Looking around and reading about A123 battery it seems there are 2 major advantages - fast charge and more stable than LiPo.

However, the LiPo is 3.8v per cell while A123 is 3.3 which means that I need to fix 4 cells against 3 cells of Lipo. Does this create a problem for ESC and/or reveivers/servos? Do we need some adjustments to be made in ESC programming?

What are the options?

Pankaj

Better answered by someone who has actually used them (like Gaurav).

I see people using them.  The disadvantages are higher weight and a need for a charger that can accommodate A123s. 

In addition to the advantages you mentioned already, I did see couple of people using two of them together to drive their receivers and servos, without having to use any regulators/BECs (which are a must if you use a 2s lipo, as most of RXs and servos are only rated for 6v).

Yes Anwar,

Well another disadvantage is the initial cost as these work out more expensive for the same watts rating.

Regarding the weight factor that you mention, my take is as follows - I think the weight of LiFe is approx 2x meaning that for the same cell count the weight of about 2000mAH in LiPo is equivalent to 1100mAH LiFe. This means that for the same cell count and weight the flying time of LiPo would be higher. But then, the fact is given the charging current, maybe the A123/LiFe can be charged in half the time there by effectively the same amount of flight time in a given day. So I think the weight kind of evens out. What is your take?


Pankaj

One issue you are missing is the effect of the added weight on the flying characteristics of the model itself.  Should not be an issue for the larger ones (I am guessing size 40+).

Anwar,

Actually I was thinking of models where you already have LiPo of around 3S1P 2500mAH or thereabouts. What I was saying is that 4 x LiFe 1100 would approx be the same weight. So if the model itself was capable of taking this weight of the battery then maybe we can get the same hours of flying per day

Pankaj

I would look at actual weights of the 3s 2500mah lipo versus the 4x1100mah A123 before concluding they are approximately the same.  They could be, I am not sure. Charging on the field is inconvenient though.

And it is my understanding that the in terms of discharge rating ("how many Cs"), A123s have an advantage over LiPos, and also in terms of a more gradual discharge rate. 

I wonder what prompted Gaurav to sell them ?

Pankaj,
I have been flying glow planes(.40-.90) for a long time, and ever since I started, i have been using NiCad, and sometimes NiMH for my RX packs. Over the last year, I built/bought a couple of gassers and hence there was a need for a more powerful RX battery pack. So i researched over a lot of forums and talked to people (who have used it )about it, and eventually zeroed on to A123 cells.

A123 batteries, though are slightly heavier than LiPo, but their voltage is 3.3V, and this was the biggest advantage I saw. With LiPo you always need a voltage regulator in order to use it for the Rx, and with A123s you can use a 6.6V pack directly without any problems.

The other advantage that made me select A123 was, that they offered a much longer shelf/cycle life than LiPo. Of course this is yet to be seen and tested, but A123 officially quote 1000 cycles when charges at 1C. I do not fly as regularly as many other people do, and did not want to be surprised with a dead Lithium block, one Sunday morning, that I did decide to go flying.

The other things about A123 is being safer, offering a good charge/discharge rate , which I am sure you know about.
They are a little heavier than the LiPo, but this was something i was not too much worried about.

A123 is a registered trademark of A123 Systems, an American company that researched and made these cells. These cells are being used in automobiles and other high end applications, apart from hobby/home use. For hobby purposes these cells are made by Enerland (A123 partner company) and the brand is called A123 Racing.
There are several other third party companies making these cells, and sold under the LiFe name.

Inspite of being a little expensive, i chose to buy the original A123 cells from Enerland. I have used them over the last 2 months in around 30 flights and have found them to be great. I bought the 2300maH 6.6packs and charge them at 1C.

For the charger, Yes yo uowuld need to buy a new charger that charges thee cells. I bought the Tahmazo charger from SingaHobby and works Ok for my purpose. The FMA CellPro may be slightly better though.

There are a few things to keep in mind when selecting and using these cells :
1. These batteries have a constant discharge curve, so when the cell is down, the voltage drop all of a sudden. So you need to time flights to ensure the packs do not  discharge inflight.

2. These cells can be discharged to 0V . Really ! . and this will give irrepairable damage. So you need to make sure never to leave the Rx switch to ON or the batteries would be drained and gone (unless the Rx uses a cutoff voltage switch)

Thats it. I think for me A123 is the future, and I will eventually replace my Nicads with this.

Now the reason for my selling : I wanted to keep only the 2300mAH batteries, and i had bought these 1100mAH which i thing i will not use.  Secondly I do not have the shrink wrap or the tabs to solder and make my own pack. I would rather just use the A123Racing packs. That is the reason I am thinking of selling this ( I may change my mind after this post though ! )

Hope that helps and pardon my typos.
Gaurav

Quote from: gauravag on September 22, 2009, 11:11:21 AM
1. These batteries have a constant discharge curve, so when the cell is down, the voltage drop all of a sudden. So you need to time flights to ensure the packs do not  discharge inflight.

I thought it was the lipos that suffered more from this sudden drop in voltage/discharge capability towards the end, and the A123s which have constant discharge rate held off better ?  Or are you talking about complete depletion ?

Guys,

I was infact thinking about using A123 on electric power system as the main power source and not as the source for rx only. So the next question would be how to take care of the ESC programming in terms of identifying the number of cells and cut off voltage etc?


Pankaj

Seems that no one has tried replacing a lipo with A123 on a electric plane.....

Hi All, I just bought 5 A123 (GENUINE A123 Systems 26650A LiFePo4 Cell w/ tabs) Batteries from HK. Right now am making a 5s pack to be used on my .40 size SPAD. I have the same question like PankajC is having...any how since I could not find a proper answer anywhere I searched, decided to give it a try this weekend. Plan is to fly it for 5 minutes, charge it to see how much maH it takes so as to plan the next flight. As for the LVC on the ESC, all I could device myself is to use the programming card to set it to low or med (2.6 or 3.2v).

samlikespad,

Well the questions were posed when I was just starting into RC and being a stark newbie in electric. I was quite scared initially about handling LiPo after watching all the youtube clips about exploding LiPo etcs. Hence A123 seemed to be much more 'stable'.
Since then I have got used to the Lipos and am currently less frightened while handling these batteries.

Anyway the question about voltage settings of ESC remains and in case you can find a suitable answer, we would like to hear it from you.

regards
Pankaj

Hi Pankaj,

I am also using Lipos currently. The quick charge capability is what attracted me to try A123 batteries. Will certainly experiment as I have them with me. Will update once I get to know.

Regards,

Sameer.