Condenser question

[tony g]

Just thinking, with all the talk of rubbish components ...

Could the condenser be replaced with a 0.2 micro farad ceramic capacitor ?

I dont use them or points but wanted to see if a 10pence part could be used instead


Tony

[MIG Wielder]

Hi Tony. The 1-line summary to your question is Yes; the original capacitor can be replaced by an external capacitor but it has to be well specified. I carried one of these in my glovebox spares kit before I went to the Lumenition system.
It is 0.22uF with a 1KV d.c. rating and a 300V a.c. rating which is a bit marginal on a.c. rating but it got me out of trouble on just the one occasion. One parameter that is not specified is ripple current rating.

http://uk.rs-online.com/web/p/polypropy ... s/0114610/

But hey; it worked.
I had it on croc; clips so I could just clip it to the coil negative and a bolt near the distributor for earth. It would work if the original capacitor went open circuit, but not if it went short circuit. The black lead to the original capacitor would have to be removed and taped back for it to work in that case.
The original capacitor value is specd; at 0.18 to 0.23uF.
HTH,
Tony M.

[tony g]

Thanks Tony, I was hoping you'd turn up, it seems crazy we arent telling the world about readily available stuff instead of rubbish repro parts we may be forced into using.

Tony

[Carledo]

Well, to be fair, most people have got the message about poor quality ignition components and gone electronic in one form or another. It's true I went to rather excessive lengths to get my tranny sparks (by changing the whole motor to something a bit newer) but it did the job!

Steve

[tony g]

Tony why is such a high voltage range needed on the cap? Is the spike that high when points open? Or is it to do with HV leakage back to the points/condenser ?

Steve yes I know what you mean but for those who choose to run points there could be better solutions. Yours is a good solution yes its one that I have on the back burner too


Tony

[Magenta Auto Sprint]

I like the idea of a condenser on crocodile clips as a get-you-home fix, because trying to replace a condenser in an AC Delco Dizzy is a nightmare of a job at the best of times.

I was also looking into a suitable replacement from the RS catalogue but most are too large to fit under the cap or in the small space that the original sat in. so I was thinking of mounting it externally as some other manufacturers did in years gone by.

I did also hear that somebody picked apart a standard condenser and compared the foil with that of an equivalent RS unit, and found that the foil was half the thickness etc, so that could be why they fail.

Malcolm

[MIG Wielder]

Tony why is such a high voltage range needed on the cap? Is the spike that high when points open? Or is it to do with HV leakage back to the points/condenser ?

Tony

Here are some scope trace measurements I did on a 6V coil some time ago. I had to do the measurements at a lower voltage of 3.0V but the results will scale linearly . The peak inductive overswing was 120V at 3.0 V which would equate to 290V at 14.5 V supply voltage.So that gives an rms voltage of 205 V. So the 300V a.c. rating gives only a 50% margin. It would be nice to have a bit more for reliability.
Tony.

[tony g]

Wow thats impressive Tony The humble condenser did some work then..

Cheers

Tony