Tach/Dwell meter

[wippb]

I found this older hand held tach/dwell meter in the garage. It's in really good condition. I've never used one of these things and of course it has no directions. On the front of the meter it says it will do 4-6-8 cylinder automobile engines. (x2 for 4 cylinder on the 8 cylinder setting). My question is will this tach work on 2 stroke engines specifically a 3 cylinder engine (x2 on the 6 cylinder setting) and if it will work where do I hook it up. Can it hook up to were the existing (onboard) tach is now. It only has a black and red lead.

 

[SeaDawg]

Re: Tach/Dwell meter

It won't work for a boat tach, according to earier posts here.<br /><br />Do a search on the word "dwell" and it sould find you the earlier post.<br /><br />Sorry.

 

[petryshyn]

Re: Tach/Dwell meter

Hi wipper...<br /><br />Does this unit use batteries, or is it parasitic?

 

[wippb]

Re: Tach/Dwell meter

I took the back off the unit and there are no batteries inside. It is "parasitic" (I like that term, never heard it before). There are only 2 wires coming out of it, red and black, on the box it says it "can be either negative or positve ground". I think it's between 10-20 years old, analog type meter movment. "Made in Japan", unfortunately this is all the information that I have on it.

 

[petryshyn]

Re: Tach/Dwell meter

Sorry w, its only good for auto ignition...

 

[wippb]

Re: Tach/Dwell meter

Thanks guys<br />I guess that's why it was in a box hidden outa site, forgotten.

 

[petryshyn]

Re: Tach/Dwell meter

I got a little circuit that may allow you to use it as a marine tach. (if you want to experiment.....)

 

[wippb]

Re: Tach/Dwell meter

Mr Schematic<br />I knew I could count on you. I would like to have a look at that circuit and see how much work it take to convert it. You can drop it in my mailbox wippb@hotmail.com if it isn't to much trouble. And thanks, I'll keep you posted on the outcome.

 

[petryshyn]

Re: Tach/Dwell meter

Basically you would just use the meter movement in the unit. I would use a 9V battery to power it. I would change the 1K resistor on the input to 10K and connect it to O/B tach terminal.......or, make a capacitive pickup that clamps over the plug wire(probably more versatile) Let me know if you need more help. total cost of circuit should be less than $8. But you gotta be willing to experiment a bit.....<br /><br /> Click me

 

[wippb]

Re: Tach/Dwell meter

Thanks Mr. Schem<br />I will definately take a look at this a little later. I'll have to study it a bit more. Right know I'm trying to get my transom fixed before fishing season starts. Where do you find all of the neat things. Thanks again.

 

[acam]

Re: Tach/Dwell meter

I realize this is a really old thread but it still comes up near the top when searching for info on how to use an automotive tach/dwell meter on an outboard and I believe the info stated above is incorrect. I believe that you CAN quite easily use an old auto tach/dwell meter to measure RPMs on a 2-cycle outboard. Post if you think that something below is not correct.

I was trying to find a way to read the RPMs on my 1975 Evinrude 70hp, 3-cylinder. After about 2 hours of reading through posts here and elsewhere on the Net I learned that the tachs read the number of electrical pulses. Auto tachs count 2 pulses for 4-cylinder, 3 pulses for 6-cylinder, and 4 p for 8-cylinder. The OMC 3-cylinder motors have a 12-pole charge coil, thus 6 pulses coming from the charging circuit. If you set an old auto tachometer for 6-cylinder, hook the red lead to the charging circuit, the black lead to ground, then it should be able to count the number of pulses and give a reading that is double of the accurate RPMs. So cut the reading in half and you have the actual RPMs, right?

I would also think that you could use this method also on any 1, 2, 4 and 6-cylinder outboard with an alternator. You just have to find out how many poles the alternators have and figure out the correct tach setting and multiplication factor for your specific engine/tach combination. Sound right? For info on how many poles your alternator has you can reference the Teleflex tachometer install instructions. There is a chart that lists the number of poles and pulses for most alternator-equipped outboards. Here is a PDF of those instructions:
View attachment TachInstallationA.pdf

For those of you who are asking where to attach the red lead take a look at the other info on the Teleflex tach installation instructions. It gives 2 nice diagrams of attachment points for tachs, one for outboards and one for I/Os and inboards. I used the yellow/grey wire attachments on the terminal block on my 1975 Evinrude 70hp and it worked nicely.