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Old Sep 04, 2014, 08:26 PM
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Help!
A123 3s2p battery pack setup help

I want to build a quadcopter but I have never built anything like this before, which is why after researching this topic I am scared to use the common LiPo batteries because of its tendency to explode violently or catch fire. This is why I am planning instead to use A123 batteries which seem to be safer and less prone to catching fire or exploding. So my first question is:

1. How much safer are the A123 batteries than using Lipo batteries? Do they also burn up / explode? And also how dangerous really are the Lipo batteries? How common is it for them to catch fire. I know it is mostly caused by user mistakes but from all the posts about them catching fire it seems that it is almost inevitable that all these lipo batteries will eventually explode or at the very least puff up and become a safety hazard.

2. Are the HobbyKing LiFePo4 packs that look like the lipo packs any good? Like this one: http://www.hobbyking.com/hobbyking/s...Search=lifepo4
And do they have the same safety advantages and longer life that the A123 batteries have? This seems to be the cheapest option to get a Life battery for the quadcopter.

So my plan is to use these A123 2500mah batteries from the official reseller of the A123 systems:

This is the site I am planning on purchasing these from:
http://www.buya123batteries.com/ANR2...300475-306.htm
which are $9.75 each and should be good quality since this is the official reseller of these batteries. So my next question about these batteries:

3. Are the batteries that come from this website good quality and good for using for this purpose? Also it would help to know how long this site usually takes to deliver them. I live in California so I'm hoping they can deliver within a week since it seems they are located in the U.S, but has anyone tried ordering from here?

I want to make a 3s2p battery pack out of these batteries so I will purchase 6 of them. So I just want to make sure I have the right idea about how to set up the 3s2p battery pack:


4. Is this the right setup for making a battery with this configuration?
I'm not sure about the order that the balance plugs go into the balance connector which will go into the charger. Does it matter at all which cell goes into which pin? Or can I put them all in any order and it won't make a difference?

5. What gauge wire should I use for the balance wires, and for the other red and black positive and negative wires? And what kind of connector should I use for the balance wires?

6. What should I use to connect the batteries together?
I was looking at these battery bars at some other site:

But I don't know where they sell this or something similar to it. And how difficult would it be to solder this onto the batteries? I also read that the batteries cannot take a lot of heat so soldering onto it should be done very quickly to make sure the battery doesn't heat up for too long.

7. What kind of a charger can I use to charge this battery?
With this configuration, I should get 5000mah with 9.9v. Is it okay to use something like an imax b6 ac charger? The only reason I would pick that one is because of the price. Also does the imax b6 charger balance the life batteries properly?

8. If I used something like imax b6 ac, how would I set it up?
If I set it to LiFe 3.3v and 5A and charge it, that would be reaching the maximum capacity of the charger, since its max charging is 5A and its max Watt is 50W, so 9.9v * 5a = 49.5W would be cutting it very close to the edge. And when it charges up to 3.6v it would be over 50W, so maybe I should charge it at a lower rate like 3A?

9. How necessary would it be to balance charge this battery?
The first time I use it, it should be balance charged right? And then after that every how often should I balance charge it instead of regular charge?

10. What kind of ESC's are compatible with LiFePo4 batteries?
Would normal ESC's that work with Lipos also work fine with these batteries, like this one: http://hobbyking.com/hobbyking/store...arehouse_.html
It says "Lipo cells: 2-4" on its page which means it needs somewhere between 7.4 - 14.8 volts, which should work fine with my 9.9v A123 batteries right? The only thing I see that could be problematic is the LVC, which would disable power going to the motors too early since it is expective a Lipo battery. Is there any way around that? Are there ESC's that are made for LiFePo4 batteries or that have the option to set the LVC at something lower like 2.5v?

Sorry for the long post, I just have a lot of questions
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Last edited by purejavy; Sep 04, 2014 at 09:21 PM.
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Old Sep 04, 2014, 09:28 PM
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Haralson County GA. USA
Joined Oct 2004
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Very good wiring site

http://scriptasylum.com/rc_speed/_lipo.html

JST-XH is by far the most common balancing leads / connector type.

Cell interconnect wiring and power leads gage depends on the max. amps. ssystem will draw. Look at the ESC you will be using and use the same gage wires or the next size larger. Power connectors is mostly personal preference, I use real Deans Ultras.

More data than most care to read about A123s here.

http://www.rcgroups.com/forums/showp...01&postcount=2

Charles
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Old Sep 04, 2014, 10:28 PM
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Ok so for the JST-XH wire, does it matter in which order I put in the balance leads? There are four different balance leads and I can't find anywhere what order they should go in to work with the chargers. Does it depend on the charger or does it not matter?

Also what kind of ESC would be compatible with this kind of battery? I need one that I can lower the LVC to around 2.5v so that it doesn't shut off too early.

And lastly, which kind of battery bars should I use that would be easiest to solder on to connect between batteries? I don't have a lot of soldering experience so I am trying to look for the least risk option to connect the batteries together.

My other option is to just purchase one of the LiFePo4 packs from HK like this one: http://www.hobbyking.com/hobbyking/s...epo4_pack.html
Are these packs good quality and long lasting? Or is it better to buy the A123 cells and make a pack out of those?
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Old Sep 04, 2014, 10:36 PM
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IMO, your best option may be to have the pack fabricated for you since you've indicated that you have little experience with such.

Balance lead wiring order is hyper-critical and must be identical to that shown in Charles' link (and opposite polarity to what you've depicted above).

For ESC, I use and recommend Castle Creations and their Castle Link.
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Old Sep 04, 2014, 10:53 PM
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Thanks for the reply.
On the Castle Creations site it seems most of their ESC cost $100+ each, which is way too high. The cheapest I could find on their site was $40 and thats max 15A which is still way too pricey.
Is it possible to get other HK ESC's to work with LiFePo4 batteries? Whether or not I choose to make my own A123 pack or get a premade pack I will need ESC's LVC to go off at 2.5v not 3v.

What do you mean it is opposite polarity to the picture I have above? Do you mean I should reverse all the wires on the balance lead? I looked at that website and tried 3s2p configuration and it looks like they have the same setup for everything.

So how good are LiFePo4 battery packs from HK like this one?
http://www.hobbyking.com/hobbyking/s...epo4_pack.html
It only has one review on it so its hard for me to judge whether or not these are good quality, long lasting batteries. And since they are LiFePo4 they should also have the same safety advantages that the A123's have right?

And why would making a battery pack out of the A123 batteries be difficult even though I don't have much experience? I have researched it and it seems to be simple enough, the only thing I'm afraid of is heating the battery too long with the soldering iron and ruining the batteries.
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