Basic auto ignition electric Q

I don't think the housing is grounded.

The primary & the secondary share a common grounding point thru a grounding wire and capacitor to ground. The coil actually fires when the points open and the electromagnetic field collapses and induces a large voltage into the secondary. So, the secondary is not grounding thru the points. There's a ground wire from the neg. primary post, thru a capacitor (which passes AC current which is how the coil works. It's like a step-up transformer) to engine ground.

'Old type' systems. IIRC the 'points' were between the coil primary and ground! In other words, in operation, the points completed the negative side of the circuit. With ignition 'on' (again IIRC) 12 volts etc. was connected to the hot end of the coil's primary. The points opened (or closed, can't remember which!) the magnetic field either collapsed or or rose (can't remember which!) and the secondary made a bl**dy big spark that was distributed by the rotor to the appropriate spark plug! Very simple system! If the 'points' got bad take them out and rub them on stone/rock to smooth them up and then a week or so later replace them or dress them up with a file! If the capacitor (condenser) went bad you could sometimes use an old radio capacitor instead hanging it below the distributor with wire! No computers then. If not 'What's a computer it was some form of 'calculator' such as a circular slide rule or something! Cheers.

Computers then were folks who sat down at adding machines or desk calculators (mechanical devices that not only added and subtracted, but could multiply) and ran long series of computations. This terminology carried into the early fifties, then disappeared.

Actually, with some ignitions of the Kettering type (coil and breaker points) the vacuum lines had both advance and retard functions, and could be considered almost a "fluidic" computer. Much more involved was the fully evolved fluidic computing going on inside a carburetor in the sixties and later. Marvels of non-electronic computing.

Right. The secondary voltage relies on a ringing (AC) voltage which is generated by the collapse of the magnetic field, inducing currennt via a series tuned circuit, IIRC.

In order to test the coil in place (without a point set), there must be a capacitor from coil (-) to ground, yes? And then ground the (-) terminal and release. Spark should be seen?

Thanks.

There will be already be a capacitor, usually inside the distributor, or maybe external to it. You should be sure that capacitor is good before you make any judgements on such a test.

Then when you ground the (-) terminal, the primary coil will charge, and when you release the ground the field will decay and you should get a spark from the HV tower of the coil to ground.

What is the value of such a cap, uF & V?

Thanks.

Both windings in the coil ground through the negative terminal.

You should find conductivity from the + terminal to the - Terminal. And from the high voltage terminal to the - terminal.

The positive terminal on the coil goes to the battery (through a switch or relay usually) On most vehicles this voltage is NOT 12 volts, it is stepped down through the ballast resistor or through resistance wire so that 6 volts gets to the coil.

The - side gets connected to the points. You will usually see a capacitor on the coil, it is there to stop radio noise and voltage spikes from going into the wiring. On the points you will see another one. It's purpose is to damp the electric pulse and keep the points from arcing.

This all supposes the old style can coils. Most of the new high voltage coils DO ground through the coil frame.

They vary. Typically they are between .15 and .25 microFarads. I know that these capacitors are subjected to test voltages up to about

I have heard this discussed, but dont know the exact working voltage of the units... A figure of 600 WV has been quoted, but I dont honestly know.

If I were going to run this test (if I were having a problem), I would buy a new ignition capacitor from the FLAPS and use it. I would replace the old one whatever the case.

Yes. Originally they were foil capacitors made with oiled paper, but these days most of them are made with thick mylar film.

Probably a lot higher than that today, because these days they use much thicker mylar film with metallization, rather than wrapping film with foil. The metallized film technology is much cheaper, and they tend to use much thicker material than necessary in order to make the caps look and feel like the old ones. This means higher breakdown voltages.

These days, condensers hardly ever fail. They'd probably last the life of the engine. In the paper and oil days, you had to replace them all the time because they would degrade pretty quickly. The thing is, you get a free condenser every time you get new points so you might as well just replace it.

Or install a Mark V capacitive discharge ignition module and then you'll never have to change your condenser OR points ever.

--scott

Condensors seldom failed even in the old days, but occasionally they did. A person would have been a fool to pull a wrench on one of those Kettering systems and not replace the condensor along with the points.

I have, once, seen a bad set of points. Fresh factory new. Shorted always.

Saludos cordiales

That is a pretty good summary, Jamie.

The shell of the coil plays no part of the process..

The (+) terminal is connected to the power source in your car some where. Normally a ballast resistor is used to reduce power in run state and use full power while starting.. This is due to battery voltage being dropped when the starter is engaged.

The (-) of the coil is connected to the points, which also has a condenser/capacitor of a value normally in the range of .047, But that varies depending on the coil that is being used.

When the points are closed, the coil will approach saturation. It is important to insure you have sufficient closure time on the points to cover for higher RPM's, (DWELL time) is important to make sure you have enough time to allow the coil to reach saturation at the highest RPM's

Some problems existed when the cam lobs wore out and it was hard to get the dell time correct with enough opening time on the points along with a bad set of bearings in the distributor.

When the points open, the capacitor(condenser) will act as a temporary shorting post. This will dampen the arch that otherwise would be at the points on open and thus, destroy them over time.

Also, the capacitor acts as a path to ground for that moment and then quickly gets charged there for releasing the current that is present in the coil. This is called collapsing the inductor (coil).

When collapsing of the field takes place, the energy then gets released from the coil is a reverse polarity. AT this point, the capacitor (condenser) will act as its path to ground which will be near 0 ohms and because there is virtually nothing loading the coil down, all of the energy that it took, in the time given to saturate the coil (Dwell), gets released all at once, which multiplies the voltage many times over on top of the coil already having a step up design internally to the plug wire..

Then the cycle starts all over again when the points close, at which time, the only current the points see is the capacitor (condenser) charge, which gets discharged of course, via the points.

Which stands the reason why if you have a bad condenser, you'll have arching which burns the points and does not allow a good path to ground to give you full potential to the HV wire. Of course, if the condenser is shorted, your car just won't start at all.! no spit or sputter!.

Hope that did something fer ya!

"hls" wrote in news:qsednY6j6dlxZUHXnZ2dnUVZ snipped-for-privacy@giganews.com:

I remember that condensers were so cheap there was no point in tempting fate by leaving the old one in when you replaced the (also cheap) points.

The reason I ask is that there is none in this system. A friend has purchased a solid-state magnetic-triggered ignition module that replaces the point set. A trigger sleeve slips over the distributer cam lobes and contains 4 small magnets.

It is new and I can't get it to work -- no spark. My next step in troubleshooting is to test the coil, but sans capacitor, I guess it can't be done. I guess I'll buy a cap just to test the coil.

BTW, I do get 11K secondary resistance and low (I forget the exact value) primary resistance referenced to the (-) terminal.

Thanks to all for your help.

OK if this is a points equipped vehicle you will probably need to run a direct battery feed for the new system. Many of the old systems used a resister in line (either a simple ballast resister or actual resister wire) to drop the voltage at the points to 6 volts or so. Made the points last longer. However a 12 volt ignition will not like the voltage that low (GM HEI unit won't even fire under 9 volts).

If it's a Ford or Chrysler it uses a separate ballast resistor. Just bypass that. If it's a GM the wire feeding the coil positive will need to be replaced.

My next step in

Sure it can. Take a spark plug. Install ONE wire to connect it to the coil.

Now take a strand of copper wire and wrap it around the plug base. Now connect the other end to the neg. terminal on the coil. Now take a feed line from the battery with pos and neg. Connect the positive side to the coil. Take the negative side and touch it to the negative terminal a second or so. Pull it away FAST. You should see a spark if the coil is OK.

I guess I'll buy a cap just to test the coil.

Yes, they came free with the points. They still do.

--scott

Woops! How was this unit set up before it was modified with this magnetically triggered module? Was it working okay when mechanical points were used?

I am wondering if something was lost in translation on this modification.