Hi Guys,
Today I went to get me some diodes and got 1x 1.3W 15v Zener, and 2x 1N4004s diodes.
Ive connected them up the correct way round, but the revotec rev counter still won't work.

I understand the 1N4004s are in series with the coil packs outputs, to stop the current flowing the wrong way, but whats the Zener doing?

Have tried changing the jumpers on the back of the rev counter too, but with no luck.

Below is a diagram of what I've tried...


diodes diagram

Anyone know where I'm going wrong?

Have also tried wiring the tacho directly to pin 2 on the EDIS with no luck...

[Edited on 24/6/06 by tom_loughlin]

Hi,

I hope when you say coil pack output you do not mean spark ! but actually the feed to the coil pack.

Okay what the diodes do is stop any reverse current, this means that you cannot screw up the spark by pushing volts into the coil pack, you also will not see any back EMF as the coil discharges abnd throws voltage backwards. The Zener diode is basically a clever diode that will restrict the voltage as well so makes sure you are not hitting your rev counter with and high volts.

Okay then, are the bands on the diodes all pointing towards the Rev counter ?

You can easily break this down into componants and test.

So just connecting the standard diode, with a meter to earth engine running you should see 12v pulsed on the output, if not its probally reversed or knackered. Assuming yes then if you put the meter behind the Zenar diode facing the rev counter you should now see pulsed voltage at twice the speed (it gets two lots of feed from each coil), although this will be regulated to a set voltage, if not the same applies as above.

Regards Mark

I used tha same method on y rev counter and to get it to work I had to connect a resistor between the output of the zener diode and + 12v, I think I used a 1k resistor .This pulls the voltage back to 12v in between pulses and worked on a smiths and a ford tacho.
Paul.

quote:

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Originally posted by tom_loughlin
Hi Guys,
Today I went to get me some diodes and got 1x 1.3W 15v Zener, and 2x 1N4004s diodes.
Ive connected them up the correct way round, but the revotec rev counter still won't work.

I understand the 1N4004s are in series with the coil packs outputs, to stop the current flowing the wrong way, but whats the Zener doing?

Have tried changing the jumpers on the back of the rev counter too, but with no luck.

Below is a diagram of what I've tried...


diodes diagram

Anyone know where I'm going wrong?

Have also tried wiring the tacho directly to pin 2 on the EDIS with no luck...

[Edited on 24/6/06 by tom_loughlin]

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Reverse the polarity of the zener diode.

It's purpose is to ensure the voltage on the rev counter falls to zero between spark events which it won't do when forwards biased as it is in the diagram shown.

Thanks gents, I tried a resistor (1k) and reversed the zener and all's good now.
I'm now confused, how can any current flow past the Zener, if it's polarity is reversed?
The bands on the two are towards the rev counter, but the Zener band is what appears backwards....

Oh well, it's working now, but I would quite like to understand why...

Thanks again

Tom

Basic English explanation...

A zener diode will conduct in the forward direction, just like any other diode. In the reverse direction it will block current flow like any other diode - up to a point, where it starts to conduct. As if by magic, it will maintain this trigger voltage level.

Alternative, slightly more techie explanation HERE

[Edited on 29/6/06 by David Jenkins]

The zener is there to make the 0 pulse with wider...

because when the voltages is dropping and it comes unther the zenervoltage... then the rpm counter reads a 0 this will be until the voltage is riseing again sow it will make the singal more clean...


if you can use a 12volts zener it will give you a very wide and good signal...

there are also rpm counters that wants to see only a flyback voltage from the coil (on the same line)

then you should use a 24volts zener

it will trigger when the flyback voltage gives the little small pulse..

Tks

quote:

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Originally posted by tks
The zener is there to make the 0 pulse with wider...

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so could someone read off the parts as i can't read the images well enough to add them to my maplin shopping list.

cheers, mike

quote:

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Originally posted by MikeR
so could someone read off the parts as i can't read the images well enough to add them to my maplin shopping list.

cheers, mike

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[cough]
when'd he edit that
[cough]

ooops! thanks, having read the first bit when it was first posted, i've just followed the bottom of the thread when it was added too.......

quote:

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Originally posted by MikeRJ
Reverse the polarity of the zener diode.

It's purpose is to ensure the voltage on the rev counter falls to zero between spark events which it won't do when forwards biased as it is in the diagram shown.

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quote:

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Originally posted by tks
the zener is there to make the 0pulse wider and to make it nicer. the coil will be during 11miliseconds 0 (dwell time) with the zener it will be seen as more time 0.

Anyway it works.

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