Re: Newbie to the group with a problem
- In general a resistor, variable or otherwise, is NOT the way to vary
the speed of a motor. Resistors waste energy through heating and with
any reasonable size of motor the resistor gets quite large and
expensive (and difficult to find). Also the motors tend to stall out
especially when starting and at low speeds. A better way to vary the
speed is to use a pulse width circuit, using a power transistor to
make/break the circuit. This lets you vary the speed of the motor,
maintains quite a bit of torque and lets the motor start even at low
speeds. It is also much more efficient. You can make a simple pulse
width controller from a 7556 or 7555 CMOS timer IC (see the "Files"
section of this group for a data sheet for this timer IC) or there
are dedicated motor control ICs available (do a search for motor
control IC). Kits are also available at:
--- In email@example.com, "Jay Stanley"
> Greetings all,12v
> Hope someone can lend a hand...I have a 12 volt DC motor .9amp this
> runs from 110v household current to a switching power supply 110-
> dc 3.25 amp...I need to put in a variable resisitor to slow themotor
> down when needed (12v runs 44 rpm...9v 30rpm etc)...any ideas ondc
> where to find this? I tried calling a company who sold a 12v 4amp
> dimmer, but they claimed it would not work with a motor...I don't
> know why.