Hitchcocks Forum

Just fitted new points and condenser to my year 2000 Classic 500. There's still a BIT of a spark between the points when it's running. It IS running well.

I've often seen this before. Is a tiny spark ok, or should there be none if the condenser's ok? Never really thought about this one before.

Thanks, Chris

You will always get some spark at the points.

That's why points are often made of tungsten or platinum coated to resist burning away.

The reason is this. . There are TWO processes of spark generation at work
It's perhaps better to imagine the process in slow motion....As the points open, there is a DC current flowing in the primary coil. This gap initially amounts to just hundredths of thousands of an inch which the primary voltage can easily bridge. As there is now an arc created the arc can be drawn over a bigger distance as the points open even more until the arc is finally extinguished and the primary current is stopped from flowing.
The second process is from the sudden collapse of the primary current which builds a rapid rise of a back EMF (Voltage) in the primary windings, but as the points are open the capacitor can absorb the reverse high voltage surge by charging up. Without the capacitor the energy would jump the now open points and another arc with much more power would jump the points gap and erode them pretty quickly. The other effect the capacitor has is by quenching the spark makes the interruption of the primary current much more sudden and creates a bigger HT voltage in the secondary coil and also extend s the burn time by causing a high frequency "ringing" as it dissipates the stored charge into the primary windings.

2ND attempt to get this message to send correctly!
The reason is this. . There are TWO processes of spark generation at work
It's perhaps better to imagine the process in slow motion....As the points open, there is a DC current flowing in the primary coil. This gap initially amounts to just hundredths of thousands of an inch which the primary voltage can easily bridge. As there is now an arc created the arc can be drawn over a bigger distance as the points open even more until the arc is extinguished and the primary current is stopped from flowing.
The second process is from the sudden collapse of the primary current which builds a rapid rise of a back EMF (Voltage) in the primary windings, but as the points are open the capacitor can absorb the reverse high voltage surge by charging up. Without the capacitor the energy would jump the now open points and another arc with much more power would jump the points gap and erode them pretty quickly. The other effect the capacitor has is by quenching the spark makes the interruption of the primary current much more sudden and creates a bigger HT voltage in the secondary coil and also extend s the burn time by causing a high frequency "ringing" as it dissipates the stored charge into the primary windings.

Ah well here is the missing section:
but as the points are open the capacitor can absorb the reverse high voltage surge by charging up. Without the capacitor the energy would jump the now open points and another arc with much more power would jump the points gap and erode them pretty quickly. The other effect the capacitor has is by quenching the spark makes the interruption of the primary current much more sudden and creates a bigger HT voltage in the secondary coil and also extend s the burn time by causing a high frequency "ringing" as it dissipates the stored charge into the primary windings.

So with a good working capacitor you will still get a spark from the DC energising current. You might think that the capacitor should stop this too but the primary voltage of 12V is constantly applied to the capacitor which is enough to allow the initial separation of the points to "draw out" a small spark, but nothing like what you would get if the capacitor was not in the circuit (or defective).....Les

PS sorry this is in 3 parts

Sorry about the UTTER mess of my message...makes me wish I hadn't bothered.....why does this happen?

First of all, thanks to everyone for replying; another small mystery solved in my head.

Les, I'm glad you DID bother anyway... I want to keep on learning stuff.

I'm not sure what you felt the computer problem was. But this bit might be of interest to you (or might not!):

As you can see, I'm sending this message in paragraphs, so it should be easier to read and I can tell where I am up to. When you want a new paragraph to appear on the noticeboard, just type in the letters b and r between the POINTY brackets. Do it twice. Like this: (br)(br). EXCEPT I USED ROUND BRACKETS HERE.... so it DOESN'T TURN IT INTO A NEW PARAGRAPH THIS TIME! Do that with the pointy < brackets: the paragraph won't appear on YOUR TYPING SCREEN but will be there on the Hitchcocks message board.

Also, when you press POST REPLY it seems to take a few seconds. I think we sometimes press it again, thinking it hasn't worked.

I hope this makes any sense at all... I'm beginning to feel like you, and wonder where it's all going. Give it a try anyway and perhaps someone will come up with a better answer.

Thanks again for the electrical info.
-Chris PS I hope after all that, that my message will work. .....still learning!

Thanks Les, good info. I knew the general theory but that fills in a bit more knowledge.
A day without learning is a day wasted, as someone once said.