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What does this damaged capacitor do??

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Old Feb 26th, 2021, 17:21   #41
142 Guy
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Originally Posted by YorkshireDave View Post
Question.
Why not fit an aftermarket 'electronic' ignition? Not only do you virtually eradicate points wear as you're only switching low voltage & low current, but the quality of spark is infinitely better across the range and interference is also virtually eliminated too.
Just a thought ...
If you are referring to the modules such as the Pertronix that just replace the ignition points, be aware that there is a potential down side to these modules. The modules appear to use a darlington pair power transistor to switch the ignition coil primary current. With ignition points, when the points are closed the voltage across the points is close to 0 volts. Because of the use of the darlington pair, when the transistor is switched on (equivalent of points closed) the voltage across the transistor is approximately 2 volts (transistors are imperfect switches). This voltage is called Vce-sat and is a fact of life for bi polar transistors.

The 2 volt drop across the module reduces the voltage available to drive the coil dwell current which generates the spark. If your electrical system is in good shape and the running voltage is around 13.8 - 14.2 volts, the 2 volt reduction in voltage applied to the coil primary will not have a material effect on the spark energy within a B20's normal rev limit of 6000 RPM. However, the 2 volt drop across the module can have a material effect during starting. During cranking of the starter motor (particularly if you have the original non permanent magnet starter) the terminal voltage of the battery will drop from 12 volts to 10 volts (or less). This is further reduced by the decrepitude of the wiring in most vintage Volvos so that the voltage at the coil + terminal can be significantly less than 10 volts during operation of the starter motor. This means that during starting the voltage across the ignition coil can be significantly less than 8 volts. This will have a material effect on the energy of the spark that the coil is able to generate.

If you have to start your car in cold weather and your battery and vehicle wiring are in less than perfect shape the ignition modules will reduce the spark energy potentially making the car harder to start.
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Old Feb 26th, 2021, 18:03   #42
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If you have to start your car in cold weather and your battery and vehicle wiring are in less than perfect shape the ignition modules will reduce the spark energy potentially making the car harder to start.
To be honest, I have no idea how they will now be designed. No doubt the accountants will have taken their 10 pounds of flesh! The last one I fitted, I built myself but it was way back when (I suspect around late 1970s). I ran that on my MGB for over 5 years and it never missed a beat in winter or summer and did wonders for both starting and fuel consumption. I do understand however that 'cold' here in the UK is not 'cold' as in Canada

I was assuming (yes I know it's dumb) that today's systems would be even more reliable... Perhaps it's best to dig out that old cct diagram from Elektor (?) Magazine and just make it yourself. Seem to recall (but may well be wrong as I'm now old) using a 2n3055 on an ali case...
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Old Feb 26th, 2021, 20:42   #43
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2N 3055 - that is an ancient (mid '60s design); but, historically significant transistor (check Wikipedia for gory details). It is still in production; but, likely as a replacement only, not for new designs. You would probably want to adopt a newer design anyway because with its limited production it comes with a very high price considering its rather middling performance by modern standards.

It is not a darlington pair; but, it does have a rather disappointing Vce sat. At a collector current of 4 amps its not bad at 1 volt; but, it rises quickly to 3 volts at 10 amps. You could definitely do better with a more modern design.

You made the comment about reliability. I think the modules like the Pertronix provide a service reliability (defined as not failing) that is probably just fine. That is a separate issue from the performance degradation that you may suffer under starting conditions. That loss of performance may never be a material issue if the engine is kept in good tune, the battery is in good condition and you are not trying a start when it is -30C.

The Pertronix and similar modules will address the issue of timing drift and detrioration of performance as the ignition points wear. However, on old car like ours that completely misses the issue of wear in the distributor mechanicals. Sticky advance mechanisms and worn distributor shafts are a real issue. I ran with a Pertronix module on my B20E for a couple of years. The module worked just fine; however, when using a timing light to check the operation of the advance mechanism I found that above about 2700 RPM the timing was bouncing around about 6 degrees - it was hard to be accurate because the timing marks just became a blur. I removed the advance mechanism, cleaned, relubed and bench checked its operation. That didn't resolve the problem so I purchased a re bush kit for the distributor; however, I was never able to get the retaining pin on the end of the distributor out so I never re bushed it. I ended up adopting the nuclear option of implementing ignition control in Megasquirt with coil on plug and timing by slotted wheel and optical pick ups. An extreme option; but, my timing marks are now nice and steady.
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Old Feb 26th, 2021, 21:20   #44
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I think the electronic ignition the other person (sorry forgot who said it now! ) may have been on of the "new breed" of contactless (rather than contact-assisted as the Elektor home-build one was [i have vague memories of it] and most other "bolt on" aftermarket electronic ignition units of the time such as the Sparkrite SX1000, SX2000 etc units that literally clipped onto the coil with plastic coated Terry clips and had a DPDT- centre off changeover switch for contact-assisted or just contacts for the ignition.

The downfall of the contact-assisted units was that over time, the contacts could "glaze" themselves as there wasn't enough current flowing through them to burn off oil residues from slightly fumy engines. This could cause misfiring and the answer was to temporarily revert to contacts only to clean them up - usually just a few days use.

https://123ignition.com/products/?filter_brand=volvo

Something like that where the distributor is rebuilt with an electronic (Hall Effect i think) trigger in it, the ballast resistor is bypassed and the coil i believe is replaced too to make it a bespoke complete electronic system is what i think was being suggested.

There are similar variations on a theme where a small module fits in place of the contact breakers and drives the coil directly, no other mods as far as i know.

These days a contact-assisted add-on unit would probably use a MOSFET instead of the venerable 2N3055 to reduce the switching voltage across the semiconductor and also provide faster switching.
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Old Feb 27th, 2021, 21:42   #45
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2N 3055 - that is an ancient (mid '60s design); but, historically significant transistor (check Wikipedia for gory details). It is still in production; but, likely as a replacement only, not for new designs. You would probably want to adopt a newer design anyway because with its limited production it comes with a very high price considering its rather middling performance by modern standards.

It is not a darlington pair; but, it does have a rather disappointing Vce sat. At a collector current of 4 amps its not bad at 1 volt; but, it rises quickly to 3 volts at 10 amps. You could definitely do better with a more modern design.

You made the comment about reliability. I think the modules like the Pertronix provide a service reliability (defined as not failing) that is probably just fine. That is a separate issue from the performance degradation that you may suffer under starting conditions. That loss of performance may never be a material issue if the engine is kept in good tune, the battery is in good condition and you are not trying a start when it is -30C.

The Pertronix and similar modules will address the issue of timing drift and detrioration of performance as the ignition points wear. However, on old car like ours that completely misses the issue of wear in the distributor mechanicals. Sticky advance mechanisms and worn distributor shafts are a real issue. I ran with a Pertronix module on my B20E for a couple of years. The module worked just fine; however, when using a timing light to check the operation of the advance mechanism I found that above about 2700 RPM the timing was bouncing around about 6 degrees - it was hard to be accurate because the timing marks just became a blur. I removed the advance mechanism, cleaned, relubed and bench checked its operation. That didn't resolve the problem so I purchased a re bush kit for the distributor; however, I was never able to get the retaining pin on the end of the distributor out so I never re bushed it. I ended up adopting the nuclear option of implementing ignition control in Megasquirt with coil on plug and timing by slotted wheel and optical pick ups. An extreme option; but, my timing marks are now nice and steady.
I only mentioned it because I have a stock of old parts including old PICs etc. Too tight to throw stuff that will 'do' in my projects away Recently used some along with LM317s (also have shed loads in stock) to increase the current capacity of the variable supply I needed. Hey, I know there are 'better' products out there but to my tiny mind it helps to use what we have rather than throw it away simply because it's no longer vogue. I'm too tight & too old to do so

Now someone has mentioned it, it might have been the Elektor kit was used in my Morris Minor. I now seem to recall a slotted disc (as you used to find in computer mice) used for switching...
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Old Feb 27th, 2021, 22:24   #46
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I can one-up you. I have a GE 6AK5, a Westinghouse 6AU6A and a Sylvania 6AT6 tube, all new and in their original boxes. I can't remember what they were for and I think the probability that they will ever get used for anything is exceedingly low; but, I can't bring myself to dispatch them to the waste bin.

Maybe I should list them on E Bay to see if there are any vintage tube collectors.
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Old Feb 28th, 2021, 00:24   #47
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Quote:
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Now someone has mentioned it, it might have been the Elektor kit was used in my Morris Minor. I now seem to recall a slotted disc (as you used to find in computer mice) used for switching...
The Elektor was a self-build thing, (not sure if there was even a PCB available) and contact-assisted.

Your Moggy sounds more like a Lucas Optronic (think that's the name or was it Lucas "Opus" Electronic?) conversion kit where the contact breakers were replaced with an opto-isolator and slotted disc, usually with as many "fingers" as cylinders that was attached to the dizzy shaft.
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