If the motor is off load and it it is a 12vdc motor on 12vdc, then it should run at minimum current with no heating.
Very little or no sparks should be seen when up to speed.
M.
yeah.
though, some sparks may still be seen around the commutator. in some motors I have, at full speed it is a small blue spark.
will add though: though that if the motor is salvaged from a 12v device, it is not necessarily a 12v motor.
a lot of electronics devices and power-tools will use somewhat under rated motors (they can get away with a lot more if only occasional or light loads are expected, as opposed to running the motor under a continuous load).
like cheaper B&D drill, may use a 9v motor and pass it off as 18v. thing gets hot even at no load.
when using the drill core in a project, replaced it with a more powerful 12v motor (and running it at 12v), the heating issue seems to pretty much be gone.
I have seen even worse and more rapid heating with a Harbor Freight DrillMaster cordless drill, haven't checked what sorts of motors these have. I have doubts it is anything great, given they were also too cheap to supply a charger with an automatic shutoff (they are basically just charging the batteries with a 24v power-brick and a resistor, and a few LEDs with resistors). how does one know when the battery is done charging? it gets good and hot.
it basically works if only drilling a few holes, not not so good for more serious work.
and, if you need to use a hole-saw... well, it is probably time to pull out a different drill.
