Flex fan

[fleming442]

I'm running v6 Grand Am fans- $10.

 

[olds307 and 403]

Its a little more work, but If I install a controller, unless its some kind of PWM deal, I have it "control" cheap, replaceable relays. I also try to soft start the fans on lower voltage, then switch them to high speed only after they are moving. The greatly reduces the amp draw, contact sparking, and the load on the system.
Dual Fans may draw only 15 amps running, but at start up they can draw 50+ amps as they get up to speed. Soft starting 2 fans in series, then switching them to parallel reduces the amp spikes.

The PWM controllers are the expensive ones but have very good reviews. Others have had relays go out on this one I have, it maybe the start up load overloads the 40 amp relay and poof.

 

[UNGN]

The PWM controllers are the expensive ones but have very good reviews. Others have had relays go out on this one I have, it maybe the start up load overloads the 40 amp relay and poof.

Start up totally spikes the amps on a DC electric motor. All DC motors have an RPM per volt they run at. If you double the Voltage, the RPM doubles. If a DC motor has a load that keeps it from running at its ideal RPM for the voltage provided, the further away from the ideal RPM it is, the more amps it grabs. A PWM controller can gradually increase voltage, so the difference ideal and actual RPM are closer, keeping the amps lower.

This is why when using only one thermal switch, I recommend running dual fans in series (both fans run at only about 6 volt speed and will usually spike at less than 10 amps at start and only use about 6 amps continuous). When the temp switch hits a set point, the fans switch to Parallel (12 Volts each) and the spike is much lower because the fans are already turning at 1/2 speed.

Starting 2 large fans at the same time @ 14 volt speed (from zero), takes a lot of amps.

 

[454GrandPrix]

That article is 17 years old so its a little dated and a little misleading.

Perhaps, though it does nicely answer the question of approximately how much additional power alternator drag requires to run an electric fan. I agree with you, though, that a thermal clutch fan when engaged would produce more drag than one which is below its thermal engagement point.

On the topic: when I first cobbled together my BBC Grand Prix, I installed a (single 15") Taurus junkyard fan. This kept my engine cool at all times, even though I only ran it on the LOW speed setting. Later, I decided I wanted more coverage in order to better pull ambient air through my transmission cooler (which is mounted on the opposite end of the radiator from the fan), so I removed the Taurus fan and replaced it with a dual 12" setup (wired in series) from a junkyard 300C. These are also dual speed fans, though I only run them in LOW speed as well. They also do a fine job of keeping my engine cool.

 

[bill cook]

I think 16" fits a factory shroud

Thank you !

 

[bill cook]

I think 16" fits a factory shroud

Thank you !

I think 16" fits a factory shroud

thanks !

 

[DJHull]

Start up totally spikes the amps on a DC electric motor. All DC motors have an RPM per volt they run at. If you double the Voltage, the RPM doubles. If a DC motor has a load that keeps it from running at its ideal RPM for the voltage provided, the further away from the ideal RPM it is, the more amps it grabs. A PWM controller can gradually increase voltage, so the difference ideal and actual RPM are closer, keeping the amps lower.

This is why when using only one thermal switch, I recommend running dual fans in series (both fans run at only about 6 volt speed and will usually spike at less than 10 amps at start and only use about 6 amps continuous). When the temp switch hits a set point, the fans switch to Parallel (12 Volts each) and the spike is much lower because the fans are already turning at 1/2 speed.

Starting 2 large fans at the same time @ 14 volt speed (from zero), takes a lot of amps.

Great info. I am not up to speed on electric fans. Just getting to that part of the project I need to make a decision. Thank you!