Can 4S1P A123 power a Feigao 7XL
 

For all those A123 users.... here is my background & question:

Background:
Due to limited space in an e-converted 1/8 Cen Matrix (buggy), I can only fit 4 cells of A123 under the body. I have also bought the Hobbywing 150A + Feigao 7XL motor.

Question:
Can 4S1P A123 (2300mah) have enough discharge current to power the feigao 7XL?

I have already killed 2 packs of 4S lipo 5000mah@22C because of the high discharge rate the 7XL requires. So I dont want to kill my A123 batteries.

Thanks in advance!
HK

they powered my mamba on a e-revo iun these specs so they easily power that feigao too!!

regards

timaneli: you run 4S1P or 4S2P in your e-revo?

A123 in 1p is NOT going to be happy IMO. Max is 30C which is only 70amps or so and that motor can pull 100amps...

You'd need 2p...

yeah, i think 4s2p would be easier on the batteries.... but how do people fit 8 cells (4s2p) in a 1/8 e-buggy? anyone who uses this config... would you mind posting a picture for reference?

I am recording peaks of 164A with Medusa 36-60-1600 with 6S1P.

http://picasaweb.google.pl/Maciej.St...79553515560514

Those cells are undestructable :)

They will do 60C for 10 seconds. I run 4s1p in my Rustler on several motors in the 3-5k Kv range

Jeff

Instead of starving the ESC/motor with batteries that can't put out the juice, I would look at ways to give the buggy more room internally. A simple mod to the body mounting posts can give you 5mm+ more clearance easily. Or, find a buggy body with a more battery-friendly shape. Or, how about centering the motor (using a different mount) over the CD and using dual 2s2p packs in series, one on each side?

Yeah, 1p A123s can supply ~70A, but their voltage does tend to drop quite a bit from graphs I've seen. You'd probably end up with close to the same voltage with a decent high C-rate 3s lipo than 4s1p A123 because of voltage drop (and weight/size will be better). Not to mention runtime on 2.3Ah will be pretty short using A123s.

So how much does good 3S high C pack weigh?

Jeff

Depends on capacity. I would assume you want between 3500-5000mAh, which would weight around 300-400 grams (10.5-14oz).

The A123's aren't that much heaver I weighed 2, 3s1P packs and they were about 100g (3.5 oz) grams under a Duratrax 4200 NiMh pack at 15 oz. Don't know why you guys always say that A123's are Sooo heavy. I'll weigh my 2s2P packs tonight and see what I get but they are not That much difference between the Lipo and LiFe

Jeff

They maybe aren't as heavy as NiMHs, but they are heavier than a lipo of similar capacity and voltage.

But not by as much as you guys make it seem. You are talking maybe an ounce or 2 for about the same capacity, and they are bullet proof.

Jeff

Ahh, but if they where in fact bulletproof then you wouldn't be asking this question!!! Send me one cell and I'll show you just how NOT bulletproof they are when I send a .223 hollow point through it or obliterate it with a .40 S&W

I guess I should have used quotes on that one:lol: . No need, I have a .270 and .357 Mag so I could test it for myself..... at, at least 100 meters or more. ;)

Jeff

Thanks for all the advice.

I will look into either 4S2P or 3S2P config. and run my buggy with the body.

skip 3s - too low a voltage.. 4s min

Yeah, I was suggesting 3s LIPO instead of 4s1p A123 because the voltages aren't that far off, because he was concerned about size. I too would opt for 4s ideally.

How about 5S1P on a 2350kv motor?
For 1000W motor, it would require about 60A (1000W/16.5V, assuming 3.3V under load). would this config work?

Probably be closer to 2.9-2.8 under load with a motor that high a Kv. And probably with 200 amp peaks.

Jeff

I run 5s2p on my Savage Flux now and get 150A spikes.

Batteries after a 20 minute run at worst come off luke warm

i run 4s2p with great sucess and power.

i know what motor you are talking about and they do best on 4s. i've seen the rotors burn up on 5s and especially 6s. that motor with a turnigy 5000mah 20-30c pack should do just fine.

Thanks for the info.

If 4S2P A123 does not fit, I will use higher quality 4S Lipo.

A little off topic:

If I were to place the motor to the front (opposite to the steering servo), that means I would have to raise the center diff 3-4mm from the chassis in order for the diff gear to clear the bottom, would this setup have any bad effects? or it is better to cut a diff gear slot on the bottom of the chassis?

Do I also have to raise the front and rear ends of the buggy as well to preserve the proper length/angle of the drivetrains?

Better to cut a diff gear slot.

A single A123 cell is able to provide between 200-300W peak (100-130A @ 2-2.3V) depending on cell temperature, cable lenghts, solder joints ... Feigao XLs might require as much as 2000W in when pushing a monster truck. A 4 cell a123 setup would not be able to provide that much power. With 800-1000W peak at your disposition (4s1p A123) a 1:8 buggy is already fun to drive but can't compete with good nitro setups. Feeding your 7xl properly would require atleast 8 cell as 4s2p A123. Power will come from Amps which is what a 7Xl needs to generate power. Your ESC also should be able to provide up to 200A burst to feed the motor properly.

On the other site: My buggy required around 400W in to maintain a calculated top speed of 44mph. With 4s1p your buggy would require around 35A @ 11.4V = 400W. At this power level your runtime would be down to 3.5 minutes and your cells would be very hot at the end of your run. The fasted i managed to deplete my A123 cell setup was in 5 minutes (running a truggy with 9s1p A123) which translated to an average Amp draw of 25A. Having less peak power at your disposition will translate in slower acceleration. If you want to maintain an acceptable runtime of say 8 minutes your average amp draw should not exceed 15A. At 15A your average cell voltage will be at 3V. Multiplying this by 4 cells gives you 4s x 3V x 15A = 180W in. With a 4s2p setup you get 360W average maintaining the same runtime. With 360W average and 1600-2000W peak power and a gearing to reach 44mph you could easely compete with high end nitro setups. Ultimatively the biggest shortcoming of your setup will be the 7XL motor as it will heat up fast when it has to generate good power levels. With a 1p setup it will stay much cooler as the cells are not able to provide as much amps as a 2p setup.

I was able to fit up to 10 A123 cell in my older style buggy. Actual buggys have a shorter wheelbase providing less space behind the center diff to arange A123 cells as 2x 2s2p or 2x 4s1p. My newer buggy only had space for 9 A123 cells. You have to be creative and solder your A123 cells yourself to fit as much cells as possible.

And +1: cut a diff gear slot.