This is sort of a follow-up to this topic: Overclocking my toothbrush
I have since measured some numbers with my DMM. Remember this is a tiny brushed DC motor in a $5 toothbrush that I am driving with a 3.7V Lithium-Manganese cell.
A worn-out motor measures 4.1 Ohms with the DMM. A motor which has only been used to deplete an alkaline cell measures 3.8 Ohms.
Both motors draw over 500mA when driven directly with the 3.7V cell. This kind of makes sense since based on the resistance I measured previously I could expect about 1A if it does not change while the motor runs. I don't really want to wear out this motor by seeing how many actual amps it draws but I should probably do it in the name of science.
Still, it leads to the question of what factors determine the effective resistance of a motor while it runs. Will it stay the same? increase? decrease?
BTW I am going to connect a 4.7Ohm resistor in series inside the toothbrush to regulate the current to about 300mA. This should dissipate about .42W and the resistor is rated for .5W... We'll see if running the motor at "only" 300mA extends its life or not.
Edit: This is gonna have to wait till tomorrow because i need to break out the dremel in order to make a cavity for the resistor to fit.