GGoodrum wrote:Very interesting, Doc. I thought they'd be closer. I wonder if the prismatic shape of the Yesa cell has anything to do with the difference in heat? Anyway, it will be very interesting to see how both of these stack up against the PSI cell. I have experience with the PSIs but not the Headway or Yesa cells. My sense is that they all should be close, but i don't know.
Since the yesa had higher voltage, but the headway had more amp hours, I wonder how the actual watt-hours delivered compare. Could you put a CycleAnalyst between the test batteries and your CBA (as the 3.5c load), then re-run those tests to see how many wh are extracted? Or do you already have a more elegant way of doing that in your well-equipped lab?
EDIT - I see on your Yesa test page you do have a for more elegant method of deriving wh than the crude test I proposed - is it possible to overlay the yesa and headway wh curves?
voicecoils wrote:Very interesting, thanks Doc!
Is it possible to test above 3.5C?
This may be quite good to know for PSI. PSI claims 10C so there should be a considerable difference in voltage sag throughout discharge between Headway & PSI for this, if it is true.
For example, if someone needs 7C cont. discharging it will be good to know whether to have: two headway cells in parallel or one set of PSI? (That comparison would be similar in price! )
Ypedal wrote:Qute DrBass " Ypedal.. how many cycles they have..?? (I just want to compare Apple with Apple..) "
The 2 x PSI cells i sent have aprox 10 shallow cycles ( 50 % DOD ) on them, they were used as a boost pack to my 72v Norco for the last 2 weeks before winter hit...
Doctorbass wrote:Here is your answers JD!:
Yesa at 1A : 33.45Wh
Yesa at 35A: 29.12Wh
Here is the graph:
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.
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?
Ypedal wrote: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.
Mr. Mik wrote: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.
oatnet wrote: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.
Russell wrote: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?
Russell wrote:Question: Does the 94mm height include the posts?
dnmun wrote: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.
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