a123 6.6v questions

[ClodMaxx]

so i just took the plunge and ordered a pair of a123's 6.6v 4600mah battery packs and their hypersonic charger. my question is this to anyone that bought similar packs from a123: is there anything special i need to know? i guess i'll find out how they fit in my battery trays (they'll currently hold 8 sxs ni-mh cells) and i ordered some velcro straps to hold them down.

will it really charge in under 15 minutes? do they stay in balance as well as everything i've read? i don't plan to run a LVC - they should drop, and drop quick, at the very end. a good visual cue to stop running.

any insight on my new purchase would be appreciated.

[zeropointbug]

If you bought A123 racing packs, you are covered for balancing and what not. And yes, they stay balanced very well; I have custom made packs and they only go 'so far' out of balance, then thats it, nothing more it seems.

Yes, they will charge your pack in 15 mins if they are at 0% charge.

What are you using these packs in exactly?

[ClodMaxx]

yep - i bought the whole kit from a123. i've thought about tearing a dewalt pack down to build r/c packs, but it just seems soooo.... scary, lol.

they're going in a 10 lb. 8 oz. e-maxx - i have a thread on the build in the t/e maxx parts section.

thanks zpb.

[zeropointbug]

anytime!

May I ask what motor you are using? It should be over 2400kv if you want good power from your truck with 13.2 volts.

[ClodMaxx]

i have a Lehner 1940/7 hi amp, which is about 161kv short of 2400.

[zeropointbug]

Oh, well then that should work for sure then, just gear it up to get your speed, and you should have lot's of power.

[ClodMaxx]

here's hoping! i just inadvertently fried a matched 7 cell pack today... i'm through with ni-mh. hopefully i'll have much, much better luck (and power) with these a123 packs.

thanks again!

[zeropointbug]

Well, as far as luck goes with A123's... LUCK IS TIER ONE!!! They are very robust/durable cells, both physically and electrically.

Power is very high, theoretically (in actual power they can deliver), but as far as running a motor type load, that's where the lower voltage holding capability is limiting you, compared to lipo. But, overall, they deliver much power for their mah rating, that's for sure, and they can handle the power too. They are very safe cells.

The only thing that gives me concern with the setup that you are proposing is the current draw. That 1940/7 is going to draw a good bit of current as it is. Running that hot of a motor in a 10+ lb truck on what will be essentially be 3.5S lipo is going to draw a lot of current.

What controller are you going to be running? If you're going with the MM, just watch the temps.

On the upside, those packs are very nice. I experimented with a couple of them when my LHS first got them in. They have punch right up until they dump and they do indeed charge in 15 minutes, although that 15 minutes is for each pack. It will take you around 30 minutes to charge both packs.

A ThunderPower 1010C should be able to charge both packs in series in 15 minutes.

[ClodMaxx]

well, i asked on here what controller to use with the LMT on 14 cells and i got a lot of votes for the MM. so that's what i chose... and on some trial runs w/14 cells this past w/e, it did get warm - as did the batts. the motor was cool, as i suspected it would be.

i'm also concerned as i'll have to gear up to about 51/20 to get the 40 mph speeds i'm looking for. i may run 5s with the a123 packs someday, and i'll most likely have to get a higher quality controller. right now i'm leaning towards a MGM, but i may be able to hold off long enough until the tekin comes out (not even holding my breath for the MMM).

The MM does do well on 4S or the equivalent nimh voltage, but that's my point. If you are just changing the power source, with all other things being equal, and running a lower voltage, it's going to draw more current if you are expecting the same performance as you had before.

[ClodMaxx]

i gotcha. that's why i'm planning to gear up to a 20t pinion (i was planning to use about a 17t on the 14 ni-mh cells) to get around the same speed. but if i go with 5s instead of 4s, i should be able to gear back down... or is my thinking flawed?

edit: going up to 5s a123 cells will require a new controller. i may 'experiment' with the MM, however. since i have two 2s2p packs, i'll have to make a 3s2p pack from the dewalt packs...darnit. but...if i bought a dewalt pack and built a 3s2p, i could use the remaining cells to make a 4s1p pack for my crawler. ding ding! we have a winner!

When you gear up, it will draw more current. Going to 5S A123 with the MM shouldn't be a problem. I can't remember if I did it or not. I ran 5S A123 in my 8ight T, but can't remember if I used a MM or Monster Pro.

[ClodMaxx]

well i called a123 to see if i could change my order (didn't have confirmation that it had shipped yet) to take one of the 2s2p packs out and replace it with 2 of the 3s1p packs, but alas - they were too quick. it was shipped already. so for the time being, i'll be running 4s instead of 5s.

so, i do plan to go up to 5s2p with the a123 cells...which is still only 16.5v. it's going to be on the heavy side...10 cells total, but i'm fine with that.

my question is this: can anyone see a downside to building a deans parallel connector to connect 2 packs that are 3s1p on one side? i would think it would be fine, just wanted to make sure. i could also tear a dewalt pack apart and build a 3s2p single pack, but i hate soldering. i'm ok at it, but i hate it.

[lincpimp]

Deans parallel connectors are fine, I use my homemade one alot and it does not get hot, so I figure that it is ok. From what I have read the deans are only good for a 60 amp draw, but that must be continous, not sure what a 60 amp continuous sytem would look like, but it would be powerful!