Roof Vent Computer Fan Mod

Discussion in 'My Favorite Mods, Tips, Tricks (and Blunders!)' started by Dubbya, Jun 23, 2013.

  1. Dubbya

    Dubbya Wherever you go, there you are...

    6,138
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    Aug 2, 2011
    Steinbach, MB
    The base of the crank on our old Elixer roof vent was broken, the lid was badly discolored and the seal was shot so we were looking at a full vent replacement as the most economical solution. One problem, a stock budget-priced vent doesn't come with a fan and the ones that do, cost more push about 30cfm and don't seem to make much of a difference in terms of air movement.

    Badly wanting a vent with a quiet, efficient and inexpensive fan, I realized an opportunity to mod something that would fit the bill. I had our dealer order a Fan-Tastic Vent Model 900 (vent only, no fan), then added a 200mm NZXT FN-200RB 166 cfm computer fan with a potentiometer (speed dial) and on/off switch. Bearing in mind that my fan (7-7/8" across) would easily have fit in a stock vent as well, I really wanted to have the option to use a bigger fan if this didn't pan out.

    Inside the box is everything needed to install the vent, screws, ceiling vent garnish, an extruded foam gasket, instructions and the warranty card, plastic protectant wipes, everything except the sealant.

    (Click the thumbnail pictures to open the larger image on photobucket.com)

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    At this point, I've removed the old vent, sealant and butyl tape and wiped down the perimeter of the vent opening with a final wipe autobody solvent (degreaser) before removing the screws that secured the inner portion of the vent and crank knob.

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    Next, I removed the two plastic plugs covering the stock switch holes.

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    I then took some measurements (the fan opening inside the shroud is about 12-5/8", plenty of room for a 12" fan if that's what you wanted to put in. Vertically, there's a ton of room as well and, of course the plastics are all molded to easily accommodate a fan and wiring.

    I needed to keep the fan a decent distance from the screen inside the vent and I didn't want the fan to recirculate air from outside either, after all, the whole point was to remove hot air from inside the camper. A trip to the building center yielded a 32"x16" piece of galvanized duct liner for $3, so I used that to draw out the ducting I'd need.

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    Using tin snips, I cut the pieces I needed, then ran them down to my kid bro's house to use his sheetmetal brake. I fashioned a pan with edges on the sides and bent up the ends to fit snugly inside the shroud. I then cut out a hole for the actual 7-7/8" duct that would not only hold the fan but that would lead down to the inside vent screen. Raising the duct 1/8" from the screen, just so it didn't make contact and distort the screen, I pop-riveted the whole thing together and mounted it inside the shroud with four more 5/32"x1/4" rivets. I cut the bottom tabs off the fan frame and inserted it into the duct snugly.

    I did a ton of research before I chose a 100 ohm potentiometer that would take my 7.4 watt 12 volt fan down to 2 watts. The particular fan I chose got a bunch of great reviews and, best of all, uses only .7 amps at full-tilt-boogie. It's more adjustment than is required but, meh, it works.

    Along with the pot, and a dial knob that wasn't too ugly, I chose a 5amp rocker switch to turn the unit on and off.

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    If you want to do this project yourself, here are the parts I used. You shouldn't have any trouble finding these cheaper on Amazon or eBay than what I paid at the electronics shop but the DW isn't one to wait patiently for parts to arrive while the camper is sitting in the garage and her baby (Mazda 3) is parked outside. [:D]

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    I wired up the potentiometer with the positive lead coming in to the #3 pole, (the right one in the photo) and the fan's power lead to the center #2 pole on the switch. Knowing how often computer fans wear out, I chose to use the Molex connector that came with the fan so that I could swap out the fan quickly and easily if and when required. I snipped off the red and black wires and removed the yellow wire and terminal from the Molex connector as well. That yellow wire is just used to monitor fan speed but was of no use in this application, so it hadda go.

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    I then mounted the pot into the shroud and drilled out the second hole to accommodate the on/off switch prior to soldering the power leads to the switch and the negative lead ends together. I used a piece of heatshrinkable tubing to seal the negative connection.

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    After some corrections, repositioning, testing and more corrections to the pan and duct tube, I used four 5/32"x1/4" rivets to connect the pan and duct assembly to the fan shroud. I then slid the fan into the duct and used plumber's Goop to secure it in place. The duct is very snug though, so the fan wouldn't likely have ever popped out of it's own accord anyway. Here's the completed assembly prior to screwing the shroud back into the vent. The pan I came up with is substantially more complicated than is actually required, but I had the time and once I started down the path, it just kinda ended up being what it is. In retrospect, I guess a couple of 16"x2" galvanized joist hangers would have worked every bit as well to hold the circular duct in place. Unfortunately, I couldn't find them locally and didn't feel like driving two hours just to go to the Home Depot.

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    Inside the camper's ceiling, I drilled a 3/8" hole through the wooden vent framing and through the steel frame behind it. I then spent an hour using a fish tape to push a channel across the roof the the one of the ceiling lights where I could make a connection to power my fan. Working the fish line back and forth, I could hear where it was inside the ceiling. When I knew I was close to the ceiling fixture, I used a coat hanger to fish the end of the fish tape through the ceiling hole and connected the wires.

    There's a high degree of frustration during this process so if you're going to try this yourself, I'd recommend that you close all doors, send your family out for ice cream or a movie and crank of the volume on the garage radio. Either that or force any and all bystanders to wear some ear plugs while you're working. [:(!]

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    I drilled a 3/8" hole through the side of the vent to run my ceiling wires through then moved on to installing the vent itself. To install the assembled vent in the roof, I placed the foam vent gasket 1/2 way onto the vent and ran a bead of plumber's Goop around the perimeter and circling each screw hole on the top of the foam, then pushed the foam all the way onto the vent and repeated the process on the bottom side of the gasket before inserting the vent into the roof and screwing it in place. I also ran a bit of Goop around each screw head prior to sinking them so I wouldn't have to seal them later.

    With the vent secured in place and wires running through the side of it, I ran a 1/4" bead of Goop to seal the vent to the roof and moved inside to finish up the installation. I used twist on electrical connectors to make the final connection and screwed the fan shroud assembly back into the vent.

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    The vent garnish that trims the vent inside the camper is made to accommodate a 4" RV roof but an oscillating tool zipped it down to 1-1/2" pretty quickly. I used my razor knife to trim off the plastic burrs and sanded the sharp edges to make inserting it a little easier. I then drilled out a 3/8" notch so it would slip past the wiring. Being that the vent sticks down about 1/2" past the surface of the ceiling, I used some 1/2"x1" self-adhesive foam strips to make up the difference and finish it off.

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    Link to photobucket slideshow: http://s638.photobucket.com/user/io_Dubbya/slideshow/1997%20Viking%202060ST%20Rebuild/Roof%20vent%20fan%20mod

    YouTube demonstration videos to follow.
     
  2. Snow

    Snow Well-Known Member

    8,814
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    Jul 19, 2007
    Ontario
    Interesting... I was thinking on doing something similar to the galley fan in the TT ...
     
  3. shelmily

    shelmily Well-Known Member

    3,005
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    Jun 7, 2012
    Northeast Pennsylvania
    Looks good Dubbya, you will have to let us know how it works for you.
     
  4. Dubbya

    Dubbya Wherever you go, there you are...

    6,138
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    Aug 2, 2011
    Steinbach, MB
  5. Dubbya

    Dubbya Wherever you go, there you are...

    6,138
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    Aug 2, 2011
    Steinbach, MB
    I found the sheet metal pan to be too restrictive (and ugly) when the fan wasn't in use, so I reworked the mod and made a fan mounting bracket using 3/4"x1/8" anodized aluminum.

    As you can see, the original pan obstructs the majority of the vent screen and that's just not cool. (See what I did there?) [;)]

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    Finding that I already had an 8' piece of 3/4" x 1/8" anodized aluminum stock leaning up in the corner of the garage, I set to work drawing up a scaled diagram with measurements and rivet locations. I saved the drawing out as a PDF and printed them out for use as a bending template. Not including the time it took to draw up the plans, the whole change took me about an hour to do.

    The bracket only only requires about 32" of the aluminum stock and nine pop rivets. Bending the aluminum stock is pretty easily accomplished using folding pliers, a bench vise, a hammer and a wooden block to prevent damage to the metal.

    Here's the newly assembled mounting bracket inside the shroud.

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    And here's the new bracket installed with the fan in place. Again, I mounted the duct about 1/8" from the screen surface to avoid distorting it. The new bracket is more than sturdy enough for this fan and there's very little obstruction of the vent screen under the fan duct.

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    Download the Template:
    Fan-Tastic-Model900-fanbracket.pdf (135KB) (Choose the 200KB download button)

    Folks with the Elixir or Ventline Ventadome manual roof vents won't be able to use the plans but the basic idea is the same, in fact, it's even easier. All you need is to cut two straight pieces for the side brackets then cut another for the rear brace (just make an "H" shaped bracket). Measure across the inside of the vent, add 2" to each piece to fold into 1" mounting tabs, drill out the rivet holes, rivet them together, rivet the 8" round duct in place and you're off to the races. Alternatively, you could build two brackets and use up to four smaller 120mm fans, two on either side of the crank channel that runs down the center of the vent. Even the most basic 120mm fan will put out 36cfm (up to 56cfm depending on how much you want to spend). They're reasonably quiet and easily replaced when they wear out.

    Just for giggles, I took a poke at my old Elixir manual vent and it looked like there's about 1-1/2" of vertical space between the crank channel that the crank attaches to and the inside screen, since the fan itself is only 1" high, it's definitely doable, just be sure to keep the bottom of the fan(s) at least 1/2" from the surface of the screen so it can get air.
     
  6. Tonimus

    Tonimus Member

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    Jul 11, 2012
  7. Dubbya

    Dubbya Wherever you go, there you are...

    6,138
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    Aug 2, 2011
    Steinbach, MB
    12-5/8" = 320 mm
     
  8. kpic

    kpic New Member

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    Jul 7, 2013
  9. fmbhappycamper

    fmbhappycamper PuP Power

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    furlongs and hectometers, oh my [8D]
     
  10. jayco1997

    jayco1997 New Member

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    Oct 1, 2012
    I also have been working on my roof fan mod. I took a fan tactic vent cover in the smoked color which was empty that I picked up on the clearance rack of the RV dealer for $8. I went to another RV store and was able to pick up a 12" panasonic fan that was just sitting on the shelf collecting dust, paid $10 for it.
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    I had to screw the fan into the vent housing because it was not meant to be used in the fan tactic vent cover. I wanted my fan to run in both directions but only one speed as I never adjust it once its on. In order to change the polarity so that my fan would either bring in the air or let it out, I needed a double pole, double throw switch which has 6 pins on it. I purchased at Radio Shack for under $5. The switch allows me to run the fan forward, off or in reverse because it will switch the polarity of the wires due to the way I land the wires on the switch itself. Now with a simple throw of the switch in either the up or down position it will move air in or out based on what I want the fan to do.
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    now I just have to install the switch, land the wires and mount it onto the roof. We do have AC but some of the places we camp do not have electric so I wanted air movement by using just the battery.
     
  11. kpic

    kpic New Member

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    Jul 7, 2013
    I warned you it is over the top for home use. ;)

    But it does beat 5/8=.625+12=12.635*25.4=320.675 :D

    Dubbya
    You do good work!
     
  12. Tonimus

    Tonimus Member

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    Jul 11, 2012
    Dubbya, I missed the template on my first read-through. Thanks for that. I think I'm going to have to order up a fan and a vent now...
     
  13. Dubbya

    Dubbya Wherever you go, there you are...

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    Aug 2, 2011
    Steinbach, MB
    No problem, Tonimus! Enjoy!
     
  14. Dubbya

    Dubbya Wherever you go, there you are...

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    Aug 2, 2011
    Steinbach, MB
    Looks like Fileswap wants to delete the PDF template so I'm now hosting it on my own webspace account.

    If Fileswap link for the download isn't working, you can download the fan bracket template here
     

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