4450KV

[soninja8]

Okay, so I got this really nice rc car at a yard sale for $5, and it goes about 40-50mph. ANd it came with a 7.2v nimh 1100mah battery, and it was nearly gone, so I replaced it with a 8.4v nimh 1600mah battery. It goes a lot faster now, but the motor gets somewhat hot. The only writing on the motor is KV: 4450, and I looked that up, but I cant find the max current that you can put into it....Is my 8.4v fine for it? Oh, and its a 1/10th scale motor...

Thanks,
Soninja

[garrettg84]

As long as the motor never gets too hot to touch it should be ok. The Kv rating only has to do with the motor's number of RPMs per volt applied to the motor. A 4450Kv motor with a 7.2v battery would be spinning in the ball park of 32000 (32k) RPM. That is pretty quick, but pushing it to 8.4 volts touches 37k rpms. I would be most concerned with the brushless motor controller (speed controller/ESC) and how hot that is getting. Cheepo controllers typically are not very tolerant of additional voltage and blow FETs rather quickly. The other issue with the controller is that most of them are actually micro-controller operated and the micro-controller likely requires some form of voltage regulator. These are typically small linear voltage regulators and the higher the voltage, the more it heats up to dissipate the higher voltage.

There is an upper limit on the baring speed for the motor, but before you reached that I would imagine you'd burn out the coils or the ESC.

[soninja8]

As long as the motor never gets too hot to touch it should be ok. The Kv rating only has to do with the motor's number of RPMs per volt applied to the motor. A 4450Kv motor with a 7.2v battery would be spinning in the ball park of 32000 (32k) RPM. That is pretty quick, but pushing it to 8.4 volts touches 37k rpms. I would be most concerned with the brushless motor controller (speed controller/ESC) and how hot that is getting. Cheepo controllers typically are not very tolerant of additional voltage and blow FETs rather quickly. The other issue with the controller is that most of them are actually micro-controller operated and the micro-controller likely requires some form of voltage regulator. These are typically small linear voltage regulators and the higher the voltage, the more it heats up to dissipate the higher voltage.

There is an upper limit on the baring speed for the motor, but before you reached that I would imagine you'd burn out the coils or the ESC.

Well the esc is always staying cool even at my 8.4v, but my motor sometimes gets very hot to the touch, like I can only hold my finger to it for about 5 seconds...
ALSO: my speed controller says 2-3 lipos and 4-9 nicad/nimh cells, so it can be up to 10.8v?

[garrettg84]

ALSO: my speed controller says 2-3 lipos and 4-9 nicad/nimh cells, so it can be up to 10.8v?

3 cell lipo is 11.1v I believe. You should be fine, make sure that you have adequate ventilation within the car to keep the motor and ESC cool. Sounds like an awesome platform for robotics! Good luck.