Technical Condensers

[Toshi 975]

The ongoing discussion
After a friends partially tuned car suffered a breakdown and had to be recovered the breakdown man blamed it on the carb so I got to hear about it pdq as I sold the carb to the guy. I expressed surprise as I said it was by far and away the best condition Panda 30 carb I had ever had my hands on, straight off a low mileage car complete with manifold and head. As Bugsymike says it is often hard to tease out the story of what happened but between two accounts I pieced it together. Car would tick over but was very reluctant to Rev and as the throttle was applied the engine would misfire with associated pops and bangs.
this sounded a familiar story to me but I did some internet research anyway focusing on condenser failures. They can just pack up or often deteriorate over time as the internals break down. One guy had written an extensive thesis on condensers including a forensic analysis of failed ones which he opened up to identify what went wrong. A number of points arose :
1) If you have an old condenser that is working leave it alone.
2) Many replacement condensers are now poor design and manufacture so more prone to failure.
3) Seek out old or original stock where possible with one guy from the US recommending getting used ones from car breakers.
4) The racing spec ones were recommended for reliability but also old Lucas condensers got a high rating.
Still waiting to hear about the broken down car but fingers crossed that a decent condenser saves the day.
Apart from Fiats I have been caught out by condensers on an old Renault 14, back of nowhere in France luckily I had the old one in the boot, also on a Saab when a new one was knackered from the start.

 

[Ant Knox]

I've no reason to doubt the breakdown man's abilities, but I wonder if "It's the carb" was just a simple roadside diagnosis? after all, the majority of recovery drivers these days probably haven't much regular hands-on experience with classic naturally aspirated motoring.
It's amazing how electrical and fuel related symptoms can manifest in such similar ways, it used to drive me nuts with my classic Vespa, which in many ways was very similar to the 500.

 

[Toshi 975]

I've no reason to doubt the breakdown man's abilities, but I wonder if "It's the carb" was just a simple roadside diagnosis? after all, the majority of recovery drivers these days probably haven't much regular hands-on experience with classic naturally aspirated motoring.
It's amazing how electrical and fuel related symptoms can manifest in such similar ways, it used to drive me nuts with my classic Vespa, which in many ways was very similar to the 500.

My thoughts exactly on recovery man
Vespa eh ? I watched Quadraphenia last night which stirred so many memories and that closing scene would be painful for Vespa enthusiasts

 

[Goldnrust]

I've have been caught out by quickly failing, or failed out of the packet, new condensers for my Daimler v8 250 and 70's Suzuki motorbike also. Clearly it's not just old Fiats where there are problems.

Ultimately the condenser requirements for any vehicle with a 12v negative earth points ignition with a standard coil are quite similar, so that does open up some options when searching for alternatives that might work. It becomes more about does it have the right connector on the end and will it fit in the distributer rather than about its capacitance values. I'm using 1980s NOS Vauxhall condensers on my Daimler and 500 currently, and so far so good!

Another avenue I'd like to explore with condensers is using a modern capacitor instead, after all the condenser is only a rudimentary capacitor. While researching information for my pre-war motorbike project, I came across this page on magneto rebuilds that recommends a particular modern capacitor that they use to replace old condensers; https://www.themagnetoguys.co.uk/condensers-theory The condenser in a 12v negative earth system is usually ~.22uF, so it should be pretty simple to get a capacitor in that size from the range mentioned in that article to try out. The biggest issue then will be packaging it so it withstands the vibration of being on an engine not a circuit board.

I wouldn't be surprised if a modern capacitor like that is what's actually inside some of the 'performance' condensers.

 

[Toshi 975]

I've have been caught out by quickly failing, or failed out of the packet, new condensers for my Daimler v8 250 and 70's Suzuki motorbike also. Clearly it's not just old Fiats where there are problems.

Ultimately the condenser requirements for any vehicle with a 12v negative earth points ignition with a standard coil are quite similar, so that does open up some options when searching for alternatives that might work. It becomes more about does it have the right connector on the end and will it fit in the distributer rather than about its capacitance values. I'm using 1980s NOS Vauxhall condensers on my Daimler and 500 currently, and so far so good!

Another avenue I'd like to explore with condensers is using a modern capacitor instead, after all the condenser is only a rudimentary capacitor. While researching information for my pre-war motorbike project, I came across this page on magneto rebuilds that recommends a particular modern capacitor that they use to replace old condensers; https://www.themagnetoguys.co.uk/condensers-theory The condenser in a 12v negative earth system is usually ~.22uF, so it should be pretty simple to get a capacitor in that size from the range mentioned in that article to try out. The biggest issue then will be packaging it so it withstands the vibration of being on an engine not a circuit board.

I wouldn't be surprised if a modern capacitor like that is what's actually inside some of the 'performance' condensers.

The extensive article I read did go into a lot of detail. The guy had carefully cut open what he called the can of a number of failed condensers plus a good one then closely inspected the internals for evidence of failure. One problem was the internal contact failing through poor design, on another the working contents of the can were free floating then another problem was substandard insulation between the internals that would progressively break down under load hence the ability to tick over but misfire when reved up.
The guy also investigated the modern type capacitors you mention and identified one he thought was indestructible so you could be right about the performance types.
I consulted a highly qualified electronics engineer about the effect of small variations in the capacitance of condensers and he said it would be negligible.
Incidentally Haynes quotes 0.15-0.20 microfarads for the 500 and 0.25 for the 126 but these days I think they use the same parts.

 

[bugsymike]

As an apprentice we used to "charge up a old condensor on the Crypton spark plug cleaning and testing machine and give it to someone, who would then get a small belt from it.
Not recommended, but as an apprentice at college we had a junior lecturer who was a bit up himself, I came up with the idea of leaving a spanner out but connected to a thin wire back to the plug testing machine, when he complained about the spanner and went to pick it up I pressed the button, he wasn't impressed shall we say.
Larger capacitors obviously can store more of a "belt", I learnt from an old customer who had been a TV engineer that he always worked inside a TV using one hand, as some of the capacitors could give off a lethal shock, the theory was if you got the shock across both hands it would pass through your heart, but if only one hand it would go down your body through your foot to earth and less likely to be terminal shall we say.
I mentioned in the past we had an 80 year retired mechanic uncle of one of the bosses who could happily stop a old car with copper terminals to the plugs by putting his hands across all four spark plugs, Usually found if I got a shock from a plug lead it wasn't the shock voltage but the way my arm shot back against something hard and banged my elbow.
I mentioned in another thread about using the radio suppressor on an ignition coil (something not often seen these days) and using it to replace a duff condensor and have found it highly successful as a get you home method, no idea what Mfds they are.
The other point when people used to modern cars work on classics and leave the ignition on forgetting that the condensor, coil and points are getting hot and probably damaged.

 

[Toshi 975]

I have gone about as far as I can with my condenser investigation now. I looked at the main UK 500 & 126 parts suppliers and they show the same condenser for both models, in fact some say that their condenser will fit just about every Fiat built in the 60’s & 70’s. Axel Gerstl show 3 different ones but no real details apart from one is credited to Magneti Marelli and an expensive one made in Japan, could this be a more advanced capacitor I wonder?
I looked at those on eBay and a range of styles and makes come up, some being obviously incorrect as was also the case with a lot of motor factors. I also looked through my workshop manual collection to get an idea of what capacitor rating was given for a range of Fiat condensers. Apart from the 500 and 600 rated at 0.15 - 0.20 microfarads all the rest came within the range of 0.20 - 0.275 microfarad.
One other thing is apparent, there are hundreds of different condensers out there many of which have the same rating range and do the same job. So the feeling I got was if you can make it fit and it is older production then give it a try as you cannot rely on the new ones. I have always said anyway that if you drive a Fiat 500 or 126 with standard ignition always carry a spare condenser.
One article concluded that old Lucas ones were preferred which was interesting as I have some that are suitable for older Fiats. On inspection some have made in France on them, I am pretty sure by Ducellier. I also looked at a Mk1 Panda one I have that was packaged as Magneti Marelli which is also made by Ducellier.
So I was quite confident fitting this alleged 30 year old Lucas condenser to my latest distributor build

 

[smart51]

I wouldn't have thought the size of the capacitor was critical. It is there to (electrically) soften the opening of the points, to reduce the sparking. A coil wants to keep the current flowing when the points open. It does so by increasing the voltage across it, which increases the spark across the points when they just open. The spark erodes the contact surfaces of the points. The capacitor provides a path for current to flow, briefly. Briefly is enough. When the points just open, you don't need a lot of voltage to create a spark. As the points open to their maximum, the voltage needed to spark is greater than you can get from the coil's primary. The capacitor just has to supress the spark long enough to let the points open a bit.

I'd guess that too much capacitance will delay the spark at the plugs fractionally, but there is a lot of energy in a coil, so it would take a lot of capacitance to do that. Going from 0.2 to 0.25 is nothing really.

 

[porta]

Strangely enough, I was looking at an old car electrics manual and noted some cross references for plugs. The thing that surprised me was Lodge, (a very old British company that was seen as the father of modern spark plugs), there was a reference to lodge ignition systems including points and condensers. I have never seen a reference to them before and I’ve done a quick internet search and can find nothing other than ignition systems for marine and aero engines!
Beware the rabbit holes

 

[Goldnrust]

I wouldn't have thought the size of the capacitor was critical….
I'd guess that too much capacitance will delay the spark at the plugs fractionally, but there is a lot of energy in a coil, so it would take a lot of capacitance to do that. Going from 0.2 to 0.25 is nothing really.

Yes, I would think that anything close to the correct value would do the job.

To prove a point, I looked up the radio suppressor capacitors that @bugsymike says were an old ‘get you home’ trick. The ones I found were 2.2uF so 10x larger than the 0.2uF book spec, and that worked at least in the short term!

When you look at what’s inside a cheap condenser I can’t imagine the tolerances are very tight. Could easily be a very large variation in capacitance between them in reality.

 

[Cornish Ian]

As an apprentice we used to "charge up a old condensor on the Crypton spark plug cleaning and testing machine and give it to someone, who would then get a small belt from it.
Not recommended, but as an apprentice at college we had a junior lecturer who was a bit up himself, I came up with the idea of leaving a spanner out but connected to a thin wire back to the plug testing machine, when he complained about the spanner and went to pick it up I pressed the button, he wasn't impressed shall we say.
Larger capacitors obviously can store more of a "belt", I learnt from an old customer who had been a TV engineer that he always worked inside a TV using one hand, as some of the capacitors could give off a lethal shock, the theory was if you got the shock across both hands it would pass through your heart, but if only one hand it would go down your body through your foot to earth and less likely to be terminal shall we say.
I mentioned in the past we had an 80 year retired mechanic uncle of one of the bosses who could happily stop a old car with copper terminals to the plugs by putting his hands across all four spark plugs, Usually found if I got a shock from a plug lead it wasn't the shock voltage but the way my arm shot back against something hard and banged my elbow.
I mentioned in another thread about using the radio suppressor on an ignition coil (something not often seen these days) and using it to replace a duff condensor and have found it highly successful as a get you home method, no idea what Mfds they are.
The other point when people used to modern cars work on classics and leave the ignition on forgetting that the condensor, coil and points are getting hot and probably damaged.

Not car related but probably worth a mention anyway. This reminded me of when we were fault finding a pressure washer motor several years ago. My young assistant had taken the cover off and we spotted a wire off a capacitor. I stopped him reaching to reattach the wire with the comment that it still might be charged. He was sceptical about this but even after sitting unused for several days it still produced a very substantial spark when the terminals were shorted. Big capacitors on mains motors!

 

[turbo500]

I wish you would have started this thread a few weeks ago. You would have saved me a lot of time and frustration.

Took apart the (new) carb 3 times, top apart fuel tank, valves, points etc before mounting my old condenser back and resolving the issue.

I've now bought a NOS Fiat condenser the seller had left over stock from a Fiat garage in the US from the 70s. Hopefully it's not a dud. But would like to see if we can make a list of 'better' condensers.

 

[the hobbler]

I wish you would have started this thread a few weeks ago. You would have saved me a lot of time and frustration.

Took apart the (new) carb 3 times, top apart fuel tank, valves, points etc before mounting my old condenser back and resolving the issue.

I've now bought a NOS Fiat condenser the seller had left over stock from a Fiat garage in the US from the 70s. Hopefully it's not a dud. But would like to see if we can make a list of 'better' condensers.

I have come across a UK firm that produces a range of high quality condensors----"Distributor Doctor". I had a very interesting phone conversation with the gent who owns this company. He was getting very annoyed with the poor quality of 'pattern' condensors, so he took apart a number of 'pattern' condensors and found that the length of wire in these units ranged from 1 metre to 1.5 metres---he fits 3 metres of wire in his condensors. As far as I can see, the best one in his range for the 500/126 engine(and fitting to the distributor) is the:---484249 condensor. This comes with a 'long bracket' which can be re-shaped to fit on the side of the distributor, and comes out at under £20 (inclusive of carriage). Of course, for those people who wish to fit the condensor away from the distributor, the competition variety (Swiftune and Shacktune) would be the best way to go.

 

[Toshi 975]

Did somebody say old condensers, this is a selection of 70’s to 80’s ones & made in England, not China as lots of eBay sellers are stressing now.

 

[bugsymike]

We used a lot of CI products as an apprentice.