Variable voltage power module

Control the brightness of lights and the speed of fans

by Julian Edgar

Click on pics to view larger images

Here is an absolute beauty – a tiny, efficient and cheap variable pulse width power module.

Hook it up to a DC fan, and you can control the fan speed via the supplied knob. Power filament light bulbs (like the dash lights in most cars) and you can control their brightness, steplessly and without flicker. Want to have a cheap variable power supply? Just add one of these to a car battery or old PC plugpack.

And for under AUD$5, delivered to your letterbox, nothing beats this module for value. To find it, search on eBay under “1203B DC Pulse Width Modulator PWM DC Motor Speed Controller Regulator Switch”.

So is the module cheap and nasty? Surprisingly, I found it to live up to its specs – in fact, to more than live up to them!

The module is rated by the maker at 3 amps, quite a high current considering the board’s diminutive dimensions. But in testing I found it’s quite happy to run at this maximum current, with the supplied heat-sink rising only about 10 degrees C above ambient. In fact, I short-termed increased current to 4.5 amps and nothing turned to smoke…

Here the module can be seen running an incandescent light bulb load, running at about 50 per cent duty cycle and with a current of just over 3 amps.

The measured pulse width modulation frequency is 25kHz. That is, the output signal is turned on and off 25,000 times per second. This is high enough in frequency that if you are controlling small motors (like those used in fans), the motor windings cannot be heard ‘singing’.

Input voltage range is 6 – 28V – so it’ll work on everything from a 6V old motorcycle through to a 24V truck!

The board is about 51 x 33 x 16mm (L x W x H), with the knob protruding about 19mm. Connections are via a 4-way terminal strip, with the correct connections written on the bottom of the board in English. Four mounting holes are provided.

At this price and with this capability, this might be a situation where it’s worthwhile buying half a dozen of the modules and putting them aside for use as needed…

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