DC motor Operation - Q&A

The risk is that a Series Wound Motor, off load will run faster and faster until it self destructs, as postulated in the original post.

Usually, what prevents this are the friction in the bearings and the windage on the rotor, which provide sufficient load to keep the speed below that where the centirfugal forces cause rotor windings to fly off.

Having said that, better not to find out the hard way that your motor is low friction and/or internall very aerodynamic!

Howard

How about one of these:

(Actually I think it's the AC sychronioser control of a power station).

Neil

If you have access Andrew to early copies of MEW you may find my series on electric motors AC and DC help. The series started in issue 15 with issue 16 devoted to DC motors and issue 18 to speed control of dc motors.

If you do read issue 15 then I made a major error reagarding star and delta contections, I typed in star when it should have benn delta, or the other way round. I still get nightmares about it.

Sorry but the theory is now well and trully lost in the mist of time so cannot easily come up with any answers.

Harold

Residual magnetism in the core?

Russell.

I'd expect it to give itself a stern talking to, get off its backside and start at the beginning; which is precisely what I'm going to do, back in the workshop.

Andrew

Presumaby a self excited shunt wound DC generator is what we would have called a "dynamo" in old automotive parlance. In which case, yes, it was down to remanance. Some vehicles had positive earth systems didn't they, in which case you had to magnetise the machine in reverse if you wanted to change the system or dynamo to the other polarity.

Muzzer