# Tachometer



## rwaudio (May 22, 2008)

gottdi said:


> I now have my sending unit from rechargecar. I tried to connect my stock tachometer from my MG and got absolutely nothing. There are only three wires. One is 12 volts and the other is ground and signal. I run 12 volts to the 12 volt wire and the ground to the ground on the tach and the signal wire to the signal connection on the tach. Power up and no go.
> 
> I wanted to know if these units are only for digital tachs or can they drive the standard analog style tach that you'd find in your car? It could be that the tach is actually dead. The tach is old and has not been used for quite some time. I have one other to test but other than that I'd need to go buy another to test.
> 
> ...


The sensor will create pulses on the signal line, so to check if that is working you need a scope or something (not sure if a volt meter would give you anything, maybe on the AC setting, or frequency if you have it). To test the tach you would need some sort of signal generator to send a square wave to the tach, even some of the "audio" signal generators for computers would give you something if you don't have a real one. Just be careful with your wiring.

I just ordered the same sensor (don't have it yet though) is there a specific distance you need to set the sensor from the ring that goes on the shaft (from the instructions)? These prox sensors usually have a fairly narrow working range.

I'll be feeding mine to a Soliton1 so I should be able to make that work then deal with the stock tach once I know I have a good signal.


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## Guest (May 21, 2011)

Ok, That sounds logical. I can connect mine to my controller too but my controller says 5 volts instead of 12. All else the same. Maybe I can just connect those up and try that. I have mine set to where it almost touches but does not. Should provide an excellent signal. Seems kinda hard to muck up that wiring. Power to red. Ground to black and signal to green. Simple enough. I will be checking my other tach here in a few after breakfast. 

Pete


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## jackbauer (Jan 12, 2008)

I made my own tach sender out of an industrial npn proximity sensor and two little pieces of stainless rod epoxyed to the end shaft. I used a 1k pull up resistor between 12v and signal so as to mimic the 12v square wave that the dash computer expects. Working like a dream. Also feeds tach signal to the controller via a 2k2 resistor , 5v1 zener and a .1uf cap for rpm limiting.


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## Guest (May 21, 2011)

Snatched my sons tach out of his bug and it works like a dream. Went to town to find an in dash tach and found one and found it was too large for the hole. I don't really want to leave a dead tach in the vehicle and mount one on a pod. I just want to replace my in dash unit. Damn. Now I gotta take it back to the store for a refund. Bummer. 

It is however good to know my sender unit works perfect. 

Pete 

This is one of those things that just slows down the whole process. What should have been an easy thing is now a pain in the butt and another wasted day and still without a tach.


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## spdas (Nov 28, 2009)

Hopefully i am not hijacking your thread, but what is the "tach" wire coming from my Zilla Hairball? Is there already a pulse there that I can go to Checkers and get buy a tach, since there is none in the car now?
thanks

francis


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## Guest (May 21, 2011)

I am sure that the tach wire is tach signal into the hairball. If you use the Warp Speed Sensor you need to let them know you have a Zilla. I will be sending my signal to my controller as well. Gotta ask about voltage but it should just work. 

Choose '0.875" exciter ring for Zilla controllers' if you plan to connect your sensor directly to your Zilla motor controller. The Zilla requires a more specific input pulse width, and this exciter ring will provide that.


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## rwaudio (May 22, 2008)

spdas said:


> Hopefully i am not hijacking your thread, but what is the "tach" wire coming from my Zilla Hairball? Is there already a pulse there that I can go to Checkers and get buy a tach, since there is none in the car now?
> thanks
> 
> francis


You would first need to feed a tach signal into the zilla to get something out.
Recharge car has a specific sensor for use with the zilla.
http://www.rechargecar.com/product/warptm-speed-sensor

I bought mine from Mike at ev-propulsion.com (normal version) and he provided service above and beyond my expectations.


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## spdas (Nov 28, 2009)

Using the sensor linked above, I don't see the need for the Hairball "Tach" connection. The sensor has + - 12v and pulse, Doesn't the pulse go directly to the aftermarket tach and that's it?

thanks
Francis


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## rwaudio (May 22, 2008)

spdas said:


> Using the sensor linked above, I don't see the need for the Hairball "Tach" connection. The sensor has + - 12v and pulse, Doesn't the pulse go directly to the aftermarket tach and that's it?
> 
> thanks
> Francis


I haven't brushed up on the zilla for quite some time, but the Solitons use the RPM signal for over rev protection, the zilla might do the same.


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## spdas (Nov 28, 2009)

Ok thanks, will ask one of the 2 sites mentioned above when I buy the sensor these questions.
Francis


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## RE Farmer (Aug 8, 2009)

gottdi said:


> I now have my sending unit from rechargecar. I tried to connect my stock tachometer from my MG and got absolutely nothing. There are only three wires. One is 12 volts and the other is ground and signal. I run 12 volts to the 12 volt wire and the ground to the ground on the tach and the signal wire to the signal connection on the tach. Power up and no go.
> 
> I wanted to know if these units are only for digital tachs or can they drive the standard analog style tach that you'd find in your car? It could be that the tach is actually dead. The tach is old and has not been used for quite some time. I have one other to test but other than that I'd need to go buy another to test.
> 
> ...


You may have it right. I'm not positive, but I think the older/analog Tach's use a small generator which puts out a variable voltage. If so, then the Tach gage is essentially a volt-meter calibrated to read in RPM (higher voltage=higher Rev's). You could verify this if you have a small variable power supply you could attach to the Tach. Since you bought Midge as an EV, you aren't likely to have the original Tach. Gen which you could connect a multimeter to to check its output.

(Edit) More likely is your tach uses pulses from the ignition coil (4 pulses/rev). From your diagram, it appears that your digital signal may produce many more than 4 pulses/rev and/or the pulses are too small in amplitude (mV instead of ~6 volts from ign coil) for your old tach.

Here's a couple links describing/calibrating Smiths Tachs, hope it helps:

http://www.classictiger.com/techtips/motach.html

http://www.mgexperience.net/article/tachometer.html


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