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Spark failure with new condenser #1336122 Mon Dec 02 2019 08:07 PM
Joined: Jul 2013
Posts: 12
G
Greg Stong Offline OP
New Guy
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.

Re: Spark failure with new condenser [Re: Greg Stong] #1336135 Mon Dec 02 2019 09:27 PM
Joined: Jan 2000
Posts: 524
D
Donsz Offline
Shop Shark
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

Re: Spark failure with new condenser [Re: Greg Stong] #1336146 Mon Dec 02 2019 11:05 PM
Joined: Feb 2004
Posts: 19,261
H
Hotrod Lincoln Offline
Boltergeist
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


The murder victim was drowned in a bathtub full of Rice Krispies and milk.
The coroner blamed the crime on a cereal killer!

Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
Re: Spark failure with new condenser [Re: Greg Stong] #1336194 Tue Dec 03 2019 05:02 AM
Joined: May 2005
Posts: 1,624
B
beltfed Offline
Shop Shark
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.


Six volt guy living in a twelve volt world
Re: Spark failure with new condenser [Re: Greg Stong] #1336201 Tue Dec 03 2019 05:35 AM
Joined: Feb 2004
Posts: 19,261
H
Hotrod Lincoln Offline
Boltergeist
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


The murder victim was drowned in a bathtub full of Rice Krispies and milk.
The coroner blamed the crime on a cereal killer!

Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
Re: Spark failure with new condenser [Re: Greg Stong] #1336259 Tue Dec 03 2019 06:44 PM
Joined: Sep 2011
Posts: 546
B
BC59 Offline
Shop Shark
Works the same as an accumulator in a automatic transmission. Electricity & fluids follow the same laws, path of least resistance, ect.


BC
1960 Chevy C10 driver
1949 GMC 250 project in waiting
G.M dealer tech since 1980 & counting
Re: Spark failure with new condenser [Re: Greg Stong] #1336273 Tue Dec 03 2019 08:30 PM
Joined: May 2005
Posts: 1,624
B
beltfed Offline
Shop Shark
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.


Six volt guy living in a twelve volt world
Re: Spark failure with new condenser [Re: Greg Stong] #1336375 Wed Dec 04 2019 12:40 PM
Joined: Oct 2019
Posts: 31
W
WarEagle1 Offline
Wrench Fetcher
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?

Re: Spark failure with new condenser [Re: Greg Stong] #1336394 Wed Dec 04 2019 03:03 PM
Joined: Feb 2004
Posts: 19,261
H
Hotrod Lincoln Offline
Boltergeist
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


The murder victim was drowned in a bathtub full of Rice Krispies and milk.
The coroner blamed the crime on a cereal killer!

Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
Re: Spark failure with new condenser [Re: Greg Stong] #1336439 Wed Dec 04 2019 08:36 PM
Joined: May 2005
Posts: 6,379
B
bartamos Offline
Master Gabster
Is this GMC truck positive ground?


I'm away on an ego trip. Will be back on Feb 30.
I'm not an Auto Mechanic, but I play one on TV.
I charge $0.02 for every opinion and I take Paypal.
Plan B is always better than plan A, by definition.


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