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Condensor Test

mojobaby

Enthusiast
Messages
1,212
#1
Can anyone tell me if there is a way to test a condensor with a multimeter?

I've tried to follow some Youtube videos but they don't explain very well. I usually change the condensor whenever I change the points but it would be nice to know if the condensor is good or bad.
And is there a difference between a condensor and capacitator?
 
Messages
321
#2
As to the words, both a condenser and a capacitor effectively do the same thing in electrical terms. The word capacitor is more usually used in reference to radios & TVs. since both use variable capacitors to tune to different wavelengths-or they used to, before the advent of digital everything!
You can't normally tell if a capacitor has failed by looking at it, unless it is leaking a brown sludge from the end, in which case it has completely failed anyway! As to testing it, if you have a multi-meter that measures resistance, set it to the highest setting (usually 2Mohms) and connect it across the capacitor's terminals-this normally means the terminal at the end of the wire and the body of the capacitor. You should see a low reading that slowly increases to a high one. If the reading is immediately high then it's probably had it. Again, the exact readings depend on the value of the capacitor, but most used in car ignition systems are of the order of 2.5-3 nano-Farads ( there is a symbol for this, but it's not on my keyboard!) To be certain, buy a new capacitor, which you know to be good, wire it as per above & observe the change in the meter reading over time for resistance. You'll know then how a good one reads when you want to test a doubtful one in the future.
 

mojobaby

Enthusiast
Messages
1,212
#3
Thanks Andrew, the capacitor in question just gives a "0" reading but I have 3 other ones which I've removed over the past 5-6 years and they all do exactly as you've described. They're still good so lucky I kept them all.
i usually just change them along with new points as they're so cheap.
I had the multimeter set on 20M ohms
 
Messages
321
#4
Glad to have been of assistance. The best way to think of a capacitor (or condenser) is as a cushion against the sharp voltage fluctuations in a circuit. A graphic (and somewhat dangerous!) way to exhibit the work of a capacitor is by removing the distributor cap & rotor arm, thus exposing the points. With the car in neutral, rotate the engine using the fan belt or crank until the points are fully closed (both sides touching) Then switch the ignition on, but don't start the engine (it won't start with the cap off anyway, but you don't want to move the points, having just positioned them!) Using something PLASTIC, open the points against the spring pressure and you should see a small flash or spark. If it's sunny you might not see it at all, which is how it should be. Now repeat this, but with the condenser disconnected and you'll see a large flash-you'll probably hear a "crack" too. It is this flash that the condenser cushions out when it's working properly, by storing the energy & releasing it back into the coil to make the H.T. circuit produce the voltage to arc across the sparking plug.

Sorry to have gone on a bit, but car electrics are a bit of a "thing" of mine!
 

mojobaby

Enthusiast
Messages
1,212
#7
Thanks again Andrew, I'm always very wary when it comes to car electrics, after being shocked a few times from the spark plug leads. They pack quite a punch! So always very happy to take your advice.
 
Messages
321
#10
I wouldn't replace a working condenser. New ones don't tend to be as good quality these days.
Agreed, although my experience has been that the cause of a mis-firing engine is too rarely put down to a worn or damaged condenser. Worn Plugs, H.T. leads or carburettor problems are far too frequently thought to be the reason, when it comes down to a faulty condenser in the end. Good quality condensers CAN still be bought, although not as automotive parts as such. This doesn't matter, as long as one side of the condenser is connected to the points & the other to earth. The fitting of the condenser to the side or inside the distributor is simply one of convention-electrically there's no specific need for it to go there! As to fitting electronic ignition, it's a "fit and forget" option, which will give smoother running and starting than conventional points, but only because the conventional timings drift out of tune over time. I think that using a dwell meter to set the points gap, together with accurate timing adjustment set using a strobe lamp when set up properly will give as good a response as electronic ignition (and it's somehow more fun-there's a sense of satisfaction in "getting it right" oneself & understanding how and why things do what they do.)
 

Cornish4

Le Dazzleur
Messages
1,544
Location
Falmouth
#11
Whether it's local to home driving, or long continental road-trips Andrew, the "fit-and-forget" approach works for me every time. I understand it's nice to spend time getting things "just right", I'm all for that, but electronic ignition removes that one basic problem with the petrol engine, pesky points.
 

Eccles60

First Renault 4 after 40 years waiting
Messages
82
Location
Solihull, West Midlands
#12
Whether it's local to home driving, or long continental road-trips Andrew, the "fit-and-forget" approach works for me every time. I understand it's nice to spend time getting things "just right", I'm all for that, but electronic ignition removes that one basic problem with the petrol engine, pesky points.
I agree. Throw the points and condenser in the bin and fit a 123 system (or similar). No more fiddling with points and modern, poor quality condensers, doesn't hurt originality much and is reversible anyway.
 

mojobaby

Enthusiast
Messages
1,212
#13
I really don't know why so many people have a problem with points and condensers.
I replace my points every 2 years or so, the condenser at the same time. I do this out of habit, not necessity and because it gives me great pleasure to tinker around with my engine. That's why I bought a 40 year old car.

I replace the points, set the timing and never touch it again until the next time. I have a video on this forum on how to set the timing and points which shows how to do it the correct way. So start off by learning how your ignition system works, how it's put together and what each component is designed to do.
And keep your car running the way it was first designed to do. Too easy to blame the points!

I'm all for progress, but when a kid can't tell the time on a "normal" watch and when people ask Alexa to order them a pizza, then thats when technology has gone too far.

And as for poor quality condensers, which so many people have complained about on this forum, I have 3 used ones from the past 6-7 years which Andrew told me how to test. None of them were faulty as you can see in the video. One of them gave a funny reading but afterwards I realised that my finger was touching it during the test. Afterwards I re-tested and it was also good.

 
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