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Model
1000AR Installation and Operation Manual
6/4/2001 © copyright 1997 by Powertec
REGENERATIVE RESISTORS
Regenerative motor controllers require a method of handling energy that is generated by the motor
and returned to the drive. Traditionally, this has been handled by two methods: (1) using the power lines
as a power sink by dumping excess energy back into the power source, and (2) dissipation as heat.
The first method was popular with DC drives, but it is becoming very unpopular because of the
disruptive effect of the electrical noise in the power system.
The first method has been used by Brushless DC drives, inverters, and vector-type controls. In motor
systems at larger horsepowers, the dissipation means can get bulky and expensive. At horsepowers in the
range of the 1000AR series of drives, they are not a big problem.
Regenerative resistors are rated in terms of resistance and power.
The resistance of the bus loader resistors must allow enough current to flow from the bus through the
resistor(s) to remove the energy at a rate faster than the motor can generate it. The bus voltage times the
bus loader current must be greater than 150% of the motor’s full power rating.
The power rating of the resistors depends on the duty cycle of the regeneration.
Powertec
uses four
ratings for the GENESIS series of drives:
1. STOPPING DUTY = used to stop the motor once per minute = approximately 10% duty cycle.
2. EXTENDED DUTY = used to stop high inertia loads = approximately 25% duty cycle.
3. LIFTING DUTY = used on cranes and hoists and inclined conveyors = 50% duty cycle.
4. CONTINUOUS DUTY = 100% duty cycle.
The standard supplied with standard GENESIS drives is STOPPING DUTY.
Any duty cycle other than stopping duty MUST BE EVALUATED BY A MECHANICAL ENGINEER.
The amount of regenerative power needed is a MECHANICAL, not an ELECTRICAL, calculation.
To avoid using many different resistors, standard resistor values have been adopted.
The standard resistor for 230 VAC drives is 25 ohms @ 420 W.
The standard resistor for 460 VAC drives is 70 ohms @ 420 W.
The standard resistor for 380 VAC drives is also 70 ohms @ 420 W.
One resistor is used in parallel for each 5 HP or portion thereof.
BUS LOADER RESISTOR TABLE - Standard Duty Resistors
Line Voltage Motor HP Resistors Equivalent R Dissipation Peak Amps Ave. Amps
VAC
HP # @ ohms ohms watts ADC ADC
230 up to 5 1 @ 25 25.00 375 15.00 1.00
230 7.5 2 @ 25 12.50 750 30.00 1.50
230 10 2 @ 25 12.50 750 30.00 2.00
380 up to 5 1 @ 70 70.00 375 8.86 0.60
380 7.5 2 @ 70 35.00 750 17.72 0.90
380 10 2 @ 70 35.00 750 17.72 1.20
460 up to 5 1 @ 70 70.00 375 10.72 0.50
460 7.5 2 @ 70 35.00 750 21.45 0.75
460 10 2 @ 70 35.00 750 21.45 1.00
460 15 3 @ 70 23.33 1125 32.16 1.50
All resistors are connected in parallel.