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over voltage of a 12vdc motor

C

CCE

Jan 1, 1970
0
I have a 12vdc motor from a power car window and I need to run it at a
higher speed. The load on the motor is pretty low. What can I expect
if I run this motor at 18 or 24 v?
 
T

Tim Wescott

Jan 1, 1970
0
CCE said:
I have a 12vdc motor from a power car window and I need to run it at a
higher speed. The load on the motor is pretty low. What can I expect
if I run this motor at 18 or 24 v?
The motor brushes get stressed by high currents; if you start the motor
on higher than normal voltages they'll get stressed more, leading to
faster (sometimes immediate) wear.

The motor bearings get stressed by high speeds; running the motor on a
higher voltage will make it go faster. Whether this causes problems
depends on your bearings.

Iron losses will be higher because the armature windings will be running
at higher than normal frequencies, but if you're loading it lightly this
may not be an issue.

The brushes may bounce if you're going at 2x the normal speed, leading
to quicker (but not immediate) wear and intermittent lower torque.

If you're driving it from something that can limit the current as it
starts up you may be fine, or you may run into brush or bearing
problems. If it's a car window motor chances are that it's running
pretty close to the limits of its design, but you can only tell by
giving it a whirl.

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

Posting from Google? See http://cfaj.freeshell.org/google/

Do you need to implement control loops in software?
"Applied Control Theory for Embedded Systems" gives you just what it says.
See details at http://www.wescottdesign.com/actfes/actfes.html
 
D

D from BC

Jan 1, 1970
0
I have a 12vdc motor from a power car window and I need to run it at a
higher speed. The load on the motor is pretty low. What can I expect
if I run this motor at 18 or 24 v?

I recall reading in a car manual that those's motors may have a
overcurrent device (polyswitch?) type device somewhere.
The device might trip with the added current from the added voltage.

Those motors are probably designed for a short run time... Given
enough time, continuous use and higher voltages will probably cook the
motor.
D from BC
 
M

Meat Plow

Jan 1, 1970
0
I have a 12vdc motor from a power car window and I need to run it at a
higher speed. The load on the motor is pretty low. What can I expect
if I run this motor at 18 or 24 v?

Eventual overheating and failure seems a safe assumption.

--
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#10 Most hated Usenetizen of all time
Pierre Salinger Memorial Hook, Line & Sinker, June 2004
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C

CCE

Jan 1, 1970
0
I recall reading in a car manual that those's motors may have a
overcurrent device (polyswitch?) type device somewhere.
The device might trip with the added current from the added voltage.

Those motors are probably designed for a short run time... Given
enough time, continuous use and higher voltages will probably cook the
motor.
D from BC

The duration is pretty short, say 5 to 10 seconds every 3-4 minutes.
This is for a hobby project and will only get used once a month or so.
 
C

colin

Jan 1, 1970
0
CCE said:
I have a 12vdc motor from a power car window and I need to run it at a
higher speed. The load on the motor is pretty low. What can I expect
if I run this motor at 18 or 24 v?

Smoke. I expect the window winder motors are not continuosly rated.

However I run those 9.5vdc cordless drill type motors at 12v,
the normal bearings dont last long so I replace them with ball types,
the brushes seem to last ok though.

It all depends how long you run the motor for and how long you want the
bearings brushes to last and how hot you let it get.

Colin =^.^=
 
P

Phil Allison

Jan 1, 1970
0
"CCE"
I have a 12vdc motor from a power car window and I need to run it at a
higher speed. The load on the motor is pretty low. What can I expect
if I run this motor at 18 or 24 v?


** Count the contacts on the commutator and find how many poles it has.

Allow 2.5 volts DC for each pole as a safe max working voltage.

3 pole = 7.5 volts

5 pole = 12.5 volts

etc.

Go much above that and expect very short life from the commutator.

Automotive heater fan motors typically have 11 poles, even though rated for
nominally 12 volts, so can take 24 volts DC long as the current draw is not
too high.

Watch out for switch on surge currents that can damage the commutator at
high voltages.



........ Phil
 
C

CCE

Jan 1, 1970
0
Thanks for everyone's input. Your posts have answered my question!
 
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