Slowing down a 12 volt motor

[shee290]

Just wondering how to slow down a 12 volt motor. Example a light and motor assembly you would see on a plow truck or mail truck.

Can I just put in a potentiometer or rheostat inline with the power supply and motor, or is there more I need to do.

I am building a lighthouse and want to slow the rotation of the motor down.

Any help would be appreciated. Thank you

 

[RODALCO]

Depending upon the current drawn by the motor.

You can use a LM 317 with a pot meter on the adjustment leg so the potmeter only carries a few mA's and the IC controls the current ( this is ok, up to 1 - 1.5 Amps).
Or, use a power transistor and control the base bias by means of a pot meter.
A 2N3055 can control up to 15 Amperes provided it is adequately heat sinked.

Better is to source a geared motor from a surplus shop and use that to drive your lighthouse lamp.

 

[stevez]

Keep in mind that if the load exceeds the available torque then the motor will stall. In some motor speed controls the power to the motor is controlled to maintain a selected speed. As the load changes, more or less power is supplied to the motor. The simpler speed controls such as those described so far do not have that feature.

A pot or rheostat is certainly a way if it can handle the power. The LM317 or 2N3055 ease the demand on the pot.

Another thing to keep in mind is that some motors depend on the rotation to move a bit of air thru for cooling. Reduced rotational speed may affect cooling.

 

[Nigel Goodwin]

A pot or rheostat is certainly a way if it can handle the power.

Yes, it's the way the Victorians did it!.

 

[Sceadwian]

It's a very poor way of slowing down a motor though, incredibly wasteful. Try a PWM motor controller, they're not overly complex to build.

 

[Hero999]

It obviously depends on the motor and application, if it's a small motor driving a small lightweight load then there's nothing wrong with using a potentiometer or a fixed resistor but PWM is the only way to go for significant power levels.

 

[sam2]

Here's a few train throttles that are easy to build, some are PWM and some are not **broken link removed**

 

[Styx]

do you have access to the field windings?