Electronic Ignition System Condenser

[ramon alban]

First Post here by Newbie.

Your valued knowledge gentlemen, please?

Seen on the attached image of a period Rover Ignition Module fitted to various RR vehicles and also Rover SD1 Efi cars, is a condenser connected between the White wire "+12 Volt Feed/Coil +ve" and "Earth".

On other period systems (eg, where the ign amplifier is on the side of the Distributor) a condenser is earthed with the coil retaining strap and connected likewise to "Coil +ve".

I would like to establish the purpose of this condenser and have come up with three possibilities.

1 - A Radio Frequency Suppressor

2 - To assist the Coil Voltage to collapse rapidly when the amplifier switches off the current thro' the coil thereby enhancing the HT discharge. IE - Fatter Sparks.

3 - To absorb the Back EMF spikes generated by the coil and thereby protect the electronics circuits elsewhere.

Does any one know if all, some or none of these reasons apply, and if None, what the heck does it do?

Much obliged.

Ramon

www.vintagemodelairplane.com

[Highway_Star]

You've pretty much hit it on the head with all 3.

Back in the day of breaker systems the condensor was vital to stop the flashover destroying the points too quickly.

Of your 3 reasons, I'd suggest Nº2 is the least important, the fast switching time of electronic systems takes care of that, you've no contact bounce to worry about either.

RF isn't as much of a problem on more modern systems, the plugs and leads are suppresive to a point. On my own Range Rover for example I had an engine speed related whine audible on some bands on my ham radio rig. That turned out to be coming from the alternator, rather than the ignition.

The back EMF issue is a good one, as I'm sure you know beack EMF spikes can be very high voltage, which the electronics in the car won't like. That said vehicle electronics, even Lucas, are amazingly robust. They have to be, in what is an electrically fairly harsh environment.

On Pico's website there are some good oscillograms of back EMF from ignition systems,

[FridgeFreezer]

You may find some familiar bits here

[ramon alban]

Thanks for the reply Highway Star, I'm thinking along the same lines. Also thanks Fridge Freezer for the V8 Owners link.

1. I recently found a 1988 RR cct diag suggesting the primary purpose of the Condenser was RF Suppression.

2. The Capacitor's ability to collapse the voltage rapidy jibes with me in that it is also across the battery and it would seem less likely to be able to do that unless the residual/intrinsic resistance of the wiring from battary thru the switch to the coil acted as a small ballast allowing the "remote" 12 volts to collapse more quickly and absorb the current from the coil likewise.

3. The suppression of spikes is, I think, important because the actual existance of the spike adds time to the period taken for the current to collapse naturally, and in many ways, spike control function would not be dissimilar to RF supression duties.

I do have another question. I am part way thro writing a "definitive" (if thats possible) explanation and test program for this type of ignition system for the Rover SD1 Efi community - which also encompasses many RR/LR ign systems of the period.

On the module in the above image in my first post there are two tags (at upper left) for the input trigger signal(s) from the dizzy inductor (or maybe Hall Effect device).

In the below image of a module I once ownedand its signal cable there looks to be a Blue or Blue/White and Red or Red/Black wires plus a tagged outer screen.

It would be a great help to nail that query down if anyone has such a module in their spares kit or on a car and can eye-ball the colours for me.

Thanks

Ramon

www.vintagemodelairplane.com

[FridgeFreezer]

This seems to be a very in-depth analysis of a component whose primary function is to go intermittently faulty as often as possible

[ramon alban]

This seems to be a very in-depth analysis of a component whose primary function is to go intermittently faulty as often as possible

Hello Fridge Freezer, I hope not, because by understanding the stresses that may be thereabouts will give me a clue as to why this component gets overlooked so frequently in the diagnosis of Rover/RR/LR (electronic) ignition faults.

Indeed, I dont recall seeing it earmarked that way on the various forums I visit, outside the context of "Points And Condenser" system which is quite weird really because they do have a propensity to fall over.

Wire colours I need to complete my representative cct diag of the 1982-86 system and hopefully the final product (article) will fit nicely into the Rover V8 Efi scheme of things on my website.

I did read the rules and I truly hope that your observation does not mean it is too "OT" for the LR4X4?

Ramon

[SteveRK]

Hi Ramon

I'm not an expert on electronics but regarding your point 2:

[2. The Capacitor's ability to collapse the voltage rapidly jibes with me in that it is also across the battery and it would seem less likely to be able to do that unless the residual/intrinsic resistance of the wiring from battary thru the switch to the coil acted as a small ballast allowing the "remote" 12 volts to collapse more quickly and absorb the current from the coil likewise.

Batteries do behave like capacitors in that they can & do absorb voltage spikes/fluctuations but I would suspect they do not respond as quickly as a dedicated capacitor? In the context of ignition pulses we are talking Milli-second time frames to resolve voltage spikes, hence the fitting of a dedicated capacitor. The alternators on Range rovers also have sometimes 2 capacitors fitted. It may be down to preventative precaution against unwanted 'noise' Just my thoughts, as I say I'm not that knowledgeable (well I did do electronics at college but that was many, many years ago) enough to be sure about this.

[FridgeFreezer]

Hello Fridge Freezer, I hope not, because by understanding the stresses that may be thereabouts will give me a clue as to why this component gets overlooked so frequently in the diagnosis of Rover/RR/LR (electronic) ignition faults.

Which component, the ignition amp or the condenser? Mostly the condenser will be overlooked because no-one ever takes the amps apart (the individual components are not sold separately by Land Rover) so they either bin it and replace, or bin it and fit a later dizzy with the far cheaper dizzy-mounted amplifier. Or bin the dizzy entirely and join the 20th century with EDIS.

Which wire colours do you need? They're almost all on the official wiring diagrams, which should be available in the technical archive.

[ramon alban]

Which component, the ignition amp or the condenser? Mostly the condenser will be overlooked because no-one ever takes the amps apart (the individual components are not sold separately by Land Rover) so they either bin it and replace, or bin it and fit a later dizzy with the far cheaper dizzy-mounted amplifier. Or bin the dizzy entirely and join the 20th century with EDIS.

Which wire colours do you need? They're almost all on the official wiring diagrams, which should be available in the technical archive.

The condenser was the component under review. Its a separate component mounted on the coil bracket, when the amplifier is fitted on the side of the dizzy.

Silly, troublesome little thing - always overlooked - but beautiful none the less, for what it does so elegantly - just like Cinderella.

Now these wire colours? Couldn't find them on Rave or similar ccts.

On this image (which needs a click) http://forums.lr4x4.com/index.php?act=atta...st&id=16812

you can see a single coil of signal cable plugged into the side of the module with an earth tag and connector at one end and a connector at the other end that plugs into the dizzy.

The wires look Blue and Red, but are they that in reality? Or do they have added stripes like Blue/White and Red/Black?

Click the link to see the image. Someone may have one of these cables on their car to compare?

Ramon

[DEANO3528]

Definitely solid red and solid blue. I have one in the shed I took from an old SD1

[ramon alban]

Definitely solid red and solid blue.

No doubt about that then Deano, As a special thanks I offer this image of my lump that might transplant very nicely into any LR4X4. Might have to stay out of the mud tho', Thanks, Ramon.