Thread: Electric fan control

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Look at it this way Roger---we're talking about the fan control--we're varying the amount of air flow thru the radiator --its the only variable that we have any control over--the thermostat will have the coolant coming out of the engine at 195 no matter which of the 3 holes you put your sensors in or even if you don't use any. You need to run the fan only if there isn't enough airflow thru the radiator to cool the liquid down enough to keep the engine under control of the thermostat--the key element here is the temp of the fluid leaving the radiator---so put the sensor at the outlet of the radiator and thru trial and error determine what the temp needs to be---set the controls so the fan comes on as the temp gets up to that temp and shuts off as it falls below that temp

If you care to really get a feel for what is best for power / economy, check the temps in and out of the raiator to find out how much the radiator will drop the temp and then adjust the sensors/thermostats, etc around that data.

I agree, but if you measure your temp at the exit of the radiator and it is too hot then that water is now going to the engine to pick up heat, so when it gets back to the inlet it's now even hotter. By the time your sensor sees cooler temps it will back off on cooling, and start the roller coaster again. If you measure your temp at the inlet to the radiator you start your fan quicker, add cooling to that hot water and minimize the added heat above set point. Feed forward control eliminates most of the trial and error of a feed back control system. Now if you want to really get fancy use both sensors, one on the inlet to the radiator and one at the outlet in a feed forward control with feed back trim. Anticipate the cooling needed and start your fan, then measure how it's doing on the outlet and adjust the speed up or down based on your feed back sensor. Only really effective with a variable speed fan though.... Throw in a little integral action on the feed back loop and you'll run cool as a cucumber.

I've never run an automatic controller, personally. I just have a toggle switch to turn the SPAL fan on when I see the gauge start to get over 180 at a light or something like entering a show. Since I constantly watch all my gauges I feel I have better control over it by doing it manually. Might be old fashioned, but it just works for me.

Don

I agree with Itoldyouso.........I had a controller on a fan and also had an over ride toggle switch under the dash. Good thing I did too....one day going to a show the controller went away. I just hit the toggle and the fan was on. I tore out the controller the next day and just left the toggle in. Like everyone else in here, you watch the gauges more than the road anyway.
The controllers are a good thing but in my mind they still have to work from an electric source and if that souce has a problem, the fan will not go on.

Yeah, I went overboard in my last description - it's more applicable to an industrial process control application than a car radiator. The key, like Jerry says is to look at the whole thing as a system and the ability to adjust on-off points is a big plus like both he and Trjohn57 said. I also like the idea of a fail safe toggle to bypass the controller - may be adding one to mine.

Originally Posted by Itoldyouso

I've never run an automatic controller, personally. I just have a toggle switch to turn the SPAL fan on when I see the gauge start to get over 180 at a light or something like entering a show. Since I constantly watch all my gauges I feel I have better control over it by doing it manually. Might be old fashioned, but it just works for me.

Don

Until that day when you forget