Looks like the new 15ah headway are available

Lock said:
I calculate the increase in volume from their 38120S at less than 16%.
Click to expand...
Check my math please?

38120 cell:
  • 3.14((38/2)*(38/2))*120=136024.8mm^3

40152 cell:
  • 3.14((40/2)*(40/2))*152=190192mm^3

volume difference:
  • 190192-136024.8=54887.2mm^3

difference as portion of 13820 cell:
  • 54887.2/136024.8=.403

40% (?)
 
More math to be checked:

38120 cell surface-area:
3.14(38)*120=14318.4mm^2

40152 cell surface-area:
3.14(40)*152=19091.2mm^2

surface-area difference:
19091.2-14318.4=4772.8mm^2

difference as portion of 38120 cell:
4772.8/14318.4=33.333%

If the calculations are correct, the chemistry is likely the same; the volume increasing 40% but the surface area increasing only 33%.

I would expect the larger cells to heat more; lowering the effective 'C' rating.
 
TylerDurden said:
Lock said:
I calculate the increase in volume from their 38120S at less than 16%.
Click to expand...
Check my math please?
38120 cell:
  • 3.14((38/2)*(38/2))*120=136024.8mm^3
Click to expand...

That Alibaba page for the 38120s lists dimensions as 38*146 not 38*120

Is that page incorrect?

EDIT: Awww crap. Of course it is... that's what the "38120" designation means...

Here is is again:
http://www.alibaba.com/product-gs/237915850/Headway_LiFePO4_lithium_battery_10Ah_800Ah.html

"Size: Diameter of 38mm, and total height of 146mm"

... so, 26mm just for terminals?
tks
Lock
 
Anyone use the BMI cells?
It is odd that the Headways and BMI cells look identical, right down to the color. BMI uses Phostech lithium power and Headway???? Either one looks to be a decent cell for the winter project, just wonder which one is better and at what cost?
 
But looking at those pics the 152 length of the larger cells is in question if the blue ones are 120. No way the cell excluding terminal posts is 26% longer. Let's get apples and apples first.

Also, while surface area is critical for the ability to dissipate heat and in that respect C rate, what does is have to do with internal resistance?

Lastly, we need to track down the actual manufacturer. Headway & BMI both went to red for their new 15ah cells, but aren't coming from the same place??? yeah right.

John
 
EVnewbie said:
Anyone use the BMI cells?
It is odd that the Headways and BMI cells look identical, right down to the color. BMI uses Phostech lithium power and Headway???? Either one looks to be a decent cell for the winter project, just wonder which one is better and at what cost?
Click to expand...

I can see differences in the endcaps. The headway protrude slightly and the bmi are flush. I think bmi uses lasers or something fancy like that to cap off their cells. In fact one of their representatives claimed that that might make the bmis more likely to last longer. :roll:
As far as i'm concerned the only thing a rep can tell me that matters is capacity, weight, volume, and impedance. And I probably wouldn't believe them anyway. All this my lifespan is better than yours seems awfully hypothetical coming from factories claiming 10 year life spans on cells they've been selling for two or three years. :oops:

But i digress.
 
The surface area to radiate heat is a non-factor for the methods used in typical Ebike pack construction which encloses the cells. If you wanted to make cells cool better, its not the surface to worry about, but rather using some passive or active system to encourage airflow. Otherwise internal pack temps act like a closed system with the outside pack material (often very insulative) exchanging heat with the air around the pack.

The much better way to control cell temps is by having low Ri.

If these cells are 10mOhm, it means when pumping out 100amps, there is 100w of heating for the cell.

If they are 5mOhm cells, then 50w of heat.

If 2.5mOhm cells, then only 25w the amount of heat.

If 1mOhm cells, then just 10w of heat, but generally it would take Lipo cells to see that from only 15Ah.
 
No, but the smaller 38120S cells are listed as 302g... From TD's calculations at 40% larger, the 40152S cells would be about 423g... .93lbs approx...

BTW, that original link to the listing on Alibaba is gone! No sign of 40152S cells anywhere... And a search for "Headway" turns up... Ms.Michelle Lu? Not Victoria?

Vickie, where are you? What happened to your 40152S's???
tks
Lock
 
Yeah, Headway logged in the other day to view the thread and then the stuff was gone from the site.

I concur with John, the 40152 size specs are still in question... it looks more like 140mm long.
 
Kinda disappointed now... disturbed about Headway actually...

I don't really need THEIR cells... Just thought that their cells (not so much their 3rd party BMS etc) enjoyed a good rep on ES.

So, how about Tenergy?

The Battery Superstore on Amazon has these listed right now at $46 bux + $5.70 shipping a pop:
http://www.amazon.com/LiFePO4-Lithium-Phosphate-Rechargeable-Battery/dp/B0021ZAWUU


Specs from that site:
Maximum discharge rate: 2C
Maximum charge current: 15A.
Maximum burst of: 45A
Recommended charging rate: 0.3C.
Dimensions(L x W x T): 245mm x 82mm x 11mm

I know these don't have the high C rates that many ES ppl lust after. And what do they mean re max charge current versus recommended? Can be charged in one hour but better to take 3.33 hours?

Anywhooo... 15 of these babys to make up a 48V 15Ah pack for $690... $1.04 per Wh... plus a "Gary" BMS...

Tenergy are good ppl, right?
tks
Loc
 
Hehe...

Earlier I asked about Tenergy... Most(all?) of the bad press on ES about Tenergy seems to be about their nickel chemistries... Not much mention about their LiFePO4 cells... (OK, the YouTube vid that Doc posted Jan1 is pretty amusing... where they are chopping up a cell that still keeps working...)

John in CR? Are you still running Tenergy cells? Anybuddy?
tks
Loc
 
Tenergy seems very expensive for a 1C cell.
 
Lock said:
Kinda disappointed now... disturbed about Headway actually...

I don't really need THEIR cells... Just thought that their cells (not so much their 3rd party BMS etc) enjoyed a good rep on ES.

So, how about Tenergy?

The Battery Superstore on Amazon has these listed right now at $46 bux + $5.70 shipping a pop:
http://www.amazon.com/LiFePO4-Lithium-Phosphate-Rechargeable-Battery/dp/B0021ZAWUU


Specs from that site:
Maximum discharge rate: 2C
Maximum charge current: 15A.
Maximum burst of: 45A
Recommended charging rate: 0.3C.
Dimensions(L x W x T): 245mm x 82mm x 11mm

I know these don't have the high C rates that many ES ppl lust after. And what do they mean re max charge current versus recommended? Can be charged in one hour but better to take 3.33 hours?

Anywhooo... 15 of these babys to make up a 48V 15Ah pack for $690... $1.04 per Wh... plus a "Gary" BMS...

Tenergy are good ppl, right?
tks
Loc
Click to expand...


A cell like that wouldn't last as long as a high C rate 10Ah cell for an application like my bike.

For example, a 10Ah LiFePO4 cell with 10mOhm Ri would be giving about 1/3rd of that cells energy away in heat when discharged at 100amps. C-rate of a cell is directly related to Ri. The lower the C-rate, the more watt/hours of your pack get wasted in heating your pack rather than moving your bike. 2C discharge is pretty embarassingly pathetic for a modern cell.

For my application, I would need to run them in 10P, 150Ah groups just to handle the current.
If they were super cheap, I could see them being useful for bulk energy storage combined with A123 to boost power density, but they aren't cheap.

For large capacity pouch cells, Kokam makes some cells safer than LiFePO4 in 70Ah sizes for $120/cell, and they have 3.7v nominal rather than 3.3v.
 
Lock said:
John in CR? Are you still running Tenergy cells? Anybuddy?
tks
Loc
Click to expand...

??? Never had any and have no interest at those prices. Higher power LiFePo4 cells can be had in the $0.50/wh range, along with toolpack LiMn including shipping and no BMS required. $1/wh is last year's prices for relatively low C lithium. I'm holding out for $250/kwh, hopefully including shipping and required electronics control.

John
mr. fingers crossed re batt prices
 
luke was making the argument for how internal resistance is heating the cells at the rates he calculated using (I^2)R.

do we know that the heating is from classic ohmic heating or is internal resistance a different type of 'resistance' similar to active devices and not passive devices such as a resistor?

i am of the impression that the internal resistance is related more to the mobility of the electrolyte inside the cell or the mobility of the ions through the elctrolyte, and maybe the separator material too. i just have doubts that we can assume the relationship is the same as a passive device and corresponding ohmic heating. all jmho, interested in other ideas too.
 
I read the 15Ah cells were being sold under an exclusive contract and will not be made available to the rest of us.
 
dnmun said:
luke was making the argument for how internal resistance is heating the cells at the rates he calculated using (I^2)R.

do we know that the heating is from classic ohmic heating or is internal resistance a different type of 'resistance' similar to active devices and not passive devices such as a resistor?

i am of the impression that the internal resistance is related more to the mobility of the electrolyte inside the cell or the mobility of the ions through the elctrolyte, and maybe the separator material too. i just have doubts that we can assume the relationship is the same as a passive device and corresponding ohmic heating. all jmho, interested in other ideas too.
Click to expand...

I don't think cells are ohmic. The amount of predicted heating doesn't seem to closely correlate to the cell's equilibrium temperature. But it seems to a be good measure for predicting voltage output under a constant load.
 
julesa said:
I read the 15Ah cells were being sold under an exclusive contract and will not be made available to the rest of us.
Click to expand...
Yes, that is correct. The 15Ah high capacity XPS cells are made exclusively for LiFeTech. They are not available from Headway. The 15Ah cells were red in color but in the last couple of weeks the factory has changed the cell color to "Platinum". They are a very high grade cell are made specifically for LiFeTech XPS battery packs and the cells are used for special projects for Government departments and the like. A typical special project I am supplying these cells for is for critical care hospital equipment (while patients are being transported between hospitals by ambulance).
You can read more info on the 15Ah cells here- http://lithbattoz.com.au/index.php?page=battery-cells
 
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