiFePo4 is safer than any other li-ion chemistry out there for your typical DIY'er.  Boeing's accident was NOT LiFePo4 (aka LFP) but a different li-ion chemistry btw.  Many threads on safety elsewhere.  Again, there is a reason motorcycle LFP batteries are inches away from your butt, but the laptop chmistry cells - NO WAY.

With LFP at 3.2v per cell, it is much easier to construct batteries that slot nicely into the common 12/24/48v range.  Ie, four of the 3.2v cells in series is a 12.8v battery, which interfaces nicely with a lot of gear.

In other words, there are many different li-ion chemistries out there, and they can all have same size, ie 18650, 26650 and so on.  One should choose wisely for both cost and performance reasons.  

For instance, most LFP powersport batteries actually use 26650's, and not 18650's inside to keep the cell count down.  Still, the LFP kind, not the laptop-chemistry.  Believe it or not, but some solar-garden lights use LiFeP04, just as the amazing A123 cells found in motorcyle batteries do.  The difference here is that the solar garden lights are what is known as an "energy cell" designed for low, long duration drain.  The A123's in higher end motorcycle batteries are known as "power cells" designed to have extremely high charge/discharge capabilities.  While one could make a small solar bank from A123's, you'd be paying for a capability you'll never use in the timid solar storage setup that is properly designed for adequate capacity.

For diy safety reasons, the main idea is to reduce the cell-count and use larger cells to provide the capacity you need.  

Thus, most who DO go with LiFePo4, use what are known as "prismatic" cells, much larger than cylindricals, such as those from GBS, CALB, Winston, Sinopoly, etc.  They are MUCH cheaper than shoveling in a box full of cylindrical cells, and with the cell count down, safer for the diy'er.

Think what it would take, even with 3000mah 26650 LFP cylindricals, to make a 12v / 100ah battery.  With large prismatics, how about just FOUR 100ah cells in series with only 3 cell-links?  Much easier and safer to deal with.

Anyway, this is a quick overview.  Stay away from amateur hacks.  Strive for simplicity to stay safe.  Put on your flamesuit and have a thick-skin when reading forum threads.  Li-ion and it's use/abuse generate some of the most informative, and yet at the same time misleading and armchair-engineering you'll ever see. <grin>

PNjunction

And of course the question always comes back to Tesla and why they are using high-performance EV-like cells in their powerwall and not large prismatics.

One answer might be that their system is designed to hang on a wall in the space that used to be taken up by your coiled-up garden hose.  They have no other choice.

You as a diy'er, may not be so limited in space and have the luxury of KISS.

westbranch

thanks PNj  this, is one of the best, simplest statements about different battery chemistries one could use...

While one could make a small solar bank from ......, you'd be paying for a capability you'll never use in (the timid) a solar storage setup that is properly designed (for) with adequate capacity. to meet the planned needs.

I took the liberty of making a few minor changes, hope you don't mind.

Dave Angelini

Exactly said!  Of all the offgrid homes I have done, not one had restricted space requirements for the battery bank.
Offgrid is the essence of free space and safety! The less is more design school!

zoneblue

And... if you happen to open up one of those tesla model S batterys, youll find some of the highest tech youll ever se near a battery. Theres water cooling, individual fusing for EVERY cell, and computerised BMS. So if you thinking of building one that gives you an idea what you are up for. Dont be educated by some 16 year old "supergenius" on youtube.

MarkC

zoneblue said:

And... if you happen to open up one of those tesla model S batterys, youll find some of the highest tech youll ever se near a battery. Theres water cooling, individual fusing for EVERY cell, and computerised BMS. So if you thinking of building one that gives you an idea what you are up for. Dont be educated by some 16 year old "supergenius" on youtube.

As an example, such "supergenius's" are buying wrecked Nissan Leafs, dis-assembling the battery/packets, tearing down the packets to individual flat packs, rewiring and installing in their EV motorcycles (and likely others).  Once these packets are out of their tightly controlled environment - anything goes (and probably fast, for a while at least).  It's all on youtube.

I own a used Leaf - its a really fine car (actually to my surprise) and super cheap because the used ones don't go very far (at least after a couple of years in hot Texas environment).  It illustrates the importance of not only proper battery management (it has that), but also proper battery environmental considerations (no purpose designed cooling for hot climate use).  I've downloaded the repair manuals (essentially design manuals for the entire battery/management/charging systems) and plan on learning a lot.  Meanwhile drive a hoot of a car (around my suburbs anyway).

Anyone making progress in harnessing the Leaf's 20KWH of energy for emergency off-grid use?, please let me know.  Likely not the most efficient energy storage (solar PV/charge controller/battery/inverter/level 2 charger/Leaf converter-inverter-stabilizer-charger and finally the Leaf battery - then getting it back at 300+ volts DC?).  I bet it's not long before we see someone on youtube doing this.  
 

softdown

I remember having some batteries in my pocket while doing wedding photography. One started to get quite hot very quickly. I fished it out and threw it in the bushes. Was a bit surprised that a fire did not start. There is a sound argument for keeping battery arrays simple and "safe/r".

JoshK

These are great lithium batteries.  And the form factor beats the heck out of trying to deal with connecting 18650s and balance charging them.  This one even has a balance charge connector that you don't see in the picture too.  I have one for portable '12v' power and it is great.

Mountain Don

Many years ago when we first started using Li-ion cells in RC it was recommended that we have the battery pack on a steel or concrete surface and hang a plastic bag of sand directly above the cells being charged. The sand made a great extinguisher. We don't do that anymore, but we also use high quality cells and chargers.

PNjunction

Josh - those are not the right chemistry for our use.  They are NOT LFP, or LiFeP04.  There is a big difference between the two in both handling and charging.  The big giveway is that anything but LFP is usually a 3.7v cell, not the 3.2v per cell that we deal with.

In addition, quality is suspect, and usually slipshod containers of nothing more than wrapping tape, shrink-wrap etc.  Can you say "swelling" or vent-with-flame, despite the use of a hobby balance charger?  I personally run Sanyo 18650b's with my own iCharger, but that is not for our application!

Here's the deal:

Should you charge your "zippy" batteries in a fireproof bag?  Yes, due to the unstable, yet very powerful chemistry.

Do you need to charge LiFeP04 batteries in a fireproof bag or in your fireplace?  Not really - consider that most LFP powersports batteries like Shorai, EarthX, Antigravity, Braille, etc - which are all LFP, are inches away from your butt-cheeks in most motorcycles.  THAT chemistry, LFP, is the chemistry I want to have around for a solar housebank, albeit using much larger prismatics like GBS, Winston, CALB.

This dovetails into the EV cylindrical cells too.  NOT our chemistry.  Not sold directly to consumers, but gotten from crash-victims.  Requires extensive knowledge on not only how to disassemble and rebuild, but operate as well to stay safe.

We're at both ends of the spectrum - TOY JUNK, and high-end EV cells.  Neither is the chemistry we use, which is LiFeP04.  THAT chemistry is easily manageable, and available to the DIY'er that isn't a one-off benchtop hack.  Common sense operations can keep it simple without having to ride the knife-edge of safety that you would with other li-ion chemistries.

Johann

kaipo_boy said:

Not sure of the cost, haven't really done the math. More like thinking out loud to see what the costs would be vs the run time and useable lifespan. On DX.com the good ones are around $4 each in bulk (more than 10), so a couple hundred of them would be $800 (this site does not charge shipping).  I can see how a wrecked Tesla would become very attractive quickly if you could cannibalize those cells cheaply. Its not a common car to find in a junkyard, though; and items like this bring new meaning to the term 'shelf life.'

Yes, I am a bit dis-satisfied with the 4 GC2 cells I have now.  Nothing wrong with them, but once you connect real demands to them (that's why I only got a small batch, to see how far I'd have to take this concept to go more or less off grid with the rest of my loads) and do the math, it quickly becomes apparent that this gets expensive quickly and then every 5 or 7 years it happens all over again.  I have since come to the conclusion that a used fork lift battery is probably the way to go, but sourcing them in Hawaii might be a bit of a wait and require a bit of opportunistic feeding at a moment's notice so liquid capital helps.  I'm still working on that one as the next step away from GC2's.  Then I saw someone on youtube with the suitcase sized 18650 banks and figured hey, that's a pretty neat idea. I've never really played with lithiums, that's why I posted this; aside from initial cost, how do they run? how far can you discharge and roughly how many cycles to a lifespan?  I know the tesla cells are atypical and not protected, and have some kind of external fire retardant system from the car factory. But none of them have caught fire (yet) unlike the stories I hear about the hyundais.

They make DC generators for 12 volt, 24 volt, 36 volt and 48 volt systems that turn automatically on when the voltage in the batteries goes down when a lot of load is applied.
This would be cheaper and you do not have to re-invent the wheel and may safe you from having a fire.

jimmyaz

Would it make sense if you can buy the Tesla model S module for 1000buck?  444cells = about 5-6kw.  This is pretty much ready for use, all the cells is already built. 

But I wonder is this safe enough to have this in your garage?  vs say AGM battery?  I am somewhat disapointed with my AGM battery as well, can hardly discharged 20-25% before the voltage drop so much... 4.5kw rated, but only can use about 1kw.

bill von novak

JoshK said:

These are great lithium batteries.  And the form factor beats the heck out of trying to deal with connecting 18650s and balance charging them.  This one even has a balance charge connector that you don't see in the picture too.  I have one for portable '12v' power and it is great.

Those type (LiPos for RC use) are the least safe cells out there.  They are used because they are the highest energy to weight ratios available, and a fire will (at worst) will destroy a toy airplane.  I use a 36V Lipo on an electric bike and store it in a shed; again, worst that can happen there is that there's a fire in the shed.

I would be VERY wary of using a large amount of those batteries in any stationary indoor application.

Estragon

I've looked into LiFePO4 a few times in the past for my boat.  It has advantages in terms of being smaller and lighter for the effective capacity.  It seems to run at least 2-3 times the cost of golf carts even using individual cells, and considerably more buying complete 12v packs.

Estragon

jimmyaz said:

Would it make sense if you can buy the Tesla model S module for 1000buck?  444cells = about 5-6kw.  This is pretty much ready for use, all the cells is already built. 

But I wonder is this safe enough to have this in your garage?  vs say AGM battery?  I am somewhat disapointed with my AGM battery as well, can hardly discharged 20-25% before the voltage drop so much... 4.5kw rated, but only can use about 1kw.

How fast are you discharging the 25%?  At C/20 your voltage should be something like 12.4 at 75% SOC.

jimmyaz

Estragon said:

jimmyaz said:

Would it make sense if you can buy the Tesla model S module for 1000buck?  444cells = about 5-6kw.  This is pretty much ready for use, all the cells is already built. 

But I wonder is this safe enough to have this in your garage?  vs say AGM battery?  I am somewhat disapointed with my AGM battery as well, can hardly discharged 20-25% before the voltage drop so much... 4.5kw rated, but only can use about 1kw.

How fast are you discharging the 25%?  At C/20 your voltage should be something like 12.4 at 75% SOC.

I was pulling about 650watts, so roughly 20amps.  it only did that for about 30mins... then battery voltage was below 21.00.    My setup is 24v 210AH. 

just starting

When I figure amp pull I use 6.5 amps @24v per 1amp at 120v so if you have 105 amps available at 50%DoD that olny 16amps 120 and when pulling a load like 5 amps 120 *6.5 is a steady 30 amp draw off the bank. That's worst case with crapy conversion. And add perkuts law. Not sure on spelling.