I've gotten this bug to replace the mechanical fan in my truck with an electrical fan. When my mechanical fan engages, it really sucks the power out of my engine and it becomes a real dog. Many who've done this to their Rangers have noticed more power available for moving the truck.
There are many designs out there covering the mechanical/physical aspect, but the controller idea is a bit lacking for wiring up a 2-speed fan (commonly found in the Taurus and Lincoln Mark-VIII). I think I know enough about circuits to come up with the general idea...but sizing the parts out, I'm lost. Since this is a critical piece of my truck, this needs to be robust.
Here is the design I came up with, followed by a description of sources and operation...and then my questions. I apologize for the bad quality of my schematic...
**broken link removed**
Starting with my battery (12v constant source), this goes into my first relay. First relay I want controlled by either a temp on/off switch or a signal tapped off of my air conditioner compressor that tells it to turn on/off. My temp switch looks like a sending unit, but normally has a high resistance up until 200 degrees, then resistance is lowered until it is cooled down to 185, which then resistance goes back up. This is one way the first relay's coil will be energized/de-energized. Alternatively, when I have my Air Conditioning (AC Request) on, I want the fan to come on in the high-speed configuration. If AC is off, then the coil is driven from an ignition switched 12v source so the fan does not keep running after shutting down the truck. The AC Request will also shut down when the truck is shut down.
My second relay simply controls high/low based on the state of the Air Conditioning system. If the compressor is off, then the relay goes to low speed state. If the compressor is on, then the relay goes to high speed state.
The motor sounds like it is pretty robust. On low speed I get the impression that it pulls about 15-20 amps. On high speed, I get the impression it is about 30-40 amps. It has been measured to pull up to 60 amps when on high and spooling up.
Now for my questions:
I've read that to prolong the life of relays, you are supposed to put a capacitor over the coil contacts. If this is true, how is this sized and what type do I use?
I've read that a free-wheeling dc fan motor becomes a generator when power is not applied. In order to prolong the life of the motor, diodes are put in series to keep power from going back through the system. However, if the fan is controlled through relays, when power is not being applied to the 12v+ wires, the relays have broken contact, so voltage cannot flow. If diodes are needed, how do I size them and what type?
When AC is turned on and fan starts from a stopped state and is trying to spool up, it pulls a lot of power. Could I add a capacitor between relay 2 and the diode to build up enough energy so that I don't need to purchase a 75amp relay and stay with a normal automotive 30/40 amp relay?
This is the third time to type this up and as I was typing, found an error and made an attempt to fix it...if something looks off...that may be why.
There are many designs out there covering the mechanical/physical aspect, but the controller idea is a bit lacking for wiring up a 2-speed fan (commonly found in the Taurus and Lincoln Mark-VIII). I think I know enough about circuits to come up with the general idea...but sizing the parts out, I'm lost. Since this is a critical piece of my truck, this needs to be robust.
Here is the design I came up with, followed by a description of sources and operation...and then my questions. I apologize for the bad quality of my schematic...
**broken link removed**
Starting with my battery (12v constant source), this goes into my first relay. First relay I want controlled by either a temp on/off switch or a signal tapped off of my air conditioner compressor that tells it to turn on/off. My temp switch looks like a sending unit, but normally has a high resistance up until 200 degrees, then resistance is lowered until it is cooled down to 185, which then resistance goes back up. This is one way the first relay's coil will be energized/de-energized. Alternatively, when I have my Air Conditioning (AC Request) on, I want the fan to come on in the high-speed configuration. If AC is off, then the coil is driven from an ignition switched 12v source so the fan does not keep running after shutting down the truck. The AC Request will also shut down when the truck is shut down.
My second relay simply controls high/low based on the state of the Air Conditioning system. If the compressor is off, then the relay goes to low speed state. If the compressor is on, then the relay goes to high speed state.
The motor sounds like it is pretty robust. On low speed I get the impression that it pulls about 15-20 amps. On high speed, I get the impression it is about 30-40 amps. It has been measured to pull up to 60 amps when on high and spooling up.
Now for my questions:
I've read that to prolong the life of relays, you are supposed to put a capacitor over the coil contacts. If this is true, how is this sized and what type do I use?
I've read that a free-wheeling dc fan motor becomes a generator when power is not applied. In order to prolong the life of the motor, diodes are put in series to keep power from going back through the system. However, if the fan is controlled through relays, when power is not being applied to the 12v+ wires, the relays have broken contact, so voltage cannot flow. If diodes are needed, how do I size them and what type?
When AC is turned on and fan starts from a stopped state and is trying to spool up, it pulls a lot of power. Could I add a capacitor between relay 2 and the diode to build up enough energy so that I don't need to purchase a 75amp relay and stay with a normal automotive 30/40 amp relay?
This is the third time to type this up and as I was typing, found an error and made an attempt to fix it...if something looks off...that may be why.
