mini question

What do you think the max amp draw is with a mini-t with Mamba 25 ESC and mamba 6800kv motor? Stock gearing and stock tires. I am look to get a 3 cell lipo to add to my TP 2 cell and need to know max amp draw
Thanks

[BrianG]

It's hard to tell without measuring. A good approximation can be found by calculating your average current draw by:
( pack_Ah X 60 ) / runtime_in_minutes
Your peak current is approximately 6 times that number (give or take).

So, if you have a 2Ah pack that lasts 25 minutes, your average current draw is 4.8A. Your peak burst current is somewhere around 28.8A.

That said, whatever current you get on X voltage, you will get more current on more voltage assuming all other things are the same (gearing/drivestyle/etc).

[lincpimp]

I would go with a lipo that can provide at least 30 amps continuous. I always used maxamps 1000 lipos in my minis and they worked fine for me.

Thanks for the good info, Brian, is higher voltage better for lower amp draw?
Will a motor draw more amps on 2 cell lipo then 3 cell lipo?

[lincpimp]

In general a motor will draw less amps as the voltage is increased. However the 6800 motor is spinning real fast on 2s and wizzing round at 3s. Problem with the mamba motors is that the are a 130s motor and lack torque. I eventually replace all of them with 280l or xl motors running 3s and just geared the vehicle to run faster. The motor/esc/battery ran cooler and I got longer runtimes from the same battery size. The lower kv higher voltage systems are more effecient and more fun too. The mini t is very light so it will be ok with that motor. I had a 5400 on 8 numh and then 3s lipo and it screamed, totally uncontrollable, but very fun. I would say a good 15c lipo in the 1100 to 1800 range will work fine in the mini t. The max amps 1100 will fit in the battery tray, it is almost square.

[BrianG]

Originally Posted by lincpimp

In general a motor will draw less amps as the voltage is increased.

I think you have that a little incorrect. A motor will draw more current with more voltage. This assumes that the motor wind, gearing, etc is unchanged.

If you increase the voltage, you have to increase the number of motor turns to reduce current.

However, if you want to run higher voltage on the same motor, you could gear down a little. That will reduce the mechanical load on the motor, which reduces the current. So, the higher current generated by the higher voltage is somewhat offset by the reduced mechanical load.

[lincpimp]

Originally Posted by BrianG

I think you have that a little incorrect. A motor will draw more current with more voltage. This assumes that the motor wind, gearing, etc is unchanged.

If you increase the voltage, you have to increase the number of motor turns to reduce current.

However, if you want to run higher voltage on the same motor, you could gear down a little. That will reduce the mechanical load on the motor, which reduces the current. So, the higher current generated by the higher voltage is somewhat offset by the reduced mechanical load.

Yes, I neglected to mention gearing both setups for the same speed. Also, if you consider the motor output(watts) constant, the the amp draw goes down with increased voltage. Now I am sure in the real world the more voltage you put on a motor the more power it can output, but there must be a limit to the power output though, mechanical or otherwise. So if you could push 10 volts into a motor with enough current draw to approach the max output of the motor and campare it to 20 volt,s the current draw would be roughly half. I do not have the pratical background, just theroretical knowlege from readin' an stuff, so I may be wrong!

[BrianG]

Actually, a motor is not a "constant power" device. The power rating for motors is the limit, not a constant.

Inductive reactance aside (to oversimplify to remain in the scope of this discussion), consider a motor like a static resistor. Amps=Volts/Resistance. So, more V = more A for a given R.

Yes, there is a limit to how much power any motor can dissipate. If exceeded, the result is melted coils.

[lincpimp]

I learn something new everyday. Tahnks for the quick lesson Brian, should keep me straight till I dethink something again. BTW thanks for the emoli cells. I made some nice 5s packs and hope to get my align 600xl powered lsp rolling this weekend.

[BrianG]

Cool! We all learn new stuff all the time.

Have you used the emoli cells yet? It must have been a PITA to unsolder the 2s2p packs.

[lincpimp]

Actually I only used the three loose cells cause I had another 7 from a new pack I took apart. Lowes made a mistake and sold me two of them for 35 bucks. They must have labeled them wrong. I bought them with a bunch of supplies for my business and did not notice till my wife/accountant asked me why I spent 35 bucks on 2 batteries. The deal of a lifetime. I think that I will keep those 2s2p packs as they are, too nicely made to take apart. Plus I may use them on my MBX buggy for a 4s setup, who knows!!