File 455 of 468
Prev | Next

fancircuit.jpg | Hits: 8399 | Posted on: 10/21/07 | View original size (32.62 KB)

2-Speed Cooling Fan Circuit only allows the fans to run when the engine is running (because it's powered by the fuel pump relay), but gives the driver control (OFF) for water crossings or (ON) in case the temperature switches fail.

In this configuration, if the HI relay contacts fail, the fan will still run at a lower speed. This circuit is NOT suited to a 2-speed motor because both HI & LO are powered.

For a single-speed system: delete the hi relay, 210 switch, & resistor. For a single-fan system: derate the main 40A fuse to 20A.

. .

For carb, splice the 3A fuse into any RUN circuit, like the ignition module or voltage regulator.

See also:

. .

https://www.fleet.ford.com/truckbbas/non-html/1997/c37_39_p.pdf

This diagram was created from this set of symbols using MSPaint:


____________________________________________________________________
It's a myth that people convince themselves of because they don't understand simple physics, and because they need to feel good about spending all that time & money re-engineering their vehicles. But it is a BASIC concept that every time energy is converted from one form to another, some of it is lost (usually as heat). It's why perpetual motion machines are impossible. The typical loss rate is around 50% (yes, half). So converting from gasoline's chemical bond energy into air pressure inside the cylinders loses a bunch of heat. Converting from air pressure to linear motion of the piston loses a little. Linear piston to rotating crankshaft loses a little. Crankshaft to belt loses a little. Here's where the choice happens... Normally, belt energy to fan (through the clutch) loses very little energy. But converting from the belt to the alternator rotor, from mechanical to magnetic, from magnetic to electric, pushing that electricity through wires/connectors/switches/relays/etc. (each with resistance), from electric back to magnetic inside the motor, and then from magnetic back to mechanical to drive the fan blade wastes a LOT more to move the exact same amount of air.

A truck pulling a trailer that weighs more than the truck has to burn more gas than a truck alone. An engine spinning a disconnected or non-functional alternator doesn't work as hard as one spinning a loaded alternator. People commonly don't understand the load of generating electricity on a car, even though it's essentially the same as generating electricity with a dam or nuclear reactor. Energy is NOT FREE. If the alternator/generator could just spin regardless of the electrical load, you wouldn't need a dam dumping water or an engine burning gas to keep it spinning - you could just spin it once, and then get 1.21 GW of electricity out of it forever. Try wrapping a pull-rope around an alternator in a bench vise, and seeing how long it'll spin. Then connect a weak (discharged) 12V battery from the output stud to the case, and try again.

So how much load is an e-fan? Well, it depends on the motor & blades, and the speed of the air passing through when the fan motor is off. If the air is already flowing at 60mph, then the electric fan motor doesn't have to draw much electricity to spin the blades at ~30mph. BUT THE CLUTCH FAN doesn't take any torque off the belt, either, under those conditions. However - if you measure current draw to start the fan motor when the air is stopped (truck not moving), it can peak higher than 100A, and reach a steady-state of 30~65A (depending on motor & blade design). You might not think that's much for a 95A or 130A alternator, but the only thing on the truck that draws more is the starter (~140A for normal cranking) or winch (~400A for a 12K winch at full stall). And the rest of the truck is already using ~60~90A for fuel pump, ignition system, EEC, lights, A/C, radio...

Then why do modern vehicles use efans if they're so wasteful? Because they're capable of VERY-precise control by the PCM, if it's equipped with MANY sensors, and a variable-speed (PWM) fan controller, and has been carefully programmed to operate the fan ONLY at the necessary speed/load. Under those VERY-PRECISE conditions, the overall performance of the efan can become slightly more-efficient (in the LONG run) than a self-regulated thermal fan clutch. BUT JUST BARELY. When you have 1 or 2 thermal switches and a dash switch for an efan, it's NOWHERE NEAR that efficient, and wastes fuel on top of the extreme cost of swapping from the (inexpensive reliable) thermal clutch to the (expensive fragile critical) efan. And vehicles designed with efans can be programmed with FailSafe Cooling strategy (FSC) so that the engine isn't damaged when the efan fails (and they DO - I've driven a few in FSC mode a few times). What you cook up in the back yard is NOT failsafe. If the fan gives out for any reason, you're probably gonna destroy the engine before you realize there's a problem. Thermal clutches tend to give more warning when they're going out.