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A123 cells actually at end of life!!!


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Flew the Tucano on A123 5s1p over the weekend, only managed 3 flights before breaking both of my props, must practise belly landings!

The multimeter measured 40 A draw and about 550W, voltage dop seemed quite a lot, about 3V under load from 16.5V to 13.5V. This then settled down to about 38 A and 500W. Battery and ESC got quite hot, but this was sat on my tool box in the dining room, with not much cooling air.

First flight she felt a bit nose heavy, and zoomed around pretty fast, she climbed well, unlimited vertical with about 150W / lb flew her for about 6 min then decided to land, but managed to break the prop on long grass. Battery was fairly cool and still had 50 % left over.

2nd flight I removed some lead out of the nose to move the c of g rearward, she flew much better and slowed up nicely. She doesn't float about and prefers to be driven around at 1/2 throttle or more, big loops and slow rolls were nice, stall turns were a bit untidy. Landed after 6 min on short grass (local football field this time) and didn't break the prop. Battery still had 50% left and was cool. 3rd flight with the spare battery flew for 8 mins, with more wide open throttle. She handles much better at higher speed. Messed up the landing this time, misjudged the ground and didn't cut the throttle. Another broken prop!!! This time the battery had 20% left, so I could probably get another couple of minutes.

All in all I am pretty happy with this setup and will be flying again as soon as I get some more props. From a 24 Ah field battery, charger set to 10A it managed to recharge the 50% empty battery in 7 minutes. Back at home with a decent PSU, charger set to 10A, it can do a full fast charge in 14 mins! Battery internal resistance measured 5.5 milli ohms.

The only problems I had was the power blipped a couple of times at full power, once on the ground during testing and once in the air. This might be due to the ESC running too hard as it is only rated to 40A, I don't know. It didn't happen again even though I tried to recreate the fault with a couple of long full power runs.

 Tom

PS - am only putting about 2050 mAh back into an empty battery, but I think this might have been my fault by getting the cells too hot when I soldered the pack together.

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Hi Tom, That sounds excellent, I would not have expected your cells to get warm at 40A but I am used to 6 cells so maybe your pack only being of 5 is the difference.

I have just upped my Sea Fury from 8S1P to 6S2P A123 with a much bigger prop to improve flight duration, it is drawing between 50 and 60A on the ground, would expect that to drop by 25% at least in the air.

Yes the amount you are putting back in is a little low, You may want to keep an eye on that. John Emms @ Puffin is now doing pre soldered 5 and 6 cell packs, if you really have cooked them.

The volts drop is a little alarming comapred to lipo, but as you have identified it stabilises and holds at that voltage until empty.

Great that you are getting on okay with them, and you wait, in a years time it will still be going strong on the same cells, provided you get the landings right

Danny

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Tom your experiences sound promising. It does sound like the cells may have been reduced in capacity a little during the soldering though..

 10S2P sounds like an awful lot of batteries/weight! 

The extra wot is about a 10lb model isn't it?

My rule of thumb has been to use 1cell per 100W and therefore about 1 cell per pound.
Adding more if power or duration arennt sufficient. You might be better with 6S2P or 8S2P

A clubmate just electrified the new YT International Adrenaline90 with 8S2P giving over 2KW max and apparently it is "amazing"

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Well 15 cells would do it I guess to give it 150W / lb plus a few more for a bit of duration!

How long does 8s2p last on the Adrenaline 90 and how much does it weigh?

Also at the moment I can only charge up to 10 cells at a time, although if I had 10S2p, I would probably look at a new charger that could charge the whole lot inside the model and turn it all around iin 20 minutes! I guess thats a pretty big charger!

Cheers

Tom

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Isn't Google great   now I have something to search for.:

What does CCA mean?
Cold Cranking Amps is a rating used in the battery industry to define a battery's ability to start an engine in cold temperatures. The rating is the number of amps a new, fully charged battery can deliver at 0° Farenheit for 30 seconds, while maintaining a voltage of at least 7.2 volts, for a 12 volt battery. The higher the CCA rating, the greater the starting power of the battery.

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You seem to have come up against the same issue as me now with using A123's, and thats the charging source is limiting!

We've thought of generators at the field - (would we only be allowed to during noisy I/C sessions??)

It would be interesting if anyone could find a lead acid battery that will last for more deep discharges. I guess maybe a true leisure battery might, as they are made to deep discharge in a caravan or boat etc. But what current will they supply without being damaged?

Don't forget that if you charge A123's at 10A and the charger is doubling the voltage, Then it has to be taking at least 2x10 from the 12V source to do it! 

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Sounds a reasonable idea, especially if its lighter to carry. But if the cost is the same as quite a few leisure batteries, then I'll stay with what I have for now.

 It reminds me that my very first A123 charges were by directly connecting my old LiPo's to my flat A123's. The LiPo's were beyond flying the planes, but they discharged to the right voltage for a fully charged A123 pack.   Not recommended without very close monitoring, but it did the job, Till the DIY chargers got built.

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I am currently using a Junsi I-charger 1010B+ which is rated at 300 watts maximum.

To get the full output however you need a PSU of 15V+ as there is an input current limit of 25A maximum.

Therefore allowing for inefficiency also, on a large capacity 12V leisure battery the sums come out at

25 ( max amps in ) X 12V ( assuming the battery holds at 12V ) X 90% ( efficiency ) = 270 Watts output.

10 x A123s require 36V to peak. Therefore 270 / 36 = 7.5A output current available.

7.5A / 2.3A ( M1 X 1C ) = 3.2

60 / 3.2 = 18.75 minutes

So although its not quite as fast as you could go roughly 20 minutes to charge 10s cells is still pretty good

( 10A is fine for A123s I believe) Indeed some have gone way past that ! .

Charging 2 x 5s in parallel would be no better, as they would need around 15A current to achieve the

same charge time, and the 1010B+ is limited to 10A output.

However with a good 13V+ PSU you could get the full 300 watt capability which would allow 10S X A123s

to be charged at 8.3A. ( 300 / 36 = 8.3A ) Input required being 330 Watt @ 25A max = 13.2V.

This brings the charge time down to around 16 minutes - assuming of course the pack was empty to start.

Think my sums are right, but it is getting late for me 

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Thanks for the link Chris.  I've also had a quote from a Chinese supplier for a 40Ah LiFEPO4 battery which only weighs 6kg.  The price is circa £310 which is pricey but over a 1000 cycle life would be quite economical.

By the way, on the subject of balancing A123s, how does DeWalt tackle this in their battery packs?  If they don't balance at all, what stops the cells going out of balance and reducing the pack capacity?

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Within the DeWalt pack, there is a device that is connected to every cell junction. It is immersed in opaque epoxy so its impossible to know for sure what it is. But being connected to all cells like it is, it is almost certainly a balancer.  Which says a lot about the need for balancing....

PS I have on test a Lead Acid battery de-sulphator. This is an electronic device wich claims to reverse the main cause of ageing in Lead Acid batteries.  It takes weeks to work, so I cant report any success or otherwise yet. 

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