brunnhilde's ventilation fan - part 1

A few years ago I designed this 200mm thermostatically operated ventilation fan in Isolde. I have been wanting to install a similar fan in Brunnhilde's bathroom skylight, but hoping to find a fan with slightly more CFM.

Finding a 12Vdc fan that is relatively quiet and moves reasonably CFM is harder accomplished than it seems. The CFMs are either really low, or excessive and there is nearly nothing in between. Compounding the challenge is I want it to be relatively light due to the planning of a removable mounting I envision. The  ventilation fan assembly needs to be easily removed so the Mini Heki skylight may be opened or closed. As it needs to be removable, there is the risk that it can fall down and damage the irreplaceable bathroom fixtures, and worst the composite walls.

I spent a lot of time looking for a fan of reasonable diameter and more CFM than the 200mm fan I used in Isolde. I simply could not find one so I settled for the same fan. Fan this size and speed can be deceiving with its CFM. Strangely you can find higher power (and thus CFM) fans in 120mm size. All the 200mm fans are low speed and power. I know as I have a very nice high power one for use with roasting coffee.

it consumes 245mA at 12.7V

This fan is perfectly balanced, quiet, and vibration free. It can balance on the improvised shim on its uneven side in the photo above running. 

I am rather skeptical with the max 129 CFM claim; I only wonder if the max number was achieved by driving it significantly over 12V before it self-destructs

only 11 oz

for the fan to work efficiently and quietly it needs to be mounted on a flat plane like you would a woofer

this is how I mounted the one in Isolde's skylight, which has a well designed crank mechanism that raise and lower the cover

I envision using the same 1/4" foam board to create the baffle which the fan would be mounted. But I wanted to build a simple prototype out of scrap cardboard first. 

this cannot be more fitting for this project; I was feeling cooler already

this is how it stays up there

next to cut a round hole

the fan is so light so it is supported by the cardboard; the foam board would be stronger and more resistant to the element even if it get a bit wet

I envision a quick attach tether in case the assembly works loose or dislodged by the wind; the tether can  be like what I improvised or using the skylight's operating handle

It is hard to gauge how effective this ventilation fan is. There is also a balance between power consumption and air extraction rate, as well as temperature differential. I would like it to be doubly stronger, but I have not been able to find one of similar size. For now some active air movement is better than passive on a still and hot day. Until I am satisfied that the fan does provide my expected benefit during my testing I am not about to finalize the construction.

One less obvious benefit of the set up is, much of the harmful sun light is blocked and much reflected from entering the bathroom. I already mapped out how to provide power to the fan while making it easy to use.

this has been something that I have long considering doing - replacing the driver side cabin window that is awning style with this sliding one to be more usable in most situations