The Stovebolt Site Forums The Shop Area The Electrical Bay Spark failure with new condenser

This is a real head scratcher. I cannot get 6 volts to the distributor with a condenser installed. I have used 3 condensers, and none have worked. Electricity flows through the coil, to the distributor, and spark is there at the points until the condenser is installed, then the electrical flow is gone. Has anybody ran into this? And, do you have a solution? Thanks, Greg

Additional information. I have a 52 GMC with a 248 engine. All ignition components are new. I have tried 2 different distributors.

Try this:
1. Disconnect the battery
2. Turn the distributor so the points are open
3. Take an ohmmeter and check from the coil side of the condenser to ground
4. If it shows a short (0 ohms), maybe you have the condenser installed wrong (no insulator on the coil side?)
If the ohmmeter shows an initial short and then "charges" to a resistance value, then that would be normal (it may just show a resistance- possibly open)
don

If there is no spark at the points when you open them, the condenser is doing exactly what it was designed to do- - - - -shunt the current to ground to prevent arcing and burning of the points while they're getting far enough open so the induced voltage in the primary circuit can't jump the gap. The place you need to be looking for a spark is at the big center terminal of the coil that is supposed to fire the spark plugs. A spark at the points is the very last thing you want to see.
Jerry

To expand a little on what Hotrod said. Capacitors are not shunts. Their construction simply put, are two conductors, like small sheets of aluminum, separated by a sheet of insulation or dielectric. So they do not conduct current as a shunt would. A failed capacitor is, but not always a breakdown of the dielectric allowing current to pass through it. Simply put, they absorb the arc voltage with the points open, then discharge said voltage when the point close.
One of the hardest things for me to understand when in school was, “capacitors block de voltage but pass ac voltage.

It used to take me several hours of instruction time to get even a few of my students to understand how a condenser (capacitor) charges and discharges, and that was in a classroom setting. It would take several months of typing on a website, and I'm sure it would be more confusing than educational. The quick and dirty version is that the condenser appears to flow current while it's charging up, and protects the points from burning immediately after they begin to open. Then the condenser discharges before the points close again- - - -otherwise the stored charge would fire across the points like an arc welder and burn them as they closed. This action can be watched on an oscilloscope primary wave pattern.
Jerry

Works the same as an accumulator in a automatic transmission. Electricity & fluids follow the same laws, path of least resistance, ect.

BC59, It is, but it also ain’t. One of the first phrases one learns in electronics is “Eli the Iceman”. ICE meaning current leads voltage by 90 degrees across a capacitor. In other words, a 90 degree phase shift. ELI means voltage leads current by 90 degrees through an inductor. That’s ‘tmi’ for guys working on an ignition circuit.

To summarize the condenser, without the benefit of the knowledge one would gain in Hotrod's class, can it be said that its primary function is to ensure that current flows across the points only when they are completely closed? i.e. to prevent arcing?

OK, one more tidbit of information, and I'm going to back out of this discussion- - - -Just as the points break the primary current as they open, the same magnetic field that collapses and induces 10,000 volts or more in the secondary winding that's attached to the big center terminal of the coil to fire the spark plugs also cuts across the primary windings. That spikes the primary voltage up to 100 volts or so every time the points break. With the points open just a thousandth of an inch or so, that voltage spike would arc across the points and burn them. The condenser provides a temporary path for the spike to travel to ground while the condenser is charging, and as the points continue to open and close, the high voltage dissipates by "flywheeling" back and forth from the insulated side of the condenser and back to ground hundreds of times, losing a little voltage each time as it makes the circuit. A proper capacitance condenser will discharge itself completely before the points close again. Now for a little perspective of how fast this happens- - - -at 2000 RPM, a set of points on a 6 cylinder engine make and break 6000 times a minute- - - -that's 100 times a second! The condenser must charge and discharge that often. He's a busy little guy! It's a good thing that electrons travel at approximately the speed of light- - - -186,000 miles per second!
Jerry

Is this GMC truck positive ground?

Wow! There are some very well educated people on here and I appreciate that. I am learning from you all. Bartamos, yes, it is positive ground. I have not yet had time to do the tests detailed previously in this thread (darn day job). I will follow up with your ideas and let you know what I find out. Thank you all very much.

Here is a great explanation of how ignition coil polarity, the condenser, coil, and points comes into the mystery.
http://mgaguru.com/mgtech/ignition/ig104.htm
http://www.mgaguru.com/mgtech/ignition/ig108.htm

Interesting article on polarity- - - -the guy has obviously never worked on a MOPAR ignition system from the late 1940's or early 50's. Those engines were notoriously difficult to start, especially in cold, humid weather, but only some of them. After years of trying every tuning trick in the book, the cause was finally discovered- - - -coil polarity. Apparently, the manufacturer they were using to supply their coils was not paying attention to which side of the primary winding the low voltage end of the secondary winding was attached. That created a situation where some of the coils were firing the spark plugs from the "cold" side of the electrode, which takes approximately 20% more voltage to jump the gap. On a cold start with slow cranking speed, some of those Dodges, Plymouths, Chryslers, and DeSotos just didn't want to start! GMC small trucks were sold with a positive ground electrical system to be consistent with the industry standard for the big rigs they also manufactured- - - - -positive ground all the way to huge tractor-trailers and all sorts of offroad construction equipment. The reason for that being done would require another several paragraphs, and my fingers are tired!
Jerry

Anyone with ignition problems, need to read and understand the links I posted. It really makes it easy to understand how it is supposed to work, and every electrical problem can be solved by OHM's law usually. The coil is simply an AC step-up transformer, the points are a switch, and the condenser makes the magic happen. Tesla was a FN genius.

Update: I mounted the condenser outside of the distributor as suggested by Bill Hanlon over on "Old GMC Trucks", and the system appears to be working normally now.

4100 Fire Truck, thanks for the articles. I did the jumper wire test and got good spark from the jumper wire, but none from the coil HT wire. However, I am now getting fire at the plugs! The real test will be if I can start her up this weekend.