Condensers. Comparing Apples with Oranges?

[RobThomas]

Will a 12V Condenser from one car suit another car if it has the same .2 microfarad capacity? Is there any specific reaso why it MUST be withing the distributor? I was looking at a Ford one which has a history of never failing and being buried with the car after a life of 200,000 miles (YMMV) and wondered if it might not be a better idea to run one outside the distributor body.

One of these ones as used on Megasquirt systems...

20uF_Cap_Ford_zps67569b26.jpg (25.72 KiB) Viewed 3972 times

[myoldjalopy]

Rob,
I would simply get a 'proper job' condensor (capacitor) from Distributor Doctor. See http://www.distributordoctor.com/distri ... ensers.htm
Cheers,
Pete

[mobylette]

Years ago I fitted a condenser from another vehicle (can't remember what) to the outside of the distributor on a Vauxhall Chevette. Seem to remember I did this due to difficult access to the distributor. All worked fine. Your plan sounds eminently sensible, and you have nothing to lose so go for it.

[RobThomas]

068.jpg (151.66 KiB) Viewed 3924 times

[oliver90owner]

Def apples and oranges if you want 0.2 and that pic says 20 micro farads! Are you sure that ford one is not a smoothing capacitor?

[RobThomas]

Could well be. That one came off of the ignition coil loom of our 200,000 mile Mondeo I scrapped and I only meant it as an example of a modern item in mass production that doesn't go all LUCAS at an inopportune moment. From what I picked up via Google, I'd need something rated for 500 volts and, as you say, 0.2 diddly-whatsits. Does that sound right?

The way the current condensers are mounted makes it hard to change them in-situ whereas the way in that pic above looks easy. If it was also possible to replace it with one that didn't fail then I'd be happier. I'll try a Dissy Doctor one.

[Sleeper]

Not wanting to drift the thread , but could someone who knows , make clear the point of condensers ( no pun intended ), is it to prevent the points burning out due to arcing or to produce a better spark due to "storing/releasing" electricity ?

John

[oliver90owner]

Basically, any arcing at the points at separation will cause burning. It will also reduce the rate of change of magnetic flux in the coil.

Also rings with the coil winding reactance, thus lengthening the spark duration.

Win, win situation.

[les]

The purpose of a condenser is to reduce the spark that occurs when the points part.

[oliver90owner]

The purpose of a condenser is to reduce the spark that occurs when the points part.

That is only part of it. The spark at the plugs would be pitifull, were the condenser not present. Further a much larger value capacitor could be used to reduce arcing at the points, even removed completely. One may wonder why Kettering used that approximate size and not any arbitrary capacitance value.

[RobThomas]

If I were to guess, I'd say that maybe a small spark has a cleaning action on the points to burn off any oil contamination?

[moggiemaniac]

Although only 12volts goes to the coil it’s output to the plugs can be about 15,000volts, but the back emf to the points can be over 300volts
The pupose of the condenser/capacitor is to create a resonant circuit with the coil.
If the capacitive reactance of the condenser was accurately chosen to be exactly equal and opposite to the inductive reactance of the coil. the contacts would just see resistance, there would be no arcing and all that energy would go to the spark plugs
Unfortunately some arcing does occur because the matching of condenser and coil is not exact.
Therefore using a higher capacitance condensor would be detrimental
The condenser must be capable of withstanding well over 300 volts, and the heat , vibration, etc under your bonnet, so an electronicy thing from radioshak may not be a good idea
Relocating the condensor should cause no probs.

[RobThomas]

Thanks. That's good info.

How is the system affected by larger gaps or a sports coil? The spark voltage is higher in each case, isn't it? It would be interesting to know what cap value was used in whatever car was the last in production to use points since it would probably use a higher voltage and big gaps.

I'm here to learn!

[Sleeper]

...and so , the Ford capacitor in the first post , no points in use there , what is its function ?

I'm also learning

John

[StillGotMy1stCar]

The Ford capacitor is a suppression capacitor, used to protect the ECU from damaging supply voltage spikes from the coil packs. Fitted to coil +ve, not the switching -ve where condensers are fitted with points ignition.
Regards John

[RobThomas]

The capacitor is there to act as a snubber so the inductance of the coil doesn't cause to much arcing of the points, not to create a resonant circuit. You can start with a nominal value suggested above and then use this to fine tune:
A condenser with to much capacitance will cause a build up (metal transfer)on the mounting side of the points. A condenser to little capacitance will cause a build up (metal transfer) on the arm side of the points.

http://www.electro-tech-online.com/thre ... on.114642/

Interesting.