Re:Re:Primary vs secondary ignition confusion

Ok this may sound dumb. But I have a ne oscilloscope. Been a dream since I was in high school automotive to learn how to use one.
So I thought I watched a video. That someone stated you needed an attenuator for when you measure primary ignition. But I thought it was the secondary side that had all the high voltage. And primary generally had just 12 volts?
Did I misunderstand what was said?

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The reason you need an attenuator for primary is you are directly touching the wire that had the voltage and as it is being fed by 12v the coils flyback voltage (what isn't used on the secondary side) comes back on the primary side (several hundred volts). Onto the secondary side it is thousands of volts and i doubt an attenuator could save your scope if it was connected to a secondary side of a coil (like inserting a probe into the end of the wire) which is why we use cop paddles or inductive wire clamps were not actually touching any voltage were just reading the magnetic field voltage created by such high voltage. Hope that helps if not im sure someone can explain it better!

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Thanks, it confirmed what I thought would happen but was not 100% sure.

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wrote:

as it is being fed by 12v the coils flyback voltage (what isn't used on the secondary side) comes back on the primary side (several hundred volts).

 

Disclaimer: This is a layman's understanding and explanation.  I welcome any corrections, or additional input.

An ignition coil is a step-up transformer. It converts low voltage and high current, from the primary side, into high voltage and low current on the secondary side.
 
Electrical voltage can be created many ways. One way is with a coil of wire, a magnet, and motion. An ignition coil has a primary, and a secondary coil of wire. When the primary coil is energized with 12v, it creates a magnetic field, which surrounds both Primary and secondary coils.
 
So, we have two conductors, and a magnet. When we de-energize the coil, the magnetic field collapses. This collapse of the magnetic field is the motion. Voltage is created. How much voltage is created depends on the conductor (Coil of wire), the strength of the magnet, and the speed of the motion. Due to the number of windings in the Primary Coil, Around 400 volts is created on the Primary side during the collapse of the magnetic field.  But remember, the Ignition coil has TWO Coils.  The Secondary winding, also, uses the magnetic field created, and collapsed, by the primary coil. The Secondary has 100x the amount of windings as the Primary,  so the voltage created in the Secondary is 100x that of the primary. 400v x 100 = 40,000v.

As Ben pointed out, when we read Primary Voltage, Your Scope lead is physically touching the circuit, and is in direct contact with 400v.  When we read secondary, we are reading a magnetic field created around the wire, the scope lead is not physically touching the circuit. Secondary Ignition probes convert the magnetic field into a LOW voltage that can be measured by the scope and translated to represent the HIGH voltage.
 

wrote:

 which is why we use cop paddles or inductive wire clamps 

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Ben, thank you....just one observation with regards to your good explanation: the "inductive wire clamps" actually are capacative probes, sensing changes in an electrical field as opposed to inductive sensors which react to changes in magnetic fields. The attachment deals with the differences between the 2 types. It might be informative as this seems to be a topic where confusion reigns to some extent.

   
 

Are there any good references or videos about using an attenuator with your scope? And when you should use one?

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The most important thing to know is: What is the maximum amount of voltage that your scope is rated for?  The 4-channel Pico automotive series can handle up to 200 volts. The Pico 8-channel, only 50 volts. Snap-on scopes can handle up to 400 volts, without attenutation. 

The important thing, is to know your scope's limitation. Also, know what kind of voltage you expect to see during your testing. Injector voltage can reach up to 100 volts. An ignition coil can reach up to 400 volts.  If you expect to exceed the limit of your scope, use an attenuator. Be sure to tell your scope that you are using an attenuator, or you will have to do the math, yourself. There should be a setting in the scope to tell it that you are using an attenuator. The scope will then multiply the signal by the same amount that the attenuator dropped it.

Thanks, I found one of the videos that explained this about 5 min ago. I am a diy guy. Was trained as a mechanic years ago. Bit my instructor never taught the sun scope. I wanted to learn it so bad. Recently bought a micsig. And already have a US open. Can't weight to do more testing

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