MARK VIII and SPAL PWM wiring question

[68nate]

Hooking up my mark viii fan and spal controller with override switch/ 70 amp relay from Jabin at gmachinz. The relay is pretty self exlpanatory, but wondering about the power wire to the fan from the relay. Should this be spliced into the power wire from the controller to the fan? I'm assuming this is correct and the fan then grounds through the controller when running off the relay. Anyone used this setup? Thanks, Nate

[CamaroMan79]

What relay are you using? I have the a Mark VIII fan and SPAL controller and mine doesnt have a relay. Just the controller and wiring harness.

[68nate]

I bought the extra override relay and switch. One switch position, the fan runs off of the controller. In the other position, a 70 amp relay is energized running the fan at full speed and bypassing the controller.

[gmachinz]

Hey, Nate- the DPDT switch is wired so that with a +12v ignition input in auto position, the controller is on, conversely in "over-ride" position, the switch drops the signal to the Spal controller, effectively killing it and triggers the switch side of the 70-amp relay (pin#86) to run the fan @ 100% fan speed. This way, you have the option of "dropping out" the controller whenever you want. Switching back to auto mode kills the relay and brings up the Spal controller again to run the cooling system. Hope this helps. -Jabin
Oh, and no splicing-just run the power wires in parallel.

[68nate]

Thanks Jabin. That's what i was thinking, was just curious if the power wire to the fan would backfeed the controller in any way while running off the relay. I'm assuming the power wire from the controller to the fan is on a relay in the controller, so it will be open circuit when in bypass mode. Fan grounds through the controller in both modes, correct? Crimp both fan B+ wires to the factory Mark VIII connector B+ wire, correct? What size fuse on the controller and relay, 40 Amp on each? Thanks Again!

[shep]

I think what Gmachinz was try to say is, you want to connect the power lead for the fan to the common post on the relay (pin 30). Run the controller to the normally closed post (pin 87a) and power from the battery to the normally open post(pin 87). Connect your switch to activate the relay (power to pin 85, ground to pin 86 or the other way around it doesn't matter). When the relay is activated power from the battery runs the fan, completely disconnecting the controller. The above pin numbers assume standard Bosch numbering scheme. You can switch either the ground or the power to activate the relay. I do not know how big the fuse should be I am not sure 40 is large enough, those fans draw a lot of current when they start. Here is a link on the inner workings of a relay http://www.6066gmcguy.org/BoschRelay.htm

[Karch]

I tested the Taurus fan at 87 amps on startup.

[gmachinz]

The in-rush only lasts for a few milli-seconds and the 70 amp relays I use can handle it. For normal operation, this is the reason for a pwm controller-otherwise using a relay alone and nothing else would require one to solder a resistor inline to help reduce the inrush if you were to wire the fan to constantly kick on and off at 100% like you would should you use a temp. sensor for activation at a specific temp. The high inrush would surely blow a fuse but not a quality HD relay.