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A123 Battery Pack Advice


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After buying loads of LiPos this year I have found my EDF's are sending them to a very early grave. This is going to be an expensive hobby I thought. But could moving to A123 be the answer? After doing a bit of research and trying a friends A123 4s1p Pack, I'm getting ready to buy some packs.

However things are never that easy. To cut a long story short, I need a 5s1p to run in a 4s lipo model. The 4s1p A123 didn't cut it. Puffin models do the cheapest ready made packs, but they don't do a 5s1p. Robot birds do, but its quite a lot of money considering what I can buy the individual cells for.

So basically I need advice on building my first A123 pack. I have a step by step guide see here and I have a friend with some experience in building NimH packs. All I want to know is where to get the battery bars from (as shown in the guide) and anyone elses experience. Thanks for any help offered!

Tom

PS - Must resist ordering ready made packs from Robotbirds!

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Go onto e-bay and buy a 36volt De Walt battery they have 10 A123 cells in them, they are already joined to make up 36volts and with a bit of ingenuaty you can break the pack apart and only have minimal soldering to do, then go to BRC hobbies and buy the ballance leads you will need occasionally to ballance the pack, I will look up the web site that shows how to do this and post it later.

 Mike

 That was quick even for me: http://www.slkelectronics.com/DeWalt/hints.htm

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Tom

 You still need to look at the link, you would only have to solder on the power leads, once you had split the pack for a 5 cell set up, and you can get the 36volt pack (10 cells) for about £60.00,   I just thought that splitting a 10 cell pack in two was easier than soldering each individual cells.

 Where did you get your cells?  the cheap Chinese clone LiFe packs they are not A123's and don't live up to the standard of them, i.e. loose capacity quickly and die very soon after being used as you would an A123.

 Mike

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I got the cells at £10 each from John Emms at Puffin. Excellent service as I ordered them Tuesday and they arrived Wednesday. Been playing around with pack configurations to get them to fit in different models and going to make a hump pack 3 cells on the bottom and 2 on top.

My only concerns are that they will suffer from the same problems as LiPo's if I get them to hot. Also the extra weight might collapse the fragile undercarriage on my Dualsky Extra and I will have to add tail weight to my MPX Twister EDF to get the CoG OK. Also I might need a bigger field battery if I want to recharge them in 15 minutes. Still I can always Ebay them if they prove to be no good. Maybe I should just spec bigger LiPos so that they don't get used above 10C

Tom

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Tom Foreman wrote (see)

I got the cells at £10 each from John Emms at Puffin. Excellent service as I ordered them Tuesday and they arrived Wednesday. Been playing around with pack configurations to get them to fit in different models and going to make a hump pack 3 cells on the bottom and 2 on top.

My only concerns are that they will suffer from the same problems as LiPo's if I get them to hot. Also the extra weight might collapse the fragile undercarriage on my Dualsky Extra and I will have to add tail weight to my MPX Twister EDF to get the CoG OK. Also I might need a bigger field battery if I want to recharge them in 15 minutes.

Tom

Hi Tom, Johns service is usually first class! I made mine using crossweave f/g tape, used a piece of thin rubber sheet top and bottom for better protection/insulation. Most folks seem to be using this method with no problem. I also use a dab of hot glue to hold the cells together before strapping them. Please remember that the positive and negative are reversed to normal EG: the "button" ( which must NOT be turned ) is negative, and the can as such is positive. Dont worry about heat they are pretty tolerant, and in fact as most cells, work much better when warm / hot - recommended maximum is 140 degrees F, although I know of people who discharge them at VERY high rates and exceed this figure ...dont we Danny

One big advantage over Lipos is their toughness, as well of course, as their fast charge rates. fast field charging is an issue - see my later postings in this thread here.

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Only just noticed this thread, sorry guys not keeping up.

I have just made up an 8 cell pack for a Seagull Sea Fury, and thought I would try John Emms at Puffin myself. The price was pretty good as there seems to be a dirth on 9360 DeWalt packs on Ebay. (not all De Walt pack are A123 be careful - 9180 18volt, 9280 28volt and 9360 36 volt.

The Puffin oneas as has already been stated don't come with solder tabs so you will have to do them yourself. The cells can be soldered and I find a good roughing up first with emery or such like does the trick. The iron you use will need to be big, I mean BIG lol or at least the heatsink. The cells sap heat away very rapidly. Usual stuff, tin the caps as best you can, as quickly as you can. I used the straps from BRC they work fine, again make sure you tin them first.

for an 8 cell pack, 4 alongside each other in a row, then two rows side by side = 2 x 4 brick. The heatshrink you will need will probably be measured flat as 130mm, most places measure across the heatshrink as though it was a circle - not very helpful. I only know his cos we have loads of different sizes from suppliers that say this is the size you want only to find it isn't.

Like Timbo we use glass tape to initially bind everything together before some heatshrink

http://forums.modelflying.co.uk/sites/3/images/member_albums/26349/DSC_7404_(Large).JPG




The balance leads for bigger packs are a pain as you will find, the trick seems to be to use 2 x 3 for six cells, 2 x 4 for 8. Then either make up adapter leads to get them into your balancer/charger.

I flew my Wotty last night on 6 x A123 driving a 13 x 6.5 (about 800 watts) for 10 minutes of aeros then charged up again at 10A for 10 mins, so I got thirty mins flying in in one hour. I Balance them ocasionally, but always first thing after the pack is made.

Chris and i have had the odd brand new cell that has been virtually zero volt and wouldn't charge, whack another good cell across it briefly (the right way round please) and that should bring it up enough to charge.

I have emailed John Emms at Puffin with regard to him/Pelikan producing the bigger packs but he doesn't feel there is a demand for these specialised pack the dirth of suitable balancers is the main reason. I would disagree as there are many 6 cell balancers around now.

Anyway John is hopefully coming to the Greenacres elctric bash next weekend 16/17th Aug so if you can make it bend his ear and persuade him there is a need.

As Timbo says you can really abuse these cells, bury them in the model away from any cooling, drain em to nothing, Chris has pulled 120A from em using nichrome wire and a bucket of water so they will certainly handle the current. We have one cell where the casing shorted against another cell and blew a hole through the side. Chris is still flying on that pack

So all in all, not quite the performane of LiPos, but not far off, double the performance of NiCd cos they are half the weight, forget NiMh's. When you consider you never take LiPos to over 80% for fear of destroying them, LiFe's are much closer to LiPos than you may think. The major snag is they are only 2300mah. My YT Hurricane will only fly for 5 minutes on that - but does recharge in 2 x 11mins if i charge one after the other, using two chargers and my big leisure battery and she is ready to fly again after 11.5 mins.

Good luck and let us know how you get on???

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I would add to what Danny has said, that I try to avoid wherever possible soldering direct to cells. The button end seems OK but the can end reaaly soaks away the heat. If your iron doesnt have the thermal capacity (i.e. a big lump of copper store heat in before soldering) then the cell reduces the iron temperature and the solder on the iron solidifies!

I generally use dewalt cells and have revived apparently DOA cells. I try very hard to use the welded tabe, they are easy to solder to. The cells from our chineese freinds come with tabs welded on. They appear and perform like genuine ones so I assume they are. (Unlike other pretenders!)
See Cells with tabs

I've had 4S packs from Puffin and they are very well put together and an excellent price.
I do with they would do 6S. Maybe we should all tell John that there is a demand??

I also find that 3S Lipo planes are getting a bit small for A123's to work well. The extra weight making more difference. So 4S and above seems to be the sweet spot.

6S in a 40 size plane is where they work really well...

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Thanks for the advice Chris & Danny, all my bits have now arrived apart from an 80W soldering iron, hope its hot enough, then I can get soldering packs togther. Will hopefully have some finished packs to talk about next week.

Yes have tried a Puffin 4 cell pack, very well put together, agree they should do larger packs. I'm guessing that A123's are perfect for large 60 sized warbirds, because all the build threads I have read (Tony Nijius?) seem to add lots of lead to balance so  the weight of the A123's should come in use. If they don't work in my EDF and 40 size Extra, I'll just have to build a 60 size warbird, shame 

Tom

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If the soldering iron has trouble, try fashioning a big block of copper to fit at the rear of the "bit" as a heat reservoir. I have twisted lots of thick solid copper wire round mine which is nearly as good. 

60 Size warbird?
I think you should do that as well

Have a look at the Electric Sea Fury thread. Now theres value for money. A 60 Size Warbird for £99 from Leeds model shop, complete with retracts.

We've moved on a little and are ready to test a larger motor. Still on 8S A123 though.
As the thread says, it might as well have been designed for electric. The bigger motor bolts straight onto the firewall, the 8 A123's have a ready made box to drop them in. Theres even a little carb box which nicely guards the cells from the rear end of motor shaft.

And Dannys making a great job of painting over the stock scheme.
Hopefully we'll have  "before and after" overpainting examples at our electric funfly next weekend. See greenacres website.

Danny is also experimenting with a Yt International Hurricane. I don't beleive that we have hit the A123 sweet spot with this one yet. Theres an issue with 2300 being too small in capacity and doubling up being too heavy. At the moment it's on 12S1P. We hope to do some bench tests with 8S2P to hopefully bring up the duration. Different motor though.

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Now I've got a A123 compatible charger I'm thinking of trying getting a 4s pack from Puffin to put in my 4s Lipo model, I know I will get a bit less power but the planes overpowered as it is so this shouldn't be a problem.

Will there be any issues with the LVC on the ESC, not sure if it has a A123 setting, and anyway I'd want to swap between packs at the field without reprogramming the ESC.

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Hi Frank, when I tried the 4s1p A123 pack from Puffin in my MPX Twister EDF, I selected the NiMh setting on the ESC and this worked really well as I managed to drag the full 2300 mAh out of the pack in a 5 min flight. The model was down on power, but flew ok.

On 4s1p LiPo she pulled 48A, 620W

On 4s1p A123 she pulled 35A, 420W

When my soldering Iron turns up, I'll be trying her on 5s1p A123, hopefully the motor won't blow as its only rated to 700W

Tom

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Hi Chris, when I put a 4s1p LiPo in my standard motored MPX Twister jet, the motor only lasted 12 flights of 5 min. The motor actually seized after trundling about on low power for a few minutes. The theory is that the motor was OK when it was travelling at a reasonable speed and getting plenty of cooling air through the duct, but on the low power run it wasn't being cooled enough. The motor was only rated to 500W, so as I was pulling 650W it was understandable it wouldn't last too long. I just don't want to repeat this costly experiment. As you say cooling is the key, unfortunately the motor is buried in the belly of the EDF model so it is difficult to monitor. Although you can always stick a thermometer up its rear end!

Tom

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Tom that sounds painful !

I don't have much experience of EDF and buried motors.
Some clubmates did used to experiment with re winding CD Rom motors, and got ridiculous powers, the secret there was to extend the shaft a little so that the windoings were getting a good blast from the fan.

If you notice, its very cheap motors that I'm over running.
I did burn one of the little ones out when our grass strip was uncut and I was chhopping up grass trying to takeoff. Now I've opened up the front of the model and it cant help to be cooled

http://forums.modelflying.co.uk/sites/3/images/member_albums/32446/S6000908.JPG

Not that this helps you with the EDF..

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Hi Mike, great minds think alike, I too have a Typhoon 2W-20 in my Twister and a Wemotec fan.

I tried a Typhoon 2W first in the standard fan, but made the mistake of drilling the shaft adapter and the fan started rubbing which ruined the motor bearings. I then learnt the secret that the shaft adapter has to be heated and shrunk fit onto the motor output shaft, plus I replaced the fan with the Wemotec which is dynamically balanced (look for the green putty) with the 2W-20 and it runs fine.

Of course I now have the problem that my 4s1p 2600  Electrolite Lipos are dying, and that's when I started this thread. Out of interest what batteries are you running in your Twister?

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