Long term (4 year) A123 26650 findings.

[zeropointbug]

After 4 years of use and abuse of my various A123 packs from a 'developers kit' I bought direct from A123, I decided to post some findings on the long(ish) term findings in these little devil cells!

First off, when I bought the developer kits (2 of them, 6 in each), I used them in a dual dewalt 850 motor/dual Novak EVX setup in a heavy 1/6 scale on road car that weighed ~15lbs. I was running a 5s2p, NON-Balanced pack, while building it, I accidentally shorted out the whole pack, blew a tab right off one of the cells. I would run this setup all of summer and fall of 2006, every other day about about 2 times, sometimes 3... run, charge up immediately after, run it again, etc. Going from 3800mah NiMH 12 cells setup, this was a real shocker as far as performance went for me, especially the flat discharge!

They sat dormant all winter for roughly 5 months still NON-balanced, never touched them nor checked the cell voltages.

I ran the 1/6 scale car for about a month in the spring? Then I had to finally go brushless, so I broke and bought an FLM maxx truck, 7XL/Quark setup and split the 5s2p pack into two 5s packs and ran a parallel harness to the controller. As you can imagine, the difference in power going from a decently fast brushed setup to a brushless one was quite apparent! I bought an Eagletree soon after this and started recording runs and found the setup was drawing consistently 150amps, and upwards of 180 amps under hard thottle... soon found out that the 7XL COULD have been a 6XL mislabeled, because I was getting much too high top speed for the Kv of a 7XL. At the pack level, they got pretty warm to touch, my guess would be 135F on a 30 'C day. Ran this setup for about 2 months, and got sick of the high temps on the Feieiyadodurkadurkago 7XL, so I bought a 1512/3D (1700kv).

Now I bought some more A123 cells from DeWalt 36V batts on eBay for a 7s2p and 7s1p pack setup. I bought a Traxxas Villain EX and used the two 5s1p packs in the boat. Packs are still NON-balanced charged, but I checked the cells voltages of each pack and all seemed well, all within 0.02volts.

Since 2007 I have ran the boat all summer every few days in a large slew/pond on our property. Runtimes were about 7 mins, so about 8.5 C discharge rates. If anyone has a Villain boat, they will know that the packs are enclosed in a tight space with zero airflow, in fact, they are getting hot air being blown on them by the motors, which get pretty toasty themselves. Pack temps were consistently running around 145 - 150F right after the run, and they did increase a few degrees after a few minutes sitting. These packs are still being used in the Villain boat with no end in sight.

Packs cycles are UNKOWN, but I would put a conservative guess of 400-450 cycles.

So today I decided to put some balance plugs on the packs and give them a few cycles on the 720i. Here is what it is reporting:

-Capacity: 2065mah Original: ~2300mah
-Cell resistance: ~32mOhm/5 = ~6.4mOhm/cell Original: ~rated 40mOhm/5 = 8mOhm/cell
-Cell balance: all within 0.01V/cell!! End of charge more around 0.04Volts/cell

So the cells after 4 years being through several different setups and used to their limits, never balanced charged, sitting dormant 4 winters for 5 months at a time, and being charged at 3.75v/cell for the last two years, AND being shorted out before the first time they were even used... still retain 90% of their original capacity, and if the 720i is to be believed, they have LOWER cell resistance! I do remember reading in the developer kit instructions that the chemistry really does DECREASE in resistance rather than increase like a traditional LiPo (although the new gen cells are more like A123's in this respect).

I would have to say I am thoroughly impressed by what these things are able to handle. The pack resistance is the thing that gets me though, going from 8mOhm to 6.5mOhm?!? I don't really know what to make of that, I am thinking that the 720i is inaccurate in calculating this? If these packs had been balanced charged and had a little TLC over their life who knows what they are able to do.

I know what battery I am using in my ebike project! (Although their new 10Ah cell )

[BrianG]

Glad to hear it.

I'm interested in those 10Ah prismatic A123 cells as well. I want to build an ebike or something and those look like they offer the best capacity to volume ratio (due to their packaging). Plenty of juice for going back and forth to work, and then some without needing to charge there.

[zeropointbug]

Yeah, and they should be around 150Wh/kg. I would like to see some Headway cycle life data, just to compare.

I just froze the pack down to -25C (-13F), did a discharge on the 720i, reported 148mOhm off the start, then just decreased from there until the end of discharge of 64mOhm.

Will post a heated test of 165F once I'm done.

EDIT: Finished the heated discharge, pack temp was 167F when I started the test, discharge function on 720i, cell iR went down to 28mOhm/5 = 5.6mOhm/cell.

That's a nice post :)

A few months ago I was also looking at A123 cells, but the thing that I don't like is that they have such a stupid size. I would really like to use them in some of my cars, but they just won't fit. My second idea was to use them in an E-Bike I wanted (and still want) to make, but as these cells only have a capacity of 2300mAh I needed to buy a LOT of them to solder some in parallel. I'm not sure, but I thought I would have needed 48 of these cells to have a reasonable runtime. At that time they costed about $7/piece, which would be $336 for all.
Anyway, my finding was that I could better go with LiPo's as they are a lot cheaper, and I could also use them in my cars. After some research I saw that I could buy these A123 cells for I thought $4/piece, which is very cheap, but they were directly from China and I didn't know anything about the quality of those A123 China cells. Then the idea "died"...
After reading your post I'm really considering buying a DeWalt pack, and some cheap A123 cells from China, to compare them and to get my first experience with A123 cells.

Could someone post a link of those 10Ah cells? That sounds very interesting!

[zeropointbug]

Yeah, you are better off for sure getting the latest lipo packs for your R/C's. However I don't see why you think lipo's are cheaper for an ebike? Do you mean Turnigy/Flightmaxx packs? If so, IMO, I would not go that route, too risky... those packs aren't quality built, you will most likely run into problems in a 2 years or less. I know Metallover is using them, but I can't see them being a long term investment, no offense metallover! Building A123 packs is surprisingly easy and fun actually, you just have to be careful not to short them out...

You are right, 48 cells is the number of cells I would be using if my brother goes the A123 route, 12s4p pack, split wired for charging. I have calculated that would give a bike a conservative ~18 miles range at a decent pace, say 35- 40km/h.

If not A123's, the the Headway 38120 10Ah cells.

HERE is the A123 10Ah cells, not much info, the 10Ah cells specs are on the bottom. Go to A123 Systems website for a pic of the cell, not much to look at though.

I am hesitant on those cheap ~$4.5/cell A123's from eBay (China) as well. We don't really know if they are genuine or not, if some cells could be dead upon arrival, whether they are used, so I don't know yet, still trying to find to people who have used them.

Jup, Zippy's/Turnigy/Flightmax I never bought an other LiPo brand as the ones from Hobbycity so I don't know anything about the quality from the Flightpower/Hyperion/ThunderPower packs. They'll probably be better, but for the price of a LiPo from Flightpower etc. you can get 3 Hobbycity packs, so I'll stay with them for now.
I've seen many people using LiPo's for their E-Bike, they all seem quite happy with LiPo's.

Those 10Ah cells look awesome, but quite big

Someone at I thought RC-Groups also said these China ones are old used cells, but nobody knew that 100% for sure.

[A RC Dude]

Originally Posted by Byte

I don't know anything about the quality from the Flightpower/Hyperion/ThunderPower packs. They'll probably be better, but for the price of a LiPo from Flightpower etc. you can get 3 Hobbycity packs, so I'll stay with them for now.

i've had two trackpowers 2 zippys, and now 2 truerc's. both of my trackpowers in a rustler with MM7700kv system lasted abut half a year before they puffed for no reason (always balanced and LVC at 3.2-3.3v/cell). my first 5s zippy-h lasted 2 months in my e-maxx with my MMM 2200kv system (LVC 3.25v/cell, constantly ballanced) before cell 2 puffed up. my second zippy lasted 5 months before cell 4 started acting funny and voltage got too low (LVC at 3.25v/cell, always ballanced) and my first 5s TrueRC lasted 8 months in e-maxx (same setup) before my ballancer somehow turned off on me wile charging and cell 5 charged slightly to far. and my second truerc has yet to get a run on it