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DRZ400
15 June 2014, 1802
Anyone check out the Calb cam72fi cells? Specs look great.....price not so great....

robo
16 June 2014, 2112
Huh. Thanks for posting that. Smaller cells would have helped me out a bit :)

I've had good luck with my CA cells so far. If these are an "improvement" then that should be a good thing.

There is that price though.

DRZ400
17 June 2014, 0616
Hey Robo, nice build! How do you like the Altrax? Im using the SE40ah cells....really happy with them, however thinking of going to the CA60 to increase my range ~30 miles now.

DRZ400
17 June 2014, 0618
Oh, do you have a CA? If go was wondering what the MAX amps has been? I max out at 280 amps...not sure if its my Kelly or the SE cells (thinking its the Kelly).

robo
17 June 2014, 2257
DRZ,

I do have a CA. Amps max has been ~420 if I push it all the way. But, on most of my commuter rides I usually don't need more than ~200-300 for brief accelerations. I ride fairly conservatively for range. It's normal for me to see 85Wh/mi.

The Alltrax has worked well. Although, I'd love regen. Not necessarily for recoup, but for lack of engine braking. I have some steep mountain roads and the descents are really, really hard on my brakes.

For hard data plots I recorded from my 60V pack (with 60Ah cells):

http://www.elmoto.net/showthread.php?3182-CALB-gray-cell-performance-data/page4

Hope that helps.

DRZ400
18 June 2014, 0548
Cool, does is there a logging function in the controller? I've used a cellog-8, did 3 runs across my 24 cells. Interesting to find 20 of my cells sagging to ~2.7 volts during hard accel, 2 close to 3v and 2 runts hitting 2.4 volts. I was going to replace the 2 low ones but they otherwise seem fine. I did a 32 AH ride yesterday and was within 3 mph of my normal top speed (71mph).

podolefsky
18 June 2014, 1843
I was just looking at these. Price is higher than other LiFe prismatics, but only by a bit. $0.60 / wh compared to about $0.50 / wh for most others. But the energy density is much higher, 260 Wh / L compared to about 140 Wh / L for most other LiFe prismatic. Similar to Headway density, and about the same price. Discharge is lower at 2C continuous and 8C peak, but that's still 580A peak which will keep up with plenty of controllers.

The nice thing about prismatics is that you don't lose as much space in packaging compared to cylindrical or pouch cells - so you should be able to get near that 260 Wh / L built up.

robo
18 June 2014, 2112
That's interesting Noah. I know Enerdels offer a "power" module and an "energy" module. It's almost as if CALB "biased" this cell design slightly towards the "energy" side of the spectrum with the higher energy density and the lower c-rate.

DRZ, my Alltrax 7245 can log through it's old-school rs-232 serial port, although I prefer logging via Bluetooth wireless to my phone using the CA instead. Hope those two runt cells keep on keepin' on their side of the bargain...2.4V is getting down there (even if it is temporary sag voltage). But, I'd smile at 71mph too.

DRZ400
19 June 2014, 0601
Have you noticed how strong the pack feels in the 90 degree temps? I drove in to work yesterday, charged at work. When I left it was 91....my top speed was up 2mph to 73 and the pack just felt stiffer. I'm debating on going to the CA60FI's now or waiting for next spring. Maybe the CAM72's price will come down.

podolefsky
19 June 2014, 0659
That's interesting Noah. I know Enerdels offer a "power" module and an "energy" module. It's almost as if CALB "biased" this cell design slightly towards the "energy" side of the spectrum with the higher energy density and the lower c-rate.

That's a good observation. The weird thing is that the Enerdel "energy" cells are cheaper than the "power" cells. Their energy cells are already pretty powerful - the power cells are super low IR, for hybrids and applications with very rapid charge/discharge.

It looks like the CAM cells have an aluminum case instead of PVC. That would save some volume, could also be more expensive to produce.

robo
19 June 2014, 1316
... It looks like the CAM cells have an aluminum case instead of PVC. That would save some volume, could also be more expensive to produce.

If the CALB CAM cells have higher IR, the aluminum casing might be for heat dissipation (PVC = not so good at that). I can't imagine aluminum is cheaper than PVC, so the aluminum must have an engineering purpose.

Aluminum's stronger than PVC w/less thickness, so maybe AL also reduces weight (in addition to volume as you said).

If CALB is playing the game of higher energy/eight and higher energy/volume specs, a relatively small drop in C-rate and using aluminum to boost these values...that's an appealing marketing tradeoff.

The Al must do something. The cells aren't made by Apple for beauty (although Apple exploits Al's heat conduction too).

I'm also not sure of the cell engineering trade-off is between energy density and IR/C-rate. Maybe more dense cells slow down the Li intercalation rate, but that's a complete guess.

Today's a good day for lots of speculation from me...

podolefsky
19 June 2014, 1446
Aluminum does help with heat, as long as you have somewhere for the heat to go. If the cells are all pressed against each other, it helps less, since heat can only get out through the outermost surface of the pack. It definitely reduces volume. I don't think it's much lighter than PVC - plastics are pretty low mass density.

Energy and power are related to the relative size of electrode and separator. A cell is basically a laminate of electrode and separator, usually in long strips wrapped up in a roll. Thicker electrode means a higher fraction of the volume is active material. That means more charge carriers per volume, but with a longer distance to move through, which means more heat produced and ion starvation at lower C-rates. Thinner electrode is the opposite, less active material but less distance to more. It's also more expensive to produce because the tolerances are tighter.

http://www.southampton.ac.uk/~ssegroup/images/thickvsthin.png

Image source (http://www.southampton.ac.uk/~ssegroup/research/3dbatteries.shtml)

robo
19 June 2014, 2146
Have you noticed how strong the pack feels in the 90 degree temps? I drove in to work yesterday, charged at work. When I left it was 91....my top speed was up 2mph to 73 and the pack just felt stiffer. I'm debating on going to the CA60FI's now or waiting for next spring. Maybe the CAM72's price will come down.

Definitely. My CA60s demonstrably perform better in warmer temps. In the winter, I occasionally rode in temps in the low 40s. Sag was larger and range was less than in the current warmer temps. That cold caused an inadvertant 52Ah ride for me once. Once.

Hard to know if the CAM cells will make the CA cells the new SE cells.

robo
19 June 2014, 2220
Aluminum does help with heat, as long as you have somewhere for the heat to go....

...Energy and power are related to the relative size of electrode and separator...


I agree much cell surface area is confined inside the pack and heat's not able to directly radiate outward. This gets even worse as adjacent pack size grows.

But, my naive understanding is aluminum would conduct heat more effectivly from the inner surfaces to the outer cooler dissipating surfaces...compared to PVC which is a better insulator.

My knowledge of thermodynamics is not strong. I'm just trying to rationalize the new CAM cell use of aluminum vs CA cells' plastic.

On energy vs power cells, that is coming back to me now- thanks. I had forgotten the thickness and tolerance tradeoffs. And, these do affect the rate (and volume) of lithium intercalation.

DRZ400
20 June 2014, 0615
Noah, where are you getting your pricing? I get $75 for a CA60 and $143 for a CAM72 1.25 & 2 per AH ??



I was just looking at these. Price is higher than other LiFe prismatics, but only by a bit. $0.60 / wh compared to about $0.50 / wh for most others. But the energy density is much higher, 260 Wh / L compared to about 140 Wh / L for most other LiFe prismatic. Similar to Headway density, and about the same price. Discharge is lower at 2C continuous and 8C peak, but that's still 580A peak which will keep up with plenty of controllers.

The nice thing about prismatics is that you don't lose as much space in packaging compared to cylindrical or pouch cells - so you should be able to get near that 260 Wh / L built up.

podolefsky
20 June 2014, 0659
Noah, where are you getting your pricing? I get $75 for a CA60 and $143 for a CAM72 1.25 & 2 per AH ??

I was quoting $ / Wh. It's a more even measure to compare cells with different nominal voltage.

Roughly speaking, for LiFe, Wh = 3.2 * Ah. So 3.2*72 = 230 Wh. $140 / 230 = $0.60 / Wh.

DRZ400
20 June 2014, 1327
Course....but in this case their both LiFe 3.2, So the CAM72 at $144 is $2/ah. CA60FA at $75 is $1.25/ah.


I was quoting $ / Wh. It's a more even measure to compare cells with different nominal voltage.

Roughly speaking, for LiFe, Wh = 3.2 * Ah. So 3.2*72 = 230 Wh. $140 / 230 = $0.60 / Wh.

frodus
20 June 2014, 1341
But you almost half the volume ....i.e. more batteries fit on the vehicle. Not to mention they're lighter by 20%

Sent from my SAMSUNG-SGH-I337 using Tapatalk

podolefsky
20 June 2014, 1421
Course....but in this case their both LiFe 3.2, So the CAM72 at $144 is $2/ah. CA60FA at $75 is $1.25/ah.

True, I just like to compare across different brands and chemistries. Using $/Wh let's me do that. For example, it tells me the CAM cells are about the same $ / Wh as Enerdel energy cells. The CAM cells are actually a little higher energy density, but the Enerdels are MUCH higher power density. If I was upgrading, I'm pretty sure I know which I would choose.

DRZ400
23 June 2014, 1421
Yeah the Enerdel cells are nice....but also pricey. I can get 24 CA60 cells for 2k to my door. The Enerdel's would be 50% more. Ive been very happy with the CALBs so far....going on my 3rd season, about 150+ cycles. The CA60's would boost my range up to ~50 miles and give less sag.

podolefsky
23 June 2014, 1446
Enerdels are the same price as CAM cells. That was my point.

Sent from my HTCONE using Tapatalk

DRZ400
26 June 2014, 0638
Agree.....I was hoping that one of the Chinese Lifepo4 manufactures would "clone" the A123 20AH cell and have it for $21.50 by now!

podolefsky
26 June 2014, 0743
That would be a deal.

Not to push the Enerdel thing too hard - but - Evolve electrics' "custom modules" come out to about $0.46 / Wh (for the energy cells). That's pretty close to CA cell prices, and it includes all the packaging and high current terminals, which saves a lot of pain in a pouch cell build. I believe they are B-grade cells, so 16.5 Ah instead of 17.5.

http://evolveelectrics.com/Enerdel.html

The one thing is Enerdels are only about 170 Wh/L once they''re packaged. CAM cells are higher, about 260 Wh/L. It would basically be a tradeoff of range for power - but then, the power is only useful if you can use it. CAM cell spec claims 576A, which would be plenty for most builds. It's a pretty big advance for prismatics, hence the price.