It so sweet and simple, it cries out "build me!" when I look at it. Is it pretty axial on the rolls?

Jack

The roll rate is fairly slow, but it is stable.

Originally Posted by Himalaya

As new lipos got so much cheaper(not to mention HK ) and lasts long, why waste time in those old/ heavy/ expensive/ tiny capacity/ less powerful/ high self-discharge/ inconvenient cylindrical shaped A123 cells?

A123 cells arn't high self discharge.

http://www.hangtimes.com/a123_batter...iants_faq.html

Well, the wind was calm today and I got plenty of time in the air powered by A123 1100mAh 3S batteries. I figured that I would be fine with 8 minute flights, leaving a big safety factor. After cycling the A123 3S packs a few times testing, I decided to use a 3 amp charge rate, plenty fast for me and the batteries never get more than luke warm.

This morning I had a blast, 8 minute flights, and when depleted from an 8 minute flights, about 8 minutes to charge with my Cellpro 10S charger. I was basically flying constantly for a while. Now as long as my thumbs don't screw up I'm set.

These A123 batteries are amazing! I am looking forward to 1000+ cycles...

It is a wonderful thing, isn't it? I try to have enough packs that a pack has cooled to the ambient before I put it on the charger.

But I have put them on to charge when they were still warm from the last flight and I'm not even sure that is going to prove bad for service life.

My A123 packs are never more than slightly warm after a flight, maybe 100F to 110F so. I know that 130F is the "instinctive release" temperature for human touch and I've never seen anything close to that.

Jack

Originally Posted by jackerbes

Himalaya,

We don't see many A123 cells do that. It would be interesting to hear more about what the pack size and type, the conditions of use were, how long it took for ...........
.........

Jack

Thanks Jack, those are very useful hints, when I post my pic I was just trying to save you a click to see high quality pic and didn't expect this could be considered offending. Thanks for the remind.

My 26650 2300mAh A123 cells were also taken from DeWalt tool packs, tabs were removed with a grind(not simply pull a part), I paralleled 3x 0.3mm thick nickle strip welded onto the cell ends as interconnectors.

the "frosted spots" are made by the liquid that leaks from the cell, not the solder. I make living on making electric stuff.

My app was a small 58cm mono boat, 26650 A123 3S2P as power source, run time is around 5~6 min. so average discharge rate is only 10C~12C. All problematic cells (like this exploded one in my pic) locates at the center of the pack, #2 cell of the 3S pack. It's a natually thought that it was the heat built up that killed the cell.

Surely this is just my case, in air apps cooling is way much better, A123 cells may still be useable.

Originally Posted by u.rusty

A123 cells arn't high self discharge.

http://www.hangtimes.com/a123_batter...iants_faq.html

Fully charge AND balance a A123 pack and a lipo pack(any decent brand), write down the cell volt reads. leave them there for two days, and measure the cell volts again, you can get your own findings.

Fully charge AND balance a A123 pack and a lipo pack(any decent brand), write down the cell volt reads. leave them there for two days, and measure the cell volts again, you can get your own findings.

Such a test will lead one to believe that they A123 do have a higher self discharge rate but this is misleading. Conduct the same test but let them set for several months or more and do a capacity test. I have let LiFePO4 cells set for well over a year and it took l20 mAh to top them off. The difference is that we charge LiPolys to 4.2 volts per cell and they only settle to 4.15-4.18 volts depending on their condition. We charge LiFePO4 to 3.6 to 3.8 or so and they settle to 3.35 to 3.40 or so. There is no real capacity above 3.35.
Note these number are from memory so may not be exact.

Here are some short term volts versus capacity test from years ago.

https://www.rcgroups.com/forums/show...57&postcount=3


Charles

Himalaya,

Thanks for the details.

"..It's a natually thought that it was the heat built up that killed the cell..."

How hot do you think those are getting in your use? And also when you recharge them?

The instinctive release temperature for the average human hand is about 130F, that is where you don't want to maintain contact or have let go and skin cells are starting to be damaged at that temp too. I have never seen an A123 cell get that hot in use and that includes sustained (6-8 minutes) static testing runs that were up in the 40A or 17C range.

As always, what Charles says is right on the money.

The apparent voltage loss is because we charge them to a little higher voltage than the cells want to be at and will wind up at on their own. I charge to 3.85V with a Terminator II and always find every cell just under 3.4V a few hours later, a few days later, and maybe a tiny bit less a few weeks later. There is no sense at all in topping them off even after weeks of storage, I just go fly them.

Jack

Originally Posted by Himalaya

...Fully charge AND balance a A123 pack and a lipo pack(any decent brand), write down the cell volt reads. leave them there for two days, and measure the cell volts again, you can get your own findings.

At the link I posted:

http://www.hangtimes.com/a123_batter...iants_faq.html

They stated that after nine months the A123 cells retained 94% capacity. I performed a capacity test after leaving an 1100 mAh 3S A123 pack fully charged for three days and couldn't detect any self discharge. The capacity was the same as I got testing two hours after charging the pack.

These batteries are simply amazing! I ordered another Dewalt pack so I can try some of the 2300 mAh batteries.

I love leaving the batteries charged overnight, ready for flight in the morning.

I love flying for 8 minutes, charging for 8 minutes, then flying again for 8 minutes.

Originally Posted by jackerbes

Himalaya,

Thanks for the details.

"..It's a natually thought that it was the heat built up that killed the cell..."

How hot do you think those are getting in your use? And also when you recharge them?

The instinctive release temperature for the average human hand is about 130F, that is where you don't want to maintain contact or have let go and skin cells are starting to be damaged at that temp too. I have never seen an A123 cell get that hot in use and that includes sustained (6-8 minutes) static testing runs that were up in the 40A or 17C range.

As always, what Charles says is right on the money.

The apparent voltage loss is because we charge them to a little higher voltage than the cells want to be at and will wind up at on their own. I charge to 3.85V with a Terminator II and always find every cell just under 3.4V a few hours later, a few days later, and maybe a tiny bit less a few weeks later. There is no sense at all in topping them off even after weeks of storage, I just go fly them.

Jack

Very hot, I just can't force myself to hold it in my hand, way similar to hold a potato from the oven. I believe the solution inside the metal can has boiled, otherwise they can't have that high pressure that pops the lid open, James Watt's model's modern version.

As for self-discharge rate, that depends on whom to compare to. To compare to Nickel cells surely the A123s are revolutionally great, but dont compare to LiPos.... Initial voltage drop seems like a common phenomenon for A123 cells.

Charles is often right, "There is no real capacity above 3.35."
Probably A123 System Inc. should modify their datasheet to recommend 3.35V as charge threshold instead of 3.6V?

Fast electric boats are extreme applications, they are NIGHTMARES for any battery of any chemistry. High/continuous amperage output, poor or no ventilation, moisture all around or even direct water contact/dip.... A123 was advertised as a natural abuse lover, I believed/ get excited/ tried them and finally found anything has a limit. by far I got 12x 26650 A123 cells into the recycle bin, 5 of them pop and leak as shown in my pic, 7 stayed at 0V forever, I can charge them back to 3.6V but leave there untouched for one day and 0V again.... by the way, my Hyperion and Turnigy Lipos survived in this same application, never get more than just warm.... even the latter was labeled 20C only.

Okay guys, A123s are amazing cells, they provide ok power and good durability but just don't push them too hard to stay satisfied, that's all I was trying to express. ENJOY!

I really don't get it, if you have the numbers right as far as discharge rates and stuff, your results are like diametrically opposed to the experiences that everyone else is having with the same cells.

You must be holding your mouth wrong or something...

Jack

And yet one RC Drag competitor over on RC Universe in the old A Racing Support Forum had his As to reach F and they still lasted a while. I have had many of my As in the 140-145 range many times and they survived just fine. I even had a 3S that reached 140F during charging (a 4min. 14 sec.) charge starting at 100 amps. and it is was my first ever A123 pack and it is still alive.

Speaking of boats one of the early A123 Thread here was about using them in boats and the ones here stated they were lasting many times longer than their LiPoys ever did and performing much better also. The earliest RC ers to really push A123s were the heli guys here on RC Groups and they made the same comparisons. Better performance and longer life than LiPolys.

Now remember back them A123s could really do 70A and over 100 amp. burst and many of the so called 20 and 30C LiPolys in the 2200 range had a hard time providing 30A cont. and 50 amp. burst.

I flew A123s in my 48" range aircraft for two years while waiting for LiPolys to grow the balls to be up to the task without dieing in under 50 flights.


A123s are still great cells but now that 3300 mAh 3S 25 -45C LiPolys are available that are 5 and 6c capable I rarely ever drag out a A123 pack anymore. The LiPolys can be charged plenty fast enough,have better power density, last hundreds of flights and are a lot more reasonable then they were just a couple of years ago.


A LiPoly / A123 comparison showin why my A123s now set.

TP PP 40 shown delivering over 700 watts while same weight / less capacity A123s are delivering 500 watts and for a lot shorter period of time.

https://www.rcgroups.com/forums/show...45&postcount=1
Charles

I received the Dewalt DC9280 battery pack that I ordered, so I figured I would add the photos to this thread.

There are two screws that are recessed, but if you drill out the holes a little with a 19/64" drill bit you should have enough clearance for the #10 security torx bit to enguage the screw.

are the cells dated Feb 2007?
What is the manufacture date stamped in the top yellow case?
The ones I found on Ebay the seller said were all 2007 packs
that's over three years old. Anyone know the shelf life of A123
cells?

Nice pics, good lighting, well done u.rusty.

Jack, thanks.