# RPM and Tachometer switch



## DONEAL (Sep 10, 2008)

Does anyone have a Rpm switch on their EV? A friend and I was talking about the problems I had trying to get my tach to work using a hall effect sensor. When I explained the importance of the Tach. He suggested also hooking up a Rpm switch. I searched the forum and didn’t find anything, but I haven’t Goggled the net yet. I will as soon as I log off. 
I did get my tach to work I purchased a reed switch and a Magnet switch from http://www.allelectronics.com/ MS-11 (PRESS FIT MAGNET SWITCH ) @ cost 2.75. The Reed switch same store .50 each min order two, shipping 7.00$. They do have Fast service. A note about the reed switch. You have to have the hands of a "safe cracker" to solder these things * smiles* LOL they are very fragile, I broke the first one. Good thing the min order was two. The Magnet switch is all one unit sealed on the end and can be hand pressed in a 3/8" inch hole. Very easy to install. I tested both using a small dc motor at 500rpm. The reed switch did bounce the tach some, ( could have been my fault ) The magnet switch was smooth with no bounce.


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## Thaniel (May 25, 2008)

DONEAL said:


> Does anyone have a Rpm switch on their EV? A friend and I was talking about the problems I had trying to get my tach to work using a hall effect sensor. When I explained the importance of the Tach. He suggested also hooking up a Rpm switch. I searched the forum and didn’t find anything, but I haven’t Goggled the net yet. I will as soon as I log off.
> I did get my tach to work I purchased a reed switch and a Magnet switch from http://www.allelectronics.com/ MS-11 (PRESS FIT MAGNET SWITCH ) @ cost 2.75. The Reed switch same store .50 each min order two, shipping 7.00$. They do have Fast service. A note about the reed switch. You have to have the hands of a "safe cracker" to solder these things * smiles* LOL they are very fragile, I broke the first one. Good thing the min order was two. The Magnet switch is all one unit sealed on the end and can be hand pressed in a 3/8" inch hole. Very easy to install. I tested both using a small dc motor at 500rpm. The reed switch did bounce the tach some, ( could have been my fault ) The magnet switch was smooth with no bounce.


This is kind of old so I'm sure you have it all taken care of. However if someone else comes by reading.

On a previous project I used a reed switch to measure the RPM of an axle shaft on my car. Worked ok but as you already noted did have some bounce. The worst news is that the switch eventually wore out after a year or so. I replaced with a hall effect and the signal was much smoother and didn't have parts to wear.

Your question of an RPM switch puzzles me. Most RPM switches I have seen switch something (shift light for example) at a predetrmined RPM fed into the switch by some other device that measures the RPM (crank sensor, ECU, Points). The RPM sensors I've read about don't actually sense the RPM themselves.

Maybe I'm missing the point. 
Thaniel


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## DONEAL (Sep 10, 2008)

Thaniel
>Your question of an RPM switch puzzles me. Most RPM switches I have seen switch something (shift light for example) at a predetermined RPM fed into the switch by some other device that measures the RPM (crank sensor, ECU, Points). The RPM sensors I've read about don't actually sense the RPM themselves.<

Well, Not sure, What I have is a cheap after market tach. I have seen the more expensive ones that have a shift light, or better put points that you can program on the tach themselves. And I also seem to remember someone posting that these could be used to prevent over limiting the motor. It may be something I would look into later. More about the magnet switch, It may be that the thing has a hal-effect sensor inside it. I like it because it’s simple to hook up.


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## Dave Koller (Nov 15, 2008)

At present I am building a speed switch into my circuit board using a Lm2917.. the board is complex but the speed switch is simple - mine will trigger the old shift light at one rpm and a relay (with limit resistor to cut back on speed) on excess rpm... So the simple one is shown below... My board gives Verbal warnings also but not needed for what you are doing.. Err I hope.... 


The other circuit is more what I will use with my own comparator circuits... hope this helps...


edit... my pickup for original tach on Saturn --- http://www.diyelectriccar.com/forums/showpost.php?p=151836&postcount=37


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