Lathe Tachometer not working - Ideas???

[John_aero]

I have installed a tachometer onto my lathe.

it is listed as 8-24v power so i ran it off the 10v from my VFD. It worked but speed was all over the place, be 1200 then 600 etc never stead.

So i tried rule out the VFD and powered it direct off a 9v battery and all i got was LLLL

Then decided run it off the 20v supply from VFD thinking 9v was to low, but still all i get is LLLL.

anyone had issue similar, weired did work but stopped when changed power supply, tach unit is getting power as LED is lit.

 

[DickyDoDah]

I have one of these on my mini mill but have never seen this display but I found this in the description on Amazon.
Over-range Display: If the rotation speed is too low, it will display ""LLLL""; if the rotation speed is too high, it will display ""HHHH""

Fudeshe Digital LED Tachometer,Red Mini 4 Digit NPN Hall Proximity Switch Sensor Durable AC 110V-230V RPM Speed Measure Meter Lathes, Conveyor Belts : Amazon.co.uk: Business, Industry & Science

Buy Fudeshe Digital LED Tachometer,Red Mini 4 Digit NPN Hall Proximity Switch Sensor Durable AC 110V-230V RPM Speed Measure Meter Lathes, Conveyor Belts at Amazon UK. Free delivery on eligible orders.

www.amazon.co.uk

The gap you have between the sensor and the magnet seems a little large, if you can keep it to about 1mm it might be better. I'd also check that you have the cables away from any AC or other "noisy" supplies.

 

[Pete.]

They don't work if the magnet is upside down. Try flipping it over.

 

[Seadog]

I installed one one my lathe in 2013.
It ran for 5 years, then one day stopped working.
Purely by chance, I reversed the polarity of the magnet and it started working again. And it still is

 

[hunter27]

I have just fitted one to my new to me milling machine and had exactly the same problem, I also have one fitted to my lathe that works perfectly. After flipping the magnet and altering the gap I realized that my mill has a power feed table utilising a windscreen wiper motor running off a 12v 25amp power supply that also powers the tacho and a light, and when using the power feed the display started giving crazy readings. I solved this by installing a laptop computers 12v power supply for the tach and the light and that solved my problem. I guess it was interference from the wiper motor through the power supply.

 

[waddycall]

I use one of these on my lathe. It even tells you surface speed. (For anyone who might be interested in getting a tachometer) -

Smiths Tach/Revolution Counter, Case & Accesories, 80216110 - G&M Tools

Good used condition.

gandmtools.co.uk

 

[xstian]

I had the same problem. I think it might be down to interference from the VFD. Even with a separate power supply it still didn’t work, but turn the VFD off and turn the lathe by hand and it seems to work fine.

I now use a manual version similar to the Smith one above. I find the m/min readings more useful than the rpm anyway.

 

[Seadog]

I feed my tacho from the VFD. I've never had a display issue.

 

[hunter27]

I feed my tacho from the VFD. I've never had a display issue.

Same as on my lathe and that works fine.
I think it's was the cheap Chinese generic power supply causing the problem down the tach's power supply rather than airborne interference as all the wires still run together but the problem was solved with the separate power supply.

 

[dieselsamurai]

I found this for a different tacho but might be relevent

I found mine was only stable running off a separate 24v power supply , I have 3 on various machines and no issues so far

Pickup looks a bit far away too

 

[John_aero]

Thanks very muchi increased the gap to see if was too close.

Was working just reading were all over the place. Then tried diff power supply and this is end result

May look at getting a separate 12v supply.

I'll run it off a battery see if works with vfd off before so any more.

Magnet is expoied in so awkward chip it out but doable

Id all else fails I'll just use a hand held unit.

 

[John_aero]

I have sopper tape and mesh so might also wrap 220v wires to reduce elec interference

Thanks for all the help seems they are intermittent for faults v reliability

 

[dieselsamurai]

those units are less than a tenner on ebay etc just get another , ive never had an issue with interferance personally

 

[John_aero]

I have ordered 2 more just to have them as spare.

Have another wired up to my mill but not finished off the VFD so once its running i can test the second one

 

[Brad93]

Cheap
Sensor

 

[John_aero]

tested it again last night with 12v laptop supply, moved sensor closer, further away etc and nothing.

Tested the one on my mill and it says HHHH all the time with the odd sporadic reading flickering up.

Gone away and bought a different cheap brand just in case ones i got are crappy of the crappiest (reviews show few had similar issues)

Must double check the power supply amps in case thats an issue with the data sheet above