Ezee battery Vs Crystalyte Vs Cellman Lifepo4

[benjy_a]

Ok so I've researched battery technology a lot but would like a few more opinions.

I will shortly be needing a battery for my Brompton conversion project (although I have a 36v pack from my Juicy Sport to test and get it up and running).

I need a fairly high capacity so I'm looking at the Ezee 14Ah (3.9kg), Cellman 12S5P (5kg, 11.5Ah), or Crystalyte high power 16Ah (3.6kg).

Can anybody tell me the advantage of going for the heavier A123 Cellman Lifepo4 battery? As far as I can work out I would get a slightly higer (39.6) voltage, a longer life cycle (potentially but no guarantee) and a battery that will hold the voltage for longer during the discharge cycle. However, this seems to be balanced against the fact that it is heavier and in fact lower capacity (the 14Ah cellman is 6kg).

The Ezee battery comes in a nice hard case and has a 2 year warranty...seems to be a winner for me but there must be something about Cellmans (emmissions-free) batteries as they have amazing reviews. Am I missing some other huge advantage of Lifepo4?

 

[jerrysimon]

I am a huge fan of A123 cells. My experience of them though is only in small capacity DIY packs.

Regards

Jerry

 

[benjy_a]

Hi Jerry,

Ignoring any cost implications, why do you prefer them to smaller, lighter more energy dense Lipo such as Ezee etc?

I am a huge fan of A123 cells. My experience of them though is only in small DIY packs.

Regards

Jerry

 

[cwah]

A123 are basically high power lifepo4. Their advantage over the lighter battery are their lifecycle:

This is a screenshot I get from cellman site:
1000 cycle at 100% DOD. Only lifepo4 can do that. But it's heavier.

So you have to decide between lighter battery with shorter lifecycle (NMC or lipo) or heavier that will last longer

 

[benjy_a]

Realistically does this mean I could get away with the lower capacity lifepo4 as I can run it pretty much flat without worrying quite so much?

(Assuming I would treat my expensive lipo nicely and not completely discharge it).

I'm also a little confused...Jerry you have spent a lot of money on titanium bits for your bike to make it as light as possible and yet you use heavier battery technology because it will last longer and save you money?

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[jerrysimon]

Benjy,

The primary reason I use A123 cells is for their safety!

As my packs only need to be small, capacity wise, weight is not really an issue. That smaller 1.1Ah pack weighs 0.5kg and will get me to work with just a little more effort than the larger 1kg 2.3Ah pack. I might add the bike weight is all about its carry weight, the bag/battery/electric components do not contribute to the bike carry wieght

I use the battery every day and charge it at work and at home. I would be very unhappy about having lipos charging at work and at home, though probably would not have to at work as their capacity would be larger for the same weight. I can leave them charging unattended/thrown in my bag and not worry.

Lipos require a lot more respect!

PS One final thing these smaller A123 packs don't really require a BMS.

Regards

Jerry

 

[Cyclezee]

Clearly Jerry does not need or want a large capacity battery for his Brompton, but when you get to the larger capacity batteries the weight difference between LiFePO4 and LiPo is quite significant.

It is also worth considering the cost and practicality of importing batteries as opposed to buying in the UK and having warranty.

 

[benjy_a]

Thanks for your reply, I am leaning towards your 14Ah battery for those very reasons...UK warranty and considerably lighter / smaller.

Can you tell me; in realistic use how much of the 14Ah capacity can you use before the voltage drops to an unacceptable level? Do you have any discharge / voltage comparison graphs or tests or anything so that I can compare to Lifepo4?

Clearly Jerry does not need or want a large capacity battery for his Brompton, but when you get to the larger capacity batteries the weight difference between LiFePO4 and LiPo is quite significant.

It is also worth considering the cost and practicality of importing batteries as opposed to buying in the UK and having warranty.

 

[hech]

The other advantage of cellman's lifepo is the huge C rate which can be matched only by rc lipos as far as Im aware. Most factory bikes come with lith ion or polymer cells with a C rate of only 1 or 2 which with a 10a/h battery means respectively 10 or 20 amps constant draw. Jerry's pack though only 2.3a/h will supply him with 23amps easily(I think?) ie at a 10C rate. So though he is range limited he is not current limited.

 

[benjy_a]

The other advantage of cellman's lifepo is the huge C rate which can be matched only by rc lipos as far as Im aware. Most factory bikes come with lith ion or polymer cells with a C rate of only 1 or 2 which with a 10a/h battery means respectively 10 or 20 amps constant draw. Jerry's pack though only 2.3a/h will supply him with 23amps easily(I think?) ie at a 10C rate. So though he is range limited he is not current limited.

Apparently the Ezee battery is rated 5c and the Crystalyte high power 10C. Do you think these are optimistic compared to the genuine A123?

I have to say it's a hard decision.. The extra weight but possibly much longer life vs UK warranty but battery will probably die after 2 years and 1 day

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[jerrysimon]

Hech is correct and raises another benefit I had over looked.

A123 cells are rated at up to 30C constant and 60C peak. So each 2.3Ah cell can be discharged at 69amps constant and 138amp peak. Not much point in using that in a smaller pack given that you would exhaust them in minutes at those rates, but in larger packs an added advantage for more powerful setups.

The charge rate is also higher at 10C, so again in this case they can be fast charged at 23 amps, not that you would want to do that and any BMS would restrict it. Chargers that can output those kind of currents would be expensive, but you can easily charge at 6amp plus reducing charging time.


Regards

Jerry

 

[cwah]

Clearly Jerry does not need or want a large capacity battery for his Brompton, but when you get to the larger capacity batteries the weight difference between LiFePO4 and LiPo is quite significant.

It is also worth considering the cost and practicality of importing batteries as opposed to buying in the UK and having warranty.

What's your battery exact chemistry? Is it NMC like BMSBattery?

Do you also have some specs such as the weight, wh/kg and number of cycle?

And of course, warranty can mean quite a lot of thing, to what % loss of the total capacity is covered by the warranty?

Because there is no way a battery would keep 100% of its initial capacity after 2 years.

Of course, if your warranty is 100% of its initial capacity after 2 years, I think it would be one of the best deal we have here

ps: My battery LiMn2O4 from conhismotor lost 1/3 of its capacity in 6 months. Very very bad deal.

 

[benjy_a]

Haha and now I'm leaning towards Cellman's battery! Heavier but likely to last a lot longer with the kind of use that it will get with me- lots of long commutes with 2 charges per day.

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[jerrysimon]

Benjy,

Might add too if he is using the cylindrical A123 cells it would be easier to replace a failed cell as well, though I think he uses pouch A123 cells now.

Regards

Jerry

 

[cwah]

Haha and now I'm leaning towards Cellman's battery! Heavier but likely to last a lot longer with the kind of use that it will get with me- lots of long commutes with 2 charges per day.

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There is a thread on endlessphere about A123 20AH prismatic cells for very very low price from Victoria:
Endless-sphere.com • View topic - Group Buy? Dr.Bass Steveo found 7s3p Module! Awesome Price!!

A bit of DIY but you may be interested. I'd even be interested if anyone wants to do group order from them.

 

[benjy_a]

Thanks Jerry,

He sent me data sheets and they are still cylindrical. How do you connect yours though? He spot welds his connections.

Ben

Benjy,

Might add too if he is using the cylindrical A123 cells it would be easier to replace a failed cell as well, though I think he uses pouch A123 cells now.

Regards

Jerry

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[jerrysimon]

Well he will no doubt spot weld tabs from one cell to another. Buy a few A123 cells with single tabs spot welded onto them. If a cell fails then cut the old cell out and solder in a new one. My current 3500 mile, 29 month old pack has had two cells replaced.

Not easy/simple and any BMS wires will have to be reattached but I think easier than sourcing and replacing pouch cells.

With care the cells should last for quite a few years. My first cell only failed because I abused the pack for the first year and the second cell failed because the replaced cell was not in balance with the other cells when I attached it.

Regards

Jerry

 

[benjy_a]

Well he will no doubt spot weld tabs from one cell to another. Buy a few A123 cells with single tabs spot welded onto them. If a cell fails then cut the old cell out and solder in a new one. My current 3500 mile, 29 month old pack has had two cells replaced.

Not easy/simple and any BMS wires will have to be reattached but I think easier than sourcing and replacing pouch cells.

With care the cells should last for quite a few years. My first cell only failed because I abused the pack for the first year and the second cell failed because the replaced cell was not in balance with the other cells when I attached it.

Regards

Jerry

Just out of interest, how would you go about identifying one faulty cell in a pack of 72 like the battery I'm considering?

Ben

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[jerrysimon]

If you suspect a failed cell you would need to measure the voltage of each cell after a bike ride!

The dodgy cell would have dropped to below 2.0v. Then again another indication is that the BMS would cut the power early because of low voltage.

To be honest if the A123 packs you are looking at have a BMS its unlikely a cell will fail for some time. I run them without a BMS and as I said abused the pack quite a bit by discharging until the LVC of the controller cut in after each ride. I charged once a day where as now I charge at work before the cycle home.

With the ones you are looking at with a BMS in the mix, they will be treated like kings!

PS here shown with low voltage. I have the probes on the wrong polarity so it should read +0.51v. Anything under 2.0v and they stand a good chance of being totally ruined. Once they start to fail when the charged pack is then used, the other good cells suck all the capacity out of dud one as they discharge. Survival of the fittest and all that

Regards

Jerry

 

[cwah]

Jerry, how do you do to cycle only with 1.1ah or 2.3ah pack?

Do you use very low amps? or do you only use electric assist on hills?

I suppose that most of the time you're below 15 mph?