Using the battery cooling fan to cool the car and the HV battery

I had a thought today and if anyone has tried this please let me know. I made a custom PCB to control the battery fan, which has proven to be very useful.

Scangauge II mounting location and battery fan modification PCB | PriusChat

One thing I've noticed is that if the windows are open a little and the fan is on, it sucks the air from the outside into the car, through the fan, over the batteries and out the back of the car. Not only does it cool the car but it also cools the batteries as well.

I have four user programs to control the battery fan and one of those programs will run the fan during the day while the car is out in the heat. Right now I'm experimenting with running the fan every hour for 30 seconds for 8 hours. I have some heat sensors coming but I suspect that if the OAT is 95 degrees and the sun is out, running the fan for 30 seconds will help but 10 minutes later I'm pretty sure the temp inside the car would get back to "very hot."

Running the fan at full speed for eight hours would pretty much kill the battery. Running it at slower speeds would help but again I'm concerned about the battery health. So I had these two ideas that I'm going to try. But, instead of reinventing the wheel, someone let me know if they've tried this or have a better idea.

My first thought was to buy a battery, like a 9 Amp hour, SLA, 12V battery. I would have a quick disconnect connector on it and mount the battery in right, rear corner of the Prius with one of those rubber straps with an S hook. So removing the battery and taking it inside to charge it would be quick and painless.

My thought is that I can use my custom board to control the fan and automatically know if the additional battery is installed. If the additional battery is installed, the program could automatically double the time, speed or whatever I need to run the fan. If it doesn't see the extra battery, the program reverts back to the "power saving" program. I could also use the Prius to recharge the SLA battery or I had this thought too.

What about if I used the additional SLA battery and also install a 5W solar panel. When I'm not using the fan, the solar panel can recharge the SLA battery and/or the Prius 12V battery as well. This helps keep the battery cool but the interior is definitely kept cooler as well.

Do I sound crazy or is this something worth making?

 

What a revelation. The only way to cool the car below OAT is with air conditioning.

I agree with parking it in the shade, however, it's not always possible. The majority of time it's not possible.

So you think carrying around a white fabric car cover in your car is easier than using a 7 pound battery that you would take in at night to charge and put in you car in the morning?

Lets say I had to travel to three places during the day in the summer. With your idea, each time I stop I have to get out the car cover and cover my car. Each time I get back into the car I have to remove the cover. With the battery fan, I press and hold the button for four seconds and I'm done. I can't see how pushing a button is more work than covering and removing a car cover up to three times a day.

 

I know a solar panel won't run the fan directly. I was talking about intermittent operation and charging the battery inbetween. Or, at a slower speed.

I had an idea years ago to put automatic shades that would come down on the insides of all the windows. That would be great for so many reasons. I never got around to really trying it. New Jersey doesn't allow tinting for both the front and back windows. I don't want to use a car cover.

While the car cover would work, I'm lazy and like things that are automatic. I need to explore the battery fan idea more thoroughly, perhaps including something else like a shade.

I've used the battery fan cycling throughout the day for the past two days and when I got in the car at the end of the day the temperature of the battery was 2-3 degrees above ambient. Does anyone know how much the battery temperature would normally increase on a hot day if the windows are up and the sun is out?

This mod also had me thinking about the winter.

Scenario: 20 degrees F and 5am. Wouldn't running the fan at a slow speed drag warm air over the battery help with FE or is it pretty much negligible?

 

Can't I just try the hardest thing first?

My car didn't come with the tonneau cover but I'm buying one off of E-bay this weekend. For some reason I didn't think about the foldable shade in the front. Using the foldable shade, tinted windows, the tonneau cover (although that doesn't stop the UV rays from entering the car) and the fan on occasion, I should be good.

 

An original piece of crap!

I'm going to get the variable speed working with my board this weekend. That will allow me to do a lot more with the fan. I have a ton of more ideas. I'm going to make a board with 20-something outputs. I want to control everything with one button! Maybe I'll add an LCD screen too.

Now, where do I attach the wings to this thing......

 

Possibly. However, I'm sure the fans that are installed in the southern US run frequently. I'm not running the fan very frequently. (30 seconds, once an hour, for 8 hours a day). If I do decide to run it more, a used cooling fan can be had for $40 if it does fail.

I don't agree. If your car is in the sun, the interior temperature will always be higher than OAT. If you're pulling air through the RIGHT REAR window, you are pulling cooler air into the fan than what exists inside the car.

Fan possibly, battery, no. In fact, now way in hell this would negatively impact the traction battery. If you leave your windows closed in the sun, eventually everything in the car rises to the temperature of the car interior. Any air that is pulled from the outside will cool anything inside the car.

 

I thought about that too except I thought about using those small remote vehicle fans (the RPM's are extremely high) and running a pipe directly to the output side of the OEM fan. I haven't thrown away the idea completely but it's more complex than using the OEM fan. The major reason why I haven't thown away the idea completely is due to the current consumption of the OEM fan. Using a smaller motor can save lots of power.

 

This is the biggest reason to have a controller for the fan after the car is powered down. The fan will not operate and in once instance I saw my battery temperature rise more than 20 degrees after I shut the car off. So far it's been working well. I'm finding that somewhere around 3 minutes is enough to keep the battery temperature from rising higher than a few degrees, although we haven't seen the hottest part of the summer yet. I may adjust it as the summer progresses.

At work we have A/C units with fresh and closed air vents. I thought about doing that but one thing hinders me at this point. I'm not very good mechanically as my background is in electronics, so cutting holes in the car or finding a good way to mount an additional tube for the air is something I have apprehensions about. The reason why I thought this would be a great idea is that you can have OAT and IAT sensors. If the OAT is less than the IAT, the valve opens and uses air from the outside. If the reverse is true, the valve closes and uses the air inside the car. Then you can include calculations for wind speed and humidity as well, which will allow you to factor in a wind chill component.

My 10 year old daughter sits on the side where the vent is and she either complains about it being too cold or she complains about the noise from the fan. The latter I can rectify with the speed of the fan but the former is more difficult and why using the air outside the car would be beneficial. I do open the window to help force the air into the fan but if she is back there, trying to do that driving 70 MPH isn't going to happen.

I was thinking that cutting a hole (and using a filter) just behind the passenger right, rear door would be really useful. The hole would be parallel to the car so most of the air flow can be captured and it would kind of look like the machine gun port on a military jet, something like this:




Not only would you be able to use the cooler air (if that's the case), the air flow itself at highway speeds (I think) would cool the battery down even if it was 95 degrees. You would also save battery power because you wouldn't need to run the fan at higher speeds or at all. So perhaps doing some calculations with wind speed, humidity and temperature in the tube would allow the system to be 100% automatic. I can do all of the programming but that hole worries me.

 

Good info, thanks. It certainly helps and seems like an easier solution. It may be the best solution. The only problem is not much air will be forced into the tube because the hole is facing down and not forward, if I understand you correctly. I guess I could throw a pipe in there and angle it but I'm wondering if I'll get extra heat from the engine, since it's on the bottom of the car and not the side.