Breaking of Universal Motor

[Rasmus Solmer Eriksen]

Hi Everyone



I am working on a project where I am utilizing a motor form a normal power
drill to drive a lift up and down I choose the drill motor because it comes
complete with gearbox, is reversible and cheap.



However, I now experience too much free run after I have released the
up/down button. Is there a good way to break such a standard "Universal
motor"?



Thank you

Rasmus S. Eriksen

Copenhagen, DK

 

[Palindrome]

Hi Everyone



I am working on a project where I am utilizing a motor form a normal power
drill to drive a lift up and down I choose the drill motor because it comes
complete with gearbox, is reversible and cheap.



However, I now experience too much free run after I have released the
up/down button. Is there a good way to break such a standard "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 http://uk.rs-online.com/web/ and search on "electromagnetic brake",
for examples.

IIUC, they have a branch in Copenhagen..

 

[Dave Martindale]

I am working on a project where I am utilizing a motor form a normal power
drill to drive a lift up and down I choose the drill motor because it comes
complete with gearbox, is reversible and cheap.

However, I now experience too much free run after I have released the
up/down button. Is there a good way to break such a standard "Universal
motor"?

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

 

[Rasmus Solmer Eriksen]

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

 

[daestrom]

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

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