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I would love to know about this. Are the fan speeds adjustable? Not sure how it's done.
I would like part numbers so I can build one for my taurus fans. Is the speed varible?
The fan speeds are fixed (High, Low or Off). They do not vary. They are controlled by the relays which energize by the temp sender and contol circuitry. One input to the two Operational Amplifiers (Comparators) is tied to the 5V regulator and the other inputs are variable by the 10K pots. This makes the low and high turn-on points adjustable. The transistors turn on to carry the higher current to the relay coils.
I posted the pics to show what I have built. I don’t know your capabilities with electronics, but if you want to attempt a project like this I just want to let you know up front, I think it would be about 4 out of 5 on a difficulty scale. You will need a lot of patience and unless you enjoy building small electronic projects, you would be better off spending the money and buying a fan controller of some type.
The sensor is from a '95 Mustang GT. I have it mounted in a '95 type water neck. Here are the part numbers and prices of the items I could look up.
Item Mftr Part number Cost Place (Pt#)
Temp Sensor BWD WT386 $3.62 O’Reilly
70A Relay Bosch 0 332 002 150 $13.20 eBay
30A Relays (2) Bosch type standard $10 eBay
Quad Op Amp LM324 $1.69 RadioShack (276-1711)
5V Regulator 7805 $1.59 RadioShack (276-1770)
Transistors (2) TIP31 $1.59 RadioShack (276-2017)
Variable Resistors (2) 10K - 15Turn $2.69 RadioShack (271-343)
Perf board $2.99 RadioShack (276-1394)
You will also need other various type project stuff like a case, wire, crimps, solder, heatshrink, fuses, and various ¼W resistors.