Positive and Negative Earth

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Page created by T August 19th 2008:

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Negative and Positive Earth Coils showing the difference in internal connections. Image by T. Click to Enlargen

 

==Positive and Negative Earth:==

The Term describes which Battery terminal is connected to the Car's chassis.

Commercially sold Holden Cars have always had the Battery's negative terminal connected to the chassis.

===British Cars:===

Many British Vehicles up to the early 1960's had positive earths. Some claim was made that it minimised corrosion in the Vehicle's body in a country where iced roads had salt spread on them.

 

===Coils:===

The Coil used on a Negative Earthed car is not the same as the coil used on a Positive Earth Car.

The reason is that the start of the secondary winding was always connected to the power supply side of the coil.

This is to ensure that the Spark jumps from the Centre Electrode of the Spark Plug to the Ground Electrode which ever Voltage is connected to the Chassis.

 

===Identifying a Positive or Negative Earth Ignition Coil:===

To identify the Coil.

 

A Negative Earth car will have the Coil Secondary connected to the +ve Terminal of the Coil.

A Positive Earth car will have the Coil Secondary connected to the -ve Terminal of the Coil.

 

The Centre Electrode of the Spark Plug is designed to run hotter than the Ground Electrode to keep the Spark Plug clean.

It desirable to keep the Centre Electrode clean so that no Spark energy finds it easier  to travel ground down the Electrode than to jump the Spark Plug Gap.

  

This hot centre Electrode means that Electrons find it easier to travel from the hot Centre Electrode to the Ground Electrode.

This is called Thermionic Emission  and is the reason that  Vacuum Tubes (Radio Valves) work.   

 

You can also place the lead end of a Pencil in the Spark Stream. The flow of glowing Electrons should be towards the Engine Block.

 

===Coil Misuse:===

Using a +ve Earth Coil in a -ve Earth Car will seriously burn the points and cause the Capacitor to fail.

This is caused by the excessive Voltage that appears on the Coil -ve terminal by the Secondary winding.

 

Using a -ve Earth Coil in a +ve Earth Car will seriously burn the points and cause the Capacitor to fail.

This is caused by the excessive Voltage that appears on the Coil +ve terminal by the Secondary winding.

 

If the Coil's Secondary winding is connected to the Breaker Point side of the Coil, the Voltage swing will be larger than the points and Capacitor can handle and they will soon fail. This is the usual outcome for interchanging the coils.

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