# Would these batteries be suitable for EVs?



## Ivansgarage (Sep 3, 2011)

timk225 said:


> For the first time ever, I got on alibaba this morning, and started searching for batteries, to see what my cost would be if I could buy directly from the manufacturer.
> 
> Would these be good for an EV application? This first one comes in 3 packs, so right away I have some parallel arrangement done for me and less soldering to assemble the entire battery pack. It looks like they have the pressure release vent tops on the cells.
> 
> ...


Why didn't you just post the link?????

Ivan


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## timk225 (Sep 19, 2014)

I tried posting the links but it was just taking me to the alibaba home page and not the exact item.

Links from the item pages:

http://www.alibaba.com/product-detail/3p-li-ion-3-7v-7200mah_60047392935.html

http://www.alibaba.com/product-detail/3-7V-2600mAh-single-cell-Solder_1921483596.html


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## Sunking (Aug 10, 2009)

My AV program will not even let me view the links telling me to get out of there.


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## timk225 (Sep 19, 2014)

I have posted links many many times, I don't know why these alibaba ones are such a problem. I just Copy and Pasted the 2 cell descriptions into the alibaba search box and it found them both at the top of the first page in both cases.


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## Karter2 (Nov 17, 2011)

Those links are going nowhere useful.
Only one way to buy good cells from china, and that is to use a recommended source. IE, one that someone reputable can confirm that they have purchased cells from that have turned out to be 100% genuine as described, and not relabeled scrap or used laptop cells..or worse.!
Too many scam cells around to gamble on with china sellers.


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## dougingraham (Jul 26, 2011)

timk225 said:


> 3p li ion 3.7v 7200mah 18650 battery pack (3 green batteries with the black end covers)
> 
> Or this one, single cells with tabs.
> 
> ...


18650 cells seems to be particularly bad with off brand labels. If you look on EBAY you can find amazing claims for capacity from Chinese clones. You can find sites that have capacity tested off brand cells and found them to be universally terrible.

I suggest you get some samples to test before you order a large number from an untested source.


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## ga2500ev (Apr 20, 2008)

timk225 said:


> For the first time ever, I got on alibaba this morning, and started searching for batteries, to see what my cost would be if I could buy directly from the manufacturer.
> 
> Would these be good for an EV application? This first one comes in 3 packs, so right away I have some parallel arrangement done for me and less soldering to assemble the entire battery pack. It looks like they have the pressure release vent tops on the cells.
> 
> ...


In general small format cells simply have too many potential failure points to be viable for EV use. Then to compound these are Lithium Ion, which is definitely a fire hazard.

What is your budget? What is your range estimation? What type/weight vehicle are we talking about?

Nissan Leaf cells come in large format and clock in about $0.26 USD per Whr. For both convenience and price, it's tough to beat.

ga2500ev


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## Hollie Maea (Dec 9, 2009)

A good rule of thumb for buying 18650s is to go down to your local department store and look at the TV section. If the manufacture of your potential purchase isn't selling a TV there, then you are treading on thin ice.

So...Companies like Samsung, LG, Panasonic, Sony, Sanyo etc. are good manufacturers. Something like "Trustfire"...not so much (If they have to put "trust" in their name, they aren't trustworthy. The "fire" part is probably accurate though).

OK, so you find someone selling some cells of one of those good brands. Demand images of the cells being shipped, and also insist on using escrow to protect your money until you verify that he sent you what you asked for.

If he is unwilling to do those things, walk away.

Edit: If anyone is saying they have 18650s to sell with more than around 3200mAh, they are lying.


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## timk225 (Sep 19, 2014)

I contacted someone I know today who does alot of computer work, and he said he had about 200 laptop computer battery packs laying around. I'm sure he will make me a good price on them.

I think that for initial testing purposes, I can get these and pull them apart and test the cells and see how they are for good and bad cells.

Perhaps use them to make a smaller amp-hour test pack for initial electric car use, then if it works out, add more capacity. Only problem is it'll be a lot of tedious work, but I'd rather do that than lay out big bucks up front on an unproven project. I would not want the hassle of trying to resell these batteries if they were all new and I gave up on the project halfway through.

Remind me, why are Li-ion laptop batteries bad for EV cars? Is it that they make heat during high charge and discharge, or some other reason? I can add a few 6 inch computer fans to the battery boxes to provide some airflow, but there won't be any complex Tesla-like cooling system.

And among laptop batteries, I'd have to use ones of all the same capacity? No mixing 2100 and 2800 and 3100 mah cells, in either series or parallel? I'll have to google search and see if there's some sort of battery charger / tester to run them through.


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## rwaudio (May 22, 2008)

timk225 said:


> I contacted someone I know today who does alot of computer work, and he said he had about 200 laptop computer battery packs laying around. I'm sure he will make me a good price on them.
> 
> I think that for initial testing purposes, I can get these and pull them apart and test the cells and see how they are for good and bad cells.
> 
> ...


Technically there is nothing wrong with paralleling 2100/2800/3100mah cells, however it doesn't hurt to try and keep a narrow band to reduce currents flowing between cells in parallel. I'm using almost new 2200mah and used 2600 and 2800mah cells, my average capacity as measured is about 2000mah with 1C testing. To the best of your ability you will want to make your parallel groups as close as possible in capacity. I haven't measured my individual cell capacities, however I have measured them in groups of 16 cells, I will then be paralleling 3 of those groups for 48 cell ~96Ah modules, the key is I can add the 16 cell groups together in such a way that all of my paralleled groups are all very close to 96Ah.

For cell holders I'm testing with these:
http://www.fasttech.com/products/0/10004028/1290405-diy-18650-battery-holder-case-box10-pack

I'll take pictures once I get to the assembly stage of my first 7S48P layer (in a 16cell x 21cell rectangle)

Good luck.


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## pdove (Jan 9, 2012)

http://www.youtube.com/watch?v=JQa5gn-7D74&list=UUcMfCkN1juSa49DJFYltOTw

I wouldn't do it but some do.


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## dougingraham (Jul 26, 2011)

timk225 said:


> Remind me, why are Li-ion laptop batteries bad for EV cars? Is it that they make heat during high charge and discharge, or some other reason? I can add a few 6 inch computer fans to the battery boxes to provide some airflow, but there won't be any complex Tesla-like cooling system.


It is pretty clear that they aren't bad for EV's. They are not convenient for DIY EV's. The common and inexpensive ones can comfortably do 2C without heating much. They can probably safely do bursts of 5C. If you need 1000 amps for 10 seconds and you have 2.2 AH cells you need 91 in parallel. If you go for 20 seconds you may be bailing out of the vehicle if you can get stopped in time.




timk225 said:


> And among laptop batteries, I'd have to use ones of all the same capacity? No mixing 2100 and 2800 and 3100 mah cells, in either series or parallel? I'll have to google search and see if there's some sort of battery charger / tester to run them through.


That would be preferable. But you could mix a few in as long as every paralleled module ends up with the same capacity. Your pack is only as large as the weakest module.


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## timk225 (Sep 19, 2014)

Can anyone recommend a battery charger / discharger that I can use to run individual cells up to 4.2 volts, then put a load on them and time how long it takes to discharge to a set point, like 3.2 or 3.4 volts? After some Google searching, I found the IMAX B6-AC at hobbyking.com, but I'm wondering if there are better units out there. Preferably something that can discharge at 1C to 2C battery capacity, so each individual cell doesn't take three hours.

Any charge / discharge units that can handle multiple individual battery cells at once and report independently on each one?


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## Yabert (Feb 7, 2010)

Tim, look at powerlab 8 or icharger 4010duo


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## dougingraham (Jul 26, 2011)

timk225 said:


> Can anyone recommend a battery charger / discharger that I can use to run individual cells up to 4.2 volts, then put a load on them and time how long it takes to discharge to a set point, like 3.2 or 3.4 volts? After some Google searching, I found the IMAX B6-AC at hobbyking.com, but I'm wondering if there are better units out there. Preferably something that can discharge at 1C to 2C battery capacity, so each individual cell doesn't take three hours.
> 
> Any charge / discharge units that can handle multiple individual battery cells at once and report independently on each one?


I use an iCharger 3010b and a lot of people mention the Power Lab 6 or 8. The iCharger will do single cells at 30 amps charge and discharge. I use it with my 100 AH cells. I also have a CBA III discharger but it will not do what they claim it will although for your purposes it would discharge at 20 amps. (They claim it can do 30 amps but it overheats and shuts down in just a few minutes at 30 amps).


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## ga2500ev (Apr 20, 2008)

timk225 said:


> Remind me, why are Li-ion laptop batteries bad for EV cars? Is it that they make heat during high charge and discharge, or some other reason? I can add a few 6 inch computer fans to the battery boxes to provide some airflow, but there won't be any complex Tesla-like cooling system.


As I stated in my earlier post, the biggest issue is the small format. You are going to have to have hundreds of batteries with hundreds/thousands of connections all working perfectly for the pack to function properly. Also locating one bad cell or one bad connection is like looking for a needle in a haystack.

The second issue is that especially for Lithium Ion, overcharging failure modes can be catastrophic.

The next issue has been discussed above. Since these cells cannot be pushed beyond 2C continuous, you're going to have to string a ton of them together to get sufficient amps without overdriving them. However, you are still limited to 3.7V/cell group. So to get sufficient voltage you'll still need to string 24-48 of those cell groups together. So it'll end up being thousands of cells, not hundreds of them.

Finally, while such cells can be repurposed for this task, they are certainly not engineered for such as task.

Let's attempt a side by side comparison with likely the best option out there, the Nissan Leaf battery module. In order to amortize the shipping cost, I'm choosing the 4 module pack which gives 30.4V * 60 AHr -> 1824 WHr capacity. The cost with shipping is $555. This clocks in at $0.30 USD a WHr in cost.

The pack can be reconfigured to 60.8V, 30Ah. So in theory to get a 120V pack, you would need two of them. This would also double the energy capacity.

Now how do you get 1824 WHr using Li Ion cells? The nominal voltage is 3.7V for Li Ion. So you would need 1824 WHr/3.7V -> 493 Ahr total. Being generous I'll use the 2 Ahr/cell figure given in a previous post. So that means that you'll need 493 Ahr/2 Ahr cell -> 246 cells to anything that's near equivalent.

Now it may seem to be an apples to apples comparison if you can get the 18650 cells for $0.60 USD apiece or less. However, you now have 246 cells that you have to match, balance, group together into cell packs, and a ton of other work just to get them going.

Note that the Leaf modules can be pulsed up to 540A (9C). Even at 5C for the 18650s you'd need 54 cells in a cell group to get that kind of current. And you'd need 8 cell groups to get the 30.4V to match. So that's 430+ cells right there.

The real question is how much is the time, hassle, and unreliability of having all those individual cells worth to you, even if they are free or minimal cost?

ga2500ev


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## timk225 (Sep 19, 2014)

You're right, I think the Leaf batteries would be the easiest way to do it, if not for money. I'm sure Nissan did a lot of research on engineering them for liability reasons alone, along with performance.

My background in computer work makes it fairly easy and low cost to get a bunch of used laptop battery packs and test and reassemble the cells. 

I certainly do not want to do all that work, but money is money, and unless someone sends me a check for $10 grand or a UPS freight delivery of a lot of Leaf batteries, this is my only real way of doing it.

I have another idea or two, I need to research it a bit more first.

How about a charger setup? Let's say I got 30 KW or however many of these Leaf cells. What battery charger would be able to charge and monitor the cells for optimum performance? Can anyone recommend an on-board charger that can accept 120VAC and 240VAC inputs and monitor the pack while charging?


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## ga2500ev (Apr 20, 2008)

timk225 said:


> You're right, I think the Leaf batteries would be the easiest way to do it, if not for money. I'm sure Nissan did a lot of research on engineering them for liability reasons alone, along with performance.


All true.


> My background in computer work makes it fairly easy and low cost to get a bunch of used laptop battery packs and test and reassemble the cells.


I understand. Hence the reason for the comparison.



> I certainly do not want to do all that work, but money is money, and unless someone sends me a check for $10 grand or a UPS freight delivery of a lot of Leaf batteries, this is my only real way of doing it.


I guess I need a clarification here. Exactly what sized pack are you trying to put together? A 36 KwH leaf pack, which is 50% larger than the actual pack in the Leaf, can be had for under $10K. 

If you are not sure of your pack needs, then can you give a ballpark on the weight/type of the vehicle and the range you expect to get. You may have done it in your initial post, but I cannot see it from here.

ga2500ev


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## aeroscott (Jan 5, 2008)

timk225 said:


> Can anyone recommend a battery charger / discharger that I can use to run individual cells up to 4.2 volts, then put a load on them and time how long it takes to discharge to a set point, like 3.2 or 3.4 volts? After some Google searching, I found the IMAX B6-AC at hobbyking.com, but I'm wondering if there are better units out there. Preferably something that can discharge at 1C to 2C battery capacity, so each individual cell doesn't take three hours.
> 
> Any charge / discharge units that can handle multiple individual battery cells at once and report independently on each one?




I am running a imax b6 now and it is slow. Found a Power lab 8 on line. 1334 watts and high discharge as well.


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## Hollie Maea (Dec 9, 2009)

ga2500ev said:


> Since these cells cannot be pushed beyond 2C continuous, you're going to have to string a ton of them together to get sufficient amps without overdriving them.


That's not entirely true. There are a lot of different options for this chemistry/form factor that differ vastly in terms of power capabilities.

I've recently been doing tests for volume constrained battery pack design, and since these cells are unmatched in terms of volume density, I did some testing on them.

The first test I did was on some LG cells. Now, these were not power cells in any sense of the word. 3Ah, rated for 2C PEAK. They were intended for a 69kWh pack, so no big deal. But I wanted to see how they would handle, so I took a damaged cell and discharged it at 6A, with no cooling. It definitely suffered significantly, sagging nearly .9 Volts. So definitely it was pushing the limits of a peak rating. I wanted to see how long it could take it without blowing up, so I kept it hooked up, ultimately until it was drained completely. That took about 13 minutes (it was about half full at the beginning). During that time it reached 79 degrees! But, surprisingly, didn't go into thermal runaway.

Next, I tried pushing it to 10 Amps. It went for just over a minute before the current suddenly dropped to zero. It was "only" reading 39 degrees, but I'm sure the interior was much hotter. After letting it cool, it worked again, but continued doing the same sudden cut off when discharging at 10 Amps. Not sure if it was some kind of heat triggered circuit breaker or what. So yeah, 3C or so for less than a minute is the most you could get out of these cells, even if you were cavalier about their health.

More interesting were some "power" cells. These have been developed primarily in response to the power tools and e-cigarette markets, and can handle much higher power than the others, albeit with a energy density hit (still, they are higher in density than any other cell on the market). The ones I tested were 2.5Ah models from Sanyo, although Samsung, Sony and some others offer nearly identical models as well.

My first test discharged a nearly full (charged to 4V) one at 3C (7.5A). It ended up taking 15 minutes to drain. It handled the current a lot better, sagging .4V and reaching a temperature of 52 degrees after 15 minutes. Certainly hotter than it would like, but not in any sort of danger zone.

My next test, 20A, aborted after 2 minutes when the battery holder melted. 

After making a new, more robust, battery holder, I found that a significant part of my "sag" (and heat production) was due to the undersizedness of the battery holder setup. I retested at 10A (4C). This time it only sagged .3V. After 10 minutes it was drained and had risen to 50 degrees.

My final test was to compare the cells, on a volumetric power density level, to some "gold standard" power cells--some little Kokams, that look like a candy bar, hold 4.5Ah, and are rated at 30C continuous, 50C peak. Unfortunately, my crude testing setup didn't allow me to push them anywhere near the peak, so I just cranked it as high as I could, which ended up being 52A. My plan was to just see how much heat they would produce at that current and then compare it to the Sanyos.

Sag was about .6V, and after two minutes, the temperature was up to 46 degrees.

For my comparison, I didn't push the Sanyos to the same power levels or C ratings. Instead, since I was concerned primarily with volume density, I calculated what the current would be required to get the same power out of a given volume. Volumetrically, the 18650s are 2.89 times smaller, if you stack them with no interdigitation. So, to match the volumetric power output of the 52 Amps, I needed to get 18 Amps out of the Sanyo.

Due to the limitations of my setup, I ended up a little higher than my target--about 19.3 Amps. Sag was nearly identical to the Kokams, 0.6V. And after two minutes, it was actually marginally cooler than the Kokams, 44 degrees.

Now, obviously numerous caveats apply: The Kokams were not running anywhere near their rated peak, so presumably they handle high heat extremely well. Also, they have a higher area to volume ratio, so the core might have been cooler than the core of the Sanyo at the end of the two minutes. Finally, This was only a volumetric comparison. Gravimetrically, the advantage of the Sanyo (45 grams) over the Kokam (125 grams) slightly lower (2.78 times vs 2.89 times). Still, my test ended up being slightly higher even than the gravametric ratio (18.7 Amps). All in all, I was very surprised at how well they hang with the legendary Kokams. Considering that they have a volumetric energy density 1.6 times higher than the Kokams, and are WAY cheaper, they look pretty attractive to me for high power weight or volume constrained packs. Of course they continue to have the age old interconnection and pack design challenges that we keep talking about.


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## timk225 (Sep 19, 2014)

I assume your temperature numbers are in Celsius? What sort of discharge C rating might typical laptop 18650 cells have? 1C to 2C would be my guess.


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## Hollie Maea (Dec 9, 2009)

timk225 said:


> I assume your temperature numbers are in Celsius? What sort of discharge C rating might typical laptop 18650 cells have? 1C to 2C would be my guess.


There are a ton of different cells that go into laptop packs, but in general, I think, they don't tend to be the high discharge types. Probably 1-2C continuous rating with 3C peak ratings.

I was just looking at some data for the Samsung high discharge cells. For the pulse test they were doing 95A for .5 seconds, 80A for .5 seconds, 45A for five seconds and 30A for six seconds (repeat with 12 second rest).

Yes, temps in Celsius.


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