maxon

+8654321+7654321maxon DC motor= 7 8*= 9 *Mechanical commutationGraphite brushesIn combination with copper commutators for themost rigorous applications.More than 10 million cycles were attained in differentapplications.Graphite brushes are typically used:– In larger motors– With high current loads– In start/stop operation– In reverse operation– While controlling atpulsed power stage (PWM)The special properties of graphite brushes cancause so-called spikes. They are visible in thecommutation pattern. Despite the high-frequencyinterference caused by the spikes, these motorshave become popular in applications withelectronic controls. Please note, that the contactresistance of the graphite brushes changesdependent on load.Precious metal brushes and commutatorOur precious metal combinations ensure ahighly constant and low contact resistance, evenafter a prolonged standstill time. Themotors work with very low starting voltagesand electromagnetic interferences.Precious metal brushes are typically used:– In small motors– In continuous operation– With small current loads– With battery operation– In DC tachometersThe commutation pattern is uniform and freeof spikes, as opposed to that of other motors.The combination of precious metal brushesand maxon rotor system results in minimum ofhigh-frequency interference, which otherwiseleads to major problems in electronical circuits.The motors need practically no interferencesuppression.CLL conceptWith precious metal commutation, the wear oncommutators and brushes is caused mainly bysparks. The CLL concept suppresses spark generationto a large extent, thus greatly extendingservice life.When driven with a pulsed power stage (PWM)higher no-load currents occur and an unwantedmotor heating can result.For further explanations, please see page 49or “The selection of high-precision microdrives”by Dr. Urs Kafader.Commutation pattern withgraphite brushesCommutation pattern withprecious metal brushes3Commutation patternThe commutation pattern shows the currentpattern of a maxon DC motor over one motorrevolution.Please place a low-ohm series resistor in serieswith the motor (approx. 50 times smaller than themotor resistance). Observe the voltage drop overthe resistor on the oscilloscope.21Legend1 Ripple, actual peak-to-peak ripple2 Modulation, attributable mainly toasymmetry in the magnetic field andin the winding.3 Signal pattern within a revolution(number of peaks = twice the number ofcommutator segments)May 2012 edition / subject to changeTechnology – short and to the point25