When you hear people talking about Pulse Width Modulators (PWMs) for their electric fan shrouds, it’s highly likely you’re asking yourself the same question as many people do, “what in the world are you talking about”? To make it simple, a PWM is a complete wiring harness that will control the amount of power that is supplied to your brushed fan motor or motors. Traditionally a brushed fan has two speeds, ON and OFF. In other words, the fans are either not operating at all, or going at 100% power. With a PWM you have the advantage of a “soft start” and the fans operating at the speed needed
to do the cooling that is required based on the reading of the temperature sensor. When we say “soft start”, we are avoiding any damaging amp spike
that you get when starting up a fan. It eliminates the high current in-rush, hence no idle pull down or overloaded connections. The PWM allows you to
draw only the power necessary and will ramp up from zero amps to the required draw for cooling the engine.