a123racing batteries

[th3tick]

Ok, they're heavy, but WOW.

http://www.a123racing.com/html/hypersonicturbo.html

Is there any other downside?

[eightythree]

i just saw some guy at the field last week running a123s in a larger electric airplane. he was claiming to have paid about 150 for his lipo pack, and 70 bucks for his a123 pack. he found dewalt batteries on ebay for 10 bucks a piece then wired them up with his own balance lead.. half price!! im not sure if anyone has been using them in helis..?? i saw a link posted in the lepton section of someone's build and had a mock up of a123 cells on the heli.. i wonder if he ever used them.

[noguy]

Just that they are heavy and the size. Oh and that they are heavy.

[kgfly]

The A123/M1 datasheet is here: http://www.a123systems.com/html/prod...650M1specs.pdf

A123/M1 cells have lots of advantages and are popular in larger models where their size and weight is more easily tolerated. For example a 10s A123 setup gives about the same performance as an 8s lipo setup on a T600 at about the same weight, although with shorter flight times. Some folks fly 4s A123 on TRex450, 7s on H550 and 12-15s on T600/e620/LogoXxx and are very happy with them.

You need a suitable charging solution that is (a) matched to their difference voltage profile and ideally (b) powerful enough to take advantage of their fast charge potential at up to 10A.

Advantages:
* Inherently safe, almost zero fire risk
* Expected lifetime of 500 to 1000 cycles
* Tolerate 100% discharge without loss of lifetime
* Up to 10A (4C) charge rate
* Mechanically robust (compared to lipo sacks)
* Non-toxic

Disadvantages:

* Only available in one size/capacity (2300mAh round cell 27x65mm)
* Lower nominal voltage (3.3V/3.6V vs lipo 3.7V/3.2V)
* Heavy per unit energy compared to lipo (3.3V 2300mAh cell = 70g)
* Lower sustained power output than premium lipos (16c/33c/50c vs 20c/25c/40c) although you should get 5 times the life from the A123 cells

Which chemistry ?
LiPo provides the highest energy density and best performance for size but is relatively expensive and somewhat fragile. Packs are easily damaged mechanically and there is a risk of fire if overloaded, overcharged, overdischarged or punctured. They also don't tolerate deep discharge. Hence they require a top quality charger, care in handling and a degree of knowledge to be safe.

Emoli (LiIon) from the V28 packs are 100g/cell at 3000mAh. They are heavy buggers but very robust and don't have the same fire risks as LiPo. They have a precipitous voltage drop at the end of the curve which can catch folks out without anough oomph to recover and land. Max current is about 35-40A. They can be good for hovering and cruising but not for much more.

A123/M1 (LiFe) from the 36V DeWalt packs are 70g/cell at 2300mAh. These are heavier than equivalent capacity LiPo but very robust and essentially zero fire risk. They are also lower voltage (3.3V nominal, 3.6V fully charged vs 3.7/4.2 for LiPo) but they tolerate 100% discharge and can be charged at up to 10A (4.3C) which makes up for the lower capacity by getting you back in the air much faster. Testing has shown that for power-system design purposes you should treat them as 16C/33C/50C if you want to get ~500cycles. Unlike the emoli, which strangle around 40A, the A123 cells are capable of very high output, certainly 70A and up to 100A briefly. Basically heat is the enemy of cell life so running them at these very high discharge rates will shorten their life, but it's nice to know they can do it if needed. Under load the cell voltage drops quite a bit, running about 3.1V at 10A and 2.6V at 40A.

The lower cell voltage, particularly under load, means you need more series cells than a lipo for the same rough pack voltage. The bigger voltage drop under load (at least compared to premium lipos) means maintaining uniform headspeed can be a bit harder and an ESC with a top class governer (eg Jazz or CC) can be useful.

The market rate on Ebay for a DeWalt 36V tool pack with 10 A123 cells is about USD$100-$120 plus shipping. Works out to around $12-$15 per cell. That makes them very cheap when compared to lipos on a total energy basis. For example a 3S 3700 lipo costs about $150. A 6S 2300 A123 delivers about the same energy for approx $85. Of course it will weigh ~450g vs ~310g for the lipo and take up more space too. By accepting shorter flight times the balance can be adjusted for easier mechanical fit and even greater savings. Hence a 4S A123 will give about 2/3 the flight time for about one third the cost and the same weight. Now only the space may be an issue. At these prices you can have three A123 packs to give you more total flight duration with faster charge times and much lower risk.

[noguy]

I wish they had more cells sizes avaliable. There are just tuff to get into a 450....
They could make great sport flying packs in smaller heli's but it's tough to fit them.
The fast charge & cycle life is the obvious TOP plus side for many RC folks, If only there were more different cells to choose from. :?
Maybe soon??????

I would probably have several 123 packs if I could afford a larger heli in the first place.

Does anyone know why this chemistry cannot be pancaked like lipo's are???
Or can it? Is it that they just haven't produced any other form factors yet?

[kgfly]

The main target for A123 is the automotive market, hybrid and pure-electric vehicles. Our use is not even really on their radar despite the A123racing product line. They have announced some much larger cells. It is unlikely they would make any smaller ones any time soon as the energy density works against them compared to other chemistries.

Use of A123 is taking off (pun intended) in medium to large sized R/C planes and definitely has a place for helis, but it is not for everyone.

[noguy]

I have actually been tossing around some figures to try to put togeather a home built 'pure-elec' compact car. The cycle life makes a123 the only choice for a pure elec. (at least one with range that's not one giant rolling batt).

I read the figures on the tesla EV and it made me start looking to building myself a less expensive more practical & useful pureEV.

This guy has about a 250mile($3.00usd to charge it) range and it's a little speed demon too!!! I could go for a $.01 per mile ride.

[eightythree]

very very interesting fellas... thanks so much for the detailed reply kgfly!

hmm 250 miles on 3 bucks.. that beats gas prices. but i wont complain, i live above where i work!! :wink: