A123 cells actually at end of life!!!

[Chris Bott - Moderator]

Today I flew a 6S pack of A123's and the flight didn't last as long as I expected. To cut a long story short, I actually seem to have a couple of dieing cells. A pack charge took 1020mAh and after a deadstick landing I would expect 2200mAh. So I knew something was up. So on to a balance charge and it took hours because it went to a very low charge rate because most cells were full. A few discharges and balances later, it is clear that one cell is tired and another on its way. Well I can't complain. This is the pack that started all the fuss over 2.5 years ago. It has been well used and well abused ever since. Most charges at over 10A with little or no balances for the first 12 months. It's been discharges at 120A. On at least 2 occasions the whole pack has been down to zero volts. In all that time it has provided hundreds of powerful, reliable flights I haven't taken the heatshrink off yet, it will be interesting to see if the cells were those that have been soldered to directly, after a crash dented them and ripped the tags off. Well there we are, they are not completely indestructible! and do have a lifespan. However to get the same amount of flying, I believe would have cost multiple LiPo's even if looked after well. And If I'd subjected LiPo's to the abuse these have had, then that would have cost me dozens of LiPo's So in the right application, these have proved very cost effective indeed.

[Paul Adams]

Was waiting to see how A123 cells preformed in long term use (abuse) before committing. By your report I will be investing soon. Thanks for submitting.  Paul

[Chris Bott - Moderator]

No probs Paul. I tend to bore people preaching about these cells They do have some disadvantages mind you:- 1 Heavier and bulkier than 2200 LiPos 2 Only really one size available (there is a 1100mAh but not widely available) 3 Seem more expensive until you weigh up total lifetime cost But the safety (no charge fires etc) and robustness, keep me coming back for more. I only use Lipos on small planes now. They are ideal in 6S form for 40-50 size planes. I flew a lot of planes on this particular pack and one other which still seems OK. Charging in 10 mins while flying the other. Nowadays I seem to be building them into the models. They do need a balance every now and again, but I do that after a session, at home, not at the field.

[Danny Fenton]

We could do our double act Chris lol, but I guess everybody on here knows us by now lol

In the right application they are perfect.

[Stephen Stokes]

Hi Chris and Danny I am not stalking you just hit the same forums...

 A123 batteries are new to me, I have used Li-Po for over 2 years now...... a few questions please.

I have Li-po charges that can cahrge Li-Io is this the right setting for A123.

 The default setting by the book is 2300mah batteries charged at 2.3A. Will this still take an hour like Li-Po to charge. Do I just set the charger at it's max of 5A

 Do you use the same balancer as Li-Po, I have Flight Power V Balancers

Cheers

[Chris Bott - Moderator]

Hi Stephen

 I'm afraid the answer is no.

Lipo's need charging to a terminal voltage of 4.2V/cell
LiIon's should be charged to slightly less, I believe 4.1V/cell, but don't quote me I haven't looked that up.

A123's need charging to a terminal voltage of 3.6V/cell  and this is a setting appearing on more and more chargers.

They need a balance every now and again, but again, this needs a balancer set to 3.6v/cell rather than the LiPo or LiIon equivalents.

To answer your last question, yoyur maths is correct, it would take an hour at that rate, or probably more. As with all these types, charge rate drops off towards the end of charge, elongating the charge time.

 We charge at 10A wich means it takes 10-20 minutes.  Note: For bigger cell counts, this requires a hefty supply battery for the charger!

[Danny Fenton]

Hi Stephen,

If you met us we would be the last people you would want to stalk lolol. Anyway Chris is away for a few days and I am sure he will give a better answer than I will when he returns, he's more of a boffin than me ( I mean that in a good way Chris)

But basically my charger has a setting for Li Fe 3.6 volts per cell. A123 will take whatever charging current you can throw at them, the more the quicker it will fill. My equipment will only deliver 10A @ 6 cells, 7A @ 8 cells. But that is more than enough. The DeWalt book shows the charge rate can be anything up to 15A but you will struggle to find a charger that will do that, and your leisure battery will really take a pasting.

At the field I set the charger to just do a fast charge and use only the main supply leads, no balance. Every 6 - 12 cycles I do a balance charge. The balance this morning after a half dozen flights of my 8 cell Sea Fury over the last two weeks, was spot on within a few minutes, the cells had not drifted apart at all. The balancer in my case is built in to the charger the one you are using I am not familiar with Though reading the specs it seems to bring all cells down to the same voltage so should work as a stand alone balancer. I am not sure if it will work under charge.

The Astro blinky is another balancer that we have used thats seems to work well.

You will not need to remove them from the aircraft for charging nor arrange for any cooling airflow, they rarely get even warm.

If you are thinking of the Sea Fury for A123 it will go well, you may want to consider doubling up for extra duration if you like to fly fast passes big loops as 2300mah is not a big fuel tank. I am happy with 2 - 3, 5 minute flights an hour but you may not.

Good luck and ask away

Danny

[Danny Fenton]

well there we go Chris had already seen your message Stephen, and there is me saying he is away.......

[Stephen Stokes]

Thanks guys,

I have Li-Po chargers, Li-Po balances and quite a selection of Li-Po's I think the marketing men have done their work well....

 To change or not to change especially when HK have well recommended large Li-Po packs.

 I would like to fly for 8 to 10 mins at a time so double 8s A123 is not looking so appealing in the Sea Fury

Weight, cost and a new charger would start to play a big part in my thoughts....

 Going to have a think. will get back to you on this one and thanks for the advice.

[Danny Fenton]

No Problems Stephen, but don't dismiss the multiple shorter flights it is not as bad as you think. You can get a lot done in 5 or 6 minutes, there are ic flyers at our club that only get that sort of duration using a YS.

If you go down the LiPo route you are into making the packs removeable and all the hastle that will entail. In fact I am not sure how I would do it in the Fury.

A route I have thought about is going a slightly bigger ESC and dropping to 6 cells A123, then doubling them up in parallel, this would mean 12 cells in two packs of 6. You will of course need to add probably a couple more inches of prop to get the required power back due to the voltage reduction of the two cells, say a 17 x 10. I may try this on the bench, or get Chris to as he already has a bigger esc in his Fury.

A123 are around the £10 a cell, so 12 cells is around £120, about the same as two Medium sized LiPo packs. You can pick up a balance charger for well under £50 from HK.

And no I don't have shares in A123, though I wish I had.......

Cheers

Danny

[Kris1]

Dan 

What charger are you using?  Where can I get one and at what cost.

 I was thinking of fitting my Sebart Angel 50 with A123s.  I currently run FP 5S 3700 using a Hacker A50 12S.  I am using an Astro 109 charger,  I read some where that if I connect A123 to it is will detect as a lipo pack but with a lower cell count.  It will charge 9S lipo at up to 7.5A.  I would like to take benfit of the fast charge of A123, but at 2P configuration then that would be 18A!.  That would be a 400W charging circuit.

The Angel has loads of power and after 8mins I put about 2 to 3A back in.  I would like to use a 6S2P setup, but this will add about 1/2lb!   guess that 6S1P will work but I like to get flights of 8 to 10mins. 

I like the idea of a 6S pack at £60, in 2P then £120 for the pack.  An I would only need one!

What are your thoughts.

Cheers

Kris 

[Chris Bott - Moderator]

Hi Kris I'd try with 6S1P to start with and see how you get on. To charge at 400W at the field takes a huge leisure car battery. Lighter means less power used etc etc... Chargers with an A123 program are quite prevalent these days. Try Hobbycity, Giantcod, Foamyjets, BRC, Puffin and many others. As you've already spotted, the main features to look for are an A123 setting and the power of the charging circuit. I believe that there is a chip available for the 109 to make it an A123 charger. Or there's a mod here (untried by us as we don't have an Astro). http://www.rcgroups.com/forums/showthread.php?t=602445 I would think the Sebart Angel would go well on 6S. Depending on yr flying style, you could eek out the duration. Don't forget that you get full power with A123's right to the last drop. Then they drop off very very quickly. So you can always use 2300mAh. Just don't be prop hanging by the ground right at the end of the flight. Use the power in bursts, (you can prop for lots of power) and cruise sometimes conserving the battery. Conserve energy between manouvres and you'll be surprised at the duration.

[Kris1]

Sounds fair to me.

Ok I will try a 6S1P and see how I get on.  I could be flying one and charging another with a quick swap.  I did change the chip in the 109 for a v2 one which has a better lipo program.  It will certainly will charge the 2300 cell quickly.

I also have an FVK Bandit, and sebart Katana  30s Both run on 4S 2500 lipo and very well.  I think these could be better suited to the A123 cells to start with.  If I can put say 6S1P in and draw 50 to 55A the duration should be good and I will have the power.  I have noticed that the four battery packs I use in thse planes FP 4S 2500, are now noticably down on power, they dropoff about half way though the flight.  I was getting 12 mins of agressive aerobatics from the Kat with prop hanging etc, now I land at 9mins and the LVC has cut in.  I charge them and they take about 1.8 to 2A.  Not so good infact only about 20 or 30 cycles from each pack disapointed..  I think the A123 are the way to for these planes.

Cheers

Kris 

[Chris Bott - Moderator]

Kris Sounds like you've hit the nail on the head. I can get more capacity for the same weight by using LiPo's but got fed up of having to treat LiPo's with kid gloves, power dropping off through the flight, capacity reductions and short life etc etc. I still use them for smaller models. Are you sure the Bandit and Katana will carry the weight? 6S A123 is a lot heavier than 4S LiPo's. I'm afraid I don't know the models, but would be very interested to know. Cheers Chris

[Kris1]

I guess we are talking an extra 10oz over the 4S 2500!!!! The Katana does have 566sq in of wing area do the loading would go up by about about 1 or 2 oz per foot.  The bandit is a hotliner and will go like stink with a higher wing loading in any case.  So not to worried.  But I guess I can then try it in the angel 50.  I think the way to go would be a higher S count of say 8 or 10 S say and stick with 1P, just draw less amps to get the duration.  problem is the motor I have in the angel 50 has too higher Kv so will need to be changed.

Also the FP packs I noted are getting very hot.

Kris 

[Chris Bott - Moderator]

You are absolutely right on all counts I have a rough rule of thumb of 100W/cell, that seems to give a good duration in many types of model. Danny and I have 90 Sized Sea Furys (see other threads) We have 8S in these giving 1100-1200W and flights are a little disappointing at 7mins or less. (proving the rule) So we are trying to find a way to increase duration without going 8S2P (which will be heavy and take longer to charge) The only way is with more cells, so we want to try 12. That means 12S and a new low Kv motor. Or we are hoping 6S2P will do the job, just by using a bigger prop. Luckily Danny has a slightly higher KV motor too, so we'll be experimenting soon.

[Kris1]

You are still going to need a charger that can supply 400W at 36V to get your fast charge of 4C  Don't know if that is possible. Or spit two 6S packs and charge them on thier own at 4C on diffrent chargers

The sea fury looks great.  I remember I had a balsa craft sea fury with a colbot brushed motor on 8 sub C nicads.  Long time ago it flew very well.

I am thinking of building the Nijhus harricane.  Will have to be new year as I rebuilding the house at the moment.

Cheers

Kris

[Chris Bott - Moderator]

I think we are going to settle for longer charge times, we each take a large 12V battery to the field, but 400W is a lot to ask from that. I do have 2 chargers that will do 6S. But if we fly in turns and have a natter in between, the models are soon ready. And I sometimes fly a smaller model in between too. If you are confident in your figures and are happy to experiment and measure volts and amps, there is another charger option FOR 6S ONLY. Maplin sometimes have these on offer at £15. http://www.maplin.co.uk/Module.aspx?ModuleNo=44736 or try ebay etc. Take the case off to allow better cooling and they do a pretty good fast charge at the 22V setting. Current actually settles at around 9A and drops off as the battery approaches final voltage. You may wish to monitor the charge manually until you have confidence. Usual disclaimers apply, this is not what the item is designed for.

[Danny Fenton]

Hi Kris,

I don't know why I wasn't getting alerts to this thread, I can only apologies for not responding. You are probably better off anyway you got a far more intelligent response from Chris

Even if you charge your 6s2p cells one after the other (6 cells) you are still looking at half the time of a LiPo charge.

As Chris says throttle management is the key

Cheers

Danny

[Kris1]

I think I will invest in a 6s pack.  Try it in the Katana 30 or Bandit first. With my Kontroniks setup in the Bandit motorcalc recons on a 95mph pitch speed and climb at 18m/s  I will see how it works. The 5s 3700 I have for the Angel are OK they will last some time yet.  The 4S 2500, are on the way out so the airframes will be a good platform to try the a123s. 

One of the main things for me with the a123 is the fast charge time.  So I recon I would run two chargers for the 2P packs. 

I have an FVK absolute neu power brushless.  It draws 215A off of 5S 3700 lipo.  Problem is the lipos don't last too long.  I recon the a123 could be a good option.

Just need to wait for payday 

Cheers

Kris 

[Chris Bott - Moderator]

Kris that is a lot of current! Whilst I have pulled 120A from A123's it was only a bench test and I didn't leave it running long. You may manage that with 2P, but at these currents A123 voltage sags considerably (which controls current). 120A is 40C and even if they would hold up at that throughout, its only 1.5 mins of power. You don't happen to be near South Staffs/West Midlands do you? You could possibly have a go with a 6S of mine..

[Kris1]

No I am in devon, but thanks for the offer

The absolute will get to cloud level in 3 seconds so motor run is about 2 or 3 second bursts, i recon on 160mph climb out.  The setup is a neu power 1509 1.5d on a 5.7:1 and a 16 x 17 rfm prop CC125..  A flight of 15mins is based around 30 to 40 seconds of total motor run!  I know the voltage drops with the FP 5S 3700 to about 10 or 11V under that load.  Extreme for any cell. I have heard of the TP V2 cells hold thier voltage and are very good, a 5S 5000, should fit.  at 50C that is 250A so within spec.

Going off the subject, but 55A of a 6S A123 should be OK for the Bandit

Cheers

Kris 

[Chris Bott - Moderator]

Hi Kris Any more thoughts on getting some A123's yet?

[Kris1]

No not at the moment,  I have got some thunderpower 5S 3850 V2’s for the absolute, which will work well and supply the amps in the 200 mark.  I think at the moment with the cost of Lipos I will stick with this technology.  However may change the pack on my bandit to a 6s1p when the lipos give up. Cheers Kris

This is an intresting link.  It is being talked about by the greater good!!!!

http://www.rcgroups.com/forums/showthread.php?t=940253

[Tom Foreman]

If your still interested in A123 and need a charger Kris1, I'd recommend the FMA Cellpro 10S, will charge 8s1p A123 @ 10A and 10s1p A123 @ 8A. I've been using mine to charge 5s1p @ 10A, charges in 15 - 20 min. The only problem I have had is when you run the cells to LVC, sometimes the charger takes a couple of goes before it will start the charge programme. Of course it also excellent LiPo charger as well.

I was using the A123's in a MPX Twister EDF, although it flew fine it lacked the duration and performance of its previous LiPo incarnation (due to the extra weight). I also had problems getting the CofG in the right place due to the bulky nature of the cells. I plan to use the cells in an Overlander Tucano next as I will be able to remove the 3 oz of lead in the nose using the heavier A123's so I should get equivalent performance. Just havn't got around to enlarging the battery hatch yet to fit them in.

Cheers

Tom