Ignition switch..issues

[Ron Kwas]

Clive;

ACC terminal should really be renamed "Everything But Ignition", because of the way things should be connected (for instance, you might want to power the Radio while parked, engine OFF, and BTW, ACC terminal does get powered when Ign is ON).

IGN terminal gets everything that needs power including IGN when you want the engine running, so I would answer yes to your question about the two white wires.

Referring to the OE Ign Sw wiring linked below, notice that term 54 is (what I call) the Ign Pwr terminal, and it is internally connected such that it is powered when Key is in the ACC position, so in a conventional Ign Sw, it would really be analogous to the ACC terminal. The Ign Coil power (an unnamed/unnumbered terminal in the Volvo Ign Sw, since inaccessible) would, in a more typical Ign Sw like your replacement, be named IGN. You could/should verify this information with a DVM voltage check, but it is quite typical of replacement Ign Switches. I hope this explanation comparing the unique Volvo and replacement Ign switches helps, and makes the function and nomenclature clear!

Finally, I also hope you didn't lunch the Elec Ign Module (they are electronic and have little sense of humor for misconnection!), but repeating, it should of course be powered by the IGN terminal.

Reference: https://www.sw-em.com/IGN%20Switch%20Function.JPG

Cheers

[142 Guy]

Originally Posted by CLIVERALLY

Thanks Derek and Ron

In short no it did not start ..but I have tracked it down to the ignition module (points replaced by electronic some years ago) as I have no spark at the king lead. All other wires to and from the coil have been traced and checked and OK. Also I have a brand new spare coil which I used to ensure the extant one was good. It seems that when I was arseing around with the car I probably shorted out the module somehow

If your ignition module is the Pertronix or the other one or two modules that look just like the Pertronix, it is moderately difficult to damage them. The common source of damage is leaving the ignition energized where the magnet on the distributor shaft is positioned such that it causes the output of the module to go into the conducting condition (equivalent of the points being closed). This causes coil primary current to flow through the module. Aside from heating up the ignition coil the module will heat up and given enough time, cook itself.

If you reversed the connections of the red and black wires on the module, then it is also possible to cook the module relatively quickly if the magnets on the distributor shaft are correctly positioned.

However, it is very easy to check the operation of the module with a simple light bulb style continuity tester. I recommend a 12 volt lantern battery and 12 volt light bulb. Connect the - of the battery to the chassis. Connect the red wire of the module to the + terminal of the battery (powers up the module). Connect the 12 volt light bulb between the + terminal of the battery and the black wire from the module. Rotate the crankshaft. If two complete rotations of the crankshaft gives you a sequence of four on-offs on the light bulb, the module electronics are working.

[Ron Kwas]

Clive; ...good info from 142Guy!

142Guy; I was under the impression that the Pertronics electronics were smart enough to know (specifically detect) when the input magnet wasn't pulsing, and to then inhibit ign coil primary current to prevent its output switch (transistor) and coil from overheating with the resulting 100% duty cycle current...so the Pertronics module really is just as "dumb" as "points"...!

Cheers

[142 Guy]

Originally Posted by Ron Kwas

Clive; ...good info from 142Guy!

142Guy; I was under the impression that the Pertronics electronics were smart enough to know (specifically detect) when the input magnet wasn't pulsing, and to then inhibit ign coil primary current to prevent its output switch (transistor) and coil from overheating with the resulting 100% duty cycle current...so the Pertronics module really is just as "dumb" as "points"...!

Cheers

Ron:

The second line in the Pertronix installation sheet reads:

Warning!!! Leaving the ignition switch “ON” with the engine “OFF” for
an extended period could result in permanent damage to the Ignitor.

I deduce that this means the Pertronix does not have any 'smarts' that would prevent thermal damage. Also, I initially had a Pertronix module on my car after I finished the restoration. I set up the initial static ignition timing using the continuity light test method I described in my previous post. In the process of setting the timing to 10 deg BTDC I would slowly nudge the distributor to arrive at non conductivity at 10 deg. I never observed the module 'timing out' which supports your observation that the module is as dumb as points.

As an aside, the Pertronix eliminates the points wear issue; but, degrades the peak performance of the ignition system. When ignition points are closed the voltage drop across the points is effectively zero. When the Pertronix module output transistor is switched on the voltage drop across the module is between 1.5 and 2 volts due to Vce sat. This reduces the peak dwell current available to the coil. On the low reving B20 4 cyl engine this is a minor running issue. It is a potential issue during starting. On my 1971 142 E the voltage at the coil + terminal during cranking was dropping to around 9 volts. With the Pertronix module the voltage across the coil was reduced to about 7 volts. This reduced the peak dwell current to about 77% of the value with points. Since spark energy is a function of the square of the peak dwell current, the spark energy is about 60% of what you would get with the points. If everything else is spot on, the engine will start just fine. If its a really cold day, your spark plugs are no longer virgin and you have managed to wet the plugs trying to start the car you may wish for that extra 40% of spark energy.

[Ron Kwas]

142Guy;

I have never seen the Pertronics data/installation sheet, but fully agree with your deduction based on the caution from it...

Your Timing technique with the Pertronics unit describes my Static Timing with Points procedure exactly...and why shouldn't it...they should be the same!

...and I can also appreciate the additional info and insights from your measurements and experience...2Vce sat is quite high for the Pertronics, and suggests a Darlington output stage to me, with it's much higher Vce sat (it would be nice if it was a MOSFET output with an ON Resistance of .01Ohms...but no such luck!). Indeed, this would make a significant difference starting with less than optimal conditions...

Cheers

[142 Guy]

Originally Posted by Ron Kwas

142Guy;
...and I can also appreciate the additional info and insights from your measurements and experience...2Vce sat is quite high for the Pertronics, and suggests a Darlington output stage to me, with it's much higher Vce sat (it would be nice if it was a MOSFET output with an ON Resistance of .01Ohms...but no such luck!). Indeed, this would make a significant difference starting with less than optimal conditions...

Cheers

I rounded up to 2 volts because I didn't want to complicate the idea with decimals; but, it is quite high which would be consistent with a darlington pair output stage.

I can't take credit for identifying the problem. It was raised in another thread, I think in the Swedespeed Amazon or 1800 forum. I was initially a little doubtful, expecting a Vce sat of around 0.6 volts so I went out and measured the module 'on' voltage and discovered that it was above 1.5 volts. I was suitably surprised and slightly dismayed. Unfortunately, I can't find the thread with the actual values I measured.

One of the issues with bipolar transistors was that when you operate them in the saturated state their switch off time increases. A fast switch off is essential to generating a fast changing field in the coil and getting a hot spark. Pertronix may have set the current bias on the module to keep the output transistor pair just out of saturation to speed up switching which may be why the on voltage is higher than I would have expected.

Mosfets have come a long way. Long ago in a previous century when I was in university they were primarily considered signal level devices - 'real men' used bipolar transistors or SCRs. I think the Pertronix was probably designed in the last century and at the time the default would have been bipolar. The market for 'improved' Pertronix modules is probably small so there is likely no financial incentive to update them. If they were to be designed new today, a MOSFET might be the technology of preference. I am using power MOSFETS for the injector drivers on my car; but, the injectors are relatively low current - 1.6 amps. I am using ignition coils lifted from a wrecked Toyota Corolla which are logic level coils. I don't know whether the coils uses Mosfets or bipolar because of the higher dwell currents. I am running about 7 amps dwell current which is well beyond the switching rating of the Pertronix module.

[Derek UK]

The original Pertronix I had no protection and would burn up the module if you left the ignition on. It was a case of, if the magnet stopped opposite the sensor in the module it would overheat and die. If you connect the red and black wires the wrong way round it's instant death when you switch on the ignition. I suffered the last one on my Saab 96 when talking to a friend and not concentrating. Expensive mistake. The Pertronix II has built in protection but may not be available for our distributors. Check the lists on their site. Worth the extra few quid and does apparently have some other features too.

[CLIVERALLY]

Ok..thanks everyone for the info.
I have already ascertained the issue is the module but thanks for the v v useful info..Seems I have fallen foul of the "ignition left on too long" syndrome. I wish that Lumenition did a kit for my car, I always used them on my stage rally cars and they never let me down...granted the only reason this broke was because I had been buggering about with the wires.