$0D Fan code running, works great except for one thing...

My Flex-A-Lite fans have been running off a crappy mechanical switch for years and it finally crapped out and made the fans stick on. So, this forced me to go on and do the $0D fan code. I bought 2 high current/high voltage solid state relays. I use these a lot at work but they are usually AC type. I am not real sure about how weather proof they are so I am mounting them inside the truck. They are switching ground to one side of the fan. The 12 volt side of the fan is tied straight to the battery. This way I am not running a big 12 volt power wire into the cab of the truck. Everything seems to work great except the PWM output seems to not turn all the way off. I noticed fan A staying slightly on and my test LED tied to the PCM output is just barley lighting up. If I take the LED out of the circuit the fan speeds up but does not fully turn on until the PWM output is fully on. Its like that output is a little leaky. I am wondering if I need a resistor across the output to completely turn the relay off. If I can not get it to work right then I can run both fans off of the B output. I made a little video showing how it works, I did not notice the problem till after I made the video, but if you look close you can see the LED on the right just barley on after the output shuts off.http://www.youtube.com/watch?v=RaFM2...ature=youtu.be

I have only ran the single fan version on a vehicle, so I can't comment on the dual fan version about any sort of PCM output issue. A pull up resistor might do the trick.

About the power wire and controlling ground versus positive switching, there is the same amount of current on the ground as there is on the positive, so keep that in mind.

I would have also used Automotive Bosch style relays, and mounted them closer to the battery and fans.

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Originally Posted by Six_Shooter

I have only ran the single fan version on a vehicle, so I can't comment on the dual fan version about any sort of PCM output issue. A pull up resistor might do the trick.

About the power wire and controlling ground versus positive switching, there is the same amount of current on the ground as there is on the positive, so keep that in mind.

I would have also used Automotive Bosch style relays, and mounted them closer to the battery and fans.

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So would that be a resistor from the the PCM output to ground?

That would be a "pull down" resistor, a "pull up" resistor has the other end attached to a positive voltage source. A "pull down" resistor would be used with a positive triggered circuit, a "pull up" resistor is used with a negatove triggered circuit.

What these do, is force the circuit to be at the the "rest state potential". I other words, it causes a positive triggered circuit to be pulled down to ground, when the circuit is not triggered to be on. The eliminates any "floating" of the circuit that can happen.

Quote:

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Originally Posted by Six_Shooter

That would be a "pull down" resistor, a "pull up" resistor has the other end attached to a positive voltage source. A "pull down" resistor would be used with a positive triggered circuit, a "pull up" resistor is used with a negatove triggered circuit.

What these do, is force the circuit to be at the the "rest state potential". I other words, it causes a positive triggered circuit to be pulled down to ground, when the circuit is not triggered to be on. The eliminates any "floating" of the circuit that can happen.

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Got it thanks, all those years of electronics school have went right out the window...its been a while.

Pull up resistor worked great, the output shuts completly off now, along with the fan.

Cool. :)