Hello.
I have a small AA battery powered desktop vacuum cleaner.
It uses 2 double A batteries

When the vacuum is not running and I check the battery voltage (combined) I get 2.95v
But once I turn ON the vacuum, the voltage surges to 7v or more.
I even measure MUCH higher voltage at the motor terminals.
I don't understand this.

However, I'm guessing it has to do with OHMs Law and the change in current?

Thanks

 

Don't blame Mr Ohm. It's due to the back-emf voltage generated by the inductance of the motor winding each time the commutator briefly switches off the coil current.

 

If you have access to a scope, look at it on the scope.

 

Ahhhh
Thanks!!

 

A DC motor also generates, and tends to oppose the applied voltage, this is what limits the current rather than purely the resistance of the armature.
Max.