A123 cells actually at end of life!!!

[Tom Foreman]

Hi Chris, well I've started to notice some degradation of the A123's, capacity is going down and the internal resistance is going up. Will have to do some more testing on the capacity, but the IR is up to 9 milli ohms from about 5.5 will keep you posted. Perhaps I shouldn't charge them at 10A and store them 100% charged?

Tom

[Chris Bott - Moderator]

Interesting Tom
How old are they and how much use have they had?

I keep mine full and charge them at 10A.
Mind you I have no way of measuring IR so I only notice any degradation by performance or flight times.

In fact I only probably notice when I try a new pack and see the difference.

I'll be sticking with them though, mainly as all my models are 40 IC sized and above.
Lifetime cost is far better than any of the LiPo's I've ever had.

[Tim Mackey]

Partial charge is still recommended for the M1 cells guys... and of course this cold weather is not helping things either.

Correct storage charge for LiFePO4  is 3.3V ( as per nominal V of course )

Doubtless indeed that they are certainly more rugged than LiPo, but to be fair, A123 systems themselves still do recommend a minimum cell V of 2 volts, and we do tend to abuse them a bit - the trade off being rising IR and lowering capacity. Remeber that those last couple of volts, ( especially the very last one  ) is when internal temperatures tend to increase quite dis-proportionally, and cell imbalance also occurs.

I agree with Chris though - the real bonus with these cells ids the incredible lifetime cost compared to LiPo.

[Tom Foreman]

Well they are about 6 months old, they got abused in an EDF about 10 cycles each, 50A max load,  10A re-charge. Then they got put to one side for 3 or 4 months then I tried them at 40A max load probably only another 20 cycles each.

Although I have never got the full 2300 mAh capacity out of them I blame that on my poor soldering skills and getting them too hot. I think next time I will buy some ready made packs. I tested a friends 4 cell Pelikan pack in the EDF and managed to put the full 2300 mAh back in. Most times I have been putting back 2000 mAh into my home made 5 cell packs, but the other day I tried re-charging at a low 1C charge rate just to see what happened. The cell was at 30% and it only put back about 1000mAh which would mean its total capacity was only about 1500 mah. But as I say I need to do some more testing to verify this result, it might have been a freak result. The only change from normal was re-charging at a slower rate.

To be honest I never notice a change of performance in the air as these changes seem to happen slowly over time. The only things I do notice is the ammount of capacity put back into batteries and when re-doing power and current measurements compared to when batteries were new. I do tend to run high power set ups, I think the lowest powered model I have is a glider with 120W per lb so I guess I'm probably running batteries a bit too hard.

The other thing is though that I have tried running bigger batteries in models so that they can handle the ampage, and on EDF models they just pull more current!!! For instance I changed from a 20C 2600 mAh 4s1p LiPo on an EDF that was pulling 50A to a 25C 3700 mAh 4s1p Lipo so that the battery would have an easier time. The currently promptly went up to 70A !!! You just can't win with EDF's

Tom

[Chris Bott - Moderator]

Tom I would think that the current goes up with bigger batteries purely because they can handle it. With the smaller ones it was the batteries that were limiting the current.

I don't think you have been pushing the A123's too hard, I think you are right, you did some damage building the packs. It is to their credit that they still performed as they have.

I make packs up, but I only use ready tagged cells and solder to the tags. These cells that have given up on me are ones that I had to solder to the ends of, because I ripped the tags off in a crash...

I'd like to make a battery tab welder, but cant justify the expense on the large capacitors I need.
No one would have a source of big electrolytics would they?

[Dave Smith]

where is the best place to get some A123 cells as i can only find 2 shops in the UK that stock them

[Danny Fenton]

Alan Fry at Importeknik were selling them, Brian Collins BRC Hobbies was selling them but can't see them on his web site any more, John Emms at Puffin Models is definitely selling them and of course United Hobbies in Hong Kong currently has stock.

Alan Fry doesn't appear to have a web site still but can be reached on 01206852209, he was doing the cells in any quantity soldered into any size pack with balance leads for £11 per cell, which is the lowest I have seen them.

If I were looking for some more right now then I would talk to John Emms or Alan Fry.

Hope this helps

Danny

[Jon]

I have now got  my Acro Wot ready for its first flight ...

just waiting for a good day.. I will be testing a pack of 5000mAh 4S2P LiPos    v   a pack of 6S 2300mAh M1s (kindly lent to me by Timbo). Early Bench tests indicate that both will get her off the ground but the M1s should improve her performance but shorten it .... The battery box I have created allows for both packs to be moved about to adjust the CofG. The E-Acro Wot comes in with an AUW of just over 6Ib...

 If it all go's to plan I will be sticking with the M1s due to the cost / short life of the LiPos... I'll report back once I have compared them in the air for the first time.

Jon

[Tim Mackey]

looking forward to the results Jon

[Chris Bott - Moderator]

Good luck Jon, hope it goes OK.

I expect you'll be using different props with the two batteries?
Have you tested curent draw is within motor and Speed controller spec with both batteries?

 Hopefully my rule of 1A 123 cell per lb will work well for you.

Let us know how it goes.

[Jon]

Was going to fly yesterday.. but far too windy.. anyboudy know a really really,  really large barn?

[260 Flyer]

If anyone is interested, Maplin are selling a 150W version of the PSU that Chris uses for charging for £19.99 which is cheaper than ebay when postage is added on.

150W Laptop Car Adaptor

I am about to get one to have a go at charging a 6S1P, spec says it will go upto 6.5A @22V.

If nothing else, it will make a good heater  for a cold day at the field. 

[Chris Bott - Moderator]

Rob, how did you get on with this?  Mine did 10A fine..

Cheers 

Chris 

[260 Flyer]

Hi Chris

As supplied I doubt that It would survive 10A and got too hot to hold at 7A. But like you I have dismembered  mine and mounted it on a sustantial heatsink salvaged from a 50A power supply. Wired up with heavy duty cable I managed to get 9.38A into a part discharged pack without too much heat build-up.

I have abandoned my efforts to revive my old  Acro as I noticed that the fuselage had developed a nasty twist in the tail. I tried heating while twisting the other way and CRACK 

I now have a Pulse XT40 as my test bed which I will get airborne once the 1KW motor arrives!

[Chris Bott - Moderator]

Good news Rob, let us know how you get on.

Which motor did you choose? Something about 700Kv should be about right on 6 cells. 

[260 Flyer]

Chris

The motor is a Turnigy SK4250 650KV.

I will start off with a 12X8 to give around 850W with a theoretical pitch speed of 65mph.

Rob

[Chris Bott - Moderator]

Sounds spot on Rob.

Its possible that you could find it does less power than that on a 12x8 as the volts are lower than lipos, but theres only one way to find out..

 With Tower pro motors rated at 670Kv  I seem to use 13x6.5 or 14x7.

Have fun.

Chris 

[SA Allan]

Hi Chris & Danny

 I have built up my first 4 cell A123 pack for a GP Ryan I'm busy with , this plane was designed for geared speed 600 and Nicads so I'm sure that weight will not be a issue .

 I had the pack spot welded and just a few comments / concerns

1.      The pack gets fairly warm during a current draw of 30 Amps.

2.      Initially it was very unbalanced but after cycling it a few times on a balance charger the cells are quite matched once charged.

3.      While discharging and watching all the cells voltages there is one cell that's voltage drops substantially more at the end than the other 3.

4.      Voltage retention under load improved from about the 5^th cycle

5.      From a resting voltage of 2.65 Volts per cell the battery takes 2150 Ma .

 So even though I took a great deal of care when putting the battery together it seems like it has a weaker /damaged cell and the metal plates used to make up the battery could have fairly high resistance .

 I hope that these cells live up to their reputation of high cycle life as this is the only advantage they have over the latest generation of lipo’s .

 So in conclusion its best to buy a ready made pack from Puffin

 Regards

[Tim Mackey]

Yes but the packs sold as ready made do not always comply with the configuration we may need such as shape or cell count. Cell imbalance at the start id not uncommon - and if you mean whilst it was discharged then it s pretty meaningless anyway, almost EVERY battery will have imbalance when empty.

A warm battery is normal - and will be working much better.... anything up to around 170 farenheight is fine.

Does sound like one cell is poor - does your charger do IR measurement?

Edited By Timbo - Moderator on 17/05/2009 17:35:47

[Danny Fenton]

Hi,

This does indeed sound like you have a soggy cell. I have an original pack I made up for my Watt4 and I used a pretty low powered soldering iron and was worried I had ruined that, but it has always been okay. Apart from a funny.....

 

The original pack from my now three year old Wot 4 exhibited strange symptoms after it was flown flat. (deliberately for research prior to a talk on A123's we were giving at a neighbouring club) I balanced it, and all seemed good, but it never had the punch it did have. I tried all sorts of things and in the end just accepted the slightly lower power, it was still adequate. Anyway I recently grabbed a quick flight with Watty and did something I have never done before flew without checking the pack was charged after the last flight. it always is. but not on this ocassion! 4 minutes in and it went deadstick, well as deadstick as A123 can. the prop turns but nobodies in  anyway to cut a long story short. Driving the cells to flat and then charging again brought them back to full strength again . I cannot explain why this should be, but we have seen that if you tickle A123 ie low discharge currents, and low charge currents they drift. give them some welly and they just come back for more. By the way, after hundreds of flights, and the two totally flat episodes it still pulled 2270 on re-charge. How many abused LiPos can do?

 

So i would suggest you fly it flat and then charge at 10A if you can, and see what happens. The one worrying thing you are getting that I have never seen on any of my packs, including the Hurricane when it was drawing 110A is they never got more than slightly warm. Even that took some real stick to get that reaction. Is the heat coming from one of the joints perhaps? also how many welds per cell did you make, A123 recomend 3 or 4 i think? Chris will know for sure as he has that sort of info on the tip of his tongue, and because he has made a tab welder

 

yes, for peace of mind Puffin is a good source. I am about to order some more cells from John Emms, he doesn't do the 6s brick shaped pack that I use unfortunately but he does a good job putting them together.

 

Let us know how you get on?

 

Cheers

Danny

[SA Allan]

Thanks for the advice

I'll remove the shrink wrap from the battery and do a bit more investigating , I'll measure across the joints during a discharge to see if there is a significant volt-drop , this should give a indication of bad joints . 

So far I've only charged at 5 amps but I'll give it a good 10 amp wack to see if it improves matters , my Hyperion 610 net gives me a IR value of 36 , this seems to be inline with A123 specs (10mOhm at 10Amps 1 sec).

I see some retailers as selling the cells for $10 each, how much heat can these cells take when soldering? , i did buy the solder bars but chickened out for fear of damage

Ironically Puffin doesn’t sell my “brick” style configuration

Thanks again

Edited By SA Allan on 17/05/2009 20:38:27

Edited By SA Allan on 17/05/2009 21:04:27

[Sparks]

Danny,

 

What motor/prop are you using in your Wot4? - presumably the battery pack is a 6S1P.

 

I've been using A123's (harvested from Dewalt drill packs) and have been very happy with their performance. Main use has been in vintage (Astro Viking & Super Scorpion)

planes where the weight up front is useful to get correct CofG.  At the other end of the scale, I have just finshed the Nigel Hawes 30" Tucano which gives blistering performance on 2S1P A123 with a high KV Black Mantis Inrunner from Giant Cod.

 

Cheers, Richard

[Danny Fenton]

Hi Richard, I am using a Tower Pro 3520-7 600kv motor from United hobbies. and it originally went on a 14 x 7 but ground clearance was a bit close so dropped down to a 13 x 6.5 which is more than enough grunt to go vertical as long as I want. Yes the pack is a 6S1P A123 harvested like you from a DeWalt battery pack stripped down and soldered together using the tabs that DeWalt fit as soldering areas.

 

I have never used less than 6S packs and as SA Allan has found, Puffin don't do the brick format we use, but I will still probably buy from John Emms and reconfigure them myself.

 

The Wotty has had hundreds of flights over the last three years and is as strong as ever. It has always had the same 6 cell pack.

 

Cheers

Danny

[SA Allan]

Hobbycity sells the tabbed developer cells for $13 (logged in price) , I have bought 2 to replace the saggy cell in my pack .

 

I am holding off converting my Acromaster to A123  untill there are more reports on the new generation of Lipo cells , the Hyperion G3 seems particularly good and quite well priced.

[Sparks]

I've noticed there is a dealer on ebay (olympics2000888) selling A123's in bulk - see item 370201426454. His feedback on the A123 sales seems good.

 

Anyone tried this dealer?.

 

regards, Richard