DC for the Hands-On Technician

Course Description

This seminar is geared to the hands-on technician, as well as those with an interest in DC repair. It will be presented in a visual format, with no math or theory. Well supported by slide format. We will have DC motors in various stages of disassembly to be used as work pieces in conjunction with West Fraser Electro/Mechanical’s repair facility and equipment as classroom training tools.

Course Outline

How a DC motor works, in layman’s terms

Opposites attract
Field flux distortion: Interpoles & Compensating windings
Function of Fields: Interpoles / Compensating Windings
What is Brush Neutral Position?

Disassembly

Visual inspection
Commutator condition
Brushes: What to check, and why
Bearing inspection
Shaft currents / axial loading / misalignment
Brushholders & Springs
Minimum Commutator Diameters

Incoming tests

Drop test: AC vs. DC
Armature testing: Surge test / Growler / Monolithic / Ductor
Testing fields & interpoles: Surge test / Current comparison / Resistance measurement

Brush Neutral

Brush seating: Tips to make the job easier
Neutral defined with graphics
AC method for setting neutral
Special cases; Back-turns, C-lead V. Assembly testing
Cumulative / Differential
Check for correct Interpole/armature relative polarity
Brush spacing
No-load test run

Commutation

Reading a commutator
Wear pattern & what they mean
Unusual brush wear: symptoms and solutions

Turn & Undercutting commutators

Blade selection
Depth of undercut
Chamfering tips Limitrac; reducing flashovers

Armature Stripping Tips

Heat vs. Cold stripping
Eddy currents & armature
Effects of excess heat on armature
Cost of Labor
An effective method for cold-stripping armatures without damage
Contamination of air supply: silicon / hydrochloric acid /chlorine
Limitrac: reducing flashovers
Spring tension: Traction / standard / North American vs. European standards
Brush grade and varying loads
Cleaning armatures
Compensating winding repair tips
Parallel paths and current: theory vs. reality