Lowest cost per cycle ebike battery

[CUDAcores89]

About 6 months ago I built an ebike and it has been working great. I use the thing every single day to get to and from work. So far I have put about 2000 miles on an ebike battery I built from "dead" laptop batteries and I have started to notice that the cells sag in voltage much more than a small lipo pack I also keep around for emergencies. I know why this is. It's because when one uses old, used cells that were simply never designed for such a high discharge rate they tend to sag quite a bit under load.

Now here is where the question comes in. I am looking at either purchasing/building (probably building to decrease the battery cost and avoid the battery murdering systems) a new battery pack. But this one I want to last as humanly possible. For the sake of argument, let's ignore the resulting weight, capacity, and size (both dimensional and capacity) of the battery and just focus on the chemistry. What battery chemistry is going to last the longest? There are several I could use, so I am going to compare them below:

Lead acid - The only advantage lead acid has is low initial cost, that it. Because it only lasts a few hundred cycles it must be replaced often meaning the cost per cycle is quite high, so that's out.

Nicd - Nicd does have some advantages over other chemistries. It can be charged and discharged quickly and last long if the battery is maintained, these cells have been proven to last thousands of cycles. The problem is not many companies make nicd batteries anymore so the initial cost is quite high just because these cells are harder to find.

Nimh - nickel metal hydride batteries are similar to nicd, but they have a higher energy density and do not have a memory effect. I could use these cells and they are an option. But I would have to find high-drain ni-mh batteries and would likely increase the cost per cycle as the initial cost would be high.

Lipo - I straight up can't use lipo. These cells are very powerful and many can (i'm speaking of HK lipos by the way) easily put out a 20C discharge rate. The problem is these things only last a few hundred cycles at best meaning the cost per cycle is quite high, so these are out.

18650 li-ion - This is the form factor I use currently. These cells have better cycle life than lipo, are safer then lipo (at least in my experience) but still only last 300-500 cycles. This is the reason why I am looking for alternatives.

Lifepo4 - This is the most promising one. Lifepo4 has a higher energy density than the nickel-type batteries, and many are rated for up to 2000 cycles. Their energy density is however worse then lithium-ion, but they make up for that due to the fact that they last much longer. They are also the safest of all lithium-type battery chemistries.

So yesterday, I was browsing ebay, and I found this:
http://www.ebay.com/itm/NEW-Box-of-80-Tenergy-LiFePO4-32650-3-2V-5500mAh-Rechargeable-Batteries-5-5Ah-/351864363778?hash=item51ecc01b02:g:YPoAAOSwoi1X87JG

I can get an entire case of 80 lifepo4 cells for $150, so this seems like a really good deal. And after checking the datasheet:
http://www.all-battery.com/datasheet/30069-0_datasheet.pdf

one cell has a maximum continuous discharge of 10 amps. This is good news. I could buy an entire case of these cells, only use 48 of them to give me a 12S4P 38.4v 22AH lifepo4 battery pack. Then sell off the rest to get some of my money back. This is currently what I am looking at doing.

To help answer my question here are my bikes specs:

36v "250w" (it actually draws 500w under load) rear when ebike hub motor I bought from ebay.

36v 10AH ebike pack built from dead laptop batteries

The motor draws around 12.5 Amps under load

So which should I do?

1. Buy those tenergy lifepo4 cells in the ebay listing, and build a pack from that.

2. I could also look at building a nicd or nimh style battery pack.

3. This wasn't mentioned but I will mention it here. I could buy 150 2500mah 18650 cells and simply only charge and discharge the pack 50% of the way. This would extend the life of the pack to 2000 cycles with about the same energy density of lifepo4.

Or is there something else I could do that I haven't looked at.

Any suggestions?

 

[amberwolf]

Or is there something else I could do that I haven't looked at.

THere are a number of "flavors" of the LiPo / non-LiFePO4 lithium chemistry; each of them has it's own characteristics.

There are also several physical formats of these cells, including "prismatic" box cells, and pouch cells. Usually the pouch cells require special considerations or compression, but not all of them.


One of the chemistries is NMC, and there are 18650 cells (that I don't have experience with) and pouch cells that EIG (and probably others) makes (that I use) that last a long time with good performance.

I've been using a 14s 1p (20Ah) pack of these since 2011 I think it is, at 4C+ peak rates and <1C rates, with only one cell in the pack aging before it's time and being replaced with a spare, a year or two ago. It does sag more now than it used to, mostly when it's colder, but it's still acceptable. I do not use a BMS with it, and it has not required balancing though I have connectors to do so and have balanced it a couple of times to within a hundredth of a volt. (typically it stays within a few hundredths cell to cell).

It's been thru hot summers here sitting in direct sun for hours on many days, which probably hasn't helped it's aging; it can get 150F+ in the direct sunlight while ambient temps are 115-120F+. I don't doubt that the cells have sat at 150F+ for most of the time they were in the sun in the summer, bike parked outside while I shopped or worked, etc. (or while riding, but there's airflow then, so it might not have gotten nearly as hot).

Mine were used when I got them, with unknown usage/conditions beforehand.

I just have them in their original cell-stackers, bolted together, in a 50-cal ammocan; there's no special pressure applied ot them and they havent' had any swelling/etc.

The only cell that has swollen is in a separate lighting pack (4s) that I accidentally left the trike's car headlight and stuff on for hours, and it drained the pack down so far that one cell (I believe it was the one pulled from the main pack previously) appears to have reversed and swollen up. The other cells are still ok and work fine as a 3s pack (I don't have any more spares).

I also had another 4s lighting pack that had a dead short across it for about a minute while I stopped, got off the trike, and ripped out flaming wiring to eliminate a short that had occured, causing a wiring fire...but the cells were perfectly fine and are still in use as the lighting pack.

They all seem to still hold full capacity; even the 3 still in the 3s pack that were once drained down to zero at a low current by accident (as a 3s pack), and then later drained to near-zero in the incident that killed the one cell (as a 4s pack), though these sag more than the other cells under high loads.


The catch is getting hold of the cells; unless you want a palletload of them it's tough to get them from EIG directly, so you'd have to find someone where you are (to avoid re-shipping costs) that already has them. Iv'e seen them for sale on ES now and then, if you search the for-sale section for EIG.


If I had money for them I'd buy more to make a huge pack for the trike, and more spare packs for extra range or quick-swaps. They've been well-behaved and nearly maintenance-free; most of the "maintenance" has been tests done on them just to see how they're doing.

 

[wesnewell]

Look at the specs on the tenergy cells with regard to cycle life.
Cycle Performance:
>2000 (80% of initial capacity at 0.2C rate, IEC Standard)
That's at a 0.2C discharge, or for a 4p pack, 4.4A. So drawing 12.5A is almost 3 times as much. so cut your cycle life down to ~ 600 cycles. Still not bad, if they perform to specs. But it's going to be a big heavy pack for 22ah. But at least it's cheap at ~10 cents per wh. BTW, HK graphene lipos are rated for 600 cycles at a much higher discharge rate and won't have near the sag as the tenergy pack even with only a 10ah pack. And you can put a lipo pack together in seconds without any welding.

 

[999zip999]

What country are you from ?

 

[CUDAcores89]

Thanks for the information, but where would I even be able to buy NMC cells? I can't really find these anywhere. Lithium cobalt oxide, lithium maganese ann lithium nickel type batteries are easy to find (IMRbatteries.com, amazon, ebay aliexpress) but I can't seem to find any NMC cells. Where would I buy these?

 

[CUDAcores89]

What country are you from ?

United States. Michigan more specifically.

 

[CUDAcores89]

BTW, HK graphene lipos are rated for 600 cycles at a much higher discharge rate and won't have near the sag as the tenergy pack even with only a 10ah pack. And you can put a lipo pack together in seconds without any welding.

Actually thanks for the tip. Now I am considering these instead. Now I have used lipo cells in the past and my experience really hasn't been very good. The lipo cells I have used in the past (this was only a coupls of years ago) swelled up under normal use after around 100 cycles and around the 75 cycle mark, started to puff up. This is why I like cylindrical cells, because they cannot physically puff up over time. Have you have good personal experience with HK graphene lipos? Because I could also build a 37v 10AH pack out of those cells for the same price ($150). As long as they last several years and perform well, I would be happy to get them instead.

 

[CUDAcores89]

Found some even better ones. These are Soshine 26650 lifepo4 cells with a maximum continuous discharge of 30 amps. They will last 2000 cycles at 100% DOD at 2C. These ones actually are much better than the original ones I bought. To build a pack out of these would cost me $200. But it would last over 2000 cycles at 2C and if I undercharged them, I could extend the cycle life significantly beyond that.

 

[liveforphysics]

A cell can use a LiFePO4 cathode or NCM cathode and have a short saggy life with rapid cycling decay into failure.

Likewise it could cycle for many thousands of cycles.

Picking a cell for its chemistry would be like picking a laptop based on the type of plastic the keys are made from or something. It really has no bearing on if the cell will good anymore than the laptop would be good by virtue of its plastic type used.

 

[skeetab5780]

Just use a bunch of Double A's they will do the trick. I hear that car batteries are filled with them if you need some.

 

[amberwolf]

Thanks for the information, but where would I even be able to buy NMC cells? I can't really find these anywhere. Lithium cobalt oxide, lithium maganese ann lithium nickel type batteries are easy to find (IMRbatteries.com, amazon, ebay aliexpress) but I can't seem to find any NMC cells. Where would I buy these?

It isn't just NMC that I was recommending, it was EIG's NMC, because I have experience with that (which I posted).

Just plain NMC cells by other vendors are available, even in 18650, but I don't know anything about them or their quality or longevity in our usages, so you would have to determine cost-per-cycle on your own by buying some and building a pack out of them and testing them over time.

As for how to find them:

Iv'e seen them for sale on ES now and then, if you search the for-sale section for EIG.

one thread
https://endless-sphere.com/forums/viewtopic.php?f=9&t=60272&hilit=EIG
google
https://www.google.com/search?q=+EIG+NMC&ie=utf-8&oe=utf-8
http://www.eigbattery.com/_eng/designer/skin/02/01_03.asp
(but as noted if you buy from EIG you probably have to get a palletload of them; you'd have to call them up and ask)

LG Chem also makes some but I know nothing about how good they might be (just the EIG).


Just plain NMC search:
https://www.google.com/search?q=+EIG+NMC&ie=utf-8&oe=utf-8#q=nmc+battery&tbm=shop

 

[CUDAcores89]

SO what I have heard so far is that is is not the cell chemistry that determines how long the cell will last, but rather the quality that determines the lifetime of a cell. The cell can be made of lifepo4, but that doesn't mean is will actually last a long time. The lifetime of the cell all comes down to how the manufacturer made them, and how long they intend for the cell to last.

It sounds like A123 systems makes very good cells, and fortunately fasttech is currently selling 18650 style A123 cells for pretty cheap:
https://www.fasttech.com/products/1420/10002801/1208601-a123-systems-18650-lifepo4-1200mah-high-discharge

I could build a 12S10P battery pack using 120 of these cells, and it would cost me around $280 just for the cells. As long as it lasted a long time I would be fine with that.

It sounds like EIG cells are also quite good, but aren't as easy to get ahold of as simply pressing "add to cart" and checking out at an online e-tailer. These ones I will have to hunt down to find, since they are not sold in small quantities.

The painfully ironic thing about all this is I live in michigan , and I actually live about 10 miles from the A123 systems battery plant there. If A123 systems sold cells right from the factory I could literally just drive down there and buy them at manufacturer price, but I can't because I already know they would never sell them in small quantities, especially to a single dude who would just want a few dozen cells .

EDIT: just found an even cheaper source of A123 cells from GWL power for $1.5 a cell:
https://www.ev-power.eu/LiFePO4-small-cells/A123-Rechargeable-Battery-3-3V-1100-mAh-LiFePO4.html

Anyone know if they are actually a real website or not?

 

[DVDRW]

If you believe specs then Lithium Titanate is the lowest cost per cycle.

If you cycle every day then battery lasts ~137 years
Nobody knows calendar life though.

 

[amberwolf]

The painfully ironic thing about all this is I live in michigan , and I actually live about 10 miles from the A123 systems battery plant there. If A123 systems sold cells right from the factory I could literally just drive down there and buy them at manufacturer price, but I can't because I already know they would never sell them in small quantities, especially to a single dude who would just want a few dozen cells .

You could try their authorized resellers, like StorTronics:
http://www.a123batteries.com/category-s/103.htm
which is in Livonia, Michigan. People on ES have ordered from them before; there is even a member here who works at A123.

Or there are various threads where they are being sold here on ES, like this one from Bigmoose for the pouch cells:
https://endless-sphere.com/forums/viewtopic.php?f=31&t=80486&hilit=a123
These are found by searching on threads by title for A123 in the for sale sections. I haven't looked at any others that come up in that search to see if they are the cylindrical cells; but there are probably some of those too.

A similar search on the rest of the forum will find several threads on how to build packs with the pouch cells; possibly sources for the cylindricals are discussed in there too.

EDIT: just found an even cheaper source of A123 cells from GWL power for $1.5 a cell:
https://www.ev-power.eu/LiFePO4-small-cells/A123-Rechargeable-Battery-3-3V-1100-mAh-LiFePO4.html

Anyone know if they are actually a real website or not?

I dunno; they used to spam the forums with their stuff.

A forum search on GWL turns up a number of mentions of them, including one thread whose title asks about their LiFePO4 stuff. (didn't read it, so don't know details).

 

[redilast]

There is more to it than just manufacturer stated cycle life at its rated capacity. People will say A123 has the best cycle life because A123 commonly rates their LifePo4 cells at 1000-2000 cycles, where most other kinds of Li-ion hybrid cells are rated at 300-500. But there is more to it than cycle life at the cells rated capacity. For example. Charge Li-ion hybrid cells to 90%, you double the 300-500 to 600-1000. Charge to 80% and you roughly 4x it. NASA has cells with shallow discharges (20-30% DOD) that have done 50,000 cycles or more. I believe they were older Sony 18650's.

I think for most applications, newer hybrid cells + reducing DOD, especially charge voltage above 4v will provide a good balance between high capacity and long cycle life. 80% on an NMC cell for example which may do 2000 cycles, is still more energy density than an A123 @ 100% DOD and more readily available. Look at the kinds of cells being used in electric cars that are often said to do 2000-3000 cycles. I don't know of any LifePo4 commonly being used.

 

[dogman dan]

As soon as you said ignore the size the weight, etc, you blew it.

Because those factors so greatly affect the c rate, which might have more to do with cycle life than anything else. A cool battery is a happy battery, but a small battery gets all hot. Make it big, so you discharge at .5c, and you might not get 137 years, but you might get a while out of them. Do bear in mind though, that lab cell never sat on the back of a bike in the sun all summer. So you will still lose some for actually using your battery out in the world.

Soo,, you wanna make it last,, carry 30 ah of it. I don't care what you carry,, hell carry 30 ah of lead and it will last pretty darn good. Cruising 20 mph, drawing 15 amps, that's .5c discharge rate if you carry 30 ah.

Bottom line,, whatever you carry, it has to be enough to not sag much. this can be 20 ah of hobby king pack, or 50 ah of half dead laptop scavenges. Either way,, beat your battery and it wears out fast.

Add carrying enough to easily afford the undercharge and stop early to the regimen, and next thing you know, your pack lasts as long as Wesenwells.

But before you go straight to hobby king and naked lipo, do consider what it will cost, one way or another, to not burn your house down with it. Same goes with other chemistries,, they can also burn your house down, but the level of care is different, between a bms protected lifepo4, and naked lipo.

 

[CUDAcores89]

As soon as you said ignore the size the weight, etc, you blew it.

Because those factors so greatly affect the c rate, which might have more to do with cycle life than anything else. A cool battery is a happy battery, but a small battery gets all hot. Make it big, so you discharge at .5c, and you might not get 137 years, but you might get a while out of them. Do bear in mind though, that lab cell never sat on the back of a bike in the sun all summer. So you will still lose some for actually using your battery out in the world.

Soo,, you wanna make it last,, carry 30 ah of it. I don't care what you carry,, hell carry 30 ah of lead and it will last pretty darn good. Cruising 20 mph, drawing 15 amps, that's .5c discharge rate if you carry 30 ah.

Bottom line,, whatever you carry, it has to be enough to not sag much. this can be 20 ah of hobby king pack, or 50 ah of half dead laptop scavenges. Either way,, beat your battery and it wears out fast.

Add carrying enough to easily afford the undercharge and stop early to the regimen, and next thing you know, your pack lasts as long as Wesenwells.

But before you go straight to hobby king and naked lipo, do consider what it will cost, one way or another, to not burn your house down with it. Same goes with other chemistries,, they can also burn your house down, but the level of care is different, between a bms protected lifepo4, and naked lipo.

This actually makes sense. So what you are saying is if I expanded my dead laptop pack (or, I will likely build a new one with new cells) and I undercharged it to say, 4v a cell at a 0.5C discharge rate, the battery would last a long time?

A few weeks ago I purchased an Iberia triangle bag for my bike where I have been housing my bike batteries.
http://www.ebay.com/itm/381276438791

This thing has about 2.5 liters of space, and if I do the math, that means I can squeeze in around 150 18650 cells in this thing.

I could literally just go back to the scrapyard where I got my laptop batteries in the first place, and pick up another 50 laptop batteries for $1.50 a pound. Them I could test each cell as I had done before, but this time use 150 of them instead of 70 of them. This would give me a 10S15P 36v 30AH battery pack that would weigh around 15lbs. The battery would be pretty heavy, but it would likely be able to deliver 12.5 amps to my hub motor with absolutely no problems at all. Then when I am discharge testing them, I could discharge test them at 2 Amps per cell, in order to weed out the high resistance cells that may have a high capacity originally but not at a high current.

Regardless of what I do one way or another, look's like I'm gonna be building a 30AH battery pack.

 

[Ianhill]

You can build the laptop battery but it becomes time consuming testing 150 cells to make sure they have good health then build a pack from cells with unknown age use said pack till a cells drops out or perform load tests weeding out the weak, I give up with it, went the HobbyKing route and never looked back old laptop 18650's are temperamental too when they are going to die some show no signs just drop to dead short and pull the battery's down in parallel with the cell destroying a string of battery's. So I tend to use as little parallels as possible and series it as high as I can go much easier to maintain balance its not a false reading of all the cells in parallel averaged so one could be low another high and the reading says fine.
At least with a larger lipo pack its 20s1p and with a BMS the voltage it sees between cells is a true figure meaning its safer in my eyes than a recycled laptop pack with crazy Internal resistance difference across the pack making hot spots in cells that take up more load than others and the BMS is in bit of a guessing game with anything over a 3p battery so a 10s15p is destined for faluire believe me I've killed a 10s9p many times and revived it when my HobbyKing is still chooching. The big scarer for the wise is a laptop 18650 when she blows releases a few wh of energy fairly low c ratings the lipo goes with a much more violent fizzle there more capacity and higher c ratings so if it do go wrong it goes big but a 1p lipo with BMS is safe in my eyes as any other chemistry when designed correctly.
So any battery with a high discharge rate can die a spectacular death but a 90c lipo is going to go out harder than a 10c whether the capacity stored makes a difference in prolonging the reaction or after the thermal runaway point its purely a lithium fire and its more to do with the reactive material present for how long it runs away for, On a side note has anyone seen a cell under going runaway take out another I've burnt a few 18650 nothing spectacular happened and I've never witnessed a lipo runaway myself even though I've covered a fair few hundred miles on them if not a thousand or so vs a few hundred on a 18650 pack that had three revival's, and I took time to capacity test all the batts and IR test them to get a close range pack and kept a low c rating and still a few would burn out after 60% capacity used in the pack as a whole so laptop 18650 don't play nice for me.

 

[dogman dan]

Yes,, if you can, discharge those laptop cells at .5c rate. Then they don't heat up.

Baby the pack, and it lasts. But you know those recycled cells were not babied. So no idea how long your scavenge cells last.

 

[Ianhill]

If the cells are free and you have the time then there's sence in it but if your buying joblots of mixed ages cells then the cost in time alone makes sense to just buy the HobbyKing or what ever is readily available in your area, China seems to be the place to get what ever type of cell u like where as in the UK its very expensive for a decent prismatic cell so the cost effective and least time consuming way becomes a decent lipo.

 

[neptronix]

On a dollars per watt hour basis.. if you do the math.. rc lipo comes second/third only to recycled 18650 packs and lead acid. Not on a per cycle basis, tho..

On a per cycle basis, lifepo4 wins..

 

[Ianhill]

If I was building a permanent wind/solar storage device within a home or shed then lead acid would be a clear winner for me, it may weigh half a ton and need deionised water to maintain it but id be able to make a massive amount of storage with forklift cells if cycled correctly and maintained there's easily 10 years of use, I've seen forklifts with 15years on stock batts before they need a change.
But it will need to be ventilated to outside as the battery's give off hydrogen sulfide when over charged or start to age but can give many volts and 1000 of amps storage for as little as a few hundred pounds and old forklift chargers are cheap as chips for a mains top up and cycling maintenance. I don't understand how the Tesla power wall has taken off so well the only benefit is lithium holds its charge better over time but if a solar cell and wind turbine is charging in intervals every few hours then its no big deal that a months time it would have lost charge as it will be constantly topped up over years there will be an energy loss but it can be overcome with enormous capacity and at a more reasonable price than a power wall.

 

[dogman dan]

Sometimes how cheap you can make it is most of the fun.

But if I'm half way to Wineboys house,, I'm 35 miles from water or a plug either way. Now I want reliability at any cost.

 

[999zip999]

I'm looking at westart graphene 20ah cell ($23.00) they have a 10ah cell. Cheapest because at 2,000 plus cycles and 200 amps. The high claimed quality of this cell and the low need of use for running an ebike they should last a long time. So not stressing the cell should give it a very long like. Long life means a dependable and cheaper battery. P.S. still investigating as this is on my newest wish list.

 

[Ianhill]

The westart graphene cells got me sold they are right up my street but with postage to UK and shipping tax etc its just out of my reach price wise I would love to be cycling a large pack of them though it would make a professional grade pack.