Hall Effect Tach on SB 9"


Mike Poore
 

Has anyone successfully installed a hall effect tach on a SB 9"? Specifically the one pictured below. My install has been giving me fits with the rpm jumping all over the place. I have tried several different things to eliminate whatever noise is causing the problem, but so far nothing is 100% successful. The sensor is really well shielded. I guess it has to be the power supply, so that's my next avenue of experimentation. FYI: The tach was to help me dial in the rpm of the VFD. I am using a separate power supply and I have already returned one tach thinking it was bad. Just writing this made me think that I may have the power cable too close to the motor. I have some of those ferrite filters. Maybe I will try one on the power cable. Any thoughts on a possible solution?


mike allen
 

        You might see if the power supply is regulated . All the un-regulated wall warts Ive seen had incredibly dirty power

        animal

On 6/22/2022 8:10 PM, Mike Poore wrote:
Has anyone successfully installed a hall effect tach on a SB 9"? Specifically the one pictured below. My install has been giving me fits with the rpm jumping all over the place. I have tried several different things to eliminate whatever noise is causing the problem, but so far nothing is 100% successful. The sensor is really well shielded. I guess it has to be the power supply, so that's my next avenue of experimentation. FYI: The tach was to help me dial in the rpm of the VFD. I am using a separate power supply and I have already returned one tach thinking it was bad. Just writing this made me think that I may have the power cable too close to the motor. I have some of those ferrite filters. Maybe I will try one on the power cable. Any thoughts on a possible solution?


Rick
 

While I don’t have that tachometer on my SB 9, I do have one on my SB 13 and Millrite mill. They are usually rock steady, but once in a while the rpm will jump for 1 second and then go right back to steady.  Not a problem for me, and all I use is a $5 eBay wall wart power supply.  Both of these machines are also running a VFD.  I used twisted pair, shielded wire to mount the Vfd controls, as this is recommended for interference suppression.


Joe
 

Not what your're looking for, but be aware that most, if not all VFDs, can provide a tach readout. All that's needed is the gear ratio for your lathe. The only down side is if you change pulley position the ratio must be also changed, but this only requires a few key strokes. I keep a table near my VFD that I created in Excel for convenience.

Joe


harry molwitz
 

Probably a bad unit.  Best to send it back.


Harry

On Thu, Jun 23, 2022, 8:25 AM Joe <joeshomeworkshop@...> wrote:
Not what your're looking for, but be aware that most, if not all VFDs, can provide a tach readout. All that's needed is the gear ratio for your lathe. The only down side is if you change pulley position the ratio must be also changed, but this only requires a few key strokes. I keep a table near my VFD that I created in Excel for convenience.

Joe


John Byghtn3
 

Some of these are sensitive to whether the "NORTH or "SOUTH" pole of the magnet points towards the sensor. 
Have you tried reversing the magnet? Use a compass to figure which way it is pointing and switch it around.

Good Luck!

On 6/22/2022 11:10 PM, Mike Poore wrote:
Has anyone successfully installed a hall effect tach on a SB 9"? Specifically the one pictured below. My install has been giving me fits with the rpm jumping all over the place. I have tried several different things to eliminate whatever noise is causing the problem, but so far nothing is 100% successful. The sensor is really well shielded. I guess it has to be the power supply, so that's my next avenue of experimentation. FYI: The tach was to help me dial in the rpm of the VFD. I am using a separate power supply and I have already returned one tach thinking it was bad. Just writing this made me think that I may have the power cable too close to the motor. I have some of those ferrite filters. Maybe I will try one on the power cable. Any thoughts on a possible solution?



Mike Poore
 

Thanks for the replies. I used cat5 cable for the VFD controls. The magnet will only work in one direction. I get nothing when it is reversed. The power supply is from an old PC peripheral running at 12v. It is not a wall wart. This is a replacement unit. I returned the first. The sensor has an LED that blinks. I have watched it at 60 rpm and it does not appear to be blink more than one per second even when the display jumps for 60 to 300 to 1100 and back to 60. The numbers are just estimates. It sort of works if you wait and use the lowest number, but it gets worse the faster the rpm. Yes, I could use the VFD tach feature and/or I could make a chart for the belt ranges and hertz, but the VFD is back against the wall behind the lathe in an inconvenient and unsafe place near the belts. The tach is right by the controls on the front of the lathe where it is easy to see. The cabling runs by the motor because it is inconspicuous.

If the power cable is picking up interference from the 3ph motor, would a ferrite filter solve the problem or do I need to use metal shielding? What about a bridge rectifier? My electronics knowledge is obviously limited. I have been messing with this for a week and it is time to fix it or give up.

On 6/22/2022 11:10 PM, Mike Poore via groups.io wrote:
Has anyone successfully installed a hall effect tach on a SB 9"? Specifically the one pictured below. My install has been giving me fits with the rpm jumping all over the place. I have tried several different things to eliminate whatever noise is causing the problem, but so far nothing is 100% successful. The sensor is really well shielded. I guess it has to be the power supply, so that's my next avenue of experimentation. FYI: The tach was to help me dial in the rpm of the VFD. I am using a separate power supply and I have already returned one tach thinking it was bad. Just writing this made me think that I may have the power cable too close to the motor. I have some of those ferrite filters. Maybe I will try one on the power cable. Any thoughts on a possible solution?



Chipbreaker13
 

I had the same problem on a similar unit I purchased from Amazon. I tried al types of adjustments, checking wiring, etc. My fix was to use a better magnet. The magnet that come with mine seemed fine but in hindsight was relatively weak. I had another magnet that was a tiny bit bigger and thicker that was laying around and I used it and it worked like a charm.  


Gary Johnson
 

My experience is with the very nice MachTach unit, sadly no longer available. I'd agree that installing the strong, rare-earth magnets is helpful, and make sure they are close to the sensor when they pass. I expoxied 4 magnets on the face of the big gear in my heavy 10 to get 4 pulses/rev. Flawless operation.

EMI from your VFD can definitely be the root cause of your problem. Ferrite common-mode chokes should be installed on both the sensor cable and the power cable, and any other cable that connects to the display unit. Choice of ferrite material and winding are important. At the expected low frequencies a Fair-Rite type 75 toroid, p/n 2675821502 is a good choice. This part is 1.22" OD and .75" ID, suitable for small cables. Wind as many turns as you can, in neat order, tightly through the core and fix them in place with a couple of cable ties. They should be installed close to the display unit. If a larger toroid is needed for fatter cable, a type 31, 2.4" OD is also a good choice. Fair-Rite p/n 2631803802. Good sources for these ferrites are Mouser and Digi-Key.

Routing the sensor cable further away from the motor leads could be helpful. Also, do not coil excess cable; that acts as a magnetic loop antenna. Cut off any excess and re-terminate.

-Gary NA6O


Mel Gross
 

I installed one on my radial ARM drill press and one one my South Bend FOURTEEN. I Just finished upgrading my mill to a VFD with new inverter grade 2 Hp motor, and installed one there. Finished last nite. All are rock steady. I did have a problem for a couple of hours with the lathe, after about a year, but found that the nuts holding the sensor in the bracket I made had gotten loose.

The power supplies are as follows. For the drill press, I designed, and made my own. A simple switching supply. For the lathe, a commercial switching supply for 240 AC, as I connected it to the output of the contractor. For the mill a different power supply I bought on Amazon. A tiny 12 VEC with 150 milliamp output, 240 AC, also connected to the contractor before the VFD.

The only problem has been the loose nuts. But if your power supply is intermittent on a short timescale, that is, in fractions of a second, and your digital meter doesn’t read fast enough to see it, you won’t be able to tell. The problem is rarely the output of those small supplies, it’s generally the AC coming into them. So check where that’s from. Some contractors and relays chatter. The problem is that it takes a while for the tach to take a proper reading. If the power drops for a few milliseconds, these cheap units will restart their readings, as they have no buffer, and since it takes several revolutions for a reading, you get junk.

MEL


On Jun 22, 2022, at 11:20 PM, Mike Poore <mpoore10@...> wrote:

Has anyone successfully installed a hall effect tach on a SB 9"? Specifically the one pictured below. My install has been giving me fits with the rpm jumping all over the place. I have tried several different things to eliminate whatever noise is causing the problem, but so far nothing is 100% successful. The sensor is really well shielded. I guess it has to be the power supply, so that's my next avenue of experimentation. FYI: The tach was to help me dial in the rpm of the VFD. I am using a separate power supply and I have already returned one tach thinking it was bad. Just writing this made me think that I may have the power cable too close to the motor. I have some of those ferrite filters. Maybe I will try one on the power cable. Any thoughts on a possible solution?


Mel Gross
 

The controls to a VFD should be shielded. Standard CAT 5 may cause noise problems. Also, make sure that the cable has 24 gauge conductors. Some older types are 26 gauge which isn’t recommended for this purpose. The shield should only be connected on the end to the VFD. The other end should be cut off.


On Jun 23, 2022, at 9:58 AM, Mike Poore <mpoore10@...> wrote:

 Thanks for the replies. I used cat5 cable for the VFD controls. The magnet will only work in one direction. I get nothing when it is reversed. The power supply is from an old PC peripheral running at 12v. It is not a wall wart. This is a replacement unit. I returned the first. The sensor has an LED that blinks. I have watched it at 60 rpm and it does not appear to be blink more than one per second even when the display jumps for 60 to 300 to 1100 and back to 60. The numbers are just estimates. It sort of works if you wait and use the lowest number, but it gets worse the faster the rpm. Yes, I could use the VFD tach feature and/or I could make a chart for the belt ranges and hertz, but the VFD is back against the wall behind the lathe in an inconvenient and unsafe place near the belts. The tach is right by the controls on the front of the lathe where it is easy to see. The cabling runs by the motor because it is inconspicuous.

If the power cable is picking up interference from the 3ph motor, would a ferrite filter solve the problem or do I need to use metal shielding? What about a bridge rectifier? My electronics knowledge is obviously limited. I have been messing with this for a week and it is time to fix it or give up.

On 6/22/2022 11:10 PM, Mike Poore via groups.io wrote:
Has anyone successfully installed a hall effect tach on a SB 9"? Specifically the one pictured below. My install has been giving me fits with the rpm jumping all over the place. I have tried several different things to eliminate whatever noise is causing the problem, but so far nothing is 100% successful. The sensor is really well shielded. I guess it has to be the power supply, so that's my next avenue of experimentation. FYI: The tach was to help me dial in the rpm of the VFD. I am using a separate power supply and I have already returned one tach thinking it was bad. Just writing this made me think that I may have the power cable too close to the motor. I have some of those ferrite filters. Maybe I will try one on the power cable. Any thoughts on a possible solution?