For hydro generators, the industry had a rule of thumb to keep the total runout on the slip rings below 0.010 in. (0.25 mm) for good brush and spring life. Staying below 0.010 in. (0.25 mm) runout has been difficult, so Helwig was challenged by their customers in the hydro industry to determine the actual requirement for total runout. The fatigue life for a constant force spring in a brush holder is very difficult to determine analytically. Therefore, we conducted a spring fatigue cycle test that simulates . . . to read the full article click the image below.