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A123 Battery Pack Advice


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Hi Danny, just waiting for the gales to subside in Lancaster, have a whole week off work, but looks like I will be building a West Wings Hawk instead of any flying.

The charger is an FMA Cellpro 10S charger, it charges LiPo, LiIon & A123. In the A123 mode it charges up to 3.65V per cell. It will charge up to 8 cells at 10A and 10 cells up to 8A. You can charge two packs at the same time as long as the total cell count isn't over 10cells, but it treats the two packs as one battery, so it only makes sense to charge two batteries at the same time if they are roughly in the same discharge state. Otherwise its quicker to charge one battery at a time.

You need a big PSU to run it at full power, it needs 25A at 12V nominal to charge 10 cells at 8A. A big 12V battery is probably cheaper. You can see on the last photo above that it is pulling 17A out of the PSU, which is nearly maxed out as it is only rated to 20A.

It has a neat feature that can measure the internal resistances of the cells, my newer LiPos read about 9-10 ohm, my older (knackered) ones read about 15-16 ohm. So it is a good way of checking how healthy the cells are as the theory is that the higher the resistance the more knackered the cell. Although there is not much information about the IR so I could be talking bull

Cheers,

Tom

 PS - good luck with the new model

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Excellent Tom I will have to keep my eye open for one of those charges FMA were one of the first to bring out LiFe chargers and I got one from the States about 2 years ago. Sounds just the job for larger cell counts though.

I spoke to John Emms (Puffin) and he has spoken to Pelikan, it looks like he may be going to start selling 6 cell A123 packs ready made up which is good news.

Cheers

Danny

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Well the MPX Twister EDF flies, same as before, maybe slightly less duration, bit faster glide due to the higher wing loading, batteries don't come out as hot, plus I can charge them up pretty fast.

Still I could have just gone to a bigger LiPo, got slightly longer flight duration and have to wait 10- 15 minutes longer to charge. Hmm I guess I don't have to worry about the battery only lasting 50 cycles, or will I .

So to sum up the 5s1p 2300 mAh A123's are a bit of a pain to solder together, but I managed it. They give roughly the same performance as the 4s1p 2600 mAh LiPo they replaced (slightly less duration, more weight to carry I guess) and they are bulky and heavy.

On the plus side they come out only warm instead of hot, they can be fast charged safely and hopefully they should last longer than 50 cycles. Time will tell.

I think they are probably best suited to larger models, like warbirds that could do with the ballast, or fun fly aerobatic models that don't need high performance. Not sure whether to use them in the EDF, although it works in the MPX Twister, think I will treat my next model West Wings BAe Hawk (EDF) to a 4s1p 3700 LiPo though.

I do have other models to try them in, so more experimenting. I have an overlander Tucano, which is carrying a lot of lead in the nose, so if I get the A123 to fit (will be a tight squeeze) I can remove the lead and should get good performance. Who knows

Cheers for reading!

Tom

PS - The Ripmax 20A PSU I use doesn't seem to mind giving 25A to the charger when I have two A123 packs on charge. So no need for an expensive PSU, the Ripmax unit never even get hot even though its only rated to 20A -

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Hi Tom great news. I must confess I would not use A123 in this situation as EDF in my experience need all the energy they can get and the power to weight ratio is more critical IMO. Chris B and I tend to work to the 100 watt per cell, so in my Wot 4 I need about 600 watts so 6 cells. 6 cells in my oppinion is a sweetspot that works quite well with 40 size sports models. The warbirds are a bit big for the capacity of the A123. My Hurricane (12 cells A123) if flown at WOT will only last 4 minutes, the Sea Fury (8 cells) will only last 5 minutes. I appreciate this is down to propping but the bigger planes really do need you to only use full throttle )or preferably less) for take-off and go arounds. If you start using more than half for prolonged periods you will be dissapointed with the duration. They are after all only 2300 mah.

Glad to see that you are giving them a go. We have packs that are three years old and are still as good as new despite being drained to zero frequently. You should find that they will keep going til they are empty as opposed to Lipos where you have to always make sure you land with 20% mah remaining to ensure you don't damage them.

Well done

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Hi Danny, thankyou for the words of encouragement, I think you are right and that they are probably not best suited for EDF, but I have a 500W Overlander Tucano, so if the battery fits, that will suit your 100W per cell rule with a 5 cell pack.

Out of intereset the A123 packs charging at 3C auto mode on the FMA charger are taking 20 - 25 mins (10% left in pack). In fact, the first pack that went to LVC and was at 0%, the charger had to make 3 attempts before it would start charging, guess the cell voltage went to low (about 2.5V), I was surprised as I thought A123's were OK at this voltage. Anyway the charger just feeds the pack 1A to wake the cells up, but only for 2min, then it times out. On the third attempt it seemed happy and started charging as normal.

The Auto mode has to guess the optimum charge rate of the pack, as it does not know the packs capacity so it starts slowly and then gets faster then will go up and down a few times until it finds the charge rate. I could just set it to charge at a constant 10A to charge it even quicker, but prefer the built in safety of the auto mode.

What charge rate do you charge your A123's at?

Cheers

Tom 

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Hi Tom, Yes thats the trouble with automated chargers. If we get a cell thats gone low and 2.5 is not low lol thats normal they do dip a lot in use.... then we dab another cell across it to lift the volts briefly. (do not do this at home children LOLOL)

I use a laptop PSU that doesn't know what its doing it just pumps out 22.1 V ( I know it should be 21.6v lol) at between 9 and 10 A. after about 12 mins from flat the current drops of rapidly to nothing. 15 - 20 mins tops for full. But this is with no balancing however which we don't do at the field we balance back at base every  6 - 12 cycles.

The reason the PSU delivers 22.1 is thats the closest setting, I could have cobbled together a resistor chain to get it accurate but thought I would risk the slight loss in longevity by overcharging slightly. I have been using the 6 s pack for well over 18 months with no loss in performance so far, and the wotty has flown a lot.

This Laptop psu was £10 but will only do 6 cells, hence all my models using multiples of 6.

Hope this helps?

Danny

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Cheers will try setting it to 10A flat out, as it is a balance charger it can only do what it is meant to do

Going to grab a quick couple of flights now, looks like the wind is dipping (looks at trusty willow tree indicators outside the window). I have a field 5 mins walk away, but its far enough with a 12V battery in your rucksack, glad its only a small 24Ah one

Cheers

Tom 

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That may be down to your ESC cutting off? have you set it to the lowest number of cells you can, preferably NiCd. That way the electronics will leave you alone.

It may well be that if you gave the cells a few moments to recover, (if you have the height) you may get another minute or two. Do you think your soldering has taken some capacity?

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Yes, I had some trouble soldering the cells togther, next time I think I might try better solder and flux as this seemed to be causing me problems. I don't think its the electronics as I have a friends 4s1p A123 pack which was made by Pelikan and this pack gives the full 2300 mAh, using the same setting (NiMh). But the voltage was too low for my jet. Although it did fly, it didn't fly fast enough!

Cheers,

Tom 

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  • 2 months later...
Tom Have you done any more tests with these batteries? I've actually had some go end of life now, but that's after over 2 years of very hard abuse. see http://www.modelflying.co.uk/forum/forummessages/mps/dt/4/UTN/4983/last/1/V/6/SP/332397698539340417482 The ones that have died are the two that I had to solder directly to after the tabs were ripped off in a crash. I think the soldering is probably significant in their demise.
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  • 4 weeks later...

Great and informative thread guys, I've read this and Timbo's electric Wot4 thread so I'm a bit forumed out!

I'm now using A123s courtesy of some 4S packs from Puffin and although I've read a lot about them there are some things I still don't understand.  

How do A123s handle changes in temperature?  Ie. are they damaged by being fully charged at room temperature and then being taken outside in the cold, as lipos are?  This is something worth thinking about at this time of year.

Secondly, what are people using as a field charging source?  To get the full benefit of A123s I want to leave them in the model and charge at 10A straight after landing (instead of my current approach with lipos which is to bring 3 or 4 precharged packs from home and not recharge at the field).  My charger will handle this without a problem up to 10S A123s but it wants to draw 25A from a 12V source.  Like Timbo said at the end of his Wot4 thread, that's not a nice thing to be doing to your car battery and anyway car batteries don't like deep discharges.

A big leisure battery is an option but oh so heavy.  These LiFE 40Ah batteries are a nice [relatively] light option but oh so expensive!  So I was just wondering what most of you A123 flyers do to solve this problem? 

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Argh... just peeked at another thread after a long typing session and its all gone from here, even opened a new tab!  Oh well... heres an abridged version:-

A123's are fine being cooled after charging, it is not an issue.

When I started with them I bought the lightest car battery I could find for about £25, thinking I needed the current capability. This worked well for a season. For the last 18 months I've been using a hybrid Leisure/Starting battery as designed for use in Motorhomes for Engine starting and deep discharge while camping.
Note: Deep discharge seems to mean 50% of capacity.
I think they can be discharged further if its during starting, but would then be charged immediately while driving.

There has been some discussion about charging sources on my A123 thread.. A123's at end of life.

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you will have square eyes mate, any questions just ask.

The charging cell/leisure battery is the limiting bit these days, it is a shame our club sites aren't more like the American and Australian ones. Tarmac, clubhouses, and mains supply layed on, I bet they even have cold drinks machine, bliss.......we have rain......

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On the subject of temperature affecting LiFe batteries, I was researching LiFePO4 batteries on manufacturer's websites and found the following graphs on the website of a Chinese manufacturer.  The first one shows the effect of temperature on cycle life:
http://i378.photobucket.com/albums/oo224/pvflying/lifedischargecycles.gif




This clearly shows that the warmer you run these cells during discharge the lower the retained capacity after a high number of cycles.

The second graph shows the effect on the cell voltage and capacity of discharging at various temperatures.  Here the opposite seems to be true, higher temperatures give better results:

http://i378.photobucket.com/albums/oo224/pvflying/lifedischargetemp-1.jpg



The "sweet spot", ie. best compromise seems to be around 25 degrees C. 

It's not clear whether the same properties apply to A123 cells but at least for softpack LiFes it seems that the graphs suggest that:

(a) You should pay attention to cooling the batteries just like you used to with lipos; and

(b)  You do need to keep the cells warm on the way to the field unless you want to suffer greater volt drop and reduced capacity.

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Peevie

I wouldn't put much faith in data on other LiFe's (as you already mention).

It seems that many of the advantages off A123's is the very small particle size (the word nano keeps cropping up). This is a proprietry patented manufacturing technique.

The advantage is so huge that they have attracted millions $ investment from vehicle manufacturers.

Have a look at this link for example.. which includes the line:-
Excellent performance over a wide temperature range (-30 to 60 degrees C).

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