Electrical discussion

[pstephens46]

Youtube is a pretty good source for animation.

I got stuff with words if you be interested. For example:

CDI THEORY OF OPERATION
In its simplest form, a CDI ignition is composed of the following elements:
Flywheel – The flywheel or rotor contains the magnets (two, three or six magnets) to generate a voltage in the charge coil and the pulsar coil. When the magnets move in front of a coil, a current is generated for the ignition. The flywheel is aligned with the crankshaft by a flywheel key for ignition timing purposes.
Charge Coil – The charge coil is a one wire or two wire coil, depending on engine size that is mounted on a timer base plate under the flywheel.
It produces an AC voltage that is delivered to the CDI box. Most 2-stroke engines (75hp and larger) use a combination of low speed and high speed charge coils.
Pulser Coil – The pulser coil is a one or two wire coil (depending on the ignition system) that delivers an AC voltage signal to the CDI box for triggering the ignition timing. The pulser coils are mounted on a timer base and are located either under the flywheel or outside the flywheel.
CDI Box – The CDI box receives inputs from the charge coil, converts the signal to DC current and stores it in a capacitor. When the pulser coil signal
is received by the SCR in the CDI box, the stored voltage is discharged to the primary of the ignition coil. The primary components of the CDI box are diodes to convert the AC voltages to a DC voltage, a capacitor to store the rectified charge coil voltage, and an SCR (Silicon-Con*****ed Rectifier) that serves as an electronic switch. When activated, it delivers the stored voltage
from the capacitor to the primary of the ignition coil.

Moving this conversation from other thread...

There has been conversation regarding primary and secondary coils. Are these part of the same device? I thought plugs were AC current. So they are DC based on above CDI description.

[boscoe99]

An ignition coil consists of two coils. A primary coil and a secondary coil. The primary and secondary coils are adjacent to each other. Primary coils has heavier gauge wire and a lesser number of turns on the coil. The secondary coil has lighter gauge wire and a greater number of turns on the coil.

In a CDI system high voltage is sent through the primary coil. Electromagnetic induction causes a much higher voltage to be induced within the secondary coil. When the voltage gets high enough a spark jumps the gap of a spark plug. That spark is direct current.

In a TCI system battery voltage is applied and causes current to flow through the primary coil. When the voltage is removed the current collapsing in the primary coil induces voltage in the secondary coil. When the voltage rises to a certain point a spark jumps the gap of the spark plug. That spark is direct current.

[boscoe99]

Ignition Coil – The ignition coil primary winding receives the 150~250 volt output from the CDI box and steps it up to 25,000~45,000 volts in the secondary winding. A high-tension lead and cap assembly then delivers this high voltage to the spark plug. A resistor spark plug cap is used with some ignition coils to reduce Radio Frequency Interference (RFI). Ignition coils consist of a primary and secondary winding and come in two different spark plug lead configurations. The independent ignition coil has one spark plug lead connected to one end of the secondary winding and one independent coil is required for each spark plug or cylinder. The Siamese or dual lead coil has two spark plug leads with one connected to each end of the secondary winding and only one coil is required for two cylinders or spark plugs. Most high-tension secondary leads are not removable from the ignition coil.

[pstephens46]

Thanks. Looks like two coils power 4 plugs on the F150TXRD. This is the waste spark concept?

[boscoe99]

This guy should work on his speaking skills IMO. Otherwise a fairly good explanation of a CDI system.

https://www.youtube.com/watch?v=0yK3Opq_i0M

[boscoe99]

Here is an explanation for what Yamaha refers to as a transistorized ignition system. Rather than the use of a mechanical rotor to distribute high tension voltage to a spark plug it is done electronically.

https://www.youtube.com/watch?v=QYx8J_5l5wY

[pstephens46]

This guy should work on his speaking skills IMO. Otherwise a fairly good explanation of a CDI system.

https://www.youtube.com/watch?v=0yK3Opq_i0M

Good explanation. He reminds me of the painter years back on PBS that would refer to happy trees and so forth.

[cpostis]

This guy should work on his speaking skills IMO. Otherwise a fairly good explanation of a CDI system.

https://www.youtube.com/watch?v=0yK3Opq_i0M

Agree with Pstephens, good simple explanation and animation.

[rodbolt17]

and I have posted this several times, I even explained how an SCR works .
it is also why even though the CDI is technically a rectified AC voltage it is a DC voltage when released into the ign coil primary.
however the discharge is so rapid it takes a special meter to monitor the peak voltage.
most meters measure RMS on the AC scale
most meters are to slow to catch the peak on the DC scale.

this capacitor discharge is turned on and off almost instantly.

once triggered(by a trigger voltage) the SCR now stays on until the current threshold for turning off is reached.

RMS is what is called root mean square, also known as wvDC,working voltage DC.
it represents roughly 70% of the A/C sine wave.
it is also why in a pinch you can measure the CDI output with a standard A/C meter and add about 30% to the reading and be close.

[ausnoelm]

In very simplistic terms, you cannot store AC, anything like capacitors, batteries and so on, are DC, similarly, you cannot generate DC, it is AC converted to DC (via a rectifier) AC is generated by (usually) a magnet being moved past a coil with a solid core through the centre of it, that's how sine waves come about, as the pole of the magnet approaches the coil, the induced voltage begins to increase until it peaks and the other pole passes the coil, inducing a negative voltage, if seen on an oscilloscope, it appears as a nice regular wave, how fast the magnet passes the coil, provides the frequency, in cycles, measured in Hertz, and just to throw in something totally useless (to most) this circular motion of a generator, inducing the sine wave, is why Pi is often used in electronic calculations....

[rodbolt17]

actually you can generate DC.
most automobiles up until the mid to late sixties used ,,,, you guessed it. a generator.
my old 61 studeabaker lark had one.
they also used an adjustable mechanical voltage regulator.
they also had to be properly polarized when placing the system into service.
with the advent of alternators they still used mechanical adjustable regulators.
the GM delcotron in the late 1968-early 69 was the first of the solid state built in regulator/rectifier altenators commonly found today.

[boscoe99]

Uh, an older style automotive generator creates AC. It is converted to pulsed DC by the commutator.

And with respect to DC it can be created. That is what a solar cell does. A thermocouple also.

[boscoe99]

Some will say pie r square. They are wrong. Pie are round. Corn bread are square.

[ausnoelm]

Of course you can create DC, simple batteries do that for us every day, but moving coils and magnets generate AC, and it cannot be stored, it needs to be rectified to DC for storage, or used by a capacitor in your CDI ignition, there is a hell of a lot more to it than that, but the basics are there.

[boscoe99]

The comment was made "similarly, you cannot generate DC, it is AC converted to DC ".

My reply to that was that you can generate DC. It does not have to first be created as AC and then converted to DC. Solar cells, thermocouples and galvanic cells create DC directly. That DC can be used by a device or stored in a device for later usage.

Batteries are normally not considered to create DC. They store it. As stated, AC cannot be stored.

Mechanical generators create AC. It is then converted either mechanically via a commutator or electronically via rectifiers to DC. That DC can then be stored in a battery, a capacitor or other devices.