PM DC motors 1

[paulmars]

Are all PM motors DC? Are all DC mtrs PM? I know its basic questions, but searching the web did not give me an answer.

 

[paulmars]

And what about davidbeach's point?

 

[waross]

Someone is telling me, that mtrs need to be PM to be used as generators. True or False?

False
That would be someone with a very narrow exposure to the electrical industry. If a conductor is moved so as to cut magnetic lines of force in a magnetic field an EMF (Voltage) will be induced in the conductor. That field may be created with either a permanent magnet or an electro-magnet. Generators above about 1/4 Hp with permanent magnet fields are a fairly recent development in the electrical industry.
Until the advent of the alternator in the mid to late 50s all automotive generators used an electromagnetic field. One of the quick tests that was sometimes performed was to power the generator on the bench. If there were no serious problems the generator would motor. This was called "Motoring the generator" With the development of high strength rare earth magnets which didn't slowly lose strength, larger PM motors and generators became feasible. In the days of steel magnets there were tachometer generators that were assembled and then magnetized. These generators could not be disassembled in the field. To do so would cause then to lose enough of their magnetic field strength that the calibration would be lost. That was about the size limit of PM machines before the development of rare earth magnets.

Bill
--------------------
"Why not the best?"
Jimmy Carter