Sizing Dynamic Brake Resistors and Chopper Modules Dynamic Brake Module Circuit Using a Dynamic Brake or Chopper•In general, the motor power rating, speed, torque, and details of the regenerative duty cycle need to be known.•Generally, a dynamic brake can be used whenever regenerative energy is dissipated on an occasional or periodic basis.•If the drive will consistently be regenerating, serious consideration should be given to returning the power to the AC utility. Gather the Information First•The nameplate power rating of the motor in watts, kilowatts, or horsepower.•The nameplate speed rating of the motor in rpm, or rps.•The motor inertia and load inertia in kilogram-meters2, or lb-ft2.•The gear ratio, if a gear is present between the motor and load, GR.•The motor shaft speed, torque, and power profile of the drive application. Example Speed, Torque, and Power Profilettt How to Choose a Dynamic Brake / Chopper•Calculate the total inertia of the system•Calculate the peak regenerative power you need to dissipate.–This will determine the maximum allowable resistance value of the DB resistor.•Calculate the average power dissipation –This will determine the average power dissipation capacity needed in the DB resistor.•Third, check to see that the peak temperature of the dynamic braking resistor does not exceed its capacity.–Plot the Average Load and Peak Load on the curve in the sizing guide. This is necessary only on the dynamic brake modules!•Dynamic brake modules should only be used on drives 75HP and smaller. How to Size A Dynamic Brake Module Step 1 - Total InertiaJT = total inertia reflected to the motor shaft, kilogram-meters2 (kg-m2) or pound-feet2 (lb-ft2)Jm = motor inertia, kilogram-meters2 (kg-m2) or pound-feet2 (lb-ft2)JL = load inertia, kilogram-meters2 (kg-m2) or pound-feet2 (lb-ft2)2 = 0.04214011 kg-m2 Step 2 - Peak Regenerative PowerJT = total inertia reflected to the motor shaft, kg-m2wb = max angular rotational speed, Rad/s = 2pNb/60wo = angular rotational speed, less than rated speed (can be zero) Rad/s Nb = maximum application speed in RPMt3-t2 = total time of deceleration from wb to wo, secondsPb = peak braking power, wattsNote: 1.0 HP = 746 watts Step 3 - Maximum DB Resistor ValueVd = the value of DC Bus voltage that the chopper module regulates at. This value will bePb = peak braking power calculated in step 2Rdb1 = the maximum allowable value for the dynamic brake resistorResistor tolerances could be built in here. +/- 10% Step 4 - Choose the Correct DB Module•KA005 - 28 ohms, 666 watts•KA010 - 13.2 ohms, 1650 watts•KA050 - 10.5 ohms, 7000 watts•KB005 - 108 ohms, 1500 watts•KB010 - 52.7 ohms, 2063 watts•KB050 - 10.5 ohms, 7000 watts•KC005 - 108 ohms, 1500 watts•KC010 - 52.7 ohms, 2063 watts•KC050 - 15.8 ohms, 8000 watts Step 5 - Estimate the Average PowerPav = average dynamic brake resistor dissipation, wattst3-t2 = elapsed time to decelerate from wb speed to wo speed, secondst4 = total cycle time, secondsPb = Peak braking power, wattswb = maximum motor speed, Rad/swo = a slower motor speed, Rad/s Step 6 - Percent Average LoadStep 7 - Percent Peak LoadAL = Average Load in percent of Dynamic Brake ResistorPav = Average dynamic brake resistor dissipation calculated in step 5, wattsPdb = Steady state power dissipation capacity of the selected dynamic brake modulePL = Peak Load in percent of Dynamic Brake ResistorPav = Peak braking power calculated in step 2, wattsPdb = Steady state power dissipation capacity of the selected dynamic brake module Step 8 - Plot AL and PL on Curves How to Select a Chopper Module and Dynamic Braking Resistor Step 1 - Total InertiaJT = total inertia reflected to the motor shaft, kilogram-meters2 (kg-m2) or pound-feet2 (lb-ft2)Jm = motor inertia, kilogram-meters2 (kg-m2) or pound-feet2 (lb-ft2)JL = load inertia, kilogram-meters2 (kg-m2) or pound-feet2 (lb-ft2)2 = 0.04214011 kg-m2 Step 2 - Peak Regenerative PowerJT = total inertia reflected to the motor shaft, kg-m2wb = max angular rotational speed, Rad/s = 2pNb/60wo = angular rotational speed, less than rated speed (can be zero) Rad/sNb = maximum application speed in RPM t3-t2 = total time of deceleration from wb to wo, secondsPb = peak braking power, wattsNote: 1.0 HP = 746 watts Step 3 - Maximum DB Resistor ValueVd = the value of DC Bus voltage that the chopper module regulates at. This value will bePb = peak braking power calculated in step 2Rdb1 = the maximum allowable value for the dynamic brake resistorResistor tolerances could be built in here. +/- 10% Step 4 - Choose the Correct Chopper ModuleId1 = the minimum current flowing through the chopper module transistorVd = the value of the DC bus voltage, see step 3Rdb1 = the maximum allowable value for the dynamic brake resistor Step 5 - Minimum DB Resistor ValueStep 6 -Choosing DB Resistor ValueRdb2 = the minimum value of the dynamic brake resistorVd = the value of the DC bus voltage, see step 3Id2 = the value of the current rating for the chopper module About Duty CycleGiven that a resistor cools off in about 15 minutes, if cycle time minus the decel time exceeds 900 then using the larger cycle time can’t be used for calculating average power.Let’s say that I decel in 10 seconds every hour. That would be 10 / 3600 or 0.002777 times the peak power. What if I decel in 50 seconds once a day? Or 60 seconds once a week? Step 7 - Estimate Resistor WattagePav = average dynamic brake resistor dissipation, wattst3-t2 = elapsed time to decelerate from wb speed to wo speed, secondst4 = (adjusted) total cycle time, secondsPb = Peak braking power, wattswb = maximum motor speed, Rad/swo = a slower motor speed, Rad/s Step 8 – Calculate Watt-SecondsPws = required watt-seconds of the resistort3-t2 = elapsed time to decelerate from wb speed to wo speed, secondsPb = Peak braking power, watts How to Size a resistor for PowerFlex 70/700 Step 1 - Total InertiaJT = total inertia reflected to the motor shaft, kilogram-meters2 (kg-m2) or pound-feet2 (lb-ft2)Jm = motor inertia, kilogram-meters2 (kg-m2) or pound-feet2 (lb-ft2)JL = load inertia, kilogram-meters2 (kg-m2) or pound-feet2 (lb-ft2)2 = 0.04214011 kg-m2 Step 2 - Peak Regenerative PowerJT = total inertia reflected to the motor shaft, kg-m2wb = max angular rotational speed, Rad/s = 2pNb/60wo = angular rotational speed, less than rated speed (can be zero) Rad/sNb = maximum application speed in RPM t3-t2 = total time of deceleration from wb to wo, secondsPb = peak braking power, wattsNote: 1.0 HP = 746 watts Step 3 - Maximum DB Resistor ValueVd = the value of DC Bus voltage that utilizes the full capability of the drive. 395VDC or 790VDC or 987VDCPb = peak braking power calculated in step 2Rdb1 = the maximum allowable value for the dynamic brake resistorResistor tolerances are built into the minimum resistances for each individual drive About Duty CycleGiven that a resistor cools off in about 15 minutes, if cycle time minus the decel time exceeds 900 then using the larger cycle time can’t be used for calculating average power.Let’s say that I decel in 10 seconds every hour. That would be 10 / 3600 or 0.002777 times the peak power. What if I decel in 50 seconds once a day? Or 60 seconds once a week? Step 7 - Estimate Resistor WattagePav = average dynamic brake resistor dissipation, wattst3-t2 = elapsed time to decelerate from wb speed to wo speed, secondst4 = (adjusted) total cycle time, secondsPb = Peak braking power, wattswb = maximum motor speed, Rad/swo = a slower motor speed, Rad/s Step 8 – Calculate Watt-SecondsPws = required watt-seconds of the resistort3-t2 = elapsed time to decelerate from wb speed to wo speed, secondsPb = Peak braking power, watts More discussions:Intermittent overhauling loads.Doubling up chopper units. 。