Keeping interior cool though out the day , roof vent

[Mobilesport]

Ok , I have a homemade roof vent $11menards vent with a 8" radiator fan in it , I have it wired to power on from my remote control , problem is I never turn my fan on because it draws like 8amps  puts out 1700 CFM.
I just use the fan to clear the air quickly if needed while cooking.
My thought was that with just my roof vented it would cool off the interior without a fan , this doesn't seem to be true. 
So I started thinking that I have a small dual pc fan that draws about 1 amp  , it puts out about 120 cfm.
So my question is if I make a mount to be able to hold my pc fan up under my roof vent will that 120 cfm help cool my interior or do I need a fan with more cfm , I noticed the fantastic fans put out about 1000 cfm but I don't want to use that much battery.
I could also go with one of those clip on fans if I could find one with a reasonable amp draw

 

[GotSmart]

I sometimes leave my FF on for days.  In the high summer it is nice to get in and find it is a little cooler than the outside.  But I have an excess of solar and battery.

 

[SternWake]

Pwm motor speed controller. Tame the radiator fan.

Or silverstone fm181 or ap182

 

[Mobilesport]

Pwm motor speed controller.  Tame the  radiator fan.

Or silverstone fm181 or ap182

I got it in my head from Electronics school makng me think about voltage divider circuits,, , lets say we built a 12 volt dc circuit powering a fan motor and then added a pontentiohmeter and divided the voltage in half , now 6 volts is powering the fan and the other 6 volts is dropped over the pot , the pot is giving off heat/power and so your not really saving electricity because even though you took power away from the fan to slow it down the power is  just lost as wasted energy in the form of heat/power when it disipates off of the pot.
Does the PWM work in a different fashion to were it doesn't lose the power when slowing down the fan?
Where does the power go?
Thanks

 ,,

 

[rvpopeye]

The Fantastic uses 3 amps on HIGH , much less on LOW. I know it's probably too late now but just FYI.

 

[Trebor English]

PWM is pulse width modulation. The power is turned on and off rapidly varying the on / off rario.  If the power is on 50% of the time the fan will be slow or the light dim. There can be less wasted power.

 

[SternWake]

Potentiometers rarely can handle more than 2 watts. A PWM motor speed controller is different. Lowering speed significantly lowers amp draw, at least on the brushless motors I have used it on.

YOu want a speed controller with 21Khz or higher frequency or you might hear the motor's windings Whine.

https://www.amazon.com/DROK-Control...99&sr=8-8&keywords=PWM+motor+speed+controller

I use a 115vac router speed controller on 20 inch box fans in my workshop. The newer fan whines at reduced speeds, and the older one works best when the fan is set on highest speed then lowered via the RSC. The amp draw is not much reduced at lesser speeds on this AC fan.

I am not sure how a radiator fan's amp draw will respond to lesser speeds Via PWM, but I'd try it before trying to retrofit another fan in place like the Silverstone ap182

My Silverstone Ap182 did not like battery charging voltages on highest speeds, the hub got stinky hot. That was likely a contributing factor to its failure, but salt air corrosion most likely was the main contributing factor.
I replaced it with a FM181 whose airflow and amp draw is significantly less. Only 0.3 amps on highest speed and a claimed 165CFM. Very quiet though. I can leave it on highest speed overnight 14 inches from my head in a conversion van window shroud.

If you try the PWM motor speed controller on your 7" radiator fan I'd love to know the results.