Would anyone be able to help me remake a rpm sensor? I need some help with an old fan rpm sensor. The problem is that that the fan itself is not a fan anymore. But I still need the rpm sensor to work properly to read rpm. I removed the coil from the circuit but now the sensor dosent seem to work. THe circuit is not damaged. I just removed the coil as having a coild there would complicate things. Anyone know why its not registering rpm anymore? i have used both digidoc 5 and my mainboard and neither registers rpm. I would really apreciate help in how to solve this problem.
What are you trying to measure the rotation of? If you can, another fan with all the blades cut off would probably do the job nicely. There are many commercial ones available, but if you want to keep things old school the insides of an old ball mouse make pretty accurate sensors. A little more information would help
We need a better desciption please. If you only removed the coils, then you should still be able to read RPM as long as you give the original circuit 12V still. If you removed the magents on the fan blades, then your screwed. The RPM sensor is basically a transistor thats activated by the switching of magnetic poles. The fan itself runs off of having permanent magnets being pushed by the coils. As the magnets rotate, the hall-effect sensor acts like an NPN transistor turning on and off as the magnets rotate past it. This means for the RPM to work, you need the magnets, the circuit with the hall-effect sensor, and also 12V to power the circuit. If you describe how you dis-assembled the fan, we can more accurately help you.
As what im trying to measure is rotaltional speed in rpm. This may illustrate better what im doing. http://wizdforums.co.uk/showthread.php?t=3143 Im constructing a flow meter for my water cooling loop. And I did leave the magnet on the fan. The sensor is atached to the circuit board and directly under the magnet (although I removed the circuit for preliminary testing of flow to avid killing it because it is not insulated.
The text does help but im not very good in electronics and need some more help. Is there any way i could take a pic of the pcb that exists and what i can do to make it work again?
That 4 pin IC near the bottom of the board is a motor inverter IC. It first provides a low frequency AC current (actually pulsed DC 180 degrees out of phase) to the coils, then syncs with the rotor using back EMF in the coils. It then works like a blocking oscillator. It uses one coil to apply force to the rotor while using the other coil as a sensor (it constantly switches back and forth). The "RPM sensor" is just a transistor that switches on whenever its associated coil is off. To use the motor as a RPM sensor, just wire the opposite ends of the coils (should be two in series. Use ends of coils) to a circuit that senses the AC voltage, essentially using the motor as a generator. To test, make the rotor spin in your desired application and use a DMM to measure the output voltage. If it's above 0.7v or so, you should be able to just connect the coils between the base and emitter of a transistor, with the emitter grounded and the collector connected to the power supply through a 10k or so resistor. The signal will appear on the collector. If it's less than 0.7v, you can use a Schmitt comparator to convert it to a logic level signal.
I cant do that. I removed the coil and it was damaged when i threw it out. I supose I may have to find a hall sensor and wire it instead.
Or a hall switch like this, as used in billions of PC fans. Panaflo fans have a many-legged IC as well to do clever stuff, but yours looks very basic. If the rotor magnet is in one spot, DO is on, DOB off, as it rotates it switches over and DOB comes on, DO off. A motor coil would have originally added a 12V pull-up resistance to the 1k resistor (marked 103 on the photo) on that LHS transistor base to turn the fan speed transistor on when the IC's open-collector switch (DO or DOB) is off. Now you've removed the coil, no pull-up. Try connecting around 100-240 ohm resistor between a 12V spot and the hall-switch end of the base resistor.
Thanks. Ill try conecting a resistor and come back with results. EDIT: would you mind taking the pic I took above and marking exactly where do I need to put the resistor? I have truble reading schematics. (Yes I know im a dumb ass)
As far as I can see, a resistor wants to go between the 12V pad and the pad marked 'A'. You should find both pads already have a solder spot where two of the coil wires went. e,c,b are transistor emitter, collector & base, methinks.
