condensors

Triton Thrasher said:
Test nominally identical OEM Lucas condensers and you would see they can or will have different “micro frad” values.
Click to expand...

Triton Thrasher said:
Frankly mate, you’re full of magic.
Click to expand...
I did say: "But if you were to test condensers from different brand bikes or cars you would see they can or will have different micro frad ratings or values than an OEM Lucas part. " And yes, two of the same brand and model condensers can vary in the readings but be in the ball part, if good.

Customers did call me a "magic man", because I could make their bikes better than anyone else that worked on them. I was known for how well my work on point/coil/ condensers bikes ran and how long they ran great for. It ain't magic, its doing the job correctly as possible with what you're working with.
 
Any capacitor with a similar mF rating and voltage rating at least as high as the original will work fine. Typically capacitors used in circuits were rated plus or minus 20% or greater variation so it would be common to see two "identical" new caps to have different readings. IOW, if anybody had actually checked back in the day (nobody did) they would have found that probably none of the (say) .022mF capacitors were actually .022mF!
 
Leslie (LAB) is correct with his list of the two roles of the capacitor.
And I thank Leslie for his great contribution to this forum.

The capacitor prime role is to help create a very strong spark.
When points are closed, current flows through the primary ignition coil windings and builds up energy in form of magnetism in the ignition coil's iron core.
The energy being built up is like coils wound around an iron core to create an electro magnet.

When the points open and stop the current flow, the built up coil energy in the coil has to convert to something so it
induces a massive rise in voltage in the secondary windings around the same iron core.

There are two things important in how much voltage is induced.

1) The amount of voltage induced depends on the ratio of the windings
(just for example say the windings have a ratio of primary 10 wraps to secondary 20000 wraps, meaning the factor is 2000 times

2) But the most important of the the two is how fast the magnetic field (induced in the iron core by the primary current) breaks down. ie how abrupt.
The faster the magnetic field breaks down (when primary current flow stops), the higher the voltage induced.

Let's look at how we can get the magnetic field to break down (collapse) really fast.
To do this we need to stop the current though the primary instantly.

When the points are closed, about 3 amps flows through the ignition coil primary. To stop it, the points open and you would think this would do the job but it does not because the moment the points slightly open, current starts to arc across the points until the points are too far open for arcing to occur. This arcing, which might take 3 or 4 milliseconds) means that the breakdown of the magnetic field is slow and spread out over the time this arcing happens.

The capacitor is installed in parallel with the points. It is an electricity storage device like a bucket for water.

When the points are closed, current goes through the points (easy path) and no electricity current goes into the storage bucket.

When the points start to open just a fraction, electricity that would have gone through the open points looks for somewhere to go and it flows into the capacitor storage bucket. (Thus theoretically no arcing across the points).

The electricity flows into the capacitor bucket (while the points continue to open) but the capacitor has a limited amount of storage and when the capacitor bucket is full, it is like the electricity hits a brick wall, and the flow of current stops. Far more abruptly that if it was arcing across. There might a a small arc of a microsecond.

The more abrupt stop of electricity causes a far faster magnetic field breakdown and thus a much higher induced voltage in the secondary winding.
The difference in spark strength can be significant. With a capacitor say you get a 25,000 volt spark but without a capacitor (or failed capacitor), the 25,000 volts can drop to less than 10,000 volts which is not enough to jump the spark plug gap, or if it does jump the gap, it is really weak

A benefit of using a capacitor is that it much reduces arcing at the points and thus having to adjust/file/replace the points too often.

Some points ignition systems will simply not generate a spark strong enough to jump the gap if the capacitor fails. Others will have a spark but less strong such that engine will run but you run into strange things like engine missing.

So if you are on a road trip and think you may have capacitor failure, close up the spark plug gaps to just a fraction and that might get you home.

As for me, any engine I have ever had with capacitor failure has simply refused to run!!

Dennis
 
DennisMo said:
Leslie (LAB) is correct with his list of the two roles of the capacitor.
And I thank Leslie for his great contribution to this forum.

The capacitor prime role is to help create a very strong spark.
When points are closed, current flows through the primary ignition coil windings and builds up energy in form of magnetism in the ignition coil's iron core.
The energy being built up is like coils wound around an iron core to create an electro magnet.

When the points open and stop the current flow, the built up coil energy in the coil has to convert to something so it
induces a massive rise in voltage in the secondary windings around the same iron core.

There are two things important in how much voltage is induced.

1) The amount of voltage induced depends on the ratio of the windings
(just for example say the windings have a ratio of primary 10 wraps to secondary 20000 wraps, meaning the factor is 2000 times

2) But the most important of the the two is how fast the magnetic field (induced in the iron core by the primary current) breaks down. ie how abrupt.
The faster the magnetic field breaks down (when primary current flow stops), the higher the voltage induced.

Let's look at how we can get the magnetic field to break down (collapse) really fast.
To do this we need to stop the current though the primary instantly.

When the points are closed, about 3 amps flows through the ignition coil primary. To stop it, the points open and you would think this would do the job but it does not because the moment the points slightly open, current starts to arc across the points until the points are too far open for arcing to occur. This arcing, which might take 3 or 4 milliseconds) means that the breakdown of the magnetic field is slow and spread out over the time this arcing happens.

The capacitor is installed in parallel with the points. It is an electricity storage device like a bucket for water.

When the points are closed, current goes through the points (easy path) and no electricity current goes into the storage bucket.

When the points start to open just a fraction, electricity that would have gone through the open points looks for somewhere to go and it flows into the capacitor storage bucket. (Thus theoretically no arcing across the points).

The electricity flows into the capacitor bucket (while the points continue to open) but the capacitor has a limited amount of storage and when the capacitor bucket is full, it is like the electricity hits a brick wall, and the flow of current stops. Far more abruptly that if it was arcing across. There might a a small arc of a microsecond.

The more abrupt stop of electricity causes a far faster magnetic field breakdown and thus a much higher induced voltage in the secondary winding.
The difference in spark strength can be significant. With a capacitor say you get a 25,000 volt spark but without a capacitor (or failed capacitor), the 25,000 volts can drop to less than 10,000 volts which is not enough to jump the spark plug gap, or if it does jump the gap, it is really weak

A benefit of using a capacitor is that it much reduces arcing at the points and thus having to adjust/file/replace the points too often.

Some points ignition systems will simply not generate a spark strong enough to jump the gap if the capacitor fails. Others will have a spark but less strong such that engine will run but you run into strange things like engine missing.

So if you are on a road trip and think you may have capacitor failure, close up the spark plug gaps to just a fraction and that might get you home.

As for me, any engine I have ever had with capacitor failure has simply refused to run!!

Dennis
Click to expand...
Great job explaining to the masses.
 
concours said:
In the old days, they were considered part of the annual tuneup and we're frequently replaced with points and spark plugs
Click to expand...
GM thought so too, uniset points/condensor
image-38-scaled.jpg
 
marinatlas said:

Could help ??
Click to expand...
It makes me think I should look and replace the original, OEM condensers in my 1968 First year Commando. But they are buried behind the oil tank, I imagine most people never knew where they were. But that is where the factory put them.

I did check two brands of new Japanese condensers I got from Coventry Spares quite a few years ago, he sells to most dealers in the USA, They were spot on . Mf wise.
 
I am going to go with the original points on my 1970 commando restoration but Frank from vintage motorcycle restoration says he will never take in a bike that has points. Is kickbacks the reason ?
 
On the subject of condensors, can anyone tell me why Lucas, in their infinate wisdom, buried tje most failure prone part of a K2F magneto deep enough that total disassembly is required to rrplace it?
 
A "VINTAGE MOTORCYCLE" restorer won't take a bike with points? ???? Sort of like a vintage clock restorer who only accepts quartz clocks!!! :)

Points don't kick back; incorrect timing or faulty advance units causes kick back. E-ignitions often kick back, there are plenty of statements to that effect on this site.
 

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