1. Will another adapter with higher or lower voltage work with this pump? I have other adapters. None of them is rated for 12V, but they have bigger current capacity. For that purpose I would like to understand how different voltage and amperage values affect the working of the motor.
2. How does the motor draw more or less current? Does it have a certain speed at which it runs, and if it runs slower than that speed, it pulls out more amps?
DC Motors have a very important characteristic which is easy speed regulation.
For
every kind of DC motor (we do not care if it has the inductor in shunt, series, large or small compound), it's speed follows this easy equation:
V=voltage applied (input voltage)
Ii=current through the induced, which means, the current that pases through the loop that rotates and hence creates the torque.
kE=a constant that depends on the physical construction of the motor
phi=flux provided by the magnets or electromagnets.
So to regulate the speed, you are focusing on V and Ii, higher V => higher speed. Higher Ii => lower speed.
Every electric machine has some nominal values, that means, the machine feels great working on those values. If you give it more, you will damage it (damaging its protections etc), and if feed lower than its nominal values, will not work as expected.
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Do not confuse you if you see that if you want more speed, then just make lower the Ii. You need power to drive what is needed to be driven. And also Ii is direct proportional to the Torque, more Ii results in more Torque.
For a larger life of the air pump, use voltage manufacturer said.. and if we had known the power required then would have been easier to find the DC source.