Lotus Elan

Wiring in Lumenition module

PostPost by: NYK » Wed Nov 06, 2019 2:15 pm

I’m putting my Plus 2 back together (bought in boxes). My wiring loom supports just a single supply wire going to the coil, so no ballast resistor set up. The live feed to the coil of course goes via the Rev counter.
I’ve also got a Lumenition module which some previous owner has marked the live feed to it coming via the coil feed. On the face of it that sounds fine but I just want to check that wiring it this way will not effect the operation of the Rev counter. So The Rev counter is looking for pulses on the positive line to the coil, if I’m drawing a low constant current for the Lumenition does this compromise the Rev counter operation?
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PostPost by: Foxie » Wed Nov 06, 2019 4:19 pm

I had a Luminition system for many years before I fitted the DTA mapped system earlier this year. It never needed looking at. I also added a Luminition "MegaSpark 2" ballast resistor & coil some time ago, but the Luminition works fine without it.

The Luminition feed comes from the ignition +ve feed to the coil.

Your tacho will still be seeing the current pulses, so it should work ok.

I also had my bouncing tacho converted to electronic operation a very long time ago. The tacho then took its signal from the distributor side of the coil.

:)
Last edited by Foxie on Wed Nov 06, 2019 4:38 pm, edited 1 time in total.
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PostPost by: englishmaninwales » Wed Nov 06, 2019 4:25 pm

That arrangement should be fine with respect to the rev counter (mine was converted to negative earth by a previous owner). Make sure the coil has the correct internal resistance otherwise you’ll cook the Lumenition module beyond repair (there is a very helpful tech support - if you ring them ask to speak to Roy - Autocar Electrical 020 7403 4334)

Malcolm
Edited to add: as Foxie says fit the Megaspark coil and ballast resistor, makes for good starting. (£27.50 + vat and post)
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PostPost by: Craven » Wed Nov 06, 2019 4:37 pm

Current through the coil will essentially be the same, the Lumenition unit replaces the contact breakers connecting the negative side of the coil to earth. Positive to unit from the coil terminal provides operating voltage for the electronics in the Lumenition unit, as you say low current, this is not the current being switched by the unit.
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PostPost by: NYK » Wed Nov 06, 2019 5:22 pm

Thanks all, very helpful answers
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PostPost by: vxah » Wed Nov 06, 2019 5:27 pm

Pretty sure I remember the tacho not working with that wiring set up. I seem to recall needing a separate feed to the Luminition module..
Are you sure you don't have a ballast? Could be in the wire.. Is there a bypass terminal on the starter solenoid?
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PostPost by: NYK » Wed Nov 06, 2019 6:53 pm

vxah wrote:Pretty sure I remember the tacho not working with that wiring set up. I seem to recall needing a separate feed to the Luminition module..
Are you sure you don't have a ballast? Could be in the wire.. Is there a bypass terminal on the starter solenoid?


Definitely no ballast resistor, I have done extensive work on the loom and also there is no separate 12 volt coming from the starter solenoid as would be the case on a ballasted system. How sure are you about tacho not working if Luminition is fed from the coil, it’ll be a bit tedious having to run another feed through.
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PostPost by: mbell » Wed Nov 06, 2019 7:17 pm

It will work if connected at the coil +ve and the tacho will still "work" but it may no longer be accurate.

The standard tacho works by "counting" current pulses to the coil, which it can convert to RPM as there one pulse per cylinder fire. Adding a Aldon/pertronix adds a transistor to the circuit that is also switching on/off at engine speed adding another current pulse per cylinder fire. This additional current pulse is small but it is sometime picked up by the tacho meaning the tacho is register more pulsed and result in a false higher rpm being reported and likely general instability as the tacho does/doesn't pickup the extra pulse.

Whether a tacho actually picks up the extra pulses is very variable, so for some people they see no issues and everything works fine. Some people see a lot variability in the tacho reading.

The solution is to simply use a different switched +ve to power the ignition module. Then the extra pulses aren't seen by the tacho and everything should work fine. It is pretty easy on the +2 to add a relay at the solenoid to add an extra switched feed. I've done this and run the my ignition module, fuel pump and electronic rev limiter from it.
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PostPost by: NYK » Wed Nov 06, 2019 7:46 pm

mbell wrote:It will work if connected at the coil +ve and the tacho will still "work" but it may no longer be accurate.

The standard tacho works by "counting" current pulses to the coil, which it can convert to RPM as there one pulse per cylinder fire. Adding a Aldon/pertronix adds a transistor to the circuit that is also switching on/off at engine speed adding another current pulse per cylinder fire. This additional current pulse is small but it is sometime picked up by the tacho meaning the tacho is register more pulsed and result in a false higher rpm being reported and likely general instability as the tacho does/doesn't pickup the extra pulse.

Whether a tacho actually picks up the extra pulses is very variable, so for some people they see no issues and everything works fine. Some people see a lot variability in the tacho reading.

The solution is to simply use a different switched +ve to power the ignition module. Then the extra pulses aren't seen by the tacho and everything should work fine. It is pretty easy on the +2 to add a relay at the solenoid to add an extra switched feed. I've done this and run the my ignition module, fuel pump and electronic rev limiter from it.


OK you’ve convinced me but what switched live are you proposing I used to energise a relay near to the solenoid? I can’t think of any ignition switched live in the engine bay apart from that going to the coil. Of course I can run another wire from the ignition switch, just a bit annoying as I’ve just bound the loom in that area.
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PostPost by: mbell » Wed Nov 06, 2019 9:56 pm

Thinking about it more, the wiring on my car has been modified to link the ballast power wire and direct 12v feed together. The 12v fed supply line come from the solenoid. So this feeds the coil power back to the solenoid, that I use to trigger a relay.

Which is basically the coil power supply to trigger the relay, which is fine as its a constant current draw so won't effect the tacho operation.
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