fan speed tach

[kaltag]

Hey there, I just got an old tach from a friend of mine today from his wrecked car and was thinking of using it in my case, i've seen them used for hard drive activity and like the idea but i like the idea of using it to monitor my case fan speed better is this possible? If so some linkage would be nice and if all else fails i can do the hard drive activity thing. *crosses fingers* thanx all!

 

[pik4chu]

Someone (CS, heh) correct me if Im wrong but I think you wouldnt be able to measure rpm very easily, you could measure current draw or what not, which would be reflected by the rpm. But not quite sure

 

[340Duster]

A car tach measures RPM by a 12v from the coil. In simple terms the needle moves depending on how quickly the voltage switches off and on comming from the coil (the speed of the firing of the engine). I don't know how you would come up with a way to produce that from a fan.

 

[Mpegger]

Actually, depending on the unit, car tach can recieve a signal from a number of different sources. The two major types of tachometers are mechanical, and electronic. Electronic tachs are the predominant type used now, even if the tach in the dashboard is a analog type. Depending on the car, there is usually a sensor somewhere that will transmit a pulse for every revolution of the crankshaft, much like there is a sensor on a rpm enabled fan. I dont know if it would be at all possible to hook up a electronic tachometer to a fan, because the voltage needed by the tach sensor itself may be more then what the fan would supply. You'd need to get some info on the fan and the tach in order to find out if the output from the fan would be usable by the tach at all.

 

[340Duster]

Actually, depending on the unit, car tach can recieve a signal from a number of different sources. The two major types of tachometers are mechanical, and electronic. Electronic tachs are the predominant type used now, even if the tach in the dashboard is a analog type. Depending on the car, there is usually a sensor somewhere that will transmit a pulse for every revolution of the crankshaft, much like there is a sensor on a rpm enabled fan. I dont know if it would be at all possible to hook up a electronic tachometer to a fan, because the voltage needed by the tach sensor itself may be more then what the fan would supply. You'd need to get some info on the fan and the tach in order to find out if the output from the fan would be usable by the tach at all.

Every car tach is electronic. The pulse comes from the positive 12v lead going to the coil. On an older car every rotation of the distributor triggers this.