SS Pede

Hey helishack, sounds like you've been successful with the 2s1p pack in a similar application as me if I got A123: a Stampede powered by a Novak SS5800. What sort of run time do you get with your 2s1p setup in your Firestorm?

mattnin

I am using a 2S1P A123 pack in my Xray T2 007 touring car, and can get about 7 minutes out of it. I am cutting it close, I know. I am going to be adding some VPX 1100mah 2S1P to go parallel with the 2300mah cells to give me 3400mah A123 pack.

I am running a Tekin R1 Pro and a Tekin Redline 362 motor. It sure runs nice too, and plenty fast for mod racing.

Druss

I'm looking into A123 batteries but am wondering??? I'm most interested in something like a 3S2P pack, this would give 9.9v w/ 4600mah which seems perfect for a lot of the newer and better brushless systems out there. I'm currently using 7.2v and 11.1v lipos and the 7.2 is ok but the 11.1 i think is way to high and everything gets hot. I'd love a 9.9v but 2300mah just seems low for me as I'd love the longer run time of 4600mah.

Has anyone built a 3S2P pack? Would A123Racing think of offering one?

helishack

Good question... I haven't timed it yet, but I'll probably get around to it this weekend. From my calculations I should be able to get around 7 minutes on the 2S1P config with my current gearing/wheel size. When running 2 of the 2S1P packs in parallel (4S1P) I should be able to be ~15 minutes.

It looks like 'mattnin' and I are running roughly the same numbers.

Druss, I have specs and pics somewhere regarding 3S2P on my 1/8 scale buggy... One word - AWESOME I basically connected (2) 3S1P packs in parallel (the buggy is nicely balanced - one on each side of the buggy).

In case anyone is wondering, I use a Hyperion EOS-0610i Duo charger for dual 10A charging. So, with 4 A123 packs, I run 1-2 batteries at a time and charge two batteries at the same time (I use a deep cycle 20A 12v battery at the field to juice up the charger). I basically race and fly planes or helis all day. LiPo's had me so frustrated with charge time, safety concerns (never had an issue) and costs (bought a lot to reduce dead-time). I was starting to leave this hobby but after building my first few A123 packs I was sold on EP R/C.

Btw, I just got my Eagle Tree brushless rpm sensor and temp sensors so I can monitor voltage, current usage, total mAh, ESC & motor temp & rpm. Whew... I'll be happy logging all of that data & posting it here.

Cheers,

Jeff

Druss

Thanks for the info. I want to put this into a 1/10 for now, may convert my ofna 9.5 to brushless in the future, so I basically need a stick pack. I'm thinking of just buying the cells and making the packs myself at this point. I have the mamba max 5700 system, VXL and xceleron. Going to see which takes this pack the best, or maybe buy enough cells to make a few.

If I ever do put a brushless together for my 9.5 though I think I'll try a 3S3P for longer run times.

SS Pede

Thanks for the info guys. Being a basher I do wish I could get some more run time out of A123 cells (2s2p pack would be fine for me if it weren't for the huge size). But I may yet go the A123 route for the fast charging and such. Run time claims for the 2s1p packs seem to really vary. Just within this thread there is a big range.

mattnin - I'm not so sure mixing 2 different types/capacities of A123 cells together in one pack is such a good idea..??

Druss

ya, you really shouldn't mix capacities as you may drain one down to nothing before noticing a loss in power. Should try to keep voltages and capacities the same when putting batteries in series or parallel.

mattnin

You can mix capacities just fine, as long as they are in parallel. It will work ok if you make two separate packs, one at 2300 mah and one at 1100 mah, but it is better if you make one single pack, so the cells themselves are in parallel. However, if you put two different capacity cells in series, that will cause problems.

Druss, the 1100mah cell won't drain to nothing in parallel with the 2300mah cell because at the same time, they have the same voltage. They auto-balance in parallel. The only time the 1100mah cell can drop to nothing is when the 2300mah cell drops to nothing. Get it?

Druss

Please explain to me how they auto balance, they are in separate packs, current would be drawn from them equally which means that the smaller pack would lose it's full capacity before the larger pack. This is why the better battery manufacturers make such a big deal about using "matched" cells to prevent the over discharge of one cell in a pack.

So again, how does this auto balance work?

mattnin

1) They are not in separate packs, they are in one pack, and the 1100mah and 2300mah cells side by side. Like this:

+
[=][]
[=][]
-

2) Current is not drawn from them equally. The 2300mah supplies more current.
3) Yes, matched cells are absolutely necessary for 6 cell series packs 6S1P. Keep in mind, I am talking about a 2 cell parallel pack, 2S2P. If you were to combine two nimh cells with different capacities in parallel, they would also self-balance. For instance, you could combine a 3000mah sub C intellect cell with a 4300mah sub C intellect cell in parallel, and they too would auto-balance.

You can also consider a parallel cell with a 2300mah and 1100mah cells would be matched to another parallel cell with the same cells.

So, this A123 pack with 2300mah and 1100mah cells in parallel is matched.

If you don't believe what I am saying, ask another person with an electronic engineering background, however you can trust what I say because I too have an electronic engineering degree.

chadr

can someone post some pics of how 2s1p packs fit into a standard 6 cell holder such as a traxxas rustler? How about ideas on 2s2p of these packs? I've seen the 3s1p hump packs but these seem rather awkward in cars. Is it easy to secure them down in a good position with velcro straps?

mattnin

Here are a couple pics I have in the touring car class, but I run these batteries in my B4 and T4 and used to run a 2S1P saddle pack in my BJ4WE which I no longer own.