Wednesday, September 12, 2012

DIY Solar Powered Holding Tank Vent Fan / Cap

There are times that the RV black holding tank creates a source of undesirable odor within the coach, especially during hot summer months. I needed something to help with the holding tank venting, so I searched the net for possible solution. I've heard good things about the Lil' Stanker vent fan device, but unfortunately it's no longer available anywhere. The Cyclone Sewer Vent device also has good online reviews, but it's not going to work with the Agile holding tank vent because of its location. The vent is located close to the awning housing preventing the Cyclone to freely rotate 360 degrees. Then I tried the solar powered vent fan made by Ultra-Fab available at CW, but found it to be noisy, big, and expensive. The Ultra-Fab fan motor makes clicking noise as it spins, which is really annoying.

So I decided to DIY a solar powered vent fan. Here are the materials you need for this project.

Using a Dremel rotary tool, I started working on the PC case fan by carefully cutting the 4 supporting legs from its square casing. I then mounted the fan facing down on one side of the 2" PVC coupling using PVC cement to glue the fan support legs on top (see picture below).

Picture of the fan assembly, 3" PVC cap, and 7.5 volt (100 ma) solar panel. The solar panel is sealed and ready for all-weather use.

The fan assembly was mounted inside the PVC cap leaving equal gaps on the sides and about half an inch gap on top for air circulation. Three stainless screws with nylon spacers were used to hold the fan assembly in place.

Side view

Top view. Noticed the half inch diameter hole I made on top of the PVC cap to clear the solar panel power connector. 

Solar panel was  mounted on top using silicone adhesive, then I painted it white.

Agile's holding tank vent fitted with screen before the fan install.

The 2" diameter PVC coupling is a perfect fit to the Agile's holding tank vent. Two stainless screws and a small amount of silicone sealant were used to held it in place.  I can literally "smell" it working :).

I was really pleased with the vent fan mod...but, when driving through windy/gusty conditions, I noticed that there is a pressure built-up inside the black tank, so I made a non-working one and tested it on my "wind tunnel". Sure enough, the vent cap produces air turbulence and somehow pushes air through the vent stack. I added holes in front and towards the back of the vent cap in attempt to minimize air turbulence but it did not make any difference, until I added my patent pending "Air Dam" Below is a video of the wind tunnel test (HD option available).

 Picture of the "Air Dam" installed. The "Air Dam" is made from a heavy gauge metal sheet then it's primed and painted for durability. Its wide enough to block the air flow to  the 2" PVC coupling behind it. This thing now looks like a duck face.

    How it works: A high air pressure area is created in front of the "Air Dam" as the air hits the sloped frontal area during driving. The air is pushed and accelerated upward thus creating a high pressure in front and in effect it creates a low pressure area behind it resulting in a slight suction effect... I'm no engineer but that would be my guess why it works.


  1. How do you fit an 80mm fan into a 50mm pipe ??

  2. Thanks for the catch. I apologize for the error. The fan is actually a 60mm PC case fan. The 2-inch PVC "coupling" ID: is actually 60 mm.

  3. Hey roadtekker - wanted to say this was a great idea. Thinking of using it myself.
    Now that its been a year since your install - is the fan and solar panel still working. I envisioned that the fan is running all the time the sun is out, sounds like that would be alot of of hours on the fan. I was wondering if a switch in the circuit is worth the effort. Any further updates.

    1. Yes, it is still running strong. I wouldn't be concerned about the fan running most of the time as it is not running at its full power due to the small solar panel, so I'm expecting it to last longer than it should.

  4. Thanks for the great modification. I am running mine off of 12v trailer power. Fan may not last as long but I'm going to build a spare for quick changeout. If specifications are accurate a ball bearing fan should last about 6 years and that's enough for me. It's amazing just how well this thing works. I have not smelled any odor from the toilet since I turned the vent on. I can appreciate the elegance of the solar power approach but I wanted 24/7 power venting and the current draw is insignificant. I had to use a 1-1/2" to 2" adapter as my 5er vent is 1-1/2". I also used a 4" cap just to give plenty of room for exhaust. BTW routed power inside the vent pipe from inside the trailer. Thanks again. No more chemicals for me.

  5. I have a solar panel covering the vent on the roof so would like to place the vent fan in the line going up to the roof. I can see the pipe when I lift up the lid covering the water pump and from the access door under bathroom when the door is open. Has anyone tried this option? I'll report back if I tackle this one.

  6. WOW just what I was searching for. Came here by
    searching for set alarm on samsung

  7. This was a lifesaver idea. Thank you. I have to adjust it slightly but maybe I'll upload to youtube or something and show you the differences. I am converting the holding tank pump out to a vent with fan for our composting toilet. Should be interesting. But your ideas helped me a lot. Thanks


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