Mod HVAC fans to run on solar power while car is parked?

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Throckmorton

Throckmorton

Lifer
Aug 23, 2007
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It's in the 100s in Texas and I've been thinking of ways to keep the interior cooler when parked... The heat damages your interior and I bet it takes its toll on the electronics too. Of course a windshield shade helps but not that much. I believe the Prius has solar panels that power the HVAC fans when the car is off to reduce the interior temperature. Why not mod other cars to do the same thing? I think all you would need is a 12v solar panel and a switch, or a relay that automatically switches over when the fans lose vehicle power. You could also add a thermostat so it only turns on above a certain temperature
 
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LTC8K6

LTC8K6

Lifer
Mar 10, 2004
28,520
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I think the Prius has a separate fan for that as an option.

The HVAC blower likely pulls too much current.
 
phucheneh

phucheneh

Diamond Member
Jun 30, 2012
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You need a battery to store the power from the solar cells. And then it would need to be its own isolated system to avoid a) discharging your car battery and b) making your solar cells worthless by charging your solar battery with the alternator.

Then there's the fact that you would need to run the blower on its maximum speed, unless you want to build a little module to use PWM to slow the fan down (as opposed to using resistor to burn off 'extra' voltage as heat).

And there's really no way to make the fan automatically switch on, unless you literally want to wire it to where it runs any time a) the fan is command off or b) when the ignition is switched off. I wouldn't recommend either, but I guess if you properly isolate the system, option B doesn't really matter. Option A involving zombie-fan wouldn't be preferable.

So, I guess you'd want to have five pin relay, with pin 87 (normally closed) as your output to the fan, and pin 87a (normally open) at an output to nothing. You need five pin rather than four so that you can use the relay to turn the system off, as it's not very easy to turn something on with no power.

Wire your relay to your solar cell circuit, which should probably be somewhere in the 6-10 volt range so that you can run the fan at a sustained moderate speed. Say your fan has four settings, I'm guessing you would want to mimic the second setting, at most. You can backprobe the plug to the blower motor and see what voltage it gets at that setting. Even if it's PWM instead of resistor controlled, you'll still see an average on a good DMM that tells you what the duty cycle is (e.g. 12v system at 75% duty cycle is 9v).

Wire that circuit in parallel with the main power feed for the blower motor. Put a diode in it to avoid your 12v system from backfeeding it and blowing up your batteries if the relay fails to hold the circuit open. The solar cells will continue to charge their own batteries as you drive.
 
Throckmorton

Throckmorton

Lifer
Aug 23, 2007
16,829
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phucheneh said:
You need a battery to store the power from the solar cells. And then it would need to be its own isolated system to avoid a) discharging your car battery and b) making your solar cells worthless by charging your solar battery with the alternator.

Then there's the fact that you would need to run the blower on its maximum speed, unless you want to build a little module to use PWM to slow the fan down (as opposed to using resistor to burn off 'extra' voltage as heat).

And there's really no way to make the fan automatically switch on, unless you literally want to wire it to where it runs any time a) the fan is command off or b) when the ignition is switched off. I wouldn't recommend either, but I guess if you properly isolate the system, option B doesn't really matter. Option A involving zombie-fan wouldn't be preferable.

So, I guess you'd want to have five pin relay, with pin 87 (normally closed) as your output to the fan, and pin 87a (normally open) at an output to nothing. You need five pin rather than four so that you can use the relay to turn the system off, as it's not very easy to turn something on with no power.

Wire your relay to your solar cell circuit, which should probably be somewhere in the 6-10 volt range so that you can run the fan at a sustained moderate speed. Say your fan has four settings, I'm guessing you would want to mimic the second setting, at most. You can backprobe the plug to the blower motor and see what voltage it gets at that setting. Even if it's PWM instead of resistor controlled, you'll still see an average on a good DMM that tells you what the duty cycle is (e.g. 12v system at 75% duty cycle is 9v).

Wire that circuit in parallel with the main power feed for the blower motor. Put a diode in it to avoid your 12v system from backfeeding it and blowing up your batteries if the relay fails to hold the circuit open. The solar cells will continue to charge their own batteries as you drive.
Click to expand...

You're making this too complicated! Are you an engineer by any chance? The fan itself has 2 leads to power it so you can wire directly to it. The simplest method would be a double throw switch to switch between vehicle power and solar power. You don't need a battery-- All you need is airflow while the sun is shining, which is what heats up a car to 150 degrees. If it's overcast or shaded, the fan is unnecessary because the car will only heat up to ambient temperature. Think of it as self-regulating
 
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Throckmorton

Throckmorton

Lifer
Aug 23, 2007
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LTC8K6 said:
I think the Prius has a separate fan for that as an option.

The HVAC blower likely pulls too much current.
Click to expand...

I think even an HVAC fan running at drastically reduced speed would have an effect on the temperature of a car. Heck, even cracking a window helps a lot. But you can't do that because of rain, vandals, thieves, etc.
 
phucheneh

phucheneh

Diamond Member
Jun 30, 2012
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Shit no I'm not an engineer. I don't design things, I make things work.

;P

I have pretty much no knowledge when it comes to solar power. But it seems awfully wasteful to have no way to store energy. It may kind of work without a battery, but with one, it will work a whole hell of a lot better.

I really listed nothing that's not needed. You can skimp on the $7 worth of relay and diode, and also try and rig up enough panels to keep your blower motor spinning at high speed with no batteries. But I think it's going to be mighty wasteful to try and go super-simple and end up with a system that does nothing.

Also, you need to rig a way for your recirc door to default to open, or else your system will, again, do nothing.

Just sayin'.
 
LTC8K6

LTC8K6

Lifer
Mar 10, 2004
28,520
1,575
126
Seems like it's a lot cheaper and easier to go with a way to block the sun, like a sunshade for the windshield, and ventshades so you can crack the windows open without fear of rain.
 
SparkyJJO

SparkyJJO

Lifer
May 16, 2002
13,357
7
81
I just have window visors on my truck and leave the windows cracked a half inch underneath. No rain concerns and no real security concern either - who wants to break into a 11 year old rusty SUV with nothing in it anyway?
 
jlee

jlee

Lifer
Sep 12, 2001
48,518
223
106
Throckmorton said:
It's in the 100s in Texas and I've been thinking of ways to keep the interior cooler when parked... The heat damages your interior and I bet it takes its toll on the electronics too. Of course a windshield shade helps but not that much. I believe the Prius has solar panels that power the HVAC fans when the car is off to reduce the interior temperature. Why not mod other cars to do the same thing? I think all you would need is a 12v solar panel and a switch, or a relay that automatically switches over when the fans lose vehicle power. You could also add a thermostat so it only turns on above a certain temperature
Click to expand...

Actually it helps a lot.
 
Throckmorton

Throckmorton

Lifer
Aug 23, 2007
16,829
3
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I can't do that because I have frameless windows on my Mustang, same with most coupes. Plus those shades look trashy. The only way to block the sun it's with a windshield shade but plenty of heat still gets absorbed by the cabin especially if your car is dark
 
N

nedfunnell

Senior member
Nov 14, 2009
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I'm with Throckmorton. Find the leads for the blower, wire it to a 12v-nominal solar panel through a DPDT switch that isolates the solar from the vehicle and vice versa. Self regulating: sun=vent. No sun=no vent. When you get out, throw the recirc switch to vent, flip the switch, and enjoy. You'll want to measure the power draw of the fan to properly size your solar panel. Hopefully you can get something small enough to just lay on the dash.

Cons: Fan will wear out quicker, you may need an obnoxiously large solar panel. Maybe a few of these? http://www.harborfreight.com/15-watt-solar-battery-charger-68692.html
 
N

natto fire

Diamond Member
Jan 4, 2000
7,117
10
76
I think you are either overestimating how much power can be developed by a compact solar panel, or underestimating how much power is needed to run the blower. I wish I still had one lying around to show measure, but I know they are usually behind dedicated 30amp fuses which is mainly for the startup current. Still, guessing that it only uses 30% of that while running, you are looking at 108 watts. Not to mention you will have to grossly oversize your panels to get that startup current to even get the motor spinning.

A battery or even a capacitor is the most feasible way to do it, unless you feel like covering your entire roof with solar panels, which I think vandals and thieves might find appealing as well.

Another thing to consider is that even though the blower can pull in fresh air, it doesn't really have an easy job exhausting the hot air from a sealed car, and most of the "leaky" spots of a car are lower, where hot air tends to float away from, or rather cold air sinks and displaces the hot air.

As already pointed out, the best way to keep the car "cool" is to avoid heating it up in the first place, block out the sun however you want, but just doing that will help out and be less complex than what you are proposing.
 
jlee

jlee

Lifer
Sep 12, 2001
48,518
223
106
Throckmorton said:
I can't do that because I have frameless windows on my Mustang, same with most coupes. Plus those shades look trashy. The only way to block the sun it's with a windshield shade but plenty of heat still gets absorbed by the cabin especially if your car is dark
Click to expand...

I drive a black on black car with leather in Phoenix. Windshield shades help a lot. :p

I have a reflective bubble one. If you think my CTS-V looks "trashy" with shades...well, IDGAF. :)
 
Throckmorton

Throckmorton

Lifer
Aug 23, 2007
16,829
3
0
jlee said:
I drive a black on black car with leather in Phoenix. Windshield shades help a lot. :p

I have a reflective bubble one. If you think my CTS-V looks "trashy" with shades...well, IDGAF. :)
Click to expand...

I'm talking about the eyelid looking things that go on top of the windows. If you put those on your CTS-V shame on you

I have a silver bubble shade too and of course it helps but if I shut down the car and sit in it with the shade in place I can feel it heat up within seconds, and this is a bright yellow car with limo tint!
 
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Throckmorton

Throckmorton

Lifer
Aug 23, 2007
16,829
3
0
mmntech said:
I had one of those. It's garbage. Couldn't even get it to fit in the window properly. Even then, it never moved enough air to be effective.

I just use a sunshade and crack my sunroof open to let hot air escape.
Click to expand...

What if it rains?
 
Throckmorton

Throckmorton

Lifer
Aug 23, 2007
16,829
3
0
Gillbot said:
Cane here to post this. There are other designs out there as well.

Otherwise you could simply get a solar panel and a 12v fan and do the same thing yourself.
Click to expand...

Those aren't an option with frameless windows or really any coupe that doesn't have rectangular windows and they seem pretty crappy anyway
 
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