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TR2/3/3A What does a condenser do?

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sp53

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What does a condenser do? I am asking because of my CRS disorder. When I was in high school, I had this really cool auto shop teacher and electronics teacher and the electronics guy would teach both.


Anyways, I thought I heard him say a condenser absorbs the static electrons being let go by the coil. That a condenser is only foil and paper rapped round in a circle and then grounded to let the static electrons to ground. He also said they go bad very rarely; and people waste money when they purchase points and condenser; they should only purchase points because the condenser technically matches the coil.


I am telling the story because I could easily be wrong, and wanted to know what others thought about the function of a condenser.
Randall love ya and miss you.
 
We need Randall for the details. Bummer. In layman's terms, though, the condenser prevents a spark from jumping across the points as the points open. Without it, the points burn in very short order. When the points break the contact to the coil, the magnetic field in the coil collapses. Since the collapsing field generates electron flow in both the primary (12v) side as well as the secondary (plug side), the voltage immediately spikes in both sides...primary as well as secondary. We use the spike on the secondary to power the spark plugs. The primary spike can generate hundreds, if not thousands of volts above the base 12v, though...and that is where the back feed through the points can cause a spark across the points gap. The condenser is simply a capacitor that absorbs the current from the spike and keeps the voltage low enough not to back feed and cause a spark across the points.

I agree the condenser must match the coil...but I have no idea how to calculate the size you need. If it is too small, it will not be able to absorb the voltage spike and will short itself out trying. If it is too big, it will absorb all the primary current, so the coil will not have a chance to build a full magnetic field.

Funny you mention high school auto class. I had an instructor say the exact same thing, that "condensers never fail". So I was driving an International Scout, and for the next tune-up I changed the points but not the condenser. We made it 12,500 feet up into the rocky mountains north of Durango CO, and the engine just quit running. We had the car towed, which was no easy feat in the 1970's 45 miles from the nearest small town...Silverton. Turned out the condenser failed and the points burned to oblivion.

They were wrong believing the condenser never fails!
 
My college Electronics 101 Professor (Dr Kim) used to tell us about Ohms Law, "If you don't understand ohm's law, you will spend the rest of your life polishing another man's electrodes". That's why I became a Mechanical Engineer, I still don't understand why electricity doesn't pour out of an outlet when you pull a plug from it.

Rod
 
I recently had my condenser replaced and what a big difference it made. Prior to that when I started my Bugeye it was hard to start and then wouldn't run past idle. Now the car starts right up and runs beautifully. I would say a good condenser is a must.
 
Dittos to 59diamond. The condensers being produced now are of terrible quality. Keep a couple in your glove box if your running points which brings me to my next point. I got tired of replacing them and one time twice in one day on the way to the Roadster Factory Summer Party. When I got there I bought a set of Petronics and it's the best thing I ever did. No condenser worries and did it ever smooth out the RPS and particularly at idle. Now all 3 of my TR's have them.
 
Yeah the blue wired condenser were what TRF sent me, although the sale indicated the yellow wire.
Which was what I considered a 'bait and switch', but times are hard over there at TRF..so

I do have the yellow wire installed. I guess I'll keep the blue wire if I ever need to replace the yellow one DD AD LUCAS 22D6 003.jpg
Distributor with Advance 001.jpg
 
I don't know, Steve, but the blue wire may indicate they are a "Blue Streak" (Standard) commercial product.
 
Maybe the blue-wires are OK, but the Distributor Doctor says he's sold a couple thousand yellow-wires with not a single failure. Many sold to racers.

The Standard brand condensers, IIRC, are made in Mexico and of indeterminate quality. Pretty easy to buy a couple of the known good ones from the Distributor Doctor.
 
I bought a couple of DD condensers and the 2 piece points....but a couple years later, TRF had this come out on sale
http://trf.zeni.net/wc/specials13.15/39.php
So I ordered the RFK 1292/HP....and received the blue wire instead of the yellow...and the red rotor strangely enough had DD on one side and AD on the other..They had their bases covered with the rotor.
Anyway I asked about the condenser switch....they said the blue was just as good as the yellow...
I probably shouldn't have expected a different response from TRF...maybe they are just as good.
 
Last edited:
poolboy said:
I bought a couple of DD condensers and the 2 piece points....but a couple years later, TRF had this come out on sale
http://trf.zeni.net/wc/specials13.15/39.php
So I ordered the RFK 1292/HP....and received the blue wire instead of the yellow...and the red rotor strangely enough had DD on one side and AD on the other..They had their bases covered with the rotor.
Anyway I asked about the condenser switch....they said the blue was just as good as the yellow...
I probably shouldn't have expected any thing different...maybe they are.
Click to expand...

One could purchase one of each, cut the ends off and unwind and compare the material on the inside.
 
Rod-H said:
My college Electronics 101 Professor (Dr Kim) used to tell us about Ohms Law, "If you don't understand ohm's law, you will spend the rest of your life polishing another man's electrodes". That's why I became a Mechanical Engineer, I still don't understand why electricity doesn't pour out of an outlet when you pull a plug from it.

Rod
Click to expand...

So I take it that even though you are in Lago Vista, Ω on the Range isn't one of your favorite western tunes...sorry but I can't seem to come up with anything like that for KCL and KVL. I do have to wonder about what that prof said though on polishing another man's electrodes, I'd say more on the subject but I'm not sure this forum is zoned for that.

Like CJD says, condensers do fail. I have a first hand datum as well from the side of the road in the Permian Basin, fortunately I have no replicates of that.
 
First, yes, they really do fail. The foil package itself is not the problem; it's the sloppily made connections to it. Some time ago, in order to understand why there were so many failures, I undertook a small study and this is what I found:

http://sprite.nonlintec.com/cap_failure/

All ignition capacitors (I prefer this modern term instead of the antiquated term "condenser") are around 0.20-0.25 microfarads. All coils have about the same inductance as well, so you can mix and match coils and capacitors with impunity. Maybe there are some that have different values, but I've never heard of them, and I think you could probably vary either the capacitance or inductance quite a bit and it wouldn't affect the operation much, anyway.

As for what they do: any time you suddenly interrupt the current in an inductor (i.e. the coil), you get a big spike of voltage at its terminals. Probably a few thousand volts, although I have never tried to measure it. The capacitor rounds that spike off to a nice, well-behaved pulse of about 150 volts. This is done not only to protect the points from arcing, but the spike would be too fast for the coil to handle, and you would get little energy at the plugs. Between the reduced energy and burned points, it's little wonder that a car with a bad ignition capacitor runs prertty badly.

Hope all that helps.
 
There are 2 numbers to consider with capacitors: capacitance, measured Farads, in this case micro-micro farads (MMF) like .2-.25 MMF or maybe .2-.25 MF. The other number is DC working volts, DCWV. If you are working with a circuit of 20 or 30 volts, checking quality with an ohm meter, with the 5 volt internal battery as a power source, OK, test away. If you get into 1000s of volts, you need a DCWV into the 1000s of volts. Failure at this voltage and internal damage is probably invisible. Polarity is also important. Going from positive to negative ground may cause sudden or early failure.

LeT
 
I do not know much about Yellow wires or blue wires bad or good. With aircraft we can not pull over, quality is foremost. Mexico China US UK follow the country. In aircraft school we opened one up to see how there are made. Much foil and paper and connecting wire to same is point of fail. Cost is much less than towing always replace. For many years I kept points but a few years ago switched to Petronics with new high output coil best move ever, starting, high RPM, seems like more power. I kept my points and capacitor my wire is orange what do I have different with orange? as back up for Petronics All the above comments are true I did not do auto shop. Aircraft school was two years 5 hours a day for four semesters. Madflyer
 
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