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MG MGB Technical - Alternator / Condensor Question

Car is back on the road after wiring harness install. (69B Roadster)

So...back on the road for a nice drive on Sunday then......

Monday..get up and go to move the car from behind the wife's car so she can get her car out....won't start...deader than whatever... Electricity into the dizzy but nothing out. Turns out it is the condensor. New condensor...vroom, starts right up. I had noticed that at the end of our drive on Sunday the Alternator light was coming on around a 1000 rpms but wouldn't go off till nearly 2500 rpms. Now go for a drive on Monday and the alternator is behaving itself. Goes on at about 500-600 rpms and off at about 1200.

1. Is there any tie-in between condensor replacement and alternator behavior?

2. What makes condensors die so suddenly? I have started asking everyone I talk to in the car business. One parts guy swears it is due to having too large a gap on your points. Most have no idea including me. I have 15 ACR Lucas Alternator with the 1 large wire in one plug and the 3 wires in the other two brown and 1 brown/yellow if I remember right.

JTB
J.T. Bamford

JT, Years ago when all cars had points and condensors I had two fail on a 53 Plymouth without any prior warning. I've had one or two other condensor failures, always without any warning. I have no idea what causes one to fail. The ones on my Plymouth wern't very old and I think one was almost new. I know this doesn't answer your question. I don't think the alternator behavior would cause a condensor to fail, but I could be wrong. Clifton
Clifton Gordon

expect I am headed to pertronix or Crane ....
J.T. Bamford

JT,

I think the biggest cause of failure with condensors is poor quality construction. It is not at all uncommon for a brand new condensor to be bad right out of the box. If you have an old one that works, don't throw it away when you replace it with a new one, you may very well need it soon.

Point gap has nothing to do with it. I can't wee any connection between the alternator and the condensor either, but who knows?
Dan Masters

Hi all.

As many of you will know, 'condenser' is an 'old fashioned' term for a capacitor.

A capacitor is simply two sheets of metal separated by an insulator, the only possible failure mechanisms are
(1) the insulation breaks down, resulting in a short circuit between the metal sheets or
(2) a connection breaks, so that one of the metal sheets no longer connects to the external connections.
It would be interesting to know which failure mode is the most common.
(A car condenser is made by rolling two insulated sheets of aluminium foil in swiss roll fashion).

The electronics industry offers a vast assortment of capacitors, including specials for rf filtering that will tolerate quite severe conditions, has anyone explored the possibility of using these ?.

I'll take my anorak off now.... Don
Don

Hello all,


Most generally capacitors fail through "short circuit"
Insuluators have a hard life; haven't they?
Back to a B electric drawing, in this case fuse never blows out because of the serial wired coil. But might
that explain the JT Bamford's "alternator warning" previously noticed to the failure ?
Get to electronic switched points: no points adj. needed, no condensers issues; and they then last long, long...
Electronically yours.
Renou

The condenser issue is almost certainly one of poor quality. There is no fuse in the ignition circuit. Points and condenser should be very reliable, I have not had either fail in service in 35 years. And since I started checking dwell at the service intervals instead of gap I haven't had to adjust the points between replacements, and they last far longer than the regulation 10k. Subject to getting good quality points in the first place. The problem with electronic triggers and ignition is that when they fail they do so totally and without warning, and unless you are carrying points and a condenser with you and can retro-fit them at the road-side (some electronic units require you to butcher the points plate making retro-fitting difficult or impossible) you will be ringing for a tow home. Points at least usually give warning, can often be readjusted, and spares are easy to carry and fit.

There is no reason in factory wiring for the condenser failure to affect the alternator warning light or vice-versa. But with PO wiring, intermittents or shorts, who knows?
Paul Hunt

This thread was discussed between 09/09/2004 and 10/09/2004

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