Yesa vs Headway vs PSI vs Ebike.ca 12Ah LFP test graph

[Russell]

My opinion about heat management and cell shape is still always the same: the more cell shape surface per Watt you have the best it is!



in fact the surface of the:

-Yesa 10Ah cell is: 243.12cm^2
-Headway 10Ah cell is: 165.93cm^2

That's a difference of 32%...surface


The energy per liter is:

-Yesa: 132Wh per liter
-Headway : 138Wh per liter

Note:(taking account of the volume required to connect the cell with the screw terminal virtual prism volume and that the Wh are at 1C rate)

Yesa have 4.4% less energy density for 32% more surface.

From now the Yesa seems to demonstrate a better form factor vs energy and heat dissipation.

Doc

Doc,

Regarding heat dissipation don't you also need to figure in how the cells will be packaged? The rectangular YESA cells will likely be placed right up against one another however the cylindrical Headway cells will have some air gap between cells. So while an individual YESA cell may shed heat better a fully constructed pack of the Headway cells might actually dissipate heat from each cell more evenly don't you think?

That said I believe I prefer the rectangular YESA cell from an ease of packaging perspective. Two rows of six cells would measure 5.5" (140mm) x 8.0" (204mm) and fit nicely in my rear bag.

Question: Does the 94mm height include the posts?



-R

[Doctorbass]

Doc,

Regarding heat dissipation don't you also need to figure in how the cells will be packaged? The rectangular YESA cells will likely be placed right up against one another however the cylindrical Headway cells will have some air gap between cells. So while an individual YESA cell may shed heat better a fully constructed pack of the Headway cells might actually dissipate heat from each cell more evenly don't you think?

-R

You are totally right Russel, I forgot to take account of that for the prismatic cell placement.

after all.. i only test one cell at a time...

I'll revise the data and update about that .

For the 94mm heai i'll double check tonight and get back to you.

Doc

[Mr. Mik]

For testing purposes you might want to add insulation to the cells, so that you can measure heat production, rather than just the result of heat production minus heat dissipation.

That can give clues for what sort of thermal management or forced air cooling might be needed for a fully constructed pack.

It is also important to continue measuring heat after the end of testing; in my experience the surface of the Vectrix NiMH cells reach peak temperature well after the end of a test (or recharging); that's because it takes time for the heat generated in the cell center to spread evenly.

Depending on physical characteristics of different cells they might also have different "thermal mass"; that means that although they might have the apparent same temperature, one type might contain a lot more heat than the other. That will make a difference when repeated charge/discharge cycles are needed in very warm or very cold weather.
A battery with a higher thermal mass will initially appear to heat up less, but it will also remain warmer for longer, and might accumulate heat if not cooled for extended periods after riding and / or charging.

[pgt400]

The PSI's were 22.50 $ US each in Taiwan, by the time i paid shipping ( Air , UPS ) duties, brokerage, currency exchange, they ended up 40 $ Canadian per cell.. not that far away from the headway cells..... all things considered.

Try and get PSI's for $22 each now that Raymond defected.... Victoria is quoting $16.50 each now, plus $5 shipping each. Thats $21.50 each shipped!

[Doctorbass]

For testing purposes you might want to add insulation to the cells, so that you can measure heat production, rather than just the result of heat production minus heat dissipation.

That can give clues for what sort of thermal management or forced air cooling might be needed for a fully constructed pack.

It is also important to continue measuring heat after the end of testing; in my experience the surface of the Vectrix NiMH cells reach peak temperature well after the end of a test (or recharging); that's because it takes time for the heat generated in the cell center to spread evenly.

Depending on physical characteristics of different cells they might also have different "thermal mass"; that means that although they might have the apparent same temperature, one type might contain a lot more heat than the other. That will make a difference when repeated charge/discharge cycles are needed in very warm or very cold weather.
A battery with a higher thermal mass will initially appear to heat up less, but it will also remain warmer for longer, and might accumulate heat if not cooled for extended periods after riding and / or charging.

+1 on that Mr Mik!

I know about thermal management of lithium cells and the heat increase after the end of discharge was also observed but not as much as i expected.. thatS, around +2 to +5 degree max..

I also can add that at Constant Current discharge the voltage decrease as the cell discharge... and having the same current with lower voltage mean an increase of the IR wich indicate an increase of Heat production enevthou the voltage is lower for the same current.

I agree on the fact that testing a single cell without any other around it is not a as representative as a, ebike pack. But cell in the middle always get warmer than the surounding cells.. So wich condiytion is the best.. a tradeoff between these cell position?.... Also the discharge i dot was done in continuous current discharge wich not represent the same use than an ebike that is more like pulsated discharge peak with a minimum discharge rate...

Discharging by pulse current help the cell to dissipate the heat better eventhough the mean current is the same in both test.

For that maybe i'll upgrade my next test to see if there uis a real difference and if the heat still increase for 2 to 5 degree after the cell discharge cut.

I think this is difficult to reproduce the same conditions of use of ebikes battery discharge. some pack are made in cube.. or prismatic, some are plane shared in many small pack... some have air blowwing on them some have not...
So for that i think keeping the cell alone for the test is the most easy way to keep a baseline for compare cells..

Adding the projected proportional heat increase to the results for every different battery construction way is still the best i think.

Trying to imitate one perticular type of battery construction for a cell test might complicate the comparaison for the overall battery construction comparaison..

At least that's what every mechanical engineer heat simulation do.. they try to keep the baseline conditoins on their test methods and then they add the different test conditions to every simulations.

Doc

[oatnet]

Hmm ... When formed into a "brick" pack, I'd expect the Yesa would have less exposed surface area than the Headway, I wonder how temps in the center of the packs would compare.

Regarding heat dissipation don't you also need to figure in how the cells will be packaged? The rectangular YESA cells will likely be placed right up against one another however the cylindrical Headway cells will have some air gap between cells. So while an individual YESA cell may shed heat better a fully constructed pack of the Headway cells might actually dissipate heat from each cell more evenly don't you think?

JINX - you owe me a coke! I think you said it better though.

-JD

[Doctorbass]

Question: Does the 94mm height include the posts?
-R

Yes.. but i revised the calculation i did an error in my calculations.. thanks for asking

Please note: EVERY CELLS IN THIS TEST WAS THE BEST CELL I HAD FROM EACH BRAND

Doc

[Doctorbass]

Here is the PSI final test graphs:

The result seems interesting.. there is only one strange thing!.. The 30 and 35A look very similar!!.. I doublechecked the parameters and this is still ok..!

Doc

[Doctorbass]

As i promissed: And... Finally the comparative graphs between these 3 cells brand:

i'll elaborate on that tomorrow morning.. now it's time to sleep!! 2:10am here.. work tomorrow

Good night!

Doc

[headway]

YES, We will have bigger cells, 12Ah and 15Ah cells. And they will be planned to come out at the end of March. This is confirmed from our G.M.

Victoria

these blue sleeved cells are much better than the older brown paper sleeved cells. flip measured 2.47V at 34A last year, and we had about 17mohm IR, so these have improved dramatically, so i am hoping they can still push to improve their cathodic powder and anode coating up to the performance of the top tier cells, such as psi, a123, and yesa. victoria mentioned they will introduce larger capacity too, 14Ah is next i think.

[headway]

Mr.Doctorbass,

Thanks very much! Your testings and comparisons are very helpful for us. Thanks again!

Here I have a request, I will send our 38120P 8Ah , which is the high power cell, can maintain a continuous of 10C, and 25c max. to you for testing, will you?

And may I have the below three pictures of the comparisions of HEADWAY, YESA and PSI? Please send to me by chcj55@gmail.com, thanks in advance!

Victoria

As i promissed: And... Finally the comparative graphs between these 3 cells brand:

i'll elaborate on that tomorrow morning.. now it's time to sleep!! 2:10am here.. work tomorrow

Good night!

Doc

[ZapPat]

Mr.Doctorbass,
Thanks very much! Your testings and comparisons are very helpful for us. Thanks again!

Yes indeed, Thanks Dr Bass!

Here I have a request, I will send our 38120P 8Ah , which is the high power cell, can maintain a continuous of 10C, and 25c max. to you for testing, will you?

This sounds like fun - very good idea, Victoria!

And may I have the below three pictures of the comparisions of HEADWAY, YESA and PSI? Please send to me by chcj55@gmail.com, thanks in advance!

Victoria - You can save most any picture you see on a web page by using your right mouse button and choosing "save image as..." (or the Chinese equivalent) to save it on your own computer.

[pgt400]

Very nice work! Everyone appreciates your efforts!

[voicecoils]

Interesting so, while at 1A or 35A Headway exhibits greater voltage drop then PSI, less flat holding of voltage throughout discharge and higher cell heating, it still manages to deliver more energy in each case.

PSI and Yesa's curve characteristics look so similar I wonder if they use the same cathode powder and manufacturing techniques.

[wanders]

Hmm, so if I read these charts correctly, Doc, if the Headway has ~9 milliohms internal resistance, these results indicate the Yesa and PSI have about 6 milliohms internal resistance. It is interesting to see what a 3.5C discharge does to make this apparently small difference seem important.

Willie

[Ypedal]

Awsome work Doc !!! keep it up ! ( curious to know what happens at the 50,60,70 amps range !!! ) !

[Mr. Mik]

I'd be careful when using cells which were specifically supplied by vendors for testing purposes.

How much this applies to Lithium battery technology is something I'm not absolutely certain about, but I have read many posts about how batteries get hand picked. This happens first at the factory, to separate the production run into batches for selling as expensive "Prime Quality" to special customers, and into normal stock or cheap crap.

Then they get sorted again by RC racing enthusiasts who want to match the cells for their packs as closely as possible; some take their testing equipment to the shop and test away until they have selected the best cells out of the entire heap on the shelves!

This is all due to the significant differences between individual cells.

A manufacturer who just sends a randomly picked cell to someone like Doctorbass would need their head read!

So I would not call it fully independent testing unless the cells tested were bought through the usual channels!

[Doctorbass]

Mr.Doctorbass,

Thanks very much! Your testings and comparisons are very helpful for us. Thanks again!

Here I have a request, I will send our 38120P 8Ah , which is the high power cell, can maintain a continuous of 10C, and 25c max. to you for testing, will you?

And may I have the below three pictures of the comparisions of HEADWAY, YESA and PSI? Please send to me by chcj55@gmail.com, thanks in advance!

Victoria

As i promissed: And... Finally the comparative graphs between these 3 cells brand:

i'll elaborate on that tomorrow morning.. now it's time to sleep!! 2:10am here.. work tomorrow

Good night!

Doc

Hello Victoria,

That will be a pleasure to me to test your 8Ah version.

As well for the 12 or 15Ah too if it's possible.

As i described I always test the best cell of each brand i receive so you can send me just one or preferably 3 samples so i will be able to post the best possible resusts of your products.

Doing a mean result of a batch of sample would take alot of time for testing all items! so that's why i prefer keeping the best sample of the batch for the posted tests.

Just pm me for the 8Ah cell..

Doc

[dnmun]

mik, we called it 'binning' where microprocessors at test would be selected and binned according to the max speed at which they would run. there is always some variability in the process and some parts would run faster than others. i don't think we need to worry that they could select an 'extraordinary' cell.

if they did that then later testing of other cells might show lower performance and then people would worry that they had lost control of their manufacturing process. so i doubt if they would do that in any case. i am so glad they have started tracking the individual cells with the bar codes, i think overall they are doing the right stuff to get the performance up there.

what seemed most important is that they cut IR in half from 17 to 9mohm, and cut 83% of the sag from the older brown cells. at 3.5 C the brown cells were at 2.47V but now 2.95V, and the psi and yesa formulation is 3.05V. so the removal of sag is much greater than the change in the internal resistance. this is not something we expected, thinking IR correlated directly with sag. maybe it does but the scale is not apparent yet. maybe the absolute minimum would be around 2-3mohm.

there does appear to be a relationship between a higher IR and the larger capacity. as though the sag reflects the difficulty the lithium ions have in getting through the matrix of granules in the cathodic structure, so they don't get used up early in the discharge cycle. but we would have to be comparing the same volumes or weight of cathode granules, imo.

[oatnet]

As i promissed: And... Finally the comparative graphs between these 3 cells brand:

i'll elaborate on that tomorrow morning.. now it's time to sleep!! 2:10am here.. work tomorrow

Good night!

Doc

Doc, thanks for working so long and hard to put this hard data out there for us. While each cell has tradeoffs that suit different applications, the comparisons I have seen so far makes me feel good about the Headway purchases I have made for mine. Yesa has also gone up a couple of notches in my regard.

Has anyone supplied you with current Lifebatt cells? I keep reading posts about quality justifying their high cost but I've seen nothing but Distributer Propoganda "testing", I'd be interested to see just how they actually compare with the the other cells in your impartial discharge test. Ping, and ebikes.ca cells would be interesting too, too bad T-Sky doesn't offer their large-format chemistry in a 10a cell so you could overlay that too.

Hmm, after all your hard work I am eager to give you more, on cells I don't even own. Sorry about that, thanks for the data!

-JD

[Ypedal]

I also sent an " Ebikes.ca " 12ah prismatic LFP cell.. ( no rush Doc, don't neglect the lady too much or she may lock the lab on you !! )

[oatnet]

I also sent an " Ebikes.ca " 12ah prismatic LFP cell.. ( no rush Doc, don't neglect the lady too much or she may lock the lab on you !! )

Ypedal, you are the one person here who might know - are those Ebikes.ca cells the same as the green ones we got from Andy in '07? I thought they looked very similar... those cells have served me very well - although a killed (2) of them through negligence, when I overheated/killed their voltphreaks single-cell chargers and didn't have an LVC to realize it. Now I keep a gap between the chargers and they do just fine. If the cells are the same maybe I'll buy some replacements from Justin, just to maintain the old x5tracycle in full repair.

-JD

PS - Here is thread on those green cells:
viewtopic.php?f=14&t=2503

PPS: The wood box they arrived in just saw new life (no pun ) holding the vacuum-assist system for my VW conversion.

[Ypedal]

exactly the same..

I don't think ebikes.ca are re-ordering them however ( could be wrong ), but they may have some cells or leftover packs to unload if you email them.

I have a few dead one's too.. when FalconEV sent me this pack, 2 of the cells in parallel were at 0v .. I recharged them but they only lasted a few cycles.. so i'm salvaging cells from one pack . powering my chopper with these and a local customer has some on a cyclone system.

[oatnet]

exactly the same..
I have a few dead one's too.. when FalconEV sent me this pack, 2 of the cells in parallel were at 0v .. I recharged them but they only lasted a few cycles...

Wow. Thanks for the tip!

Thanks to opportunity charges that got me through the day, mine have probably seen 600-900 cycles, including the 44.7mph 90ah discharge test on my Kelly, with no problem but me. I don't ride the bike they are currently mounted on very much these days (after cracking a rib in a fall on a prototype I favor my TidalForce bikes for their balance), but I was still pulling the same amount of WH from them without seeing the voltage drop at the end of the ride.

-JD

[Doctorbass]

Ypedal.. Next test on the list: 12Ah green cell from ebikes.ca!

This is a great luck i have to get acces to every of these different cells in my lab.. I admit thatfor sure, these tests will be helping me to decide on wich i'll choose for my electric car project!

That's why i pay attention to every details about these test! I want a great test job for me too!!

The 12Ah cell is begining the first charge for the first 0.1C discharge!

Doc