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  #1  
Old 05-26-2008, 11:24 AM
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Default Tach options

What options to EVs have for tachs? I think I remember seeign Gav hooking up some kind of wire system to the motor. Does that mean you have to have a dual shaft motor for a tach?
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Old 07-16-2008, 06:29 PM
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Default Re: Tach options

Hi onesojourner.

I am myself investigating the re-enabling the tach on my car. When the time comes.
I do not think you need a double shaft.
It depends on the equipment you have but as far as I know...

The electronic tach are an electronic counter. The tach count the pulse from the ignition coil. 4 cylinders two pulse per rotation. 1000 rpm equal 2000 pulse.

The only reference material I have is for the Pontiac Fiero, I beleive my tach on the Pontaic Sunfire will be a modernized version. I will know when I find the references or when I open the thing up.

Aparently some systems will have a field (magnet) and will count the teeth on a gear, like the flywheel's. That could be one pulse, for one rotation.

I have seen an EV, somewhere, the owner had an homemade optical system with white and black marks on the tailshaft. The same would work inside the bell housing using the starter opening. I do not have the technical knowledge for such a device. I can follow instruction, I cannot conceive such things.

I myself will investigate using rare hearth magnets and reed switches. I am not shure how fast they close. Yet.
http://en.wikipedia.org/wiki/Reed_switch

Two magnets, two pulse. Just like my 4 cylinders car. Plus that would keep the shaft balanced.


Take care,

DP
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Old 07-16-2008, 10:40 PM
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Default Re: Tach options

I missed this post...

What I did on my Geo Metro EV was...

1. Drill two holes in the outside edge of the flywheel 180deg apart.
2. Epoxy 2 neodymium magnets from radio shack into the holes.
3. Open a small 12v relay and take out the coil.
4. Put a 12v zener in parallel with the coil to clamp off large spikes.
5. Put the coil in a tube and pot it with Epoxy but leave the tip of lamination sticking out at the end.
6. Drill a hole in the bellhousing large enough for the tube and mount the tube in the bellhousing about 1/4 from the magnets.
7. Wire one lead to the car's chassis ground and one to the tach lead. You may need to reverse these depending if your tach reads a high or low pulse.
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Doc: "Are you saying that the problem is the dia of the shaft or the small length and shape?"
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Old 07-17-2008, 08:01 AM
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Default Re: Tach options

Hi Lazzer.

Thank you for a working solution. Did'nt know what what zener diode from a snitchel till now.

The relay then is just an easy and cheap source fro the coil? any small coil than can be fitted should do.

I presume the magnet indude a current in the coil. The zenner let the power through. Simulate the ICE coil pulsing. The tach is happy.

This five thumbs mechanic can assemble that.

Thank you, thank you, thank you.

DP

PS with my luck the tach will not be air-core based and will be some sort of digital aberation.
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Old 07-17-2008, 09:30 AM
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Default Re: Tach options

Quote:
Originally Posted by e_canuck View Post
Hi Lazzer.

Thank you for a working solution. Did'nt know what what zener diode from a snitchel till now.

The relay then is just an easy and cheap source fro the coil? any small coil than can be fitted should do.

I presume the magnet indude a current in the coil. The zenner let the power through. Simulate the ICE coil pulsing. The tach is happy.

This five thumbs mechanic can assemble that.

Thank you, thank you, thank you.

DP

PS with my luck the tach will not be air-core based and will be some sort of digital aberation.
The zener clamps off any excessive voltage to help prevent damage to the tach's electronics. It may or may not be needed but safer to try it first. Some tachs are driven by the factory ecu and a 5v pulse is all that is needed.

It worked flawless for me on my Geo just how I explained. Good luck.
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