Sometimes we don’t know how they did it, but back in the 1960s and 1970s many cars had a mechanical fan blade for cooling the radiator. It operated at engine speeds, so it pulled less air through the radiator at idle than it did at higher RPM. Sitting at idle in the heat of the summer with a mechanical fan caught a lot of people watching the temperature gauge, anticipating the light to turn green.
Real estate is at a premium with our ’65 Mustang, finding a safe spot for the Derale fan controller takes some creativity.
The mechanical fan was replaced by a fan clutch on many cars, and there were two types: thermal and non-thermal. To engage or disengage the fan clutch, the thermal type relied on air temperature, and the non-thermal type relied on shaft speed. Unfortunately, both fan clutch types operated at engine speeds, so even fully engaged neither one was capable of pulling sufficient air through the radiator at idle on a blistering summer day.
As the electronic age hit the automotive world with all sorts of electrical devices and fuel injection, electric cooling fans began to replace the mechanical fans. They were capable of pulling large amounts of air through a radiator at idle; they could be switched on when the temperature is warm like the thermal fan clutch, and they don’t rob power from the engine at higher speeds, much like the non-thermal fan clutch.
Electric fans, however, are typically an “on-off” type of device that only pulls air when the temperature reaches a certain degrees. So what if we combined the performance of a fan clutch with the functionality of an electric fan? Derale Performance has something that combines the best of both types of fans with their Pulse Width Modulation (PWM) Fan Controller Module.
The PWM is a sophisticated unit wrapped in a little red box.
Upgrading to an electric fan works great on a musclecar; at idle the fan helps to keep the temperatures down, and they are a good solution to overheating at long stop lights. But they need to be switched on, and the problem with the switch-under-the-dash method is that if you forget to turn the fan on, you’re reminded a little too late - usually after you see the steam coming from under the hood.
Pulse Width Modulation (PWM) Fan Controller Module
Thermal fan clutches work on the principle that the fan doesn’t engage fully until the temperature rises. The fan essentially ‘freewheels’ until the air is hot, then the fan clutch is engaged and the fan pulls more air through the radiator.
The PWM works with a probe or a mechanical sender to operate the fans.
Electric fan controllers work on the same principle as the fan clutch: they’re designed to switch the fan on and off based on the coolant temperature. Typical fan controllers, however, only allow the fan to operate at two speeds: 100% and 0%.
Derale Performance has taken the concept of a thermal fan clutch and an electric fan controller and combined their individual features into one controller box. Like the thermal fan clutch, the PWM will keep the fan spinning, even when the temperature isn’t at the highest setting. Even though the fan may not be at 100% speed, it will still spin at a lower rate and still pull some air through the radiator.
Unlike typical fan controllers that utilize a probe that registers radiator inlet temperatures (upper hose), the PWM Fan Controller uses a probe, or temperature sensor, that mounts at the radiator outlet (lower hose) and monitors the engine coolant temperature after it’s been cooled by passing through the radiator.
By varying the fan speed, the coolant temperature remains more consistent. This not only increases the life of the fan, but also the battery and the alternator, as well. -Mike Murphy
Mike Murphy, of Derale Performance, tells us, “By varying the fan speed, the coolant temperature remains more consistent. This not only increases the life of the fan, but also the battery and the alternator, as well.”
By not cycling the fan on and off at full power, the electrical system doesn’t see repeated spikes of up to 50 amps every time the fan is switched on. Where typical relay systems will have a broader range of temperatures ranging from 20-25 degrees, the PWM has a much tighter range, keeping the temperature within about 5 degrees.
Rather than shutting the fan off completely, the fan speed is reduced until the temperature rises to the set temperature, and the fan remains at 100% speed until the temperature drops. Conventional controllers turn a fan on at a desired temperature, and then turn the fan off when the temperature is roughly ten degrees below the setting. This allows the temperature to rise and drop in cycles, whereas the PWM will merely slow the fan down as the coolant temperature drops. By keeping the temperature more consistent, Murphy says that it will help with economy and power.
After programming the PWM, a simple connection to the cooling fan, ignition, and battery was all that was left.
The PWM Fan Controller Module can control up to two fans, supporting up to a maximum of 65 amps. It works with one or two fans, but instead of switching one fan on later than the other, the PWM Module adjusts the fan speed on one or both fans by reducing voltage to the fan motor. This reduction in voltage slows the fan down at lower temperatures, and ramps it up at higher temperatures to more accurately control the temperature of the engine. The PWM does, however, have a manual override feature to switch on the cooling fans.
The idea behind this is to keep engine temperatures more consistent instead of constantly turning a fan on and off at various stages of the temperature cycle. The module can be set at a specific temperature and will adjust the speed of the fan(s) to maintain desired temperature. The fan speed is controlled by PWM from 0 to 100%, constantly making adjustments based on the temperature input.
Adjusting the controller to turn the fans on is a simple task that can be done by removing the cover. The controller can be adjusted to turn the fan on in ten-degree increments from 160 to 210 degrees using a multimeter to read the calibration terminal voltage. Turning the potentiometer on the controller will provide the different values when the multimeter is contacted, allowing for complete fan control.
Programming the control module is simple: just remove the cover and measure the voltage across the two terminals. Adjust the potentiometer to set the 'fan on' temperature based on the chart included with the instructions.
The compact module should be mounted within five feet of the battery, but for remote battery applications connecting to a junction directly from the battery will suffice. The kit includes a built in, automatic resetting circuit breaker for safety, as well as an air conditioning override circuit to switch cooling fans on at 100% whenever air conditioning is being used. Mounting hardware and all electrical connectors, circuit breaker, and wiring is included with the kit, as well as detailed instructions to connect the PWM Module.
Inside the fender well was about the only place we had plenty of room, despite the compact size of the PWM.
It’s recommended to keep the module itself away from high heat areas near the engine. We chose to install the controller about the only place we had room for it on our 1965 Mustang, Project Biting The Bullitt. With a supercharger, a pair of fluid coolers, and miles of hoses, wires, and tubing, you can imagine that the engine compartment was cramped, to say the least. But up inside the front fenderwell was a great little spot for it, out of the way and easy to get to.
We mounted the PWM high enough to keep it away from the elements, but this Mustang probably won’t see a lot of wet roads… 1,100 horsepower and wet roads on street radials is not a good combination.
Since this module does connect directly to the battery, if you don’t have a battery cutout switch it’s recommended to use a relay that is switched on with the ignition. Keeping the fans on until the engine cools down could drain down the battery once the engine is shut off.
After installing the controller, the simple task of setting it up and making the final wiring took about an hour. The included 50 amp circuit breaker will protect the conrtoller, and the 65 amp capacity will allow you to control up to four electrical cooling fans.
The fans cannot be controlled independently of each other with just the one PWM, but using either the temperature probe or the thermal temperature sender will help to maintain the desired temperature. We installed the thermal temperature sender on the radiator for an accurate reading of coolant temperature, and we’ll let the PWM controller do the rest.
To learn more about Derale and their extended line of fluid cooling products, visit the Derale website where you can find the PWM and other fan controllers.