Solar powered cooling fan mod

Discussion in 'Honda Hybrids' started by msantos, Jun 14, 2009.

  1. msantos

    msantos Eco Accelerometrist

    Yes. I gave in and I've ordered the parts. :(

    Now, some of you may be thinking what's the point of all this?

    Before answering these questions, I will briefly direct you attention to this mod I had performed on my HCH-II's:

    Guide: Installing a solar panel on the HCH-II (step-by-step)

    Anyway, I recently added a second panel to the one I installed before, therefore bumping the maximum generated power to almost 5 watts. But because the solar panels are inside the car the total power output is measurably lower and according to my measurements, this combo will output just a little over 3 watts under direct sun light.

    As you recall, the original purpose of this solar panel mod was to keep the 12V battery healthy during the winter months. During the summer the 12V battery does much better and does not need as much tendering at all.

    So that is why after seeing and reading how well the solar cooling option works on the 2010 Prius, I thought of getting the surplus solar power to do something else instead: To also cool the cabin while the car is parked in the sun.

    To achieve this while still allowing a trickle charge to go to the 12V battery I literally banked on a compromise. I chose to go with an 80 mm cooling fan instead of 120 mm simply because of its power requirements (0.08 amps @ 12Volts) and also because I did not want the ducting to be larger than the space I am afforded in the HCH-II's trunk area.

    You see, the HCH-II does have space behind the trunk liner that is under utilized and my goal is to route some custom/lightweight tubing through there.
    The final goal of this thinking is that I do not have to lose even a square inch of the trunk space. It must also look clean and be effective enough and that means that I do not want the trunk to heat up either. ;)

    So these are the "special" parts I just ordered (enough for two cars):
    * Air Flow (CFM): 20.72
    * Bearing: Hydro Dynamic Bearing
    * Cable Length (mm): 500
    * Connector: 3 Pin Molex
    * Current (A): 0.08
    * Dimensions (mm): 80 x 80 x 25
    * Fan Speed (RPM): 1600
    * Noise Level (dBA): 18
    * Safety Approvals: CE, RoHS Compliant
    * Static Pressure (mmAq): 1.05
    * Voltage (V): 12
    * Warranty (years): 5
    * Weight (G): 55

    and this...

    Rocker button SPECS:
    Illumination Colour: Blue
    Rating: 16A 12V/DC (Working for 9-14VDC)
    Type: 3 Pins with LED
    Contact Resistance: 50 milliohm Max
    Insulation Resistance:100M Ohms minimum
    Operating foree: 2+/-1.0N
    Switching life: 10000 cycles


    Now, that 0.08A max current is what I was looking for because that will guarantee that the fan will run even when the sun is not shining directly on the solar panels. The switch is only there to ensure the fan can be turned OFF and ON at will. We will need that since we want the fan to be OFF when heating the cabin in the winter or cooling it in the summer.

    For now I am thinking of installing the switch right there on the rear dash tray (just behind the high mounted stop light). The fan will be installed on the underside of the tray and will be drawing the cabin air into the trunk though an 80mm hole that I will cut on the tray. The air pulled into the trunk will be routed around and behind the trunk liner and the hot air will be released near the rear vent vane right under the rear bumper.

    Anyway, what can we expect from this type of a mod? Is it reasonable to expect the car to remain cooler when parked all day in the sun?

    Cooler yes. Cool, no.

    The key is to leave the front dash vents in the open position and turn on the button. That is all there is to it. Heck, it can even work while the car is being driven... and while the fan can only push 20CFM (Cubic Feet per Minute) of air out of the passenger cabin, that is better than nothing... and even sweeter because it is as green and clean as the sun light we get. ;)

    Anyway, as soon as I receive the parts I will post some pics and the results.


  2. drimportracing

    drimportracing Pizza driver: 61,000+ deliveries


    And the cost of this mod? :D - Dale
  3. msantos

    msantos Eco Accelerometrist

    Hi Dale;

    Solar panels 2x2.4 Watts units = $10.00 each + tax (already have these on)
    Ultra quiet 80 mm fan = $3.95 + $4 shipping
    Rocker button = $2.00 + free shipping

    labor ? Well, that's the fun part ;)

  4. bomber991

    bomber991 Well-Known Member

    Good idea, but you know those windshield sun blockers you can put in your car when parked? I saw one somewhere on the internet where you basically put it over the top of your car so that it covers all of the windows. It has weights in the cloth to keep it from blowing away, and you just close one of the weights in the door so that it can't be stolen. I think that would work a lot better than one 80mm fan too.

    I saw it on the truth about, but I don't remember the name of the product at all.
  5. msantos

    msantos Eco Accelerometrist

    Hi Justin;

    Yes, a cover of that sort would work much better at keeping the interior cooler. No doubt about it. However, such a thing would block the solar panels and those have an original purpose/mission I do not want to defeat.

    Also, the 80 mm fan is pretty conservative but not necessarily the biggest and highest CFM I can deal with. In fact, my earlier calculations proved that I have enough solar power to go all the way up to 120 mm and ~50 CFM. But like I said, I'm trying to ensure some charge still makes it to the battery. ;)

  6. xcel

    xcel PZEV, there's nothing like it :) Staff Member

    Hi Manuel:

    ___You are saving $1,800 vs. the Prius-III's system ;)

    ___Good Luck

  7. msantos

    msantos Eco Accelerometrist

    Hi Wayne;

    IMHO, the solar option on the 2010 Prius is too sweet for words and depending on how much air it is actually able to push through the cabin, this little mod can only hope to do 20 CFM for now.

    Sadly, the solar option on the Prius can only work while the car is powered off and that is a bummer. Can you imagine if it worked well enough to reduce AC use even further while the car is in motion?

  8. psyshack

    psyshack He who posts articles

    Hope it works out well. :)
  9. uabcar

    uabcar Well-Known Member

    I agree - the PIII solar vent setup sounds awesome. I'd also LOVE to have the electric pre-cool functionality (on my non-hybrid 08 civic).

    I've considered doing exactly this same setup. I can't wait to hear how it works for you. I don't need the extra battery charge so if I do it, I'll likely get the bigger fan(s) for more flow.

    Maybe I missed it, but where are you mounting the fans? I assume the rear deck. Are you just venting the exhaust into the trunk area? Sounds like you're using the factory HVAC vent system for the fresh air input end of the system.
  10. msantos

    msantos Eco Accelerometrist

    Yes, at first I thought of mounting in the rear deck but I have not excluded the possibility of mounting the fan just by the driver's side exhaust vent (under the rear bumper).

    It all depends on a series of factors to be determined by the final ducting since there are packaging and performance differences between pulling the air or simply pushing it through.

    The fresh air will enter via the HVAC ducting and the cabin air filter. In other words, fresher air enters through the front and stale hot air exits through the rear.
  11. bomber991

    bomber991 Well-Known Member

    Hmm I wonder if you'd get enough of a trickle charge if you used the solar panel as a grill block?

    Sorry I've never played with solar panels before so I don't know if they need direct light or if shaded light would work too.
  12. msantos

    msantos Eco Accelerometrist

    Anyhow, I am almost done with this little experiment and as you'll see I had a bit of time to ponder about my approach.

    I decided not to place a hole in the rear deck for several reasons:
    1. If I had created a 120 mm hole through the deck the metal structure right under it would be weakened. May not seem like that but this horizontal metal structure is an integral part of the body structure and carelessly cutting through it should be avoided.
    2. I would have needed some extreme ducting to channel the cabin air directly to the exit ports. Unless this ducting is smooth, wide and of limited length it will impact the air flow. Have a look at the following pictures to get an idea how difficult a task it would be to create lightweight ducting that would snake around the exiting hardware without consuming any trunk space.
    3. If you perform an air tightness test you'll see that all the cabin air exits through the vents ports on the rear of the car. With this fact in hand, then why not leverage the normal path of the airflow and keep it all simple?
    Here's a view of the IPU from the trunk. Notice I removed the trunk lining and much of the custom sound proofing insulation so that I could expose as many of the hard surfaces as possible.

    Next, have a look at the rear venting ports. These left and right vent ports are designed with the usual one-way vent vanes. Very usefull indeed, and it does not take much force to get them to swing open. This is very critical as you'll soon see . ;)

    Look on the lower right corner for the left vent

    Look on the lower right corner for the right vane... also used by the IPU exhaust. This is where I will instal the first batch of fans.

    And now meet the fans.

    These are no mere fans. No sir.

    These are rated for a maximum of 80mA each and they will spin with as little as 18mA. Each is rated for a little over 20 CFM and the pair combo will push at least 40 CFM.

    I measured 132mA at full power during my tests which means I can still install at total of four similar fans with the solar power I have available which would grant me 80 CFM of air pushing power.
    And here they are tied together.

    Next I decided to apply a bit of a crude gasket around the edge of the combo that will contact the vent assembly (just to keep noise and vibration low).

    With this last step complete, it is just a matter of mounting it against the vent assembly. As you can see, this arrangement with 80mm fans is an almost perfect fit. I simply used a bit of aluminum tape to get the binding air tight and resonably secure.

    And a test ensued not only to experience the fan assembly but also to try out the new switch.

    Does this approach work?

    So far, it appears to. It is simple, inexpensive and able to leverage the OEM air flow characteristics of the car. In the upcoming days I will be producing some temperature numbers to demonstrate this system's effectiveness.

    So if the fans are going to be hidden then how do I know they are working?

    That is why I got a switch with an LED pilot light. The light will be on as soon as there is enought power to get the fans moving. Not perfect, but functional and simple as well.

    Thoughts and counter-points?

    Please post them here and lets evolve this thing ;)


  13. psyshack

    psyshack He who posts articles

    So you did use the IPU side. So the hard duct for to IPU cooling just leads to the soft duct that could be described as the trunk liner.
  14. msantos

    msantos Eco Accelerometrist

    Hi Jeff;

    Yes, I did an air tightness test just to make sure I could identify and quantify the airflow and I noticed that almost nothing flows through the IPU enclosure (too much internal air resistance compared to the alternate flow paths).

    Also, it helps that there's a fair amount of distance between the fans and the IPU exhaust.

    The other airflow pathways are quite revealing and the rear deck is literally a sieve. Cabin air also flows around the rear seat cushion.
  15. msantos

    msantos Eco Accelerometrist

    Anyhow, I realized that I had a fair amount of solar power left over and last night I added a second pair of fans to the left rear outlet. This means that both rear outlets are going to be venting courtesy of a total of 4 fans for a total combined air flow exceeding 80 CFM. Will this be enough? Lets see.

    Today, I parked my car where it is going to be nailed by the afternoon sun and I am going to measure the temperatures with the setup turned OFF and ON just to see if it makes any difference.

    1. I have a switch on the dash that will turn on the power to the fans. Whatever leftover power is not taken by the fans will still trickle to the battery.<good>
    2. If I power off the fans, then all the solar power will go to the battery. <good in the winter>
    3. This morning, the fans were working as I was commuting. No joke. I actually had the climate control entirely off instead of having it venting on the lowest fan speed. The venting was being done by the solar fans. I just donlt know if all of them were actually moving, but I know some of them were (I used a diode to step the second set of fans). <Ok for now>
    4. If this setup works well then I will likely apply it to the upcoming 2010 Prius as I do not like the way the solar option on the Prius works. Heck, the solar option cannot be used while the car is moving and there are too many governance variables that limit its effectiveness. I am also doubtful it will perform adequately under a wider variety of scenarios... even though the 2010 Prius solar option can produce up to 60 Watts !!!! <my alternate reason to buy the base model>
    5. The 80 mm fans I used look and feel fragile and are certainly not made with the industrial robustness I would expect to see in an automotive application. Yes, they will spin easily with almost no current and at a mere 4.5V but still, with time I need to inspect them to make sure they still work. <not so good>
    I'll post some pics of the dash switch along with the solar panel arrangement and second fan set, soon. The "temperature" numbers will follow as mother nature allows.

  16. msantos

    msantos Eco Accelerometrist

    And here is the preliminary and crude schematic for this implementation:


    Some comments:
    • The four fans are shown (two on the left rear of the car and two on the right rear)
    • The right rear fans start after the left set of fans and if there's enough power. The D1 diode provides this effect.
    • The D2 diode ensures that only solar power will power the fans.
    • The XMM1 is a current measurement device and can be had on eBay for $20 or so. It does suck power too so beware of that as every mA counts.
    • You can use less fans and fans with more CFM. In the end it is a game of balance.
    • The fuse should be rated at 1A or less. 0.5 A would be ideal.

  17. msantos

    msantos Eco Accelerometrist

    A few more pics that were to accompany the previous posts along with some preliminary performance results:

    This is the left mounted pair of fans. With this addition, the car now has four fans pushing a little over 80 CFM of air.

    So what does it take to power all four fans pushing this hot air out of the car? Well, this is a start:

    These 2.4W units are held down by double sided adhesive foam pads and industrial Velcro (for easy panel removal but also secure and strong fastening):

    So, how does it all work?

    Today I had a good run at it. While there was a northern wind that kept the ambient temps in the low 20's C ( 72F), the sun managed to warm-up the inside of the car a fair amount placing the inside temps in the 46-48C (118F) by noon.
    Once it reached this temp at roughly 12:30, I flipped the switch to ON and the fans were kicked into action. Despite these being some of the quietest fans I could buy, you could still hear a little hum coming from the back of the car.
    Two hours later I return to the car and read the cabin temperature at 38C (100F). Ambient temps were orbiting the 24C zone (76F).

    Did it work?

    Kind of. At 38C the car was still hotter than the ambient temp but definitely not the furnace I would expect to find on a regular basis. Perhaps the results would have been a bit better if I had left the fans ON in the morning. In any case, I'll have a chance to try it a few more times over the upcoming days to get a better feeling for it.

    I can safely say that using a car shade in combination with this mod will be my regular hot summer day routine from here on.

    What's next?

    I am thinking of buying a higher wattage solar panel since this solar panel mod has evolved well beyond the simple charging of the battery. This future enhancement will allow me to install higher current/CFM fans to make it even more effective and still have enough trickle charge left for the battery.


  18. abcdpeterson

    abcdpeterson Well-Known Member

    at that price for a panel it would be fun to just play with. where did you pick it up?
  19. msantos

    msantos Eco Accelerometrist

    Got a box of these at Walmart a while back when they were at clearance prices $39.95->$10 ;)
  20. Right Lane Cruiser

    Right Lane Cruiser Penguin of Notagascar

    That's a mighty impressive setup, Manuel!! I look forward to seeing your results once you've had a chance to simply leave the fans on from the time you park the car. :)

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