2 speed Taurus fan controller

[bjhines]

First I want to give a little background...

 

Track cars ~can~ get away with little or no cooling fan power for a variety of reasons. With that said, I have seen many track cars overheat on the grid. I have seen drivers start and stop the engines every time they move up and accidentally kill the battery on the starting grid. I want NONE of that. I admire the BMW drivers that can sit on grid with the AC running, while discussing technique with their instructors(I have a BMW M3 and love it).

 

I have tried a few options for electric fans in my time, on a variety of cars. Most of the aftermarket fans are wimps that would not cool a go-cart on hot/humid summer days in the SE USA. To provide proper cooling power you need something that draws ~30-40 Amps(400-500 Watts).

 

Proper cooling power is easily attainable with DUAL fan motors. Unfortunately, most of the dual fan setups are too big to fit on our small radiators. If you can fit them, then I would definitely use DUAL fans. Dual fan motors are within the amperage ratings of fog-light relays. This means that parts to run them are cheap and replacements are as close as your nearest Walmart.

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Enough on dual motors vs 2 speed motor, I have a Taurus 2-speed fan and I need to control it.

 

This fan motor was available on a variety of Ford cars for over a decade. There are a variety of shrouds and fan sizes that all seem to use the same 2-speed motor design. Ford really loved this fan. The Factory replacement is priced over $400, but Dorman offers an aftermarket replacement for $150. This thing is POWERFUL!!! It uses a little less than 20 AMPs on LOW and nearly 40 AMPs on HIGH. The high speed current draw is well known for melting foglight relays. You can get 50A mini relays but they are pushed to the limit with high ambient temps in the engine compartment. There are 70A mini relays available if you know where to look.

 

I wanted an adjustable, 3-state(OFF/LOW/HIGH), 3-wire(2-speeds w/ground) Ford Taurus fan controller that uses a single sender. I have seen many ways to SWITCH the 2 speed fans and their high amperage requirements, but I have not seen a neat way to control the relays automatically.

 

I have a list of considerations I used in my design;

 

Low cost parts

IN-stock parts availability

Temperature Sender to fit 1980s GM thermostat housing with 3/8"NPT port and weatherpack electrical connector.

Regulated/isolated circuit design

fully adjustable temperatures for off, low, and high speed

Proper change in temp from on to off state(hysteresis)

HARD switching for the main relays to reduce arcing and fouling

indicator lights to aid adjustment and confirm operation(ON, LOW, HIGH, OVERRIDE)

AC/override control to force high speed ON

 

I designed a circuit that uses an adjustable voltage divider with a single thermistor(sender) to drive a pair of transistors through Zener diodes to control a set of micro relays. The micro-mini relays will ensure that the main fan switching relays are switched solidly no matter what.

 

The circuit is very simple in theory, but getting it to work properly adds complication. The voltage divider uses one sender but has 2 branches to allow 3 states. It was a little tricky getting the ON-OFF states close together without putting too much current through the sender/thermistor. I used Zener diodes to keep the change in states very close together. The other problem is that changing one set point changes the set points for all the states. I was able to minimize that issue with some more parts.

 

I end up with 2 adjustment screws... The low speed screw sets the LOW-ON temperature, The high speed screw sets the difference between the LOW and HIGH ON points. The off state temeratures are built into the circuit design to be ~10 degrees lower than the ON states. This hysteresis is not consistent over the entire adjustment range, but it is within a few degrees over a wide range of temps.

 

The temperature settings I am using now are what I have seen discussed in books and forums.

.......LOW....HIGH

..ON..185.....200

OFF..175.....190

 

The settings are adjustement-repeatable and precise. I use a 240F heater and thermocouple to measure temps. I get no more than a degree of variation in tests. I have run tests with the circuit at 40F degrees and the circuit at 180F degrees. I only get a 3 degree variation.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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Edited December 19, 2010 by bjhines

[cockerstar]

Excellent work!

Looks to be very professionally done!

Maybe you have something to stick in the vendor's forum, as there really doesn't seem to be a good way to control these fans right now from the minimal research I've done.

[Dan Juday]

Keep us up to date on your testing. I keep burning up relays. I use an aftermarket dual fan controller that I've wired with additional relays to run the Ford two speed but the GM relays don't hold up. And the temp sensor is a bulb in the radiator fins (not the best way to go). You have thought this out well. Get the bugs worked out (if any) and I'll be your first customer.

[bjhines]

Dan,

Which relays are you currently using? This is the next phase of testing for me. I am trying a variety of suppression techniques to see what works best on the scope.

[strotter]

This is awesome and wonderful and great, and something I wish had been around when I was putting my car together. I've been using a pair of Bosch 75A relays - not "bosch style", but actual Bosch, model "0 332 002 150" - to run my fan since I upgraded the system for operation with my new ECU. You have to be careful when you're ordering relays, the word "bosch" has become like "kleenex", something between a rip-off and a generic term for relay. I opened one up last summer, and it was in great shape, you might say virginal, with a few thousand hours of operation. They're great big things, 1" tall and 2" square, a pair of 1/4" or so space connectors low voltage, screw connectors on the high-amp side, everything plated. Also expensive, as I recall, like $40 each. I put diodes in the system (for the rundown voltage, if that's what it's called, when the fan is spinning w/o power), but there are similar ones with internal diodes. Dan, buy some of these, or wait until BJ builds some for sale.

 

BJ, one other thing you should consider is putting an "A/C override" input of some kind, something that will kick the fan into HI for the a/c. Or, even better, it would increase fan output by one "level" - if the fan is "off", it'll go to low-speed, if the fan is on "low", it'll go into high speed, that sort of thing.

[bjhines]

Strotter, I am with you there on the additional functions.

 

I included an override input to force high speed operation.

I also included an input that switches to ground(800mA)on high speed which could run additional relays, or indicator lights, or other functions.

I could add any number of additional features like delays for on/off/functions, etc.

[Dan Juday]

Dan,

Which relays are you currently using? This is the next phase of testing for me. I am trying a variety of suppression techniques to see what works best on the scope.

 

These are the fan relays from 3rd gen f-body cars, but the same relays were used in a bunch of GM cars. They're shaped like an oval cyclinder about two inches tall. They have the diode built-in. They work fine for the low speed but I've melted two in the high speed circuit.

 

When I get my car back together I'm going to steal the relays out of Scotts Z while he's not looking.

[bjhines]

I think there are cheap/small relays that will do the job for these fans. I think that many failures of the Mini-relays are due to improper suppression and arcing across the contacts. I need to design a good surge/spark supression circuit for these 50Amp Mini-relays.

 

I do not think the large 75A relays are a good choice. They do not make a changeover(nc/no) version, they are too expensive, too big, require too much coil current, they do not fit neatly into sockets, and the contacts need boots to insulate the connections.

 

I would prefer to use only 2 relays to do the entire switching job. One 50A single throw for power ON-OFF, and One 25A/50A changeover for low/high speed.

 

Edit...

My method is actually dissapating more power(heat) through 2 relays right now(one for ON/OFF, and one for switching HIGH/LOW). I will rewire the relay outputs to allow 2 independent fan relays One High and One Low relay fed by a branching power wire.

 

I am currently testing RC suppression as my best option. Diodes are not working out with the 3 wire motor very well.

Edited December 23, 2010 by bjhines

[lumberjackj]

I like this idea, would you be interested in either making these, or releasing the specifics on the wiring so we can make one of these magical fan control boxes?

[bjhines]

I am still working on this design. I like the way this one performs, but I think that a different design using OP-AMPs would be more stable and easier to adjust. The differential inputs on the op amps could be used to eliminate errors due to voltage variations and ambient temperatures.

[BobsZTwins]

One thing to consider for high speed fan control is wiring two 30A Bosch relays in parallel if you want to avoid the expense of 70A relays. MAD Electrics recommends this method. I've used it for about 3 years in the Florida heat, no problem. I'm in the process of rewiring to use two thermal switches so I can use both speeds. I'm going to try a 50A for the high and two 30A for the low and switching between speeds, we'll see if that holds up.

[LanceVance]

Bummpp

 

Has anybody tried anything like THIS? This guy used a Volvo relay in conjunction with a Audi/BMW thermoswitch to control the Taurus fan. HERE is another thermoswitch option.

 

Time to start scouring the boneyards, seems like this might be a cheap and reliable option for e-fan control.

[darom]

I used the instructions and parts list from this site (posts my Tim65GT):

http://www.stangnet.com/mustang-forums/threads/taurus-fan-wiring-problem.796649/

 

I saw the rx-7 thread when I was researching it and preferred Tim's setup.

 

A used Taurus fan from a junk yard was $25. The most expensive parts were good relays (75amp), circuit breakers and 6 and 8 gauge wire. It took some time to fine tune the turning on/off fan mode via the potentiometers. The hand held laser temp gun helped a lot. My wife really disliked my lab in the kitchen though

[redneck1545]

The bmw switch and volvo method have been used before and would most likely prove to be the easiest route. I'm using a volvo relay hooked to a rocker switch and it works flawlessly. I will soon be buying the metric adapter from JTR and make the fan fan come on automatically with the bmw switch.

 

 

 

I would go with whats been proven in the past with a collection of various OEM parts vs making your own circuit board and such.