A123 5s or 6s runtime question
 

Hi guys,

Was just out at the track today with my newly converted B-Revo, which ran awesomely. Its running a Mamba Max ESC with a CCBEC and a 8XL motor. ESC and Motor were warm after putting 2 battery packs through so I'm happy with that setup I guess.

My question is this. I was running 5S A123 2300mAh packs. If I go up to 6S (my Monster Mamba Max is still coming, if the Mamba Max can't handle 6S), will I get a little more run time? I know if they're in series, I'll get more voltage , but does anyone know if the runtime will change at all?

The reason I ask is that the club I race at does 6 min races, and so with a decent run, you can put in 6-7 laps, 8 if you're very fast.

The first pack today died about half way through the 6th lap, and the 2nd died just before finish line to complete 7 laps.

thanks!

I would expect slight less run time. You motor will be demanding more current and if you are not getting up to your top speeds, will then be running less efficiently. From my experience you need to be running 2p A123.

if the rest of your trucks setup remains the same your runtime will increase due to the increased voltage will lessen the amp draw from the motor

I have had quite a bit of experience over volting motors and everything I have seen makes it so that you are consuming more current upon increasing voltage. The resistance of the coils of the motors remain the same so when you increase voltage the amperage must increase too.

If load is kept the same (gearing), then current will increase with an increase in voltage. If you regear to get the same top speed you have now, then yes, you'll actually end up with a little extra runtime (how much, I dunno!). Think of adding another A123 cell as like adding another 150-200 watt hours (I'm assuming 3.0 volts at 60 amps? I could be off with that number, so you may be adding slightly more or slightly less energy) to your battery pack. More energy in the pack with that extra cell, so if you regear so as to reduce your current draw back to what you were drawing originally with your current setup, if not less, then you will experience a runtime gain.

Hahah theres a few different thoughts there.

So basically, if I increase voltage, there will be a corresponding increase in amperage due to resistance etc, but provided that I re-gear to keep the amps down, I could end up with a little bit of extra run time, right?

I could just bite the bullet and run 5s2p but that makes for a very heavy battery on 1 side of the Revo. I have tried 2p before and the jump in amps was negligible, I'm just trying to avoid having a phat 10 cell pack in my car lol.

What about changing motors to a higher or lower kv? Would that make a difference in run times?

6S has more energy then the 5S.

If your setup does not change the energy will enter and leave motor much faster. Of course that energy will be converted to Power and your truck will be flying around, if you can control it. If you take it easy on the throttle, to the point of similar power and speed as you get now. You will have slightly longer run times.

I would suggest regearing though so that you can have a more effiecent setup at the new voltage range. In which case you should have similar performance that you have now. You will get longer run time. 1/6 more E onboard for the cost of a few ounces.

Just make sure you are in a safe RPM range for you motor. (I don't know KV of 8XL)

Highflier

8xl on 6s a123 may be a bit too much. I would say to step to a 9xl and go with 6s a123. Gear your setup for the same speed and you should have extra runtime, maybe a few minutes.

This is wrong, more voltage to the motor will increase the amp draw, unless you alter the gearing to achieve the same top speed with both battery setups. 6s a123 on an 8xl will most likely run hot, due to increased rpm over ideal for that motor.

True but only if you throttle to the same position which is more power. If you back off the throttle a bit you will be putting the same watts to the ground with less amps. But if you are to peg the throttle your amps will be higher and and your watts to the ground will be alot higher, thus shorter run time.


8XL may be to much power, but should be ok on a 6s1p A123 pack IMHO

Under load the 6s1P pack will sage Voltage a bit, A123's are lower then Lipo to start. I figure at most you would be around 35,000 RPM.

Just gear it right and you should be OK. All that said their certainly is better motor options, but that is if you want to spend the money.

I have a 9xl and it is plenty of power for me. I do have some heat issues on the motor, The esc is fine. I don't run any fans. I rather upgrade to a better motor. I will as soon as I can make up my mind. Medusa or Nue. I wish Mike would carry Medusa so I could support him no matter which choice I am to make.

Highflier