N/A 4AGE 16V in AE86 - help needed, trying to "VEMS it"

[rob@vems.co.uk]

Never apologise for being noob.

[uzelac]

I just tend to repeat steps, often repeating what other ppl just said. To be sure I understood others correctly, and that they understand me.

So, what do you say, should these parts work, ok specs ?

[rob@vems.co.uk]

The Zener looks fine, although the diodes I've used are the 1N4007 ones that come in the "rescue" pack that they send out in the little plastic bag.

[uzelac]

Not sure where the rescue kit is, so will have to buy new one :/
Here is what's avaliable at local supplier:

Code: [Select]

product name description Producer
1N4007 T/R 1000V 1A UFM1.1V/1A IFM30A IR5uA DCC
1N4007 GLX 1000V 1A UFM1.1V/1A IFM30A IR5uA GLX
1N4007G GLX 1000V 1A UFM1.1V/1A IFM30A IR5uA, Glass GLX

Looks to me, anyone will do the job. Am i correct ?

[rob@vems.co.uk]

Yes for some reason I'd go for the non-glass ones...

[uzelac]

Trying tonight

[rob@vems.co.uk]

Just to check "connect the two (diodes) to the cathode (-) striped end of an 18V Zener"

[uzelac]

Just to check "connect the two (diodes) to the cathode (-) striped end of an 18V Zener"

Argh
Friend who "knows things" assured me it will work this way.

Will make opposite version also

Thanks

[uzelac]

Done.

Tested on voltmeter, anything below 18V is not passing, and the difference above 18V is flowing, so when i tested with 30V i got ~12V after zener.
Hope it works tonight.

Muchos gracias

[uzelac]

Nop, couldn't make it work. But we succeed to short circuit one COP, +12 to common ground so have some burned wires.
Just hope VEMS and all IGBT's are OK.

Will see where are we tomorrow, hope to be more lucky

[GintsK]

Is it for tach driving?

Just as alternative. My way to drive old tachs is use relay coil as fake ignition coil. Tach output configured to one of I259 outputs with IGBT. And relay coil (just coil, other mechanical parts thrown out for keeping this thing quiet) connected between IGN+ and this output. Output goes to tach. This makes high enough voltage spike for old tachs. Be careful: cut any resistors or diodes out of relay - these elements are for spike eliminating - we do not need it in this case.
It results a bit simpler/cleaner install than with diodes.

Gints

[uzelac]

It's great to see many different options
Unfortunately, I don't have spare iGBT, so can't try this one.
Today I will try with the diode trick again, just need to revive wires to coils.

[rob@vems.co.uk]

You need to use the Zener to clamp the voltage to ~18v:

With the stripe of the Zener towards the other diodes.
What you've done is not clamp the voltage, and may have damaged the tacho.

[uzelac]

I did it just the way pictured here, resoldered it when you noticed the Zener is reversed.
Now it is like here. Part numbers are different, but shouldn't make a difference?!

What does clamp voltage means ?
As i said, nothing above 18V passes, and above that voltage starts to flow.
If i test put 30V on coil 1 or 2, i get ~12V at Tacho . Makes sense to me, although still not sure WHY that should work with tacho

I use BMW Bosch COPs, they look like this:


Three wires:
 +12V / ground / Coil -

I tried to connect two diodes "input" to Coil- but a friend "figured" a way to shortcuircit Pin1 and Pin2 (12V and ground) .... I hope i got just blown fuse, not blown COP or even worse IGBT or something in VEMS.

[rob@vems.co.uk]

Personally I would keep friends away from your engine, unless they are prepared to pay for the mistakes they're making while learning...
The tacho is expecting a signal from the coil as it discharges, the zener is there to clamp the voltage lower than the HT spike that will be kicked out when the coil sparks.
Without the zener clamping the voltage you may find that theres a small wire transmitting HT voltages to the back of your tacho - that would be a bad idea.

Rob