Breaking of Universal Motor

I think that word that you need to search on is "brake" rather than "break".

However, have you tried shorting the motor out - rather than leaving it open circuit, in the "off" position?

Essentially, you need to absorb the kinetic energy by dumping it into something. There is a wide range of small electromagnetic brakes available -

Try

IIUC, they have a branch in Copenhagen..

-- Sue

You mean "brake", as in slow down, not "break" as in damage.

The problem I can see with a series universal motor is that it will make a lousy generator. Can you find a drill that uses a permanent magnet DC motor instead? Portable (battery powered) drills all seem to use PMDC motors, and I've seen AC line-powered routers with PMDC motors, so perhaps there are line-powered drills with such motors too.

The advantage of a permanent magnet motor is that it makes an excellent generator, and if you connect the motor terminals to a low-valued resistor you get a nice braking torque that's proportional to current. If the load is a resistor, current and torque should be proportional to shaft speed.

Dave

If it is a reversible motor maybe a short shot of reversing on shutdown? Eric

Rasmus Solmer Eriksen brought next idea :

You could use DC braking.

A universal motor runs on AC or DC. That's why it's called 'Universal'.

There are electromagnetic brakes availible.

My apologies... I just had a "duh" moment :)

Yes, I am looking for a electrical solution. The problem with utilizing DC-breaking is the non-existence of a magnetic stator field when the motor is not energized. Somehow I need to energize the stator coil and short-circuit the rotor coil to achieve braking.

I have seen such a system working on a Bosh power drill but have been unable to reverse-engineer the solution.

/Rasmus S. Eriksen

That would require switching to reverse the connections to either the rotor or the "field" plus additional switching to meter out a short reverse shot.

With about the same amount of switching (or less), one could arrange to short out the armature and place a DC current on the field windings.

I haven't throught through what would happen if one simply shorted out the brushes and maintain AC on the field. I suspect that would also quickly slow down the motor.

That's referred to by some as 'plugging' a motor. It used to be quite common in a lot of controllers for conveyors and that ilk. The trick is cutting off the power just as the shaft reaches a dead stop. Some old systems used simple switches that were driven by the shaft through a friction clutch. As soon as the shaft stopped, a spring would open the switch and kill the plugging circuit.

daestrom