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Tachometer Wiring Questions

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TomS

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#1
I bought one of those inexpensive LED tachometers off eBay but it didn't come with any wiring instructions or diagrams. Can't expect much for $9 I guess.

After searching a bit I found some basic info on the probe wires and tach terminals. I've attached a diagram of how I believe it's supposed to be wired.

What I found for the probe is the brown wire is 12 vdc+, the blue wire is 12 vdc-, and the black wire is signal. The tach has five terminals and what little info I found is terminal 1 is signal input, terminal 2 is signal ground, terminal 3 is NC, terminal 4 is input voltage "+", and terminal 5 is is input voltage "-".

In my diagram the black probe wire is connected to terminal 1 (signal input), the blue probe wire is connected to terminal 2 (signal ground), and the brown probe wire is connected to terminal 3 (NC). The 12 vdc power supply is connected as shown.

I'm still working on the installation so I haven't tested anything yet to see if it will work. Not sure if my wiring is incorrect if it will smoke the tach.

Let me know what you think.

Tom S.
 

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hman

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#2
I don't think your circuit would work. There's no power supply connection to the probe. And incidentally, the N/C on the middle terminal of the tach indicates "no connection."

I'm attaching part of the schematic for the wiring of my variable speed drill press to give you an example of how one of these might be wired. The output of the photosensor (WH) switches between floating and connection to ground. The 100 ohm resistor causes the tach input terminal to go high (+12) when WH is floating. I don't know the specifications of your probe, so you may have to modify what I've done. Hope it gives you a starting point.

NOTE - It appears that your tach and mine have reversed power input polarities, so wire accordingly.
Screen Shot 2017-02-20 at 11.22.12 PM.jpg
 

mksj

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#3
Sounds correct. Blue is usually (EU, Asia) neutral or (-), brown power or positive. It would help to have a picture of the tach board, but it sounds all good. Remember that the sensor is sensitive to the N-S orientation of the magnetic, so it only works in one orientation. I always wave the magnetic in front of the sensor to check that it is oriented correctly before fastening it in place.
 

TomS

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#4
Thanks guys. Needed some direction so I don't work myself into a corner.

Tom S.
 

TomS

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#5
Got the tach and probe mounted and wired. Did not install a diode hoping it would work without one. The local electronics store is about 45 minutes away. Probe signal wire connected to tach terminal 1. Probe ground wire and -vdc connected to terminal 2 and 4. +vdc connected to terminal 5 (assumption is the PS wire with the long white stripes is +). Plugged in the power supply and the probe light is on. Set the gap to .043 - .045. Moving the magnet past the probe tip the probe light flickers slightly. Flipping the magnet over and moving it past the probe no flickering. So I guess the first orientation is the correct one.

Still need to epoxy the magnet in place but wanted to run this past you first because removing it would probably destroy it. What is the proper gap? Should I see anything on the tach screen when the magnet passes under the probe?

Thanks,

Tom S.
 

mksj

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#6
I would tape the magnet on first and make sure it is working correctly at low rpm, allow about 0.1" clearance. You should see some movement on the tach if you run the magnet back and forth over the sensor. The board has a little + and - on the board for polarity, but if it lights up it is working. I have not seen the need for a diode, unless it is used to prevent you from damaging the tach if the power polarity is reversed.

His wiring diagram is correct, some have the sensor directly connected to power, others have a separate lower fixed volt supply with separate connections to the sensor.
 

TomS

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#7
I would tape the magnet on first and make sure it is working correctly at low rpm, allow about 0.1" clearance. You should see some movement on the tach if you run the magnet back and forth over the sensor. The board has a little + and - on the board for polarity, but if it lights up it is working. I have not seen the need for a diode, unless it is used to prevent you from damaging the tach if the power polarity is reversed.

His wiring diagram is correct, some have the sensor directly connected to power, others have a separate lower fixed volt supply with separate connections to the sensor.
Thanks. I'll give it a try in the morning.

Tom S.
 

TomS

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#8
Adjusted the probe to ~.100" gap and no reading on the tach. I'll double check the wiring. Off to our grand daughter's softball game so won't be able to get to it until tomorrow morning.

Tom S.
 

TomS

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#11
I rewired the tach using the wiring setup that FanMan provided and it's working now. For info I searched eBay for LED tachometers and found no less than four different wiring schemes. My tach didn't come with any wiring instructions so it was a guessing game from the start. I'm not complaining as the tach cost me $9 delivered. Just a heads up to anyone buying one.

Thanks FanMan, hman and MKSJ for your help.

Tom S.


20170226_095025_resized_2.jpg
 

mksj

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#13
There are many different variants on these tachometers. The older designs connect the NPN sensor power directly to the incoming power plus a trigger line. Most of the newer designs I have seen/use have a separate power input with a wider input voltage range and a separate regulated voltage connection for the NPN sensor. They have a speed range of around 4-99999 RPM. These are usually available through eBay, and maybe a little less confusing to wire.
RPM Wiring.jpg
 

GLCarlson

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#14
Reflective optical sensor is easy too. Just use a piece of silver tape on the pulley. Easier than mounting magnets. TCRT5000 sensor works fine with these tachs, can mount with double side foam tape.
 
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