condensor outside the distributor, experiments with Powerspark

[RobH]

12 hours ago, Fred Winterburn said:

f you go for an alternative condenser, keep the lead lengths as short as possible. Adding a foot or two of wire reduces the effectiveness in arc suppression considerably. I was surprised that it makes as much difference as it does keeping the lead lengths short.

The condenser and lead(s) inductances are a series resonant circuit.  Ignoring the internal inductance of a wound condenser the standard lead length gives an inductance of around 30nH which with a 0.22uF capacitor resonates around 2MHz.  If the lead length is 10cm  the inductance is circa 100nH and the resonance comes down to 1MHz.  With a 30cm total length the resonance is around 600kHz.

A series resonant circuit becomes high impedance at the resonance which prevents current flow so it is entirely possible that longer leads will affect the suppression properties if the spark frequency is near the resonance. 

 

[silverfox4]

This seems the logical to tack-on my query.

Does anyone recognize this condenser which was removed from my Malines TR4A.  It was attached with the the forward bolt for the coil.  I could not see any purpose so just removed it when I installed the Pertronix

Cheers,

Alf

[Lebro]

Probably to suppress radio interferance from ignition.

Bob

[Z320]

Hi,

a german producer of ignition parts is "BERU", I have their catalog found at the internet.

you can download it here, second row, the one in the middle

The condensors for most badges are from page 234 - 242, the "ZK174" for Lucas is on page 236.

If you compare them you will see, it is very short, special to fix and it's diameter is only 17 mm, instead of common 18 mm.

Means: if you condenser fails, and you don't get exactly the suitable, you are "aufgeschmissen".

Then you better fix any condenser (all have 22 uF) outside the distributor.

Ciao, Marco 

 

Edited October 6, 2020 by Z320

[john.r.davies]

Aufgeschmissen?  Nien, Marco, ganz und gar nicht!     I've said it before, here, but no one listens,

If your condensor fails, then you are "nicht verloren"!        Remove the offending item and carry on!      Your points may only last 1000 miles instead of six or more, but you will get home!

[Fred Winterburn]

15 hours ago, Lebro said:

Probably to suppress radio interferance from ignition.

Bob

Yeah, Probably a radio noise suppression capacitor. Presumably connected from the ignition switch side of the coil to earth. Ford used to do that back in the day and a few others. Fred

[silverfox4]

Thanks All,

Noise suppression seems to be most likely.  Anyway it's sitting in the box as I see no need for it.

Cheers,

Alf

[Fred Winterburn]

On 9/30/2020 at 5:26 AM, RobH said:

The condenser and lead(s) inductances are a series resonant circuit.  Ignoring the internal inductance of a wound condenser the standard lead length gives an inductance of around 30nH which with a 0.22uF capacitor resonates around 2MHz.  If the lead length is 10cm  the inductance is circa 100nH and the resonance comes down to 1MHz.  With a 30cm total length the resonance is around 600kHz.

A series resonant circuit becomes high impedance at the resonance which prevents current flow so it is entirely possible that longer leads will affect the suppression properties if the spark frequency is near the resonance. 

 

Rob, and anyone else interested. I've been scratching my head on this one for some time. The problem is the frequency of the no-load sine wave when the points open is about 2.5 kHz, way below the resonant frequency that any added lead length could possibly give. I know for a fact that long lead lengths from the points to the condenser does indeed increase the arcing at the points. Roughly 15% more arcing with an extra two feet of wire. I've finally found an article that explains it. It is not addressing condensers in cars, but transient voltage suppression devices. Please see the attached article. Fred W.  

Vishay_AN88441.pdf

[Andy Moltu]

You don't really need a get you home condenser. if it fails take it out and the points will burn quicker but you should get home.

I'm with Lebro -bin the points and carry a spare electronic ignition module. Easier to swap an identical unit than to change the points and condenser.

[Fred Winterburn]

Not too many engines will run without the condenser. If the engine is already warm and the plug gaps are extremely small, there might, just might be enough spark to make the engine run, albeit very badly. Normally condensers go open circuit and the engine misfires like crazy. Open circuit is the same as taking the condenser out of the circuit. The condenser does more than keep the points from burning. To put it simply, it prevents energy loss through the arc and in doing just that, it ensures there is enough available voltage to fire the plugs. Fred

[ctc77965o]

 

2 hours ago, Fred Winterburn said:

Not too many engines will run without the condenser.

The arcing of the points weakens the spark, the condensor acts to reduce the voltage spike across the points, that reduces the wear on the points and also strengthens the spark.

https://en.wikipedia.org/wiki/Delco_ignition_system

If you find that theres metal build-up one side or other of your points, thats a tell-tale that the condensor is not matched to the coil. A condenser with too much capacitance will cause a build up (metal transfer)on the mounting side of the points. A condenser too little capacitance will cause a build up (metal transfer) on the arm side of the points.

[Z320]

7 hours ago, Fred Winterburn said:

Not too many engines will run without the condenser. If the engine is already warm and the plug gaps are extremely small, there might, just might be enough spark to make the engine run, albeit very badly.

Fred

Fred, 

it was in my mind to ask today if anyone really drove his car without condenser,

because that's what I also found at the literature (not at the internet), but I'm to often the killjoy here:

the spark will be very week and the engine will probably not run.

The reason is the coil wants to keep the current after the contact braker has opened,

but a strong spark needs a as fast as possible changing field (to zero) and therefore as fast as possible no current anymore.

This is the real job of the condenser. To delete the spark on the braker contact is what you can see and what the story is told about.

An electronic braker does exactly this: very fast no current anymore, very fast changing field ( to zero) and because of this a stronger spark.

Never tried this myself, as told above I found it at the literature.

Ciao, Marco

Edited December 8, 2020 by Z320

[ianc]

Way back in the early 1960s, my TR2 started misfiring badly and could only limp along at about 50mph.

After checking various things in the ignition I found that the clamp which holds the condenser in position was no longer soldered to the body of the condenser.  Out with the soldering iron and the clamp was fixed back.

Car then ran faultlessly.

Marco and others are correct - ignition system does not work properly without a condenser, for reasons described.

Ian Cornish

[Charlie D]

33 minutes ago, ianc said:

...ignition system does not work properly without a condenser...

When I was an apprentice with the GPO we were told never to use the word “Condenser”.

We were told that :

“Condensers are only to be found on steam engines and the electronic component was called a “Capacitor”

If we did use the word “Condenser” we were made to wear a very heavy metal clad capacitor tied around our neck with a piece of jumper wire. It had the words:

“I am not a condenser I am a capacitor” written on it in felt tip.

I suppose that sort of thing would be classed as cruelty to children these days and banned by the EU.

Hence the now popular use of the word “Condenser”.

Charlie.

[BlueTR3A-5EKT]

Hanging the condenser on the exterior of the distributor is also a Magneti Marelli ignition style.

The one screwed to the outside of Fiat/Lancia/Alfa points ignition cars is available for just under a fiver to just under a tenner based on manufacturer.  https://www.autodoc.co.uk/car-parts/ignition-distributor-parts-10248/fiat/126/126-1972/2565-600?categories[0]=690

I did have the one on my Fiat shake the attaching screw loose on a long motorway journey once and that resulted in poor running, like IanC experience.

Cheers

Peter W

[Andy Moltu]

I didn't suggest they did but having experienced them fail on me, effectively bipassing the points, removal was  enough to get me home on a an egine that was warm.

The market has been plagued by cheapo points with the longevity of a novelty Xmas hit.  To be honest poor quality condensors is not a new phenomenon I recall working in a garage in the late 70s & early 80s, before electronic ignition was commonplace, failures were common back then. They were treated as service items when a decent capacitor should last years.

[RogerH]

2 hours ago, Z320 said:

 

because that's what I also found at the literature (not at the internet), but I'm to often the killjoy here:

Ciao, Marco

Hi Marco,

you are never the killjoy. Please keep on stating your point of view. If it is different to others then we can have a good debate.

 

Hi Charlie

I am with you on the capacitor side of things.  The term capacitor is used exclusively in electronics.

The ludites in the automobile world still use the original term 'condenser' as some sort of respect from where it was invented (Leyden) and its age.

However there is no difference between the two terms.

 

Roger

[Z320]

Hi Charlie,

shure my translation was wrong, this part is named "Kondensator" at Germany.

But your story made me smile, reminding me to a similar issue during my apprentice.

Sorry, therfore you have to lern some German: a drill is a "Bohrer" and what you do with a "Bohrer" is a "Bohrung".

It is very popular to call that "a hole", but "a hole" is very rough, without any definition.

 

If we spoke about "to make a hole" we have been disgraced and told by our teachers:

"if you want to make a hole take a spade and go out in the garden, but YOU - want to be a mechanic?".

This is deep in me and it always hurts me to read about a "hole" in relation of metal.

Maybe someone explain me what a british mechanic does with a drill, please?

Ciao, Marco

 

Edited December 8, 2020 by Z320

[RobH]

The name 'condensor' comes from the early days of electrical experiments and has its origin in the 18th century when people were messing about with Leyden jars (basically a jam-jar with metal foil on its internal and external surfaces).  It's only in the latter half of the 20th century that 'capacitor' became the name widely used.  

As Marco says, the strength of the spark from a Kettering system depends on the speed of collapse of the magnetic field in the core of the coil as the points open.  The faster the collapse, the higher the induced voltage  (proportional to Bl/t where B is flux density and l is the length of the conductor).  Arcing between the points as they open slows down the collapse and so reduces the peak HT as well as affecting the spark timing.  Whether or not an engine may still run (badly) without the condensor depends on the engine tune and the particulars of the coil, plug gaps and HT system.  The higher the compression ratio the less likely it is the engine will run as the voltage required at the plug increases with gas pressure.  

 

Edited December 8, 2020 by RobH

[RogerH]

12 minutes ago, Z320 said:

Hi Charlie,

shure my translation was wrong, this part is named "Kondensator" at Germany.

But your story made me smile, reminding me to a similar issue during my apprentice.

Sorry, therfore you have to lern some German: a drill is a "Bohrer" and what you do with a "Bohrer" is a "Bohrung".

It is very popular to call that "a hole", but "a hole" is very rough, without any definition.

 

If we spoke about "to make a hole" we have been disgraced and told by our teachers:

"if you want to make a hole take a spate and go out in the garden, but YOU - want to be a mechanic?".

This is deep in me and it always hurts me to read about a "hole" in relation of metal.

Ciao, Marco

 

Hi Marco,

our languages are not so different. Yours is perhaps 'purer' ours is a mixture of many languages.

You have a 'Bohrer'  we have a machine that Bores.  But we also have people that Bore (send to sleep)

With our boring machine we drill into solid material. The Oxford English Dictionary suggests that a hole  is   (noun  -  a hollow place in a solid body or surface.)

Even in electronics - when an electron moves away it leaves a 'hole' - this allows technology to work.

Don't ask about the French cersion

 

Roger

[stillp]

2 hours ago, Z320 said:

 

Maybe someone explain me what a british mechanic does with a drill, please?

 

 

Hi Marco, in Britain we use a drill to make a hole!

Pete

[Fred Winterburn]

10 hours ago, ctc77965o said:

 

The arcing of the points weakens the spark, the condensor acts to reduce the voltage spike across the points, that reduces the wear on the points and also strengthens the spark.

https://en.wikipedia.org/wiki/Delco_ignition_system

If you find that theres metal build-up one side or other of your points, thats a tell-tale that the condensor is not matched to the coil. A condenser with too much capacitance will cause a build up (metal transfer)on the mounting side of the points. A condenser too little capacitance will cause a build up (metal transfer) on the arm side of the points.

I've actually tested this because I wanted to know why points burn on the other contact when a too-large condenser is used (and yes I'll keep calling it that because historically that is what it has always been called). Without a scope you would never see why and it doesn't make sense on the face of it that points would burn on the opposite side just because the condenser is made larger. When the condenser is sized too large, the no-load (no spark) sine wave that begins when the points open, reduces in amplitude (lower voltage) and also decreases in frequency (the period is longer). Because the available voltage is lower, under compression the percentage of misfires increases (where no spark forms). If the spark is struck, all is well as the no-load sine wave exists for only part of the first 1/4 cycle and then the energy dissipates quickly within the system and the spark channel. However, if the available voltage isn't high enough which can easily happen at mid range rpm where the dwell is reduced (less energy also equates to lowering the amplitude of the no-load sine wave) with the engine under load, misfires result. Perhaps not enough to be felt in seat of the pants testing, but they can be there nevertheless. On every misfire energy is bottled up in the system and the sine wave continues with energy oscillating between the coil inductance and capacitances in the circuit including the condenser. The energy does decay in a typical 1/4 decay, but the lower frequency keeps the energy in the system longer.  The timing is such at mid range rpm that when the points close, that coincides with a portion of the sine wave driving current in the opposite polarity to when the points open. Even though the percentage of misfires can be quite low, and the energy is reducing by 1/4 decay, the pitting is bad because the arc intensifies with the closing of the points. It is this current flowing in the opposite direction on points closure that causes metal transfer to the other side.  I did the testing on the same test rig my father knocked together in a hurry probably in 1961, possibly 1960. (see Wikipedia on Capacitor Discharge Ignition and look at the homemade rig that Lloyd Winterburn was using) For my test I doubled the condenser value to 0.44µF and opened up the spark gap wide enough that there were misfires occasionally at approximately 2000rpm (8cylinder). Then I opened up the gap so wide that there were misfires 100% of the time and had a good look at the scope. It's been awhile since I did that experiment but I believe the points closing coincided with the 2nd positive peak on the sine wave. If the condenser is sized properly at about 0.22µF, there won't be burning of the points when they close, or extremely little burning of the points. This is because the frequency is higher and the energy dissipates fast enough that by the time the points close there is very little left over.  Fred   

[john.r.davies]

That is most interesting Fred!    You demonstrate the value of investigating the way that our machines function, rather relying on theory or received 'knowledge'!   (it's called "Science"!)   

Thank you for you insight.     If you could do the experiment again, and provide pictures of the waveforms that would be really good!

John

[TriumphV8]

On 12/8/2020 at 7:36 AM, Z320 said:

Fred, 

it was in my mind to ask today if anyone really drove his car without condenser,

because that's what I also found at the literature (not at the internet), but I'm to often the killjoy here:

the spark will be very week and the engine will probably not run.

The reason is the coil wants to keep the current after the contact braker has opened,

but a strong spark needs a as fast as possible changing field (to zero) and therefore as fast as possible no current anymore.

Back to the topic I can say that all condensors are not the same and all transisitors not, too.

I came up to the capacitor problem by Hifi where interesting caps with silver gold sheets are used. They reduce resistance significantly.

A cap in reality is a cap plus a resistor in line what never interested me before, until I came up to the problem because we learned that our MegaSquirt delivered different spark lengths with identical coils. We have an old Bosch Tester to pull the spark length until it fails.

Fitted are the TO220 shape transistors where the BOSCH type BIP373 is very famous. Meanwhile it is superseeded by the IRGB14C40L. Unfortunately I fitted a third type that gave a spark, was reliable but the spark was weak, causing problems on start on and maybe powerloss on high revs. It did not open fast enough.

Although I did not test it, I would expect a weaker spark with an old cap where the inner resistance rises by nature causing a not so steep rising of voltage curve. It is difficult to judge from the outside if the equipment fitted gives the best spark possible and from that I would try to fit the best I can buy. On the TR4 that might be of less interest because there is not the need of a fast spark delivery but the TR6 needs a very good spark system.

With the normal ignition setup we triggered the spark by MegaSquirt and played with the time the points are closed to "load" the coil. It is called the dwell time. Depending on the coil this varies from 1 to 10ms where normally 2-4ms is normal with sports coil 3 ohms. What we found out is that required dwell time to avoid misfire at high revs is pretty close to the time that is availiable between two cylinders firing. The conclusion is that TR6 normal points ignition must have a sports coil like the red BOCH and must be in best shape not to cause powerloss.

[RogerH]

2 hours ago, TriumphV8 said:

Back to the topic I can say that all condensors are not the same and all transisitors not, too.

I came up to the capacitor problem by Hifi where interesting caps with silver gold sheets are used. They reduce resistance significantly.

 

Capacitors are also affected by vibration.  A good many Hi-Fi nerds will stick 'BluTak' to the capacitors to stop them vibrating..

In theory this will clean up the signal.

 

Roger