Baker D30R User Manual - page 57

Surge Test Applications 

12/3/2009 | 71-022 V6 

D30R 

57 

Bar-to-bar surge test 

Bar-to-bar armature surge testing is the most effective method to test DC armatures and 

detect winding insulation weaknesses and faults. In many cases, where the impedance of the 

coils in the armature is very low, it may be the only method possible to test the armature. 

Span testing 

This method uses the brushes of the assembled DC motor to make the connections with the 

commutator for testing of the armature. Any number of bars can be used in this test. Either 

adjacent bars can be surge tested or a specific number, or “span” of bars can be tested. The 

number of bars tested in each span for an individual motor must be the same during the 

entire test. In the repair shop, a fixture can be used in place of the motor’s brushes. 

Span Test using the motor’s brushes 

The wave pattern produced in this test represents the voltage oscillation between the tester 

and the coils for the specific number of commutator bars spanned. For example, any 10 bars 

spanned in series on the armature should give the same pattern as any other 10 bars 

spanned. As the armature is rotated, all the commutator segments and therefore their 

respective coils, pass into the “test area” between the hot surge test lead and the GRD lead. 

Note:

  It is important that the same number of bars (and therefore coils) always be in the 

“test area”. The test wave pattern for each span should match a reference wave pattern on 

the display for the complete armature if the coils are all good. 

1)

Remove all brush pig tail connections from the leads at the brush rigging for all sets of 

brushes to isolate the armature from the power source. 

2)

Place the tester leads in a grounded position. Connect test lead #1 to one of the brush 

assembly pigtails. Connect the GRD test lead to the shaft or other good ground on the 

frame. 

CAUTION:

 When testing armatures that have bars that are wired in series, it is very 

important to ground at least two bars of the armature a few bars away from those 

that are being surged. If this is not done, very high potential voltages to ground can develop in 

the armature due to a transformer effect in the coil. 

3)

Select the adjacent set of brushes or the brushes of the bar corresponding to the desired 

span. Connect test lead #2 and #3 to the pigtail of that brush assembly. 

4)

Select the TLS position #1. Be sure the Function switch is set to Surge. 

Fig 8-4: Span test setup