Distributor - Breaker Points

This topic contains 2 replies and was last updated by nicky-hansard 8 years 7 months ago
February 4th, 2013 11:36am
I'm just wondering if somebody can clear up what and why distributors need breaker points. I understand that it is necessary to drop the voltage to the outer coil, which produces a magnetic field due to the different lengths of the coils so the inner coil can create a large voltage spike. How do systems that don't contain the contact breaker work? What about when you move the position of the distributor cap, does it also move the position of the breaker points? Thanks for your help.
February 5th, 2013 3:47pm
When they first did away with "points" they used a magnetic pick up to replace, in effect it did the same thing as points but did not require as much maintance and or replacement, turning distributor does not qaffect point gap, it changes spark timing to spark plugs, advance or retard depending which way distributor was turned.
February 6th, 2013 1:24am
The breaker points are simply a mechanical electrical switch. When the switch is closed, it allows electricity to flow through the coil and the rest of the PRIMARY system. When the points open, the current wants to continue to flow (surge) and jump the gap at the points. This surge current causes a voltage spike to occur, jumping from 12 volts to maybe 150 to 200 volts. This voltage surge then can create the firing voltage on the SECONDARY side of the ignition system. The amount of windings in the coil, and the ratio of PRIMARY vs the SECONDARY winding create the potential of the 40,000 volts to fire the plugs.

That surge of current flow at the points would quickly cause them to burn out. The surge current is controlled by the condenser in the distributor. The condenser is like a "false ground", an alternative route the current flow can take and result that the arc no longer happens at the points, increasing their life.

If you have ever seen an oscilloscope wave pattern, you would see the firing line when the points open with a large spike, anywhere from 8,000 volts to 40,000 volts, and then a wavy line afterwards. This the rebounding that occurs between the condenser and the coil. Each rebound results in lesser rebound after it. Each if those oscillations could result in another flashover through the points, decreasing their life. Control of that surge current is extremely important.

In the olden days, cars were tuned up every 6 months or so, replacing plugs, points and condensers, checking the wires, cap and rotor, timing the engine; and sometimes, rebuilding the carb. There was always lots of work for good tune up mechanics.

The electronics revolution occurred. A transistor (an electronic switch) replaced the points as a switching device, and the capacitor replaced the condenser as a surge protector. Usually with a points system, the primary current flow was limited to about 2 amps so that you would get sufficient life from the parts. With the electronic system, current flow was often increased to possibly 7 amps, From this you get what was called the high energy ignition systems, capable of generating 60,000 volts, and lasting much longer between tune ups.

The old point system was controlled by a small multi lobe cam inside the distributor. As the distributor shaft turned the cam lobe would lift the point arm of its base, cutting the current flow, making and breaking the circuit.

With the electronic system, the cam is replaced by the pickup coil. The pickup coil was also on the distributor shaft. The pickup coil actually generated a very small voltage and current flow which is used to turn the transistor on and off to control the coil and the primary system.

Then advancing to the computerized systems, the computer has many sensors to locate the cam shaft and/or crankshaft; throttle position sensors that indicate drivers intent ( how fast he wants to go), MAP sensors to judge the load on the engine and lots of other things going on. The entire engine operation is monitored and continually adjusted by the computer many time a second. A whole different story with its own different problems.

But the computerized system still has the primary and secondary ignition systems. It just may have 1 ignition coil per cylinder or 1 ignition coil for the entire engine. The engine will still have spark plugs but because of the computer, they can last for years. The engine may not have any distributer at all, using the computer to control when, and if, the cylinder fires. I say if, because many computer systems turn off some cylinders during cruise operations, when power is not needed.

Now, with all of this, I have probably created more head scratching than clearing the clouds. Maybe it will help.

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