J-Cube

I heard about this battery a little while ago and I learned it's a safer chemistry than LiPo. It seems to have many advantages over LiPo such as shorter charge times, but I was wondering, what is with the weird voltages they're sold as? A one cell A123 is 3.3V. That makes a 2S 6.6V and a 3S, 9.9V. I need any voltage between 7.2 and 8.4 to get the most from my Mamba, safely. Does anyone know where I can find a 7.2V Li-Ion battery? I know they exist. Thanks.

tashspop

My Feedback: (1)

these batteries pack a punch. even though they are lower voltage than lipo, thats a small trade off. going from nimh or nicad, you'll see better performance with low voltage packs due to the increased amp output of the a123's. why can't you use the 9.9v?

AresROC

Funny according to LG Li-Ion's are more dangerous than Li-Po's:

http://www.theinquirer.net/gb/inquir...ll-bloke-cover

J-Cube

I don't know how Li-Ion can be more dangerous than LiPo. LiPo causes fires. That said, all battery chemistries should still be properly cared for to prevent damage, fire and/or explosion.

Li-Ion is cool and all and, yes I could use the 9.9V pack (I just double checked some things), but I think I'll still end up with LiPo. I already have all the equipment for it.

Check this pic out. It's the equation for how the battery stores all it's power. Notice it starts with A123.

BuzzBomber

My Feedback: (4)

Lithium Ion is kind of a catch-all term. AFAIK, Li-ion, LiPo, LiMn, and LIFE04 are all lithium ion derivatives.

FWIW, if you'd like to try out the A123/M1 cells without spending $$$ on a new charger, SLK Electronics sells an adapter to safely charge them with a nicad/nimh charger. See here: http://www.slkelectronics.com/lipodapter/index.htm

Access

Anything with lithium is inherently unsafe if misused. A123 is a little more fault tolerant than LiPo, but it's no excuse to misuse them, if you do you are looking for trouble.

If you look at this thread I talk about a high-power device you can build yourself that is 90-95% efficient for converting voltages. You could combine 3 cells for 9.9V and then step down to the 7.2V you need. The concept is pretty much the same as a switching BEC except it is designed for much higher power. You can build a step-up convertor also, like the 'boost' device A123 used to or maybe still does sell, though with much higher power capabilities, and then run off 6.6V. Like the type I use for stock racing off 6-cell NIMH today. But overall it would be a larger design and a tad less efficient to step up vs. step down.

http://www.rcuniverse.com/forum/m_64...tm.htm#6479887

BuzzBomber

My Feedback: (4)

The way I see it, anything carrying CURRENT and VOLTAGE is inherently unsafe if misused.

Seriously, I've seen nimhs explode after a bad crash dead-shorted a cell...

...nice innovation there with the dc-dc converter btw.

cheech4

LIMN are also claimed to be safer chemistry to LIPO

iamnot

Any instructions on building the device itself?

Access

It's not a trivial thing to build, you will need to order
PCBs from www.expresspcb.com
electronic components from www.digikey.com
and you need to be able to assemble and solder a small (2.5" by 1.7") PCB.
The design is 100% throughhole, no surface mount, but it's still going to require some basic soldering skills and decent equipment to not overheat the parts (or burn them up). And it is static sensitive, so you need to take proper precautions there also.

I can post the plans, but the 50A version has only been tested in SPICE (simulation). The 27A version is the one I'm using on my trucks right now, but 27A continuos might be a little on the low side for a mamba.

AresROC

Yeah! This voltage stabilizer would be a great project after my NiMH-safe discharger project! For some applications it even has the potential to turn a cheap 9.6v 40A battery into a 7.4v lipo-like.

Is this A123 the battery that fits many of the new LED flashlights? Those flashlights use 3 AAA batteries so that's actually 4.5volt...

What's the A123's max charge voltage per cell? Where can I buy them?

Marshl

No.

3.6 or 3.7 volts depending on who you believe.
http://www.fmadirect.com/support_docs/item_1229.pdf

A lot of places offer them now but you can order a developer's kit directly from A123 systems

http://www.a123systems.com/

Or if you are so inclined you can buy preconfigured batteries and chargers from their "racing division"

http://www.a123racing.com/


BTW there is a forum section for these batteries here--------------> http://www.rcuniverse.com/forum/forumid_450/tt.htm

Access

Also with the A123 cells can't you overcharge them to 4.1 or 4.2V? But it will shorten the cycle life of the cell... I thought early on when the cells were in development they stated something like that. That the cells could be 'safely' overcharged (to 4.2V) and safely discharged to 2.0V.

Once fully assembled the board will end up looking like this, I'll post the link once I upload the files.

Takedown

My Feedback: (23)

No A123 cells are alot more bash tolerant than regular lipo/li-ion cells. Here is the proof- http://youtube.com/watch?v=A9ayuFBDrSg

Access

Alright I posted the files you need to build the design as-is here.
http://geocities.com/shutaro/index.html
You can msg me or just post if you have any problems.
Hopefully you find the device useful. There is an on-road racing group in my city that races every other sunday, I stopped by today, most people are racing stock, and stock brushless is allowed (13.5 motor, sintered or whatever)! Most of the stockers are running brushless, it looked like a good class. I'll try racing with and without this device and see what happens. Stock brushless is one of those applications where it can work fine as-is, giving you a near-perfectly flat voltage response out of your batteries which otherwise typically change over the course of the race or depending on how hard you are driving. So hopefully it helps a racer drive more consistently. It's not the type of track where a step-up convertor would be of any benefit, stockers as they are aren't going to hit the true 'gearable top speed' even on the longest straight especially if they are allowing sintered brushless. You could run the track off 5 cells and I doubt you'd notice any difference over someone running with six, it's an ideal testing ground for this type of thing. Only drawback is the added weight.

RBMike

I've been using A123's (lithium magnisium) to race for a few weeks now. I built a 2S2P pack that gives me 6.6V/4600mah. These sells are not as fast as nimh or lipo as far as voltage goes but will charge to 95% in about 15 minutes. My 4 cell A123 pack weighed in at just over 10 oz compaired to my MaxAmps 4400 sadle pack at just over 8 oz & a 4200mah nimh pack at 15.6 oz. I'm using a chager that has an A123 mode (hyperion1210) and I chage them at 10 amps. They NEVER get hot, not in the car, not on the charger. With a full charge I will get 20 to 23 minutes of run time at a race pace on the track in my B44 with a Novak 5.5 bl & GTB speed controller. Here's a pic of my car with the pack in it:
http://i8.photobucket.com/albums/a43/RBMike/B44A123.jpg

snellemin

Looks great RBMIKE! Nice to see some more A123 users. You have enough amps at your disposal to gear up and make up for the voltage deficit.

RBMike

I thought about that but instead I got the 5.5 motor, most guys running my class (4wd mod) at our track are running 7.5 or 6.5 for the motor. The motor is over kill with regular packs but works well with the A123's. I'm running an 18 tooth pinion on the stock spur but like I said the motor & speed control are cool when it comes off the track. I could gear up alot I think but I'm just getting back into electric & don't even have a pinion selection in my tool box yet.