Tachometers with hall proximity sensor question

If you have 10v available maybe try it and see if that makes a difference?
 
Even though they say 8-24VDC, I run them at 12VDC because I have had them burn out at 24V. In most cases you cannot use the power supply from the VFD, as the internal VFDs ones are only designed to be used with the VFD low voltage inputs that are a few mA's. The tachometers can be 50-100mA and draw too much current. It is unclear how you have it wired up, the speed pot has nothing to do with the tachometer. If you have erratic readings there are several things to consider, one is the power source to the tachometer can be picking up electrical noise so requires a simple noise filter, second if you uses shielded cable for the tachometer sensor do not ground it at either end (direct experience it doesn't always work), third check the orientation of your magnet (if it is backwards N-S pole, it will not work).
 
I have a RF clone ad were I installing a Hall effect tach on it, I would make a plate for the magnet to attach to the underside of the spindle pulley. I have .8" of clearance there so plenty of room. The plate would be fastened to the pulley with the screws short enough so as to not interfere with the belt. To eliminate vibration at high rpm, I would add a counter weight on the opposite side. Below is an illustration of the concept. In practice, I would make the plate as small as practical.
RF Magnet Mount.JPG
 
mksj said:
Even though they say 8-24VDC, I run them at 12VDC because I have had them burn out at 24V. In most cases you cannot use the power supply from the VFD, as the internal VFDs ones are only designed to be used with the VFD low voltage inputs that are a few mA's. The tachometers can be 50-100mA and draw too much current. It is unclear how you have it wired up, the speed pot has nothing to do with the tachometer. If you have erratic readings there are several things to consider, one is the power source to the tachometer can be picking up electrical noise so requires a simple noise filter, second if you uses shielded cable for the tachometer sensor do not ground it at either end (direct experience it doesn't always work), third check the orientation of your magnet (if it is backwards N-S pole, it will not work).
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I checked the pole of the magnet before I super glued it into the ring I made and it does give a reading on the display when moving the spindle by hand so I think I got that right. I will try the 10v supply as BladesIIB suggested. Do you think that can work or would it be better to get an external 12V power supply? The tachometer is only wired to the 24V and cm terminals of the vfd currently. The box I made is earthed though. Below is my quick and dirty sensor and magnet setup. I went with our members advice on the setup.
20210909_161139.jpg20210909_134423.jpg
 
They draw 36-40 mA at 24VDC and 45+mA when the sender is triggered that I have measured (even though its lists 30 mA). I have no idea as to the VFD you are using and the connections, but most of the VFD input power supplies are not designed to power other components. It may have just enough current to run it but not when it pulses on, also could effect the input signals. Why don't you try a small 9VDC battery, that will tell you if it is a power supply issue/noise.
 
azscooby said:
I tapped into the 12V fan power on my VFD…..
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I am not sure if I know how to go about doing that and I guess I must check if it's fan is running on 12v. I am not a buff on electronics although I have learned a lot this year,I am still a novice.
 
mksj said:
They draw 36-40 mA at 24VDC and 45+mA when the sender is triggered that I have measured (even though its lists 30 mA). I have no idea as to the VFD you are using and the connections, but most of the VFD input power supplies are not designed to power other components. It may have just enough current to run it but not when it pulses on, also could effect the input signals. Why don't you try a small 9VDC battery, that will tell you if it is a power supply issue/noise.
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I will try that. My alpha drive micro vfd can supply 200mA. Don't know if this makes sense to you.
 
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