I have a really bizarre issue here…
I'm using this 6-24v DC motor which I connect to a 18v power source. When I connect it as it is, it runs smooth and strong, high rpm. All good here! BUT once I attach a small fan to it, it suddenly runs very slowly, weak, and in pulses (not in constant rate).
This video demonstrates the problem (turn sound on to hear how weak and irregular the motor runs with the fan on it).
Can anyone explain me why this happens? How to try and solve it?
I have no idea what is happening here.
(The fan is made of 3d printed parts (PLA) and a metal sheet, and it is lightweight)
Electrical – strange problem with a DC motor
dc motor
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Best Answer
The power supply is probably not capable of providing the necessary current. The fan may seem to be lightweight, but the inertia may still present sufficient load to pull enough current to shut down the power supply. As soon as the power supply shuts down, the load drops and the power supply recovers.
Unfortunately the seller does not provide full specifications. The motor is likely to pull 10 amps or more during acceleration. With nothing on the shaft, the motor comes up to speed before the power supply reacts to the high current. The current may not even rise to the maximum during the quick, no-load acceleration.
The power required to drive a fan is proportional to the cube of the fan speed. If you measure the voltage and current at one speed and calculate power = V X I, the required power will be multiplied X 8 at 2 X speed and X 27 at 3 X speed. Since the required voltage is proportional to speed, you need V X 2 and I X 4 for 2 X speed and V X 3 and I X 9 at 3 X speed. Those numbers are a rough guide since they don't account for motor losses.
If you buy a motor that has published specifications like a Mabuchi motor, sufficient data is provided to determine the current for long term operation without overheating and the corresponding voltage, torque and speed.