5
P-3026 • Doc. No. 60881 • Boston Gear
®
Ratiotrol
®
DC Motor Speed Control
General Information
Variable
Regulation
Load
Line
Field
Temperature
Method
Change
Voltage
Heating
(1)
95%
±10%
Cold/Normal
±10ºC
Standard Voltage
Feedback with IR
Compensation
2-3%
2%
5-12%
1%
Optional Speed
(tach) Feedback
0.5%
0.5%
0.5%
0.5%
Standard Features
1. Power Conversion --– NEMA Code K
semiconverter power bridge consisting of two
SCR’s, two diodes and a freewheeling diode.
Power bridge is an integrated, encapsulated
component. (
See Figure 5, page 21
)
2. Reference Power Supply – +10 VDC
regulated, with respect to common.
3. Feedback – CEMF voltage with adjustable IR
compensation.
4. Control Transformer – 24 VAC secondary
isolates all operator controls and magnetic
control logic from the AC power source for
operator protection. (
See Transformer T1,
Figure 5, page 21
)
5. Motor Contactor – Provides positive
disconnection of motor armature from the
controller output, and undervoltage
protection. A phase-off circuit ensures that
the contactor does not make or break DC.
(
See Figure 5, page 21
)
6. Motor Overload – Positive motor protection
by an electronic nonadjustable current (load)
monitor. This circuit shuts down the drive
when the motor armature current exceeds
120% for 80 seconds. An optional current
(load) monitor (Option Kit Cat. No. 60177) is
available which provides an adjustable trip
range and an adjustable time delay range.
This option provides a relay with one set of
Form C, 2 ampere (120 VAC – 28 UDC)
contacts which can be used to signal audible
or visual alarms, or auxiliary control devices,
e.g., lubrication pumps, fans, valves.
7. AC Line Disconnect – Provided by a single-
pole, magnetic-trip only circuit breaker with a
5000 ampere interruption capacity. (
See
Figure 5
) An optional two-pole circuit breaker
(Option 30, Kit Cat. No. 60169) is available
which opens both lines of the input supply.
8. Line Transient Protection – Provided by a
metal oxide varistor (MOV) suppressor
across the AC input line. (
See RV1 on Figure
5
)
9. UL Listed – File E60208
Adjustments
The following adjustment potentiometers are
located on the standard circuit boards in the
controller. (
See Figure 5
)
1. Maximum Speed – 60 to 100% of motor base
speed
2. Minimum Speed – 0 to 30% of motor
base speed
3. IR (load) Compensation – 0 to 100% of
rated load
4. Current Limit – 50 to 150% of full-load torque
Options
Standardized pre-engineered optional
equipment can be supplied with Controllers at
additional costs.
See Section VI
for option
listing.
Section I
Table 2 – Speed Regulation Characteristics
(1)Does Not Apply to Permanent Magnet Motors.