Solar Powered Venting Fans for Honda Insight

Sit right back and you'll hear a tale... of good ideas implemented with frailty and of robust solutions installed with vigor.

I. The Great Idea

I was in Target one day and one of these Auto Vent things fell into my cart as I was passing by the vacuum cleaner aisle. It was a sign. I was intrigued. It seemed like a great idea. Use the sun to power a little fan to vent hot air out of your car when parked. The pictures on the box looked great - a happy person returning to her parked car which has been kept all nice and cool from the tremendous cooling action of the raging torrent of hot air forced out of the car by the powerfull solar fan. Heck, it even removes humidity and odors! What more can you want. Installs in seconds.

You also have to figure that the "not recommded for use while driving" is like those yellow signs that recommend going 15 mph on a curve that even a fully laden ox cart could take at 50 mph without spilling a single turnip. So I let the little thing stay in my cart and took it home to put it through the paces. I stuck it on the window as directed. I waited for the sun, and it obliged. I imagined that I could feel air venting out of the thing, as I saw the fan blades spinning and surely that meant that air must be moving. It must just be my insenitivity to wind that made it seem like not much is happening. So I was very encouraged. I figured kind of like apples and $100 bills, if one is good, then two will be even better. I went back and got a second one and installed it right next to the first.

II. Mysterious Birds have Nested in my Head

They looked great and powerful like huge turbines. The coiled plastic shells dripped with energetic plasma. In strong sun I could see the fans turning, so there was air. Natural air conditioning! I took my trip South. I parked the car with the solar panels for the fans facing the afternoon sun. I was ready for the magic. The only trouble was that the dramatic cooling, deodorizing and dehumidifying didn't seem to be happening. Apparently the amount of air wasn't quite as promised. Even this dual fan system didn't really seem to do anything meaningful to cool the car. Darn it. I was still hopefull. It's such a great idea, I said.

I didn't have anywhere to drive. so I left the car parked in place. I checked it again later, and I could swear air was flowing and odors were deodorizing (not that there were any there anyway). The test would be the next day when I had to leave again. Would I return to a cool car while all around me the trees and bushes wilted and drooped in the hot sun? I would see the next day. I wonder what those birds are in the trees? They must be very tiny, as I can't see them, but I sure hear them. Said I to myself. I left everything in place.

When I was ready to leave the next afternoon, I came back to the car. The solar fan security feature had worked, as no one had stolen the car. There were more birds than ever in the trees, but I still couldn't see them up there. I got in the car, didn't see humidity and odors. Check boxes two and three. So far so good. Then, Uh oh! Only one fan was spinning. The other was dead and wouldn't spin. The bird noises were incessant and only increased in the car. No sun problems, as both fans had equal sun. Maybe those birds were in my head. I couldn't find them in the car. I was bummed, as apparently the lifetime of the fans was about that of an adult Eastern Dobsonfly.

I couldn't live with that, and besides, the chirping was making me dizzy. I had to find out the source. As I was contemplating how to open my head to find the nest full of hungry fledglings clamoring for some regurgitated insects, my girlfriend suggested that perhaps the bird noise was in fact coming out of the remaining solar fan. I scoffed. What nonsense was that! Luckily for the integrity of my cranium, I set aside the bone saw and brain tongs, and I stuck my finger into the fan blades to see if that would arrest the chirps and high pitched twittering. I avoided injury from the incredible force of the spinning blades, but more importantly the birds grew quiet at last. Apparently these noises where the death agony of the second fan!

I was still convinced that these things had touched on a great idea, but it had just been implemented poorly.

III. Clear the Cobwebs. Regroup and Prototype.

Clearly the idea of using a solar powered fan to vent hot air from a parked car was a splendid one. In order to accomplish it you just had to have more than a 15 cent fan and a solar cell bigger than a matchbook. The logical extension of venting hot air while driving was a no-brainer, and then you would have the aid of the airflow into the car from the fresh air vents and maybe a bit of cracked window. It was with great hope I started the prototyping. I sure liked the suction I got when I hooked up an oscillating 12V fan to some ducting and pumped air out the passenger side cargo bay vent. I could feel the air pushing out of the cracks and the other vent on the driver side. I sure hoped it was also blasting outside into the body panel cavity that the vent opens up into (doesn't it?). I blew smoke behind the fan and it was wisked away to vanish mysteriously into the void. It would have been very invigorating to see smoke spew outside the car, but unfortunately it just vanished mysteriously.

I was just a bit bummed when I found that even a pretty decent 5W 12V solar panel didn't have much hope to power that kind of fan. I was thinking, where can you get a fan that moves air, is small, runs off DC? Visions of RC aircraft flitted about in my head, and I went to the local hobby shop on Laurel Street (whose name I can't remember). They were very helpful. While they told me not to buy anything they had there, they did suggest trying something like a PC case cooling fan. I wondered why I hadn't thought of that. I had a handy old broken down PC from the days when 500 MB was still a big drive which happily loaned me its fan for some tests, and while the airflow didn't match that of the behemoth 6 inch oscillating fan, it ran off the mere hint of sun and gave some decent air without breaking the solar bank. Clearly this was the ticket. I wanted something that would scale up with more sun, but not be totally dead on partly cloudy days. Several prototypes came and went. Finally the path was clear to a final 'working prototype', so it was time to document the process. The one ever present problem is that having a 'working' prototype means I will never build a production model because that would mean taking out the 'working' prototype! The result is that every modification always stops at the working prototype stage, because that is good enough, and we don't want to rip it out. Hmmm... That might explain why every step of the way here could be improved upon somehow.

IV. Third Iteration gets an Ovation.

To make life simple, I will skip all the preliminary chit chat and witty banter to jump right into the 'working prototype' production as was originally digitally documented. There are a few missing bits where the digital documentarian didn't do his duty, but you can fill in the blanks. You should also do your own optimization to what is described here. I cut some corners since I didn't know if it really would work, and you can measure twice but only cut once as Norm always says.

I'll include a parts list at the end. The only tools you need are a soldering iron, some pliers, screwdrivers and their ilk.

Most of the work goes on in the cargo bay, or it's just under the cargo mat. I did not exert much effort to hide wires and such. Luckily it didn't take much effort to hide them and they are mostly hidden so the installation looks pretty good. Now that you know this works, you should make sure your wires are well hidden and secure. You can tell me if any panels only come off and don't go back on again.

V. Wiring the Wiring.

I am doing a quad fan installation, so I need power at the passenger and driver side vents both. I start by routing wire along the back of the trunk from the passenger side vent area around to the driver side vent area. I figure I want the main power coming up on the driver side, since that is the seat that moves back and forth the least and is the safest spot for connectors and such. In case I forget to mention, you should use the same piece of wire to run all the way from the front power source to the passenger side vent area and tap off of it rather than use pieces you then splice together. Oops. I was timid about ripping out the panels and felt, so sometimes things are not fully secured behind panels.

I started by routing the wires around the corner at the rear passenger cargo side and behind the cargo storage bin (up above the bin).

When I had them around to the driver side vent, I tapped into them and added a Molex connector for the fans on the driver side. I spliced onto the bare ends you see here to run wires for power from the driver seat area

I also tapped at the same junction to run wires up around the contour of the hatchway to terminate at the top of the hatch.

I did this originally because I was going to run power from the hatchback solar panel(s) directly into the system by hardwiring it in here. It would come in in parallel to the power from panels in the front of the car. However, the final design ended up with a DPDT switch to let me swap between solar and 12V DC battery power, and that is not compatible with a hardwired solar panel. It seemed like I had wasted time and energy to run the wire up to the top of the hatch, but it turns out there is power to spare with the soalr panels I am using and the wires are well placed for powering a ceiling fan. Of course, I could pretend I planned that all along. At the moment the wires are just dead ended and tucked under the hatch boundary weather stripping.

I ran the wires for power to the fans up in the handy channel pre-cut in the stiff foam which goes from the CD changer foam block (unless you have your CD changer in place) all the way to the battery wall. I cut out some of the foam at the fan area to make extra space for the fan connectors. I didn't want to rip out the panels around the battery wall because they didn't seem easy to get back in place, so the wires are exposed as they run over the battery wall. If you are brave, you can put them behind that panel yourself.

The wires come out behind the driver seat down at the base of the wall panel at the bottom of the battery box. I ended them with a Molex connector for connection to the 'black box' power. You could run them directly into your black box, or permanently mount the whole nut.

What you would see if I had documented it is that the wires are in place now for the fans and magic box. There are Molex terminals at the driver and passenger vents and dead ended wires at the hatch top (for the ceiling fan) and Molex terminated wires out behind the driver seat for the main power source as it comes from the black box. The idea is to make the fan circuits able to be modified and independent of the power source. That way you can add or remove fans and change power sources without fiddling with the wiring.

VI. Wiring the Fans.

I first went to a local electronics supply place and got two 90mm 12V case cooling fans, but they took too much power and didn't run in really low sun with the first setup. Plus, they weren't sized exactly right. I'll likely use them for ceiling fans maybe, now that I have more power. Anyway, after that I stood for 17 hours staring at all the case cooling fans at Fry's trying to figure out which seemed to give the best airflow for the least power. I picked the best candidates, and after taking some home to test out, I settled on this one because at 80mm it was about the right size for stacking to match the vent opening and ran under the least sun. I tried some smaller ones, but they used the same power and gave a lot less airflow. They may be good for judicious placement around the cabin. I hope you can read the label, in case I forget a parts list.

I stacked two fans one on top of another (at 80mm two stack up to just about perfectly cover the vents). An obvious optimization would be to either remove the plastic vent covers to improve airflow, or even better, to mount the fans directly in the wall space to push air immediately to the outside rather than into the vent cavity. Once again, I wasn't certain it would be a permanent installation, and I was leary of damaging the panels. The vent plastic covers seem like the devil to get out, and I didn't see how to get them back in once out. I wired the two fans together into the Molex pins.

Then I put the pins in the connector and repeated for the two fans on the other side to get the two dual fan blocks for the quad fan system.

I connected their power connectors into the welcome and willing Molex power connectors set up in the preliminary wiring installation.

I put the two dual fan blocks over the vents. I put the cargo mat back down, and voila!

VII. Take a ride on the Magic Box.

Now all we need is power. After many iterations of preliminary trials, it became clear that one should run the vent fans off the car DC source during driving. When you are driving the sun can be a bit fickle as you follow the course of the road, and safety is an issue (panels on the dash can cause reflections on the windshield). Therefore, we couldn't hardwire the solar as we thought originally. However, we didn't want to be sorting through bundles of wires for connectors all the time. We tried that. It didn't work. The solution was clearly a Magic Box, or at least a black box.

As a blast from the past I went to Radio Shack to get a black 'project box' and a nice DPDT (Double Pole Double Throw) switch with On/Off/On configuration. We ran our solar panel power into it, and added input power cords for 12V DC car power as well as a power cord providing the 12V DC power output to drive the loads. Bear in mind that while the car always stays at a good 12V the solar panels vary in voltage with load. They come in close to 12V with the fans, but with a lot of sun it can creep up easily if you don't have enough loads. Things are within tolerances, but I am not regulating the voltage. I also got a new 40W soldering iron from Radio Shack as my old one melted its own handle and then refused to work. The new one from Radio Shack is very nice. Go and buy yourself one!

Traditionally the beauty of a black box is that the outside looks nice, while inside is a huge mess. I certainly did not want to break tradition.

In fact it only looks messy. I retained the in circuit fuses for each of the solar panels and the original solar panel DC connectors since they are hardwired into the panels. I figured the panels are the only expensive (not too expensive) part of the system, so I would rather keep them intact and use a bigger box to hold them. One never knows what other uses they might have in the future. The box just has the three Molex connections and the rest is the coiled excess wire on account of keeping the fuses and DC connectors of the solar panels.

Since this installation is actually in Jane (GFs Insight), I put some handy labels on the box to indicate what is what.

The panels I am using in the final prototype are from Uni-Solar, and they are each 5W (peak about 300 ma at 12V DC). Two I leave portable for placement in the cargo area.

Or on the dash.

The third 5W panel I semi-permanently placed on the hatch back glass using suction cups. Its dimensions are such that it doesn't block any of the rear view, and it still gets full sun from most sun angles. The little black dimples block a little sun if the angle is low to the front of the car. At first I used the gromets for the suction cups, until I realized that you don't need to at all and can fasten it better with a forest of cups just nudged around it. The entire panel weighs in at about 1 lb.

VIII. Look Ma, No Fingers!

Insight drivers are known to pass on minor safety inconveniences (who said 120 psi was too high a tire pressure, it gives me an extra 0.001 mpg on my commute!) if it gives them better energy consumption statistics, so I chose not to put any so called 'finger guards' on the fans because they block airflow. I have yet to lose a finger, but when these babies are revved up in full sun, don't let your kids near them. They also suck fluff and floating things like feathers pretty fast, so maybe some foam cover is in order. I haven't decided. I think I'll wait until the first blood. Here is a set of fans spinning away merrily.

IX. Hey, is that my Reflection!

In this shot you can can see two things. You see a fine looking red podlike car which just might be Jane's boyfriend Edwin, and you see the generous reflections of the white portion of the solar panels. They are white because they run better when cool, and making them black would make them run hotter and be less efficient. The side effect is that they can cause a hefty reflection in the windshield and make it unsafe for driving with them on the dash. That's too bad, as the three 5W panels makes the fans really rip and it's sad to have that solar energy wasted while driving. The best thing would be to put them on the outside of the car.

X. Partial Passel of Parts


I used leftover wire I had lying around, which is mostly solid copper 14 guage. This is nice because you won't see all that much voltage drop-off. The thicker the better. I also used the cord from my crappy melted soldering iron. I used bits of wire from the unused power connectors for the fans. Some 12 guage stranded copper of which I have a 500 ft spool for no apparent reason.


I used Molex connectors for most of the connections because they are male/female paired and thus prevent silliness like putting one panel at cross purposes to another. They are cheap. They are easy. They are convenient. They are pretty much all hidden from view. They aren't exposed to the elements. I used 0.093 connectors for the main power circuits and 0.062 connectors for the feeders and fan connectors.


I used Vastech's 80mm Brushless 12V DC Fan. Model RDM8025S. It says it only uses 0.11A on the fan itself, the box said 0.13A. It definitely used less than comparable ones. I couldn't measure airflow, but it claimed something just over 30. I can't remember, and I don't have the box handy since I recycled them. I think it has a low startup voltage.


In the first tests I started with some really cheap battery charger 12V panels on sale at Kragen, but the cases fell apart when a butterfly flapped its wings in China (i.e. I think I know why they were on sale for so cheap). A little research on-line pointed me to Uni-Solar UniFlex flexible panels which are used in Marine and RV applications a lot. They are close to state of the art. I got a pair from what appeard to be a nice company in NH called Sundance Solar and another with some misplaced trepidation on account of the super low price from a place called (which had by far the best prices). It turns out MrSolar is just fine and their prices are super low. These panels are really fantastic. My only fear is that if I am constantly moving them around I will eventually degrade with wires or scratch the surface. I stow them in a plastic bag to keep them from getting scratched, so that shouldn't be a problem. You can get state of the art rollable panels from Sundance Solar, but since it is easy to stow the flat Uni-Solar panels behind the driver seat, I don't see why you would need the rollable panels. They are lighter, however. For Edwin's system I may use the 11W Uni-Solar panels.


I used the Radio Shack DPDT Heavy-Duty Center-Off toggle switch Catalog ID 275-1533 which cost a hefty $3.49 but was ponderous enough to give authority to the system. You could use another one, but it had a nice solid feel and has good action. I used their 6x3x3 project box which cost more than the switch but was well worth it for that highschool electronics project feel.


To get that retro feel, I used a Dymo labeler to make the magic box switch labels.


Heat shrink tubing. That corrugated Split-Tubing stuff for bundling the panel wires. I think it was 1/2 inch. Everything else, I think, was supplied with the solar panels (connectors, fuses, etc.). I did salvage a fused male connector to take power via the 12V 'accessory' plug. I'm running a 1A fuse, and I may switch to a 750 ma fuse. The four fans shouldn't used more than 500 ma according to their ratings.

Linked Pages: