Electric Acro Wot ?

[Jon]

Thanks Timbo

I did search for "A123" ....dont understand why I got a nil?????!

jon

[Tim Mackey]

I am afraid the forum search tool is pretty useless TBH - better one planned for the new site in the new year. Search in google for the "word / topic" you want, and include also the words modelflying.co.uk.

EG google ....... " modelflying.co.uk A123"

typical result here...

[Jon]

Thanks for the tip Timbo..... have not stopped reading the last link you gave me yet!  ... think i'm hooked on A123s... cant think why I have not got any cash left this Christmas

john

[Tim Mackey]

Sorry, but thats typical of this hobby huh ! merry Xmas

[Tom Foreman]

Hi Jon, have done a bit of experimenting with A123's and they are definetly suited to your application, you could try a 6s pack as already suggested, but in case you havn't noticed yet they only have 2300 mAh capacity. Although you could run two packs in parallel to give you 4600 mAh, depends on how long you want to fly.

Chris Bott gave me good advice on this forum that you should aim for at least 1 cell per lb, so a 6s pack from puffin models should do it. You have to set your ESC to NiMh mode as the cells are only 3.3v and you need a charger with an A123 or LiFe charge program that charges to 3.65v per cell. The cells are heavier than LiPo's so they are not suited to smaller models or EDF's (although they will fly them) but they are excellent for your type of model. As already stated you can fast charge them, but it will depend on your charger, 10A is a good charge rate that will re-charge in 20mins from empty. I only have two packs as you can fly one while charging the other. Also you can run them down to empty unlike Lipos so you have the full 2300 mAh available.

 Merry Xmas

Tom

[Tim Mackey]

Just a few small points of order here gentlemen .

Charge terminal voltage should be 3.6V not 3.65 and although it is very true that these cells ( GENUINE A123s incidentally not the cheaper clones that are around ) can tolerate abuse much better than Lipo, it is still not really recomended to drop them lower than 2V per cell, especially if one wishes to gain maximum life span from them.

Another misconception is that they do not need balancing, which they do, especially if you do allow the cell to drop down to 1V or less. It is this deep discharging which generates the most heat, in all cell types and this allows inbalance to occur, and reduces life.

The capacity limit of 2.3A is indeed a little lower than we would like, and although doubling up is a way to go, the weight starts to pile on. Better perhaps to use higher cell count in series, matched to the right motor prop combo to suit resultant higher voltage and lower current.  Of course these higher S packs is where charger limitations ( and indeed PSU ) start to kick in

For example, I use an 8S pack in my WOT4 and this requires( for 15 - 20 minute charges ) a charger capable of supplying almost 29V @ 9A ( albeit for a short time during CC phase ). That equates to 261 Watts out, and if your charger is limited to 12V input...that needs to be able to deliver aroound 25A.

[Jon]

Thanks Timbo

I did search for "A123" ....dont understand why I got a nil?????!

jon

[Tim Mackey]

Try A123 systems ( the company name of the manufacturer ) The cells are also sometimes known as M1s.

[Jon]

Have spent hours reading about A123's v LiPo's.... and at the end of it came to the following conclusion.. unless you know better

I have a 240v/12v IMAX B6 charger which can charge both LiPo's & A123's (at a max of 5 Amps)Will buy a bigger charger later in the spring time... if she lets me that is.

I currently use a pair of 4S 20C 2500mAp LiPo's which at best are only giving me 590w for 9-14 mins and they take over two hours to charge up each time at 2.5Amp. They are currently on special offer from BRC at £92.78 for a pair!..

If I was to use a single 6s 30C 2300mAp A123 it would only give me about 4-6 mins flying time. The made up pack can be purchased currently from Puffin for just £65.95. Charging time should only be about an hour and I'm in the air once more... Running at just under 22v it should also give me a far better and more constant power output reading. Will I get 800w or more when on max?

The ESC & the Motor that I have are both rated ok for the A123's set up.. but I did read somewhere that the ESC may need a reprog for LiFe's....is this correct? and do you agree my findings chaps...

Any comments really welcome before I part with the cash...

Jon

[Always broke]

I am no expert on A123, but I am sure you want more than a 6s pack in your model, that is unless you want very short flights. be interesting to here timbo's views on this.

Have a great Xmas Jon

Regards Simon

[Jon]

Hi would be nice AB....

but there would not be room fore 2 x A123's in parallel, also the weight of my pair of LiPo's is 518g but the weight of just one 6s A123 is 474g..... so although the flight time is shorter the planes all up weight is 42g lighter and the recharge time is much shorter too.

Once I get a better charger I'll be recharging just about as quick as an I/C plane can refuel plus the batteries will last for so many more cycles thus saving so much dosh... worth the compromise it me thinks but only if the power rating is higher than 590w

 Have a nice Hic Christmas!

jon

[Tim Mackey]

Jon said..

"If I was to use a single 6s 30C 2300mAp A123 it would only give me about 4-6 mins flying time. The made up pack can be purchased currently from Puffin for just £65.95. Charging time should only be about an hour and I'm in the air once more... Running at just under 22v it should also give me a far better and more constant power output reading. Will I get 800w or more when on max?

The ESC & the Motor that I have are both rated ok for the A123's set up.. but I did read somewhere that the ESC may need a reprog for LiFe's....is this correct?"

Firstly your estimate of 4 -6 minutes time is only a guesstimate. It is impossible to accurately predict flying time with no real data. The A123s hold voltage quite well under load, but remember that they are only 3.3V nominal and under  load probably will be around 18 V only for a 6s pack, NOT 22V. To get 800 watts from them would require 42A ( 800W / 18V = 44 ) and although they are perfectly capable of supplying far more than that, duration could be very short .

AT WOT ( which I appreciate you will not be constantly at ), but for the sake of example ....

(44A  / 2.3A = 19 ) therefore 60 mins / 19 = 3.1 minutes.

One of the problems I mentioned earlier was that the motor Kv requires a higher voltage to get the revs up for the acrowot flying style, and 4s Lipo was too low ( 14.5V under load ) 5s might be better ( 17.5 ) and the 6s LiFe would be OK, but at 2.3A capacity.... the amps are too high.

To fast charge you will need a higher output ( watts ) charger as you have already realised

The "standard" ESC LVC is only a problem for Lifes if you do 1 or both of the following...

1)  Fly to LVC, which you should not do anyway.

2) Worry about running your LiFes down past 2V. 

 The thing that causes a problem is that the ESC will likely try to shut off your motor before the pack has given its all, so fool the ESC into thinking yoiu are using Nickel based cells instead, and then it will keep the juice flowing until the pack hits 6V or so, and you should have really stopped flying by then anyway if you follow rule 1.

If it might help, I have an 8s A123 pack here which you can happily borrow to trial - just the cost of postage to and from yourself. Let me know, and I will send it to you...keep it as long as you like to try it before deciding.

If it works well, I may even consider selling it to you at a fair price.

[260 Flyer]

Gents

One point to remember is that the Power 46 is only rated for 5 cell LiPo and might get a tad warm on a 26V 8 cell LiFe,

Merry Christmas

Rob

[Tim Mackey]

Ah yes, good point Rob... I could always add 6s tap if you want Jon.

[Jon]

Wow what a chap you are Timbo, your a bit like Father Christ really..( are you bearded too?). that's a most kind offer, thank you so very much...

Yes, it would have to be a 6s as that's the max I can charge at the moment apart from the max motor rating...

On the Puffin web page they show 2 types of 6s, a flat pack with a length of 208mm and a triangle pack which will fit better and allow plenty of movement to help adjust the CofG. I have just had a re think and a very simple internal layout mod would allow the 208mm pack to fit much better but the CofG adjustment would be less with the longer battery however its a few grammes lighter too.

What are the dimensions of your 8s pack Timbo? is it 4 over 4 cells or what? but if only for a bench test tapping in at 6s I could  just fit it on a temp basis anyway.

I'll get back to you after Christmas is out of the way as I know your busy..Thank you once more. 

Thanks also Rob for the reminder about the 5s LiPo rating of the motor... but me thinks I may just get away with a 6s A123 since the voltage is a little lower and as Timbo says's it will drop further below 22v while under load, anyway if it smoke's it I 'll have an excuse to buy a bigger one then wont I .....

Any way Xmas is on us and I now have other things to do for the next few days...

Merry Christmas all...

Jon

[Jon]

Is there any little birdy out there that could tell us when we will be able to buy some 6s 5000mAp A123s with an all up max weight of say 500g.

Jon

PS. I wrote and asked santa for some but I think they must have got lost in the post!

[Jon]

My PC is being sent back under warranty.. so will be off the forum for a week or so... but I'll be back!

Jon

[Jon]

Well its been 10 or so long days without the Laptop, I could have got soar thumbs from twiddling them but thanks to Timbo I have been busy testing a 6s pack of A123s. The results are quite pleasing but like most things there's always a down side....

I was impressed with the wattage readings but as predicted am a little concerned with the shorter flight times and especially with what I call the "sudden death effect". When this pack starts to run out of power its almost the same moment that the voltage drops to the minimum...No warning like the sluggishness type of flight that I was getting with my LiPos which was a signal to land. Its more like an almost sudden switch off! Easy to be caught out with no power left.

For direct comparison (if that's possible) I'll repeat the Lipo readings before the A123 readings.

The LiPo set up was...... 12x8 prop with 2 x matched Flightpower 4S EVO 2500 mAh  20C 50Amp Cont 30C 75Amp max bursts  ie: (5000mAh @ 14.8v)

1/2 throttle for 30 sec I measured 12.7A @ 19.2v  240w0w & 55mA consumed

3/4 throttle for 30 sec I measured 28.3A at 15.2v 430w & 230mA consumed

Full throttle for a further 9&1/2 Min's I measured a peak of 39.9A at 14.8v 590w at 1300mA consumed That's almost 100w per 1Lb !

The A123 set up was the same apart from the battery which is a 6s A123s pack ie (2300mAh @ 22.3v)

Watt meter at start showed the voltage was 22.3v  

1/2 throttle for 15 sec I measured 12.7A @ 19.2v  240w & 80mA consumed 

3/4 throttle for 15 sec I measured 28.3A at 17v 490w & 250mA consumed

Full throttle (on and off) for a further 4 Min's I measured a peak of 55A at 17v 900w (most times it read 800w @ 48A)  at 1233mA consumed...   RPM were 9200     That's almost 150w per 1Lb on the peak!

So.....

50 cycles of a 5s 5000mAh LiPo with approx 10Min's flight time and a very long recharge time

or

1000 cycles of a 6s 2300mAh A123  with a lot less flight time but a much shorter recharge time

Am I also right to say that If I compare/consider the cost .....I would need the multiply the cost of the LiPos by some 200 times to equal the life of a A123 ....

What do you think?

[Always broke]

What I think is GO AND FLY IT. then make up you mind. If it flys for long enough on the A123  then no contest. I think you will be happy with the A123 set up.

Enjoy Simon

[Ben Mullins]

Well if you know how long you've got at full blast on the A123 you can set a timer, making sure you dont have a sudden switch off! If it were me I would go with the A123s as you can give your fingers a rest but have them flying again quickly.

just my thoughts

Ben.

[Jon]

Yep... but more landings means more chance of a poor landing but if we were all thinking like that we'd never get of the ground would we.

I was hoping to give her a maiden yesterday but other things got in the way! think your right A.B.  but I also want to learn more about the A123s v LiPos ....reading reading...& more reading

[Ben Mullins]

have fun! Im still sat here making up my E-Pioneer with a broken finger . How are you so much quicker

[Jon]

Sorry had to amend a minor point in my last but one post...jon

[Jon]

thats a good question Ben.. I'll have to ask the wife!

[Danny Fenton]

Hi Jon, I have never flown my A123 into "deadstick" Apart from one time when I was getting some data for a talk myself and a couple of friends were doing. I use a timer and I am religous about obeying it. The first flight is always short ( i like the challenge of landing and taking off, which helps) anyway I just keep lengthening the flights and measuring the charge taken out. You have to remember to deduct a minute duration if its windy. And if you fly aggresively with the throttle your times will obviously be shorter.

The longevity of life of the A123 packs makes it an easy decision for me, A123. All my packs seem as good today as they were when I made them.

I set the timer on my wot 4 to 8 minutes, land before 9, and that is enough for me. I rarely use a full pack, and the recharge time at 10A is usually between 10 and 15 mins, just enough time for a coffee and a chinwag.

Cheers

Danny