Stearns 300, 200, 55, 500 manual III. Torque Adjustment, IV. General Maintenance

AC Voltage Coil Connection

Class H Coil (colored)		Class B Coil (black)
For	Power Line A	Power Line B	Tie Leads
Low voltage	1 and 3	2 and 4	–
High voltage	1	2	3 and 4

Figure 4

Table 1

	Nominal	Maximum	% Torque	Required Torque	Original
Series	Static Torque	Counterclock-	Reduction	Adjust Screw	Spring Height
	(lb-ft)	wise Turns	per Turn	Length (inches)	(inches)
55,500	1.5	4	12	2	1
55,300	3, 6 & 10	4	12	2	7/8
55,500	15	3	16	2-3/4	1-27/32
55,300
55,000	1.5	3	16	2	1-1/8
55,000
55,200	3, 6, 10 & 15	3	16	2	1
55,400
55,000
55,200	25	3	16	2-3/4	1-7/8
55,400
57,500
57,500	10	3	16	2	1
57,500	15	3	16	2	7/8
55,000
55,400	20	3	16	2-3/4	1-7/8
57,500

Figure 5	Figure 6
DC Voltage Coil Connection
Class H		Class B

Mechanical Switch (Old Style)

Electronic Switch** (New Style)

*Arc suppression used for coil above 48 Vdc. **Follow polarity for switch to operate.

Figure 7

motor terminals as shown, or other equivalent combinations. If a 230 volt brake coil is connected as shown in Figures 5 or 6, the motor can be operated on either 230 volts or 460 volts with no adverse effect on brake operation.

B. DC coils

1.All Stearns DC coils are single voltage dual winding. A high current pull-in winding is initially energized to start the plunger movement, while a low current holding winding is momentarily shunted from the circuit until the plunger has pulled in. The older design incorporated a mechanical switch mounted to the solenoid frame and actuated by an arm mounted to the plunger to bring the holding coil into the circuit. In addition, coils over 48 Vdc have an arc suppression module in parallel with the switch contacts to protect the contacts from arc erosion and suppress EMI. The polarity of the incoming power supply is immaterial with the mechanical switch. The new electronic switch design incorporates an electronic timing circuit to allow the plunger to pull in, then electrically switch to the holding winding. Polarity of the power supply to the electronic switch and coil must be maintained. Refer to Figure 7 for proper wiring.

Caution! Never use a series resistor to drop power supply voltage to the coil as brake malfunction will result.

2.Due to high initial current demands of a DC solenoid, a separate DC power source of adequate current capacity is usually required.

Caution! For electrical release of brake, apply full rated coil voltage instantly. Do not increase voltage slowly.

III. Torque Adjustment

These series of brakes are factory set for nominal rated static torque which is maximum torque. Torque may be decreased for increased stopping time, see Table 1. The torque on the 1-1/2 lb-ft brake may not be reduced.

Note 1: Torque adjust screws on older brakes are 1/4” shorter than shown in Table

1.For replacement screws use part number 8-009-501-00 and specify 2” length needed or use part number 8-009-503-00 and specify 2-3/4” length needed, based on series and torque from Table.

Note 2: Both adjustment screws (11), Figure 8, must be turned equal amounts counterclockwise to decrease torque.

IV. General Maintenance

Warning! Any mechanism or load held in position by the brake should be secured to prevent possible injury to personnel or damage to equipment before any disassembly of the brake is attempted or before the manual release knob is operated on the brake.

Observe all cautions listed at the beginning of this manual before attempting to service brake.

A. Adjustment for friction disc wear (see Table 2 and Figure 8)

1.Manually lift solenoid plunger to maximum travel. Depress and allow solenoid plunger to snap out several times. Measure solenoid air gap between mating ground surfaces of solenoid frame and solenoid plunger. (On vertically mounted brakes, it will be necessary to push solenoid plunger into solenoid frame to

Figure 8

Table 2: Air Gap Settings

Nominal Static	55,000	55,500
	55,200		57,500
Torque (lb-ft)		55,300
	55,400
1.5; 3	13/32”	13/32”	–
6	1/2”	1/2”	–
10	9/16”	1/2”	9/16”
15	9/16”	9/16”	9/16”
20; 25	9/16”	–	9/16”

S-652-2