1p A123 in my buggy... Enough?

[lydiasdad]

Higher output lipos would not do much more if the system is not pulling more from the batteries. My system does not pull 70 amps. These cells provide plenty of amps for what I am running. It doesn't matter if the batteries are capable of 1000 amp continuous, My setup does not require high amp output. I have seen other brushless/lipo vehicles, both in person and on-line believe me my buggy has great punch.

[jhautz]

Originally Posted by lydiasdad

Might seem like it's doing ok? HA! I got to get a video camera.

Love to see the video... Please do post if you can.

Originally Posted by AAngel

I suppose it's all a matter of how you want to run. Knowing jhautz (having seen videos of his stuff and how he runs), I think I can safely say that the 1P config isn't going to work very well for him.

AAngle, the goal on this one is a little different than my typical.

In all honesty I'm not that great of a driver on the track and the point of going to a smaller motor was to take it down a notch in power allowing me to have a little more control. Now I cant say that the 1930 is really less power than the 1512 that was in it before which is why I'm looking to tame it out by going to a lower voltage. Like I said before its still a little to much for me on 4s and 3s isnt quite enough. Which is why Im thinking the 4s A123 will be like a 3.5s lipo. Right about where I want it.

I could build a 4s2p pack from the reamining 8 cells I was jut thinking that with the smaller motor and a 1p pack I could get a nice lightweigh setup to draw less amps.

I was skeptical that A123 would be able to deliver the power that it states in the specs without stressing the cell severly which is why I originally asked this question. It sounds like some of you have seen what I was suspecting. The cells can do it, but its less than optimal. Others seem to be having sucess. If the cells deliver what they are speced at I was thinking that they would be capable of doing what I want, but just barely.

The cells according to the spec sheet are rated for 70A constant and 120A peaks. With the 4s Lipos setup I was running I saw around 80A peaks at 14.8V = 1184Watts and I averaged only around 13.5Amps over the entire run. So based on this I'm calculating:

Power with 4s Lipo:
89A * 14.8V = 1317 Watts peak
and
13.5A * 14.8V = 200 Watts Average
and
the 4350mah pack gives about a 22 minute run time.

To generate the same power using 4s A123 I would need:

1317Watts / 13.2V = 99 Amps peak
and
200W / 13.2V = 15.15 Amps avarage
and
the 2300mah pack should give me around 9.1 munite run time if the above assumptions are true.

Now according to the spec sheet the a123 cells rated at 70A constant and 120 Peak should be able to do this. And in reality I actually want to generate a little less power than I did with the 4s lipos. I know that real world doesnt translate directly like my example here, but it should be at least a reasonable estimate.

I think what I just calculated is correct... If I'm missing something can someone let me know what I'm missing.

I guess there is only one way for me to find out... I'll use the 8 cells and build two 4s1p packs. Run it with both the 4s1p and then with both packs in a 4s2p configuration and see what I get on the eagletree and more importantly how the whole setup "feels".

The only thing that I see missing is accounting for the voltage drop of the A123s under load. Running them in a 1P configuration is going to drop the voltage to a point where you aren't going to realize the rated capacity of the A123 pack. I'm thinking that your runtime is going to be more like 6 or 7 minutes, but that's just a guesstimate. I'd go for the 2P setup. It's an extra 280 grams, but I think it would be worth it and you'd still reach your goal of a milder race setup.

[zeropointbug]

You know what, I think 5s setup would work for you better, just taking into account the voltage drop you will see, the voltage should be roughly 12 volts at a 80-90 amp burst. With my MAXX truck, I consistently get 135 amp bursts.

I never got a chance to do an Eagletree test with 5s1p compared to 5s2p. But I did run it, and I can say the punch was a lot less, particularly at speed, but I would be drawing 130 amps peaks, that's heavy duty for 2300mAh!

Maybe just make temporary 4s pack, see how it performs, if it needs a little more, then add the extra cell? :032:

HERE is a Eagletree of my truck with 5s2p A123, Quark/7XL, geared 18/51, and hard bashing.

[starscream]

Originally Posted by jhautz

6s is more voltage than I want. The controller wont handle 7s or 8s and even if I did have a controller and motor suitable for 7 or 8s It would defeat the purpouse of going to a light setup. I might as well just use the motor and controller I already have and run 4s2p. Same weight and cell count. Besides that... 7 or 8s is just way more voltage than needed IMO.

4s lipo should be more than enough voltage for racing, and for me the voltage of the 4s A123 is enough for the track. I'm just wondering if thet can handle the amp draw at 1p.

Maybe I'm misunderstanding what you mean????

I've never run these cells in parrallel so my point is that if you're worried about weight then 4s2p would be the best formula for you. You simply won't get much power with 4s1p due to the voltage drop. 4s2p will probably get you a little over 10 minutes on the track (race conditions) with enough power for you MT to effectively compete.

[Serum]

Thanks zero; that's what i was looking for; they have got a huge drop in voltage; on 2P they drop to 2.5V per 2P cell on a 100A load.

Good lipo's hold up to 3.6V per cell on a 110A burst load

So in 4S a good 14.4V on a 110A load.

[zeropointbug]

Actually, the rule of thumb for A123's I just remembered is ~2.5 volts for 30C discharge (rated). (pulse discharge cycle)

Please note, that those Eagletree tests are also a bit off as well, that's when it was not working properly. I did get it fixed, but I don't have any saved, and with my Quark gone at S&T, I can't get any proper tests for you. Sorry.

I guess you are going to have to try it yourself? :032: :030: :027:

[Sammus]

Any more on this? I like my revo's running style on 7s1p A123, and was about to build a buggy with 5s1p A123.. now im not sure...

[Serum]

That's quite an old thread you found!

You see the voltage drop on the A123's?
less than 2.5V on only a 100A load in 2P. a 270A burst would be waaay bellow 2V...

[Finnster]

I had a first a 5s2p pack in my revo/8XL and it was pretty much identical to the 4s 8000 mah TrueRC pack I had as well. Later on I went to a HV setup and changed the pack to 10S1P on a 1515/2Y (1100kv.) Powerful and amp draw no more than ~65A. I have lots of ETs of the setups, but can't get to them now.

For me, the cells dropped to 2.7-2.8v/cell @ ~65A. Same as 5s2p when I was hitting ~110-120A @~14V. I wouldn't push them too much harder.

Doh!!! old thread!!!!

[Sammus]

Yeah sorry for digging it up... I got interested in it reading from the beginning and it just kinda petered out...oh well.. I guess I'll see how 5s1p goes for me.. I'm not exactly a speed demon like so many here, I'd be content with 30-35mph out of it.

[Serum]

that will be easy on 5S1P.

[othello]

I too think you will not have troubles reaching 30-35mph with 5s1p. My heavy (10s1p A123) 9lbs buggy needed a little more then 400 Watt on asphault to maintain 42mph. My latest speed test in another buggy with 8s1p A123 revealed 320 Watt for 33mph (with offroad tires).

This buggy (not mine) runs 6s1p A123+MGM 12018+Lehner 1930/12


It only needed around 330 Watt to maintain 38mph.

Eagletree graph from one of its run


Watt, Amp and RPM distribution of this run (sorry only in german)


Summary:
. A light weight buggy may only need around 300 Watt to maintain 30-35mph (hard packed type of surface). 300 Watt equals to 20,6A@14,5V (2.9V per cell with 5s A123). Running constant full speed would give you a runtime of around 6 minutes with 2200mAh.
. One A123 cell can deliver between 200-250Watt (short bursts: 100A@2-2,5V depending on cell temperature and length of the burst). 5 cells may give you 1000-1250 Watt peak. Higher Watt capability translates to faster acceleration (limited by grip conditions). But your top speed is not limited by your cells wattage. I recorded a max peak of 1800 Watt in my buggy which was geared for 42mph (with 10s1p A123). Buggys hardly do need more then 1000-1200 Watt especially if you drive on a loose surface. My first Brushless buggy was limited to 700 Watt (small ESC). More then enough power to loose grip on asphault when accelerating and have fun with.
. High Amp peaks (70-100A - where voltage drops badly in a 1p config) only occur for a very short time (only 1/10th of a second) and represent a very small percentage when looking at an amp draw distribution over a whole run. I would expect your Amp draw to stay beetween 0-40A for 80-90% of your runtime.

I hope this gives you more confidence in trying a 5s1p A123 setup in a buggy. If you keep it light, don't expect high performance and long runtime it should work.

[highflier]

I run a E-maxx 9xl on 6s1p. Personally I like it.
Off the line I may loose a little due to voltage drop. But heck it makes it controlable. As the truck comes up to speed the amps drop a little and voltage rises to give you a reasonable top end. I was suggest going to 6s1p and skipping the 5s option. It will give you a little more run time and top end as well as punch. Not to mention if you config your packs as 2 3s packs you can have some cool charging options.

In general if you know your lipo setups, Just add 1 cell to a A123 setup and you have a good starting point. Assuming that you are not at some ungodly voltage.

highflier

[Sammus]

I'm running a Mamba Max which I dont want to push to 6s A123 from all the recent reports I've heard of them frying just plugging in a 5s lipo pack.