Battery questions

[x88x]

Hey all, I've been lurking for a while but I'm running into a wall so I figured it's time to join in.

I'm fairly new to the EV scene, but I've got a lot of ideas and I'm going to be starting work on a few of them over the next couple months. My current mid-range goal is an electric motorcycle, but I'm going to be starting with an e-bike and a couple little electric scooters I picked up cheap to figure out what I'm doing before I get into the serious money that the motorcycle is going to require...especially since I plan to make my own BLDC motors for all of them.

So, anyways, point of all that for this thread is that I'm trying to decide what batteries I should start with. I want to be able to pull a lot of low-end torque out of the motor(s) I'll make, so I want a high C discharge rating on the batteries. I was pretty well set on using A123 18650 cells, but yesterday and today I found some things that are confusing the matter for me. Before that though, the reason why I was set on 18650's instead of 26650's (at least for the first stage of projects) is because in the looking I've done on eBay, if I buy in bulk I can get the 18650's for as little as $2.20 each, whereas the 26650's seem to bottom out at around $8.20 each. Granted, I would have to run two 18650's in parallel to match a single 26650, but the cost difference is just too high when space isn't as pressing an issue.

So, like I said, I was pretty much set on the 18650's, but yesterday I ran across this thread and the Turnigy nano-tech 45C/90C cells. Then, today I ran across this thread where gblast123 mentioned the A123 32157 cells. This was the first I had heard of the 32157's, so I did a bit of research. Despite A123 apparently starting to make them way back in 2007, the only place I could find that I could actually conceivably buy them was a company called A8 Power Company. A8 doesn't list a price, but if gblast's estimate of $25 is correct, they could be quite appealing, falling square between the 18650's and Turnigys in $/Wh, and weighing in at less than either.


So, my questions to whoever might know are these:

Are there any other known sources for 32157 cells (preferably somewhere I can buy less than 200 at a time) or any other 32-series A123 cells? If so, how much are they? If not, does anyone have any experience with A8 Power Systems?

Does anyone know the charge/discharge specs for 32157 cells? Or, really, any proven specs?
Like I said, that thread was the first I'd heard of these, and the only stuff I can find online is A8 Power Systems and a bunch of news and forum posts from 2007, speculating about what they might be like. I'm assuming they're at least as good as the 18650's and 26650's, but A8 doesn't list those specs on their site, and of course A123 is no help...heck, as far as their website is concerned, they might as well not even make the things... Unless someone recommends another source, I'm going to go ahead and contact A8 to at least get prices and more specs...since from what I've seen, contacting A123 directly even just for specs would be pointless unless I want to buy a few million of them. -_^ ..I understand why, but that doesn't make it any less annoying.

Lastly, does anyone have any thoughts at this stage about what batteries might be better to use? The Turnigy Nano-tech's are very appealing (225A peak continuous out of each cell?! ), but I haven't seen anything yet verifying their charge rate (HK says 'up to 15C', but some other forums I've looked at say anywhere from 8C down to as low as 3C max -_^ ), how long they can sustain that 90C discharge rate, or their long-term durability.

Here's my current estimates. For the first stage I'm thinking a target of a 36V 10Ah pack.

Turnigy Nano-tech 5.0Ah 5S
2S-2P
37V 10Ah
370Wh
450A peak continuous
900A peak burst (?s)
possibly up to 15C charge?
4 at 715g $78.99 each
2,860g/6.3lb
$315.96
$0.85/Wh

A123 18650
11S-10P
36.3V 11Ah
399.3Wh
330A peak continuous
660A peak burst (10s)
110 at 39g $2.20 each
4,290g/9.5lb
$242.00
$0.60/Wh

A123 26650
11S-5P
36.3V 11.5Ah
417.45Wh
350A peak continuous
600A peak burst (10s)
55 at 70g $8.20 each
3,850g/8.5lb
$451
$1.08/Wh

A123 32157
11S-1P
36.3V 8-10Ah
290.4-363Wh
peak continuous?
peak burst?
11 at 252g $25 (guestimate) each
2,772g/6.1lb
$275
$0.95-$0.76/Wh

 

[dogman dan]

The easy answer would be to play with some turnigy lipo to start with. Why? cuz you get to play with them the day they arrive, not weeks later after you learn to solder or spot weld an a123 pack together. And they are small and light, so perfect for little scooters and such.

But do get some A 123's and play with them too. For a motorcycle, I'd think the pouch cell A123's Cellman had would be very interesting. Not sure if more are avaliable or not.

 

[x88x]

Good point on the immediate usability of the Turnigys. I hadn't really looked at the lower C packs, but looking at them now, they're a lot cheaper..some under $0.50/Wh, nice. Nice for learning/experimenting where I might accidentally blow something up.. <_< >_> And come to think of it, the little scooters I'm starting with probably won't be able to pull anywhere near 90C anyways, even after I re-do the motors. By Maryland law I'll have to limit any motor modifications to ~1800W (2.4HP for "motor scooters"), so 20-30C peak boost is probably a more realistic max pull for this stage.

I just found out about the A123 pouches yesterday too. Rather, I knew A123 had been making them for a little while, but I had been searching for 'prismatic', not 'pouch'..then I saw someone in another thread referring to them as 'pouch' cells and ended up finding cell_man's store (then later realising that's what it was ). Those definitely look more friendly for the size pack I would need for a motorcycle (my current estimate is starting at 150V 20Ah, so just 46S1P of the 20Ah ones)...not cheap, but I think the easier (and smaller) pack construction would balance that out. Here's hoping they become available somewhere sometime between now and when I get to the point of starting the motorcycle build.

 

[Samba]

a123 has a 32113 cell on their homepage - but no specs. Their division thats selling upgrade batteries for Prius - 5KWH packs - appears to use the 26650 cells - about 2000 of them. I take that to mean that either they don't have high-volume production of the larger cells yet, or its all tied up on one of those multi-megawatt-hour powergrid buffer projects they've taken.

90c = drained in 30 seconds.

I've heard 70A for the a123 26650 batteries thats 70A/2.3AH = 30C
If they are made into a 11.5AH pack then 30c is 350A
30c = drained in 2 minutes

1800 watts from a scooter is 36v*50A. If its a 10AH battery thats 5c. 50a/10ah=5c
5c = drained in 12 minutes

Electric motors are rated based on their sustained wattage at design speeds. An efficient operating range around 65-90% of their no-load rpm. When they are accellerating hard from a stop, they can draw 2, 2.5? times that rated wattage. Thats what those peak burst numbers are for, tho different battery companies spec it differently - 10s,15,30seconds. The motor controller has to handle those peak amps too, and the selection gets really limited at 125+amps.

 

[x88x]

Hmm, ok, I haven't gotten to the point of starting into the heavy research for the motors yet, so I wasn't sure what to expect for starting current draw. In retrospect, even if it hits 4x the run-speed (20C) at launch, that's still within the capabilities of those cheap 15/20-22C Turnigys. Ok, I'm convinced, I'll go with those for the scooters. ..hmm, or, since I do have two identical scooters to play with, and I want to try out the A123 18650's as well, I might set one scooter up with the cheap Turnigys and one with A123's.. Eh, it's still a few weeks till I buy anything..gotta move first.

Oh, and btw, I was looking into it today and apparently the big 2MW grid-stabilization units use the prismatic cells. Between those and the contract that A123 recently got with Navistar (International's parent company), which I'm assuming is also going to be using the prismatics, maybe they'll become available again at some point! Well, I can hope anyway.