Current Density in Carbon Brush

About Carbon Brushes:
1. Carbon Brush	2. Why Carbon is Selected as the medium?
3. Current Density in Carbon Brush	4. Why Carbon Brushes are split?
5. What is Patina?

Current density is normally expressed as amps per square cm or amps per square inch. Current density is simply the value of current that is passing through per unit area of carbon brush.

There are some points that effects the current density of carbon brush such as temperature, vibration, nature of operation continuous or intermittent, speed etc.

Current density in a carbon brush using in DC motor can be calculated with the following equation:

Current Density Equation

In Brush circuit contact area from Total number of brushes half brushes are used to carry in the current and half brushes are used to carry out the current.

For bottom angled brush the contact area is not just width X thickness but the contact area should taken into account. 

A carbon brush should not be operate in low current density. Low density operation is more dangerous than over density operation.