Beckwith Electronics

Hamburg, Illinois 62045
(618) 232-1139
(618) 232-1172 fax

Hurst Manufacturing

	Brushless DC Motors Introduction Selection Guide BLDC		Introduction to Stepping Motors Introduction to Controls LSD & LSG PAS & PBS BAS RAS & RBS SAS & SBS TS YAS35 & YAS42 SCS
	Synchronous Motors A & AB BA PA & PB RA SA & SB SC T & TA YA		Timing Motor and Timers Discontinued for reference only M Series Cycle & Interval Timers
	Reluctance Synchronous and Induction Motors -  KH & KN  KS		Brushed DC Motors KD Series
	Synchronous Motors, Hysteresis Discontinued for reference only AR-DA & PC-DA DA & DB EA & EF MB HB CA GA		Permanent Magnet, Linear Acuators LA/LB & LAS/LBS SSL, SLB, SLS, & SBLS

Hurst Motor Selection Guide
Variable Speed	NT Dynamo Brushless DC Motor
	Advantages Dynamic Braking High Efficiency No Brush Wear Reliable Reduced EMI & RFI Low Rotor Inertia	Disadvantages Requires Controller Complex Drive	Analog Control	50 oz-in	DMA
			External Control	50 oz-in	DMB
			Digital Control	50 oz-in	DMC
			PWM Control	50 oz-in	DMD
			Spur Gear	200 oz-in	DM
			Planetary Gear	149 in-lb	MM
			Other Gear
	Brushed DC Motor
	Advantages Dynamic Braking High Efficiency	Disadvantages Demag at low temperatures Brush Wear EMI	Direct Current	237 oz-in	KD
	Hybrid Stepper Introduction
	1.8° Step		Size 17	25 oz-in	H17
			Size 17	44 oz-in	H17ET
			NEMA 23	83 oz-in	H23R
			NEMA 23	187 oz-in	H23S
	Permanent Magnet DC Stepper
	7.5° Step		35 MM	150 oz-in	LS 35
			42 MM	150 oz-in	LS 42
			Square	200 oz-in	PAS
			Compact	200 oz-in	SAS
			Compact	20.5 oz-in	SCS
			Heavy-Duty	250 oz-in	TS
	15° Step		Square	200 oz-in	PBS
			Compact	200 oz-in	SBS
Fixed Speed	Permanent Magnet AC Synchronous
			35 MM	150 oz-in	LY 35
			42 MM	150 oz-in	LY 42
				150 oz-in	A/AB
			Square	200 oz-in	PA/PB
			Compact	200 oz-in	SA/SB
			Compact	20.5 oz-in	SC
			Heavy-Duty	250 oz-in	T
	AC Induction
			High Slip	250 oz-in	KH
			Normal Slip	250 oz-in	KN
	Linear Actuator
			Linear	10 lbs	LA/LB
			Linear	15 lbs	SL/SBL

Application Information...Applications for Hurst Motors and other information

Torque is the product of a force and the radius at which it is applied. The British unit of torque is pound-feet and in smaller motors this unit is reduced to ounce-inches. The metric unit of torque is Newton-meter.

Few motors produce a single value of torque over their entire speed range so that a torque vs. speed curve is often necessary for torque evaluation. Definitions of terms used to describe specific points on the curve are listed below along with definitions of some other commonly used terms for motor torque specification.

Pull-In Torque: the maximum torque at which a synchronous motor (stepping motor included) can accelerate its load to synchronous speed.

Pull-Out Torque: the maximum torque which a synchronous motor (stepping motor included) can develop and still maintain synchronous speed.

Full-Load Torque: the torque developed by a non-synchronous motor at its rated full-load speed.

Breakdown Torque: the maximum torque that the motor can develop; it occurs as a point on the speed-torque curve below synchronous or full-load speed.

Locked-Rotor Torque: the torque developed with the rotor at standstill (stalled).

Holding or Static Torque (Stepping Motor): the torque required to displace the rotor from its equilibrium position with one or more stator phases energized with the rotor at rest.

Detent or Residual Torque (Permanent Magnet Motor): the torque developed in an unenergized motor when the permanent magnet rotor is displaced from a position of minimum stator reluctance.

VARIABLE FREQUENCY OPERATION OF AC MOTORS

Sometimes a single motor is specified for both 50 and 60 Hz operation. Since inductive reactance and capacitive reactance vary dissimilarly with frequency, optimum performance must usually be compromised when a single winding/capacitor combination is operated at different frequencies. Some types of motors are more sensitive than others to frequency changes. As a general rule synchronous motors and especially permanent magnet motors are more sensitive than induction motors. The factory should be consulted before 50/60 Hz operation of a motor is planned.

Operation over a wider frequency range is extremely difficult to accomplish with capacitor phased motors and is not recommended. Reliable operation requires a two phase power supply with applied voltage a function of frequency.

If gear units had no losses, the torque at the output shaft of a gear motor would equal the motor torque multiplied by the reduction of the gear train. Since all gearing does have some internal losses, the actual output torque will be less than the calculated no-loss value by a factor known as gearing efficiency. The efficiency of a gear train will vary with the number of gears. For rough approximation a value of 7% to 10% loss per gear may be assumed. When precise calculation is necessary for a specific gear reduction, values should be obtained from the factory.

When high gear reductions are used, the torque at the output shaft may exceed the strength of the gearing. For this reason a maximum torque value, a gear torque rating, must be specified to prevent gearing damage. Gear torque ratings are based upon a uniform, steady torque load. Dynamic or shock loads impose stresses which can exceed gearing strength or cause early fatigue failure. To some extent this can be taken into consideration in a reduced gear torque rating. However, dynamic braking with inertial loads or locking of the output shaft can force the gearing to absorb destructive amounts of kinetic energy stored in the momentum of the load or the rotor with immediate or rapid failure. As an example, permanent magnet motors with gear trains should not be stalled since the inherent pulsating nature of the stall torque can cause gearing damage in a short period of time.

TEMPERATURE RISE AND INSULATION SYSTEMS

Temperature has an effect upon electrical resistance, magnetic characteristics, viscosity of lubricants, rate of volatilization of lubricants, dielectric strength of insulation and life of physical components in general. These effects must be taken into consideration in each motor application.

The temperature rise of a motor is the difference between the measured temperature of the motor winding and the ambient temperature. Electrical insulation systems are classified according to the maximum temperature that they can withstand. Hurst motors have either Class A or Class B insulation systems which are rated at 105^oC and 130^oC respectively for the hottest-spot temperature. A hot-spot allowance must be made for the difference between the measured temperature of the winding and the actual temperature of the hottest spot within the winding, usually 50 to 150^oC depending upon the type of motor construction. The sum of the temperature rise, the hot-spot allowance, and the temperature of the ambient must not exceed the temperature rating of the insulation.

The temperature rise of a motor should also be specified at a particular operating point, e.g., no-load, full-load, or locked-rotor. Many of the Hurst motors are "impedance protected," that is, they are designed with enough impedance in the windings to limit the locked rotor currents to values that do not cause the motor to overheat beyond a safe temperature. Other motors are available with a thermal protector, a device installed adjacent to the stator winding which will disconnect the motor from the line should the winding temperature increase beyond a safe value.

The life of the electrical insulation and of the lubricants are adversely affected by high temperatures. A generally accepted "rule of thumb" is that for every 10^oC increase in operating temperature, life is halved.

UL and CSA Certifications for our products

UNDERWRITERS' LABORATORIES RECOGNITION
MODEL	QUALIFICATION	UL CARD
A & AB	115V, 60 Hz Standard Rotor	E37163, Component - Time-Indicating and Recording Appliances
AR-DA	115V, 60 Hz	E53578(N), Componet - Impedance Protected Motors
CA	115V,60 Hz	E37163, Componet - Time-Indicating and Recording Appliances
DA-DB	115V,60 Hz	E37163, Componet - Time-Indicating and Recording Appliances
EA	115V,60 Hz	E37163, Componet - Time-Indicating and Recording Appliances
GA	115V,60 Hz	E37163, Componet - Time-Indicating and Recording Appliances
HB	115V,60 Hz Class 105(A) Insulation System	E52207, Componet - Systems, Electrical Insulation
KH, KN, KS	115V,60 Hz Class 105(A) Insulation System	E52207, Componet - Systems, Electrical Insulation E53578(N), Componet - Impedance Protected Motors
LA & LB	115V,60 Hz Standard Rotor	E53578(N), Componet - Impedance Protected Motors
MB	115V,60 Hz Class 105(A) Insulation System	E52207, Componet - Systems Electrical Insulation E52177 Componet - Motors
PA & PB	115V,60 Hz, Standard Rotor	E53578(N), Componet - Impedance Protected Motors
PC-DA	115V,60 Hz	E53578(N), Componet - Impedance Protected Motors
RA	115V,60 Hz Standard Rotor	E53578(N), Componet - Impedance Protected Motors
SA, SC	115V,60 Hz	E53578(N), Componet - Impedance Motors
T, TA	115V Standard Rotor	E53578(N), Componet - Impedance Protected Motors