Adding a Fan Speed Control to my Range Hood

[Blacklane]

I have a Hengs range hood in my RV. The fan is effective, but sometimes too noisy and powerful, particularly when just venting a little heat and steam from a coffee pot early in the morning. I decided to add a Pulse Width Modulator (PWM) fan control to it. I picked it up from Amazon and it came with a remote control knob.



The advantage of a PWM controller is that it is much more efficient at reducing power than a resistor pack, since resistors simply turn excess current into heat.

Thankfully, Heng provided a generous wire channel between the front panel and the fan. There is plenty of room for a PWM controller in there.



PWM controller mounted in wire channel. This particular model mounts with 3mm screws; not provided.



I mounted the control knob on the front panel. I had to keep it close to the existing fan switch so it would not interfere with re-installing the wire channel.



Now, I can choose a low, quiet setting for morning coffee and a full-force setting for cooking bacon.

[Carb_Cleaner]

Very nice. Thanks for the detail. I can do that. Easy peasy.

[Blacklane]

You do have to isolate the fan negative wire from the group of white negative wires (one to ground, one to light, one to fan), all connected by a wire nut. Then disconnect the black fan wire from the front-panel switch. Now you have the black (+) and white (-) wires that connect the fan to the output of the PWM.

Add a black (+) wire from the switch to the PWM (+) input and a white (-) wire from the white ground wires (-) to the PWM (-) input.

I used crimp connectors and short pigtail wires to make it easier to assemble. If you use wire nuts, be sure to tape them, since wire nuts in RVs tend to vibrate off.

Mount it with 3mm screws and re-assemble everything.

Yes, the switch is still used. Note that the speed control rheostat has to be mounted fairly close to the switch, or the wire channel won't fit back on without bending or cutting.

[Carb_Cleaner]

Two pairs of wires. One pair 12V hot and neg. in and one pair out? Is it that simple? Do you wire the PWM before or after the fan's switch? Does it matter? Our fan has a two-speed switch.
I really like this idea. Thanks for sharing.

[tvman44]

I have been wanting to build a adjustable voltage regulator to control the fan on our vent hood because it is so noisy, ours is a Jensen but is made identical to yours except for the name on the front tag. But like your idea, so I just ordered one on flea-bay for $4.69 with free shipping. It will be coming on a slow boat from China but for that price I can wait another 3 weeks for it. This will make all kind of brownie points with SWMBO. 🙂 $4.69

[Wet_Coast]

wow, thought of making one of these up myself, but why not support the economy instead. Should also work for dimming lights too eh? Thanks!

[westend]

Link to PWM controller

[Son_of_Norway]

I also installed a PWM on the vent fan in my bathroom. They are marvelous little gadgets with many applications.

Miles