pulse width dimmer

[H3Jim]

All you electrical gurus out there,

I am looking at purchasing Intellitec's system for lighting and electrical control.  It uses and outputs 24 volts DC. They have a built in dimmer system that uses pulse width technology.  It turns the circuit on and off many times a second rather than reducing voltage.

My question is, can I use this for low current DC fan motors?  and can I use it sucessfully on Halogen bulbs?  I'm pretty sure I can use it on the bulbs, but I'm not sure how the DC motors will react.

[TomC]

Personally I don't like the pulse width dimmer.  I can see the light (halogen) flicker at low levels.  Some can't, I just must have more sensitive vision.  Without experience, I don't see why it wouldn't work on a low draw electric motor like a fan motor.  Good Luck, TomC

[Tim Strommen]

Hey Jim,

Yes - PWM can be used for controlling DC motors (it's actually the new favorite method among engineers due to the ease of interfacing with microprocessors, higher efficiency, and lower heat output).  There are a few things you'll want to watch out for though:

• Electric motors have a bare minimum starting current (and it's usually higher than the lowest running current).
• Thus, when starting a motor it's best to give it a "spike" of current and ramp down to the desired operating speed

Some say they can see a flicker with PWM dimming, but this is usually only true if the longest period of "off time" is greater than 20 miliseconds (or about a 55Hz cycle).  Another reason you'll want to check the PWM frequency before getting into the Dimmer module is that if it's in the audible spectrum (20Hz to 20kHz) and the current is high enough on the motor - you may be able to hear it whine.  Typically 30kHz PWM modules are the minimum norm for "inaudible" current regulation.

Cheers!

-Tim