Questions about A123 cells

Hey guys, a couple of weeks ago, I was talking with the guy that owns my LHS about A123 cells and packs. Well, when I walked in today, he surprised me with a box full of A123 products. His question was, "well, what can we do with these?" I explained the pros and cons of the A123s, as I understood them. He said that he was unsure and wanted me to play guinea pig for him with some of the batteries, because he didn't want to sell a product that wasn't proven.

We discussed it for a few minutes, and he decided to let me use a couple of packs and a charger. I wanted to really push the packs to see what they were capable of. I decided to take one 2S1P pack and one 3S1P pack, to run in series for 5S. The test vehicle was my Losi 8ight T conversion running a MM esc and Feigao 9XL, with 40 series Moab tire running 12/44 gearing.

My subjective impression was that the small capacity battery pack had all of the punch of my 4S2P 8Ah pack and it was strong until it dumped. I'd have to imagine that the voltage must have taken some serious dips, so the 6 minute or so runtime that I got weren't bad. I'd also imagine that I could expect 15 minutes of runtime with a 2P configuration, if not more. After they dumped, the little 1P rig temped at 130*F. The esc temp was under 100* and the motor was at 140. This was after some serious running. I'd also imagine that the motor temp would drop a bit too with a 2P config, with the voltage drop not being so bad.

Now, this was probably more info than I needed to share, but I wanted to share it. Now for the questions...

1. The manual (if you want to call it that) states that the A123 cells can be charged to 4.2v "without hazard." Does that mean that we can just charge the cells to 4.2v all of the time? What does "without hazard" mean? Does it mean that it won't vent, or does it mean that we can charge the cells to 4.2v without adversely affecting the life of the cell?

2. I have a Thunderpower 1010C charger, which will charge A123 packs, or so it says on the TP site. At what rate can I charge these A123 cells. If it can charge in 15 minutes, that would be a rate of 9.2A. Does this mean that I can just build a 5S2P pack out of A123 cells and charge it at a 9.2A rate and have a fully charged 4600mAh pack in 30 minutes?

3. Can I balance the A123 packs using any lipo balancer? I have a thunderpower 205. Will that do it?

4. I know that some of you are doing surgery on Dewalt packs to recover the A123 cells. I want to use the commercially available A123 cells. The cells come wrapped in cardboard sleeves. Are the sleeves necessary? If they are, can I remove the sleeves and use shrink wrap around the cells instead. I'd really like to recover the space being taken up by all of that cardboard.

In the event that the cardboard sleeves are necessary, can I run two sleeveless cells in parallel (both electrically and physically) and then just shrink wrap the two cells together? I want to build a 5S2P pack using two 5 pairs in series.

If there are any points of interest that I missed, please volunteer the information. I'd really like to know as much as I can about these cells. From what I've seen so far, I really like them and will convert over to them. I might be selling some lipo packs cheap.

BTW, can anyone give me an idea of what sort of runtime I could expect running my 8ight in truggy form (standard MT size tires/wheels) with a MM and 9XL on a 5S2P A123 pack?

Once I get my Quark back from S&T, I'm going to see if my LHS will let me "borrow" three more 3S packs. I'd like to try a 6S2P config with the Quark. I know that the Quark doesn't like 6S lipo, but the 6S A123 might be more to the Quark's liking.

Thanks.

[BrianG]

1: From what I've read, you can charge them to 4.2v because after a certain point, they simply won't accept any more charge. So they are saying you can't overcharge them. Still, I would either use a A123 charger, a lipodaptor, or a charger with a settable 3.6v/cell CC/CV threshold voltage.

2: I have also read you can charge at more than 1C on the A123 cells. However, I don't know what this does to the life of the cells. I wouldn't go much more than that just to protect the investment. If time is that critical, I'd just get an extra pack or two.

3: Any balancer should work as most will simply equalize cells whatever their voltage. Some balancers may not function if it sees the cells lower than a certain value. Since the A123's LVC is about 2.2v (IIRC), this might cause some balancers to not work until the cell gets to a minimum value. Can the 205 work? I dunno. I'm sure someone here has used one before and could explain further.

4: Most cells use the "can" as the - terminal so the sleeves ARE ABSOLUTELY NECESSARY. Otherwise the metal "can" would touch the adjacent cell causing a short circuit. The sleeve is the insulator. I suppose you could remove the cardboard and replace with decent heatshrink if you were worried about water deteriorating the cardboard. If you are paralleling two cells, then the - terminals are touching anyway, so it shouldn't be an issue.

Just remember that these cells are 3.3v/cell nominal, 3.6v/cell CC/CV threshold, and 2.2v/cell low V cutoff. This means that LVC units may not function right with certain cell counts. People say that the dropoff is quite abrupt so a LVC isn't really needed anyway.

As always, runtime depends on the setup, driving style, terrain, etc. As long as you aren't pushing the current limits of these cells where you start losing Ah, you should get as much runtime as a similar capacity lipo.

6s A123 is 22.2v at a 3.6v/cell full charge. 5s lipo is 21v at a 4.2v/cell full charge. 6s lipo is 25.2v at full charge. So, 6s A123 is sorta like 5s lipo.

Thanks Brian. I was just asking about the charge rate, because I am now using the Hypersonic charger and it does, indeed, charge a depleted pack in 15 minutes. That would necessitate a 4C charge rate wouldn't it? I would imagine that the guys at A123 Racing wouldn't have designed their charger to degrade the life of their cells, but I was hoping for some sort of confirmation.

I did email A123, but I thought I'd ask here because unlike RC Monster, A123 Racing is not open 24/7 for questions.

[BrianG]

I just did some poking around and people are charging at up to 4C rates. However, I didn't find anything about how this affects long-term cell life compared to 1C charging.

If you are going to charge 6s A123 at ~9A, you'll need a charger that has at least a 195W power limit, and a 12v power supply capable of at least 250w (~21A @ 12v).

Well, my TP1010C can do 5S at 10A, so I should be able to get pretty close to 9A with the 6S A123. In any case, the charge time will be significantly less than one hour, as it is with the lipos.

As for the power supply, what do you think of this...http://www.radioshack.com/product/in...entPage=search

[BrianG]

I generally don't like to get "nice" things from RadioShack because they are usually overpriced. So, I've never used that PS before - not sure if it'll do what it claims while keeping a steady and noise-free voltage.

If an adequate computer power supply won't do it for you, I've had good luck with my Aston 25A PS. Nicely built and you can tweak the voltage up a bit. I pumped mine up to 14.5v (typical vehicle voltage with enging running) so the current doesn't have to be as high for a given power requirement.

Brian, is that Aston or Astron? I did find the Astron and the price isn't bad.

I do have a BK Precision bench supply, but it can't handle that much current.

Do you have any suggestions for a source on your power supply?

[BrianG]

Oops, that was a type-o. It is Astron. :)

I got mine off ebay for $72. It was a little more than I wanted to spend, but worth it if it is a solid PS. I use that when I go to the track since I can use both my chargers at once (had to add an extra set of outputs on the front panel). At home, I just use one of my converted PC power supplies.

At 14.5v, 25A generates 362w. That's just about enough for my Hyperion 7i (120w power limit) and my Xtrema (180w power limit) running at the same time, if I don't run the Xtrema at full capacity.

I'm going to start looking for one. I like to run a PS at the track too. I have one of those small Honda generators (EU2000i, I think) for the track too. It's nice having the right setup.

[MetalMan]

Sorry I didn't get my input in sooner, but here are my answers:

1. 4.2v won't cause damage, but it could reduce the cycle life rather dramatically. And if you do charge to 4.2v, a higher charge rate should be utilized, and you should end the charge shortly after it enters the CV phase. This will help keep the cells in better shape.

2. You can charge A123 cells as fast as you want. If you had the appropriate charger you could do a 12C charge (5mins). The TP-1010C will charge A123s properly when you have the updated software.

3. Some Lipo balancers won't balance below a certain voltage. In the case of the TP balancers, they will balance A123 cells, but they won't do it all that precisely (which is fine, since these cells don't really need to be balanced much at all).

4. The sleeves that the cells are in are good. If the cells are dropped, they can absorb a portion of the energy of the fall to keep the cells from denting as badly. You could use shrink wrap, but the cardboard is better IMO :).

I'm running 5s2p A123 in my Revo (zeropointbug is also running 5s2p in his E-Maxx). 5s2p is an excellent setup - good charge times (I charge at 8.30A using my "hacked" Astroflight 109), strong power right until it dumps (and it dumps HARD), 15min. runtimes, excellent safety, and super low cost (this pack cost less than $120 after building materials expenses).

Balancing with A123 cells isn't really all that necessary. These cells can tolerate overcharge/overdischarge quite well. With Lipos, good balance is critical since bad balance can lead to overcharged/overdischarged cells, and Lipos are much more sensitive than A123 cells. The first 5s2p pack I made has a damaged balance connector, so I haven't even balanced it in at least 10 runs. Right now, the highest cell is at about 3.73v, and the lowest is at about 3.57v (at beginning of CV phase). This difference may seem large, but what intrigues me is that the pack balance actually becomes better as the CV phase gets closer to finishing (the highest cell DECREASES in voltage).
The balance of my other pack has also been quite good, but I do still occasionally balance it just because I can.

As for a power supply, I'm running a PC server PS that is rated at 30amps on the +12v line. This power supply actually came bundled with a second power supply in an enclosure that is meant for use in IBM servers (total output of 60amps on +12v line). The cost of the entire enclosure/PSs was only $40, and maybe $10 for shipping. The individual PSs are a little large (not that large, though), but they work VERY well and don't drop their voltage at all with about a 15amp load. Unfortunately these PSs are no longer sold, otherwise I would buy more and sell them for profit :).

MetalMan, if you're getting 15 minutes of runtime on your 7XL setup, I should be able to get more with my 9XL track setup. I'm still waiting for my Quark to get back from S&T. I've been toying with the idea of running 6S2P A123s with a 10XL. I'm just a bit concerned about the weight and the way it will affect the way my truck flies.

I've thought about getting the Dewalt packs and breaking them down, but my LHS is cutting me a deal that makes it worth it to me to just get the cells with the solder tabs on them. I just really don't want to have to deal with all of the welded joints on the dewalt cells. I'm going to go read your thread on the subject again. I may change my mind.

Thanks for all of the info.

[BrianG]

AAngel, just to clarify; just because you are running a 9XL doesn't mean you will necessarily get better runtime. You will if you are running the same exact weight, gearing, and tires as MetalMan with the 7XL. But if you gear up to compensate for the slower speed of the 9 vs the 7, the added load will pull more current. Net runtime gain will be close to 0.

You probably know this, but didn't want newbies thinking that you can get high speed AND high runtime simply by swapping a motor.

It's just funny the way the caveats in the game can throw you so many curve balls. LOL.

Yeah, I'm running the lower kv motors and gearing them just enough to put a sufficient load on them. I'm really not minding the sacrifce in speed. It really is weird the way you can take a setup out to a parking lot and it will look slow, but when you get it on a track, things change. I've progressively gone from a 7 to an 8 to a 9XL motor. I don't like to over or under gear my motors. I want to keep them as comfortable as possible. If I'm running a setup and I want to slow it down, I'll just go to a lower kv motor rather than under gear a motor just to slow it down.

I do have to say that going with these "slower" motors is the way to go. My truck gets down our straight so quickly that people's jaws will drop. Those that have never seem my electric vehicles before, anyway. Of course, it's only topping out at around 30 mph, but it gets there it the blink of an eye.

When I ran my truck last night, the track was about as loose as it ever gets. With the setup I was running last night, which was the 9XL on 4S lipo geared 14/44 with the stock tires, I can exit the turn coming into the straight and give it full throttle and maintain control until it's time to hit the turn at the end; and after half an hour of running, my 8Ah pack only took a bit over 6A when I charged it.

I'm thinking that I might try a 10XL on a 5S 6Ah pack. Thank goodness these Feigaos are so inexpensive. They make for relatively cheap experimentation and I'll be able to make a better informed decision when I do get a Neu or two. Once I do have my Neu, I'll also have a battery of spare motors for other projects.