Digital Tachometer

rbeall · Nov 16, 2019

Good morning all, since my B8200 HST has an alternator and not a generator I no longer have a tach. I purchased a digital tachometer and a proximity hall sensor.
https://www.amazon.ca/ELING-Universal-Digital-Tachometer-Backlight/dp/B0755JF9FK
https://www.amazon.ca/Yosoo-NJK-5002C-Proximity-3-Wires-Normally/dp/B01LX0J9H4
I have installed the proximity sensor that take a reading off the engine front crank pully. With all the wiring connected I turned on the ignition and the tachometer lights up with all 8’s then goes to 0 RPM and 0.0 hours. Then start the engine and the RPM stays at 0. I attempted to follow the instructions for adjusting the tachometer readings by pressing the button on the back, went through all the settings in increments of 50 from 1-300. No change, 0 RPM.
The proximity sensor was bench tested and once the engine is running the led on the back of the proximity sensor is on.
Any ideas of how to test the tachometer on the bench?

200mph · Nov 16, 2019

What are you using to trip the proximity sensor?

Roadworthy · Nov 16, 2019

I don't think the sensor will sense any change in the rotation of the crankshaft pulley. I think you have to attach a small magnet. It then senses each time the magnet passes the switch. If that's the case you could test on the bench with an electric drill spinning.

William1 · Nov 16, 2019

Yup a tiny disc magnet or even just a blob of metal that will cause a change in the magnetic field. In some cases, a notch works too.

rbeall · Nov 16, 2019

You guys are correct about a magnet. I had installed a magnet glued to the pulley at the correct distance from the proximity sensor prior to the original post. I have now also noticed the hour meter internal to the gauge is also not counting. I am good no to try and contact the seller to find out if the gauge is just faulty.

Roadworthy · Nov 16, 2019

Your gauge may be faulty. The pickup could be defective. A third option is the possibility the wires are connected incorrectly - either by you or internally in the sensor. Whatever the reason, Amazon is really good about exchanges and refunds.

Russell King · Nov 16, 2019

There is a company called TinyTach that has a tachometer that reads off the injector pump pulses, if what you now have doesn’t work out.

Sent from my iPad using Tapatalk

dlsmith · Nov 16, 2019

Russell King said:
There is a company called TinyTach that has a tachometer that reads off the injector pump pulses, if what you now have doesn’t work out.

I put a TinyTach on my BX and it works great.

rbeall · Nov 18, 2019

An update.
After a couple of emails with the seller of this tachometer, I got enough information to hook it up properly. I asked what type of sensor is required for this tachometer and learned that it needs an AC signal to work. The proximity sensor that I tried supplies a square wave DC signal, so it wouldn’t work. So, to get the proper signal YouTube was my friend. The “W” tap off my alternator was not there. I opened up my alternator and connected a wire to one of the coil ends before the diodes and bingo, a working tachometer.
This was really easy to do after having enough information to actually connect it up.

Dave_eng · Nov 18, 2019

Thanks for the update.

How are you linking the alternator signal to the actual engine rpm?

The alternator will be turning faster than the engine.

Dave

rbeall · Nov 19, 2019

Dave_eng said:
Thanks for the update.

How are you linking the alternator signal to the actual engine rpm?

The alternator will be turning faster than the engine.

Dave

The tachometer has a setting button on the back that I needed to adjust. The instructions said to set the tachometer to the number of poles in the alternator. Once the idle speed displayed was between 600-800RPM, I was at the correct setting. Full factory throttle displays 2700RPM.

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Digital Tachometer

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