Condenser life span

[Mervyn Hyde]

That MG thread is very interesting Fred. I have tried this one I mentioned earlier and it also works, at least for the period I tested it.

It would seem that the ancient design of the 'condenser' as we know it is on the way out, as the components are becoming poorer and poorer quality and failure rates increase. Older ones that will also eventually fail may not be able to be replaced with like-for-like quality and alternatives (and likely improvements) will need to be sourced.

[Fred Winterburn]

I've been thinking about this issue for a long time. With the CDI that I use, the condenser is under-stressed electrically speaking, and not necessary unless one wants to switch back to Kettering mode. I have never had a condenser failure, or at least an outright failure in all of the years I have owned cars with points, but in recent years many failures have been reported. My recent tests with a good polypropylene film capacitor and the ceramic capacitor have shown that they will out-perform a conventionally made condenser of the same approximate capacitance(better arc suppression leads to more spark energy and prolonged contact life). I think this in almost entirely due to the internal terminations which are also the weak link for longevity with the traditional foil/plastic dielectric condenser.
The ceramic capacitor, although much more expensive ($11CAD) than a modern polypropylene capacitor (varies, but about 50 cents) is the better option because of its temperature rating (in my opinion). A good high voltage polypropylene film capacitor will take the voltage, but might not take the temperature, being rated at best 110 degrees C. On the Brit cars, the condenser is usually located inside the distributor for an even hotter environment. It is very important to keep the capacitor as close to the points as possible with short lead lengths, so this most likely means high temperatures. I believe,125 degrees C should be the minimum rating, which makes me wonder what the temperature rating of the cheap condensers available today really is, considering I can't find a replacement film capacitor with the voltage rating and the temperature rating that I think is required.
The ceramic capacitor by Kemet (C350C224KDR5TA) seems to fit the bill for a good replacement, but it should be encased within an old condenser shell and epoxied inside for structural reliability. A bit of a fiddle and some soldering skill required, but most likely the last condenser the car will ever need. Fred

That MG thread is very interesting Fred. I have tried this one I mentioned earlier and it also works, at least for the period I tested it.

It would seem that the ancient design of the 'condenser' as we know it is on the way out, as the components are becoming poorer and poorer quality and failure rates increase. Older ones that will also eventually fail may not be able to be replaced with like-for-like quality and alternatives (and likely improvements) will need to be sourced.

[Mervyn Hyde]

Very useful advice Fred for most of us, eventually.

[Fred Winterburn]

So, Here's the result of potting the ceramic capacitor inside an old Lucas condenser shell. It should be just as easy to do with a Bosch shell. I posted this on the MG forum. I don't know what the forum rules are for cross-posting, but since I made the post and did most of the work, I don't see why not.
I potted the Kemet ceramic capacitor (C350C224KDR5TA - Multilayer Ceramic Capacitor, 0.22 µF, 1000 V, Goldmax, 300 Series, ± 10%, Radial Leaded, X7R) in a Lucas condenser shell. One lead soldered to the shell inside and the other soldered to a short piece of teflon insulated wire (because I had a short scrap). At 7000rpm (8cyl). The 'new condenser' ran cold to the touch generating less heat after 10 minutes than the Ford condenser that is physically twice as large. EDIT: Forgot to mention that this last test was done with 20V applied to the coil as in the worst case test for the unpotted capacitor) The older condensers must have a huge ESR value compared to the modern ceramic capacitor. Certainly, the the poorly made terminations inside the standard condensers don't help in that regard. What surprised me is what an effective heat sink the steel can is for dropping temperature even in still air, not bolted down to the distributor. I fully expected based on the last test with the ceramic capacitor un-potted, that even in the Lucas shell it would generate more heat. Instead, it ran the coolest of the three. See the picture. By the way, for potting epoxy I used JB weld. It has some iron in it, but despite that, it has a huge dielectric strength, so don't let the iron content concern you if you decide to use it. Also it doesn't shrink (or at least not much) compared to some epoxies, so is good enough for this application. Just don't use 5 minute epoxy (junk and cures too quickly). Fred

I've been thinking about this issue for a long time. With the CDI that I use, the condenser is under-stressed electrically speaking, and not necessary unless one wants to switch back to Kettering mode. I have never had a condenser failure, or at least an outright failure in all of the years I have owned cars with points, but in recent years many failures have been reported. My recent tests with a good polypropylene film capacitor and the ceramic capacitor have shown that they will out-perform a conventionally made condenser of the same approximate capacitance(better arc suppression leads to more spark energy and prolonged contact life). I think this in almost entirely due to the internal terminations which are also the weak link for longevity with the traditional foil/plastic dielectric condenser.
The ceramic capacitor, although much more expensive ($11CAD) than a modern polypropylene capacitor (varies, but about 50 cents) is the better option because of its temperature rating (in my opinion). A good high voltage polypropylene film capacitor will take the voltage, but might not take the temperature, being rated at best 110 degrees C. On the Brit cars, the condenser is usually located inside the distributor for an even hotter environment. It is very important to keep the capacitor as close to the points as possible with short lead lengths, so this most likely means high temperatures. I believe,125 degrees C should be the minimum rating, which makes me wonder what the temperature rating of the cheap condensers available today really is, considering I can't find a replacement film capacitor with the voltage rating and the temperature rating that I think is required.
The ceramic capacitor by Kemet (C350C224KDR5TA) seems to fit the bill for a good replacement, but it should be encased within an old condenser shell and epoxied inside for structural reliability. A bit of a fiddle and some soldering skill required, but most likely the last condenser the car will ever need. Fred

That MG thread is very interesting Fred. I have tried this one I mentioned earlier and it also works, at least for the period I tested it.

It would seem that the ancient design of the 'condenser' as we know it is on the way out, as the components are becoming poorer and poorer quality and failure rates increase. Older ones that will also eventually fail may not be able to be replaced with like-for-like quality and alternatives (and likely improvements) will need to be sourced.

[Mervyn Hyde]

Excellent work Fred. I noticed that on my colleague's Ferrari exhaust temp sensor that a similar epoxy encasing is used to insulate the circuitry. I have ordered a couple of Kemet ceramic capacitors to test them also.

[Mervyn Hyde]

Today I installed a Gammatronix ignition module (Henceforth referred to as a Gamma). I had a Permatune installed so no capacitor in circuit anyway. Connected it up as per the instructions in 20 minutes including adding end terminals to interface with a stock system. Turned the key with a couple of pumps of the gas pedal and it fired up and settled down to a 650 rpm idle. Obviously it did not know I had messed with the ignition. If the Gamma should fail it will take less than 5 minutes to go back to stock as I have left the capacitor wire ready to be reconnected with a male and female push on connector. Just like with the Permatune the points will not wear but I anticipate having to adjust them as the points lifter wears down against the distributor cam lobes.
10% of the price of a Permatune and about 12% of the size. I anticipate no change to performance but if it is worse I will report back with negative feedback.
No worries now about capacitors.
If it works as expected I will probably buy a few more for the spare engines.
I installed it using velcro for now but will likely figure out a more acceptable mounting in time.
Note the size disparity with the Permatune mounted above the Gamma.

David I can see that you connected the Red Gamma wire to the coil supply directly. On their instructions I can see a discussion about ballasted and non-ballasted coils. They seem to suggest that with a ballasted coil (are ours?) the Red should be connected to a switched voltage source other than the coil?

Merv

[David Jones]

12 volt system requires a ballast but not needed on 6 volt Merv.

[Mervyn Hyde]

Thanks David.

[Craig Richter]

David, please explain "12 volt system requires a ballast"

[David Jones]

Craig, ballast resistors came in with 12 volt systems to limit coil voltage after starting to extend coil life. Many cars have 8 volt coils and when cranking the engine the ballast resistor is shorted out so full battery voltage is applied to the coil which at that time is more like 10 volts, therefore better spark and easier starting. I recently melted a Bosch 12 volt coil by omitting the ballast with a Crane Cams optical ignition system. I should have read the instructions more carefully. 6 volt systems don't need one because there are apparently no 4 volt coils.

[Martin Benade]

Lots of 12v coils (VW for example) do not run a resistor. It depends on what the primary winding of the coil was designed for/ how much current it will draw.

[David Jones]

The Crane cams system specifically calls for a ballast resistor for their 12 volt version Martin but it also goes on to specify that it is only needed if the coil resistance is lower than 1.8 Ohms. One has to read the instructions all the way through. I confess I have been guilty of not doing that.

[Craig Richter]

David, I remember ballast resistors from old American cars: a small ceramic "boat" a few inches long with a wire coil down the length to dissipate some voltage. Back in the day, Bosch made a red coil that came with such a resistor, but I haven't seen one of those for years. I don't think that little "boat" was very reliable. The Bosch 12-volt coils 356's use don't come with any ballast resistor, hence my question. The coil resistance must be greater than 1.8 ohms. Thanks.

[David Jones]

I ran a 12 volt Bosch blue coil on the F Vee and only ever killed one in 30 years. No ballast resistor.

[Mervyn Hyde]

The context of the question I was asking was in relation to the instructions that Gammatronix publish. It affects which source of switched power you need to use for their unit.

"Some vehicles have what is called a Ballasted Coil. These systems supply full voltage to the coil when the engine is starting, then drop it to a lower level whilst it is running, using a resistor in the coil power supply (David's comment above). This arrangement provides an extra high voltage spark when starting, but not during normal running as this would overload and overheat the coil over time. If you do not have a ballasted coil (full voltage supply at coil with engine running) you can connect the red power lead to the coil's ignition switched supply directly at the coil. If your system has a ballasted coil, you MUST take power for the unit from another "full supply voltage" ignition-switched source. If you are not sure if you have a ballasted coil, measure the supply volts to the coil's power terminals with ignition on and engine running – it should be at least 6v (for a 6v system) or 12v respectively for a non-ballasted system. Red Wire: Fit the Red wire to the coil supply terminal or another source of DC power switched from the ignition switch if you have a ballasted coil."

So the question is what is the acceptable voltage for the Gamma AT the coil supply on the 356 with the engine running on a 6 volt car with one of the newer (e.g., Bosch silver) 6V coils? The engine-off/IGN on voltage is 6.4V and running, it is about 7.3-7.4? So, both outputs should be fine with the Gamma Red wire connected to the coil supply terminal, I believe. I will check with the Gamma people and report back.

All good to connect to the supply at the coil on the 6V 356 according to the advice of their tech guy. Will do a trial of the Gamma today.