Ideas to modify a 12v air pump to pump high pressures

[momaka]

Re: Ideas to modify a 12v air pump to pump high pressures

Thanks for this. So the poor connection on the motor, did it cause a voltage drop and thus a lower stall current?

Yes, the poor connection caused the motor to see a lower voltage, which also means lower stall current and thus also lower maximum output torque. With the maximum torque being lower, it's possible that the motor kept being stalled or used in a very inefficient state. And the thing about DC motors is that their stall current is usually much much higher than their optimal running current. So even though the voltage was lower, it's possible that the motor drew more current (than normal / in optimal state) in order to output the same torque as before that the pump requires.

So again, the motor didn't draw more current because it was trying to make up for the lower voltage. Rather, it was drawing more current because it was trying to output the requested torque going to the pump.

[caphair]

Re: Ideas to modify a 12v air pump to pump high pressures

Yes, the poor connection caused the motor to see a lower voltage, which also means lower stall current and thus also lower maximum output torque. With the maximum torque being lower, it's possible that the motor kept being stalled or used in a very inefficient state. And the thing about DC motors is that their stall current is usually much much higher than their optimal running current. So even though the voltage was lower, it's possible that the motor drew more current (than normal / in optimal state) in order to output the same torque as before that the pump requires.

So again, the motor didn't draw more current because it was trying to make up for the lower voltage. Rather, it was drawing more current because it was trying to output the requested torque going to the pump.

What determines the output torque? Just the general construction of the motor? Windings?

[momaka]

Re: Ideas to modify a 12v air pump to pump high pressures

What determines the output torque? Just the general construction of the motor? Windings?

Correct.

The maximum stall current is dependent on the resistance of the rotor windings. And the rotor windings are affected by rotor size. That is, the rotor size determines how much copper will fit on it - i.e. a choice between wire thickness and wire length (number of turns).

The rotor's physical specs also affect the torque and speed (i.e. you can have the same wire thickness and length for the rotor, but you will get different torques depending on if you have a "fat" short rotor or a "skinny" long one... or something in between.)

Then there's the number of rotor elements. The small/miniature DC motors usually have 3. More sophisticated and expensive DC motors usually have more.

And finally, there's also the stator. For a permanent magnet motor, bigger stator magnet size = higher torque, lower maximum no-load speed. Magnet composition also matters (ceramic/ferrite vs. Neodymium vs. other composition). With universal motors (DC motor capable of running on AC - i.e. motors in regular wall-powered vacuum cleaners, some washing machines, and corded drills), the stator windings specs/size will also matter just like for the rotor's.