MWH Series
Motor Winding Heater Controller
The MWH Series keeps AC induction motors warm and moisture-free during extended shutdown periods — preventing condensation build-up and protecting your motor investment. Fully automatic operation requires no operator interface.
| AC Supply Voltage | 200 – 690 Vac |
| HP Ratings | 3 to 900 HP |
| Amp Ratings | 10 to 80 Amps |
| Models | MWH-10, MWH-25, MWH-50, MWH-80 |
| Installation | Wire in parallel to magnetic starter |
| Temperature Setting | +5°C to +10°C above ambient (factory set) |
Easy to Install
Wire in parallel to the magnetic starter's line and load connection — installation is complete in minutes.
Simple Adjustment
Output voltage factory set to maintain +5°C to +10°C above ambient — field adjustable as needed.
Self Protected
Built-in fuse protection, RC snubber circuit, and MOV protection against voltage spikes for reliable maintenance-free operation.
Fully Automatic
Turns on when the motor starter turns off. Built-in 1-minute timer ensures motor field has collapsed before injecting DC power into windings. Instantly turns off when motor restarts.
Built-in Overload Sensing
Optional shutdown input connects to the N.O. auxiliary contact on the thermal overload relay — disabling the heater during overload for faster cool down.
Ideal vs Strip Heaters
Generates heat evenly throughout the motor stator windings — no hot spots. More effective conduction to rotor, bearings and shaft.
Current Ratings
| Model | Max Amps | HP @ 208V | HP @ 240V | HP @ 480V | HP @ 575V |
|---|---|---|---|---|---|
| MWH-10-P-* | 10 | 3–40 | 5–50 | 10–100 | 15–125 |
| MWH-25-P-* | 25 | 50–100 | 60–125 | 125–250 | 150–300 |
| MWH-50-P-* | 50 | 125–200 | 150–250 | 300–500 | 350–600 |
| MWH-80-P-* | 80 | 250–300 | 300–400 | 600–800 | 700–900 |
MWH Series
Technical Specifications
Adjustments
Output voltage factory set for +5°C to +10°C above ambient. Field adjustable via control trim — maximum range approximately 15% of line voltage.
Output Voltage
Factory set to 8–9% of line voltage (measured with RMS AC voltmeter).
Fusing
Two fuses (F1 / F2) protect the MWH. Class T 600V replacement fuses recommended.
Transient Protection
RC snubber circuit across the SCR + Metal Oxide Varistor (MOV) protects against voltage spikes.
LED Indicators
POWER ON, ENABLE ON, OUTPUT ON status indicators on the front of the unit.
Built-in Timer
1-minute delay after motor stops before energizing windings (allows magnetic field to collapse).
Wire Sizing
MWH-10: AWG 14 | MWH-25: AWG 8 | MWH-50: AWG 6 | MWH-80: AWG 2 (75°C minimum, 600V class)
Replacement Fuses (F1 / F2)
MWH-10: 15A Class CC / 20A Class CC Time Delay
MWH-25: 30A / 70A Class T 600V
MWH-50: 60A / 100A Class T 600V
MWH-80: 100A / 150A Class T 600V
Operation
Fully automatic. Turns on approximately 1 minute after motor stops; instantly off when motor restarts. No operator interface required.
Overload Sensing
Optional shutdown input connects to the N.O. auxiliary contact on the motor starter's thermal overload relay — disables heater control during overload, returns online when overload is reset.
Mounting
Vertical with the line connection (L1, L2) at the top — required for proper convection cooling of the SCR.
Enclosure
Open chassis (front cover is fiber-glass insulation against accidental contact). Optional NEMA 1 enclosures available.
Open Panel Dimensions (H × W × D)
MWH-10: 6.2" × 4.5" × 6"
MWH-25: 8" × 6" × 6"
MWH-50: 10" × 8" × 7.9"
MWH-80: 10" × 8" × 8"
NEMA 1 Dimensions (H × W × D)
MWH-10: 11" × 7" × 7"
MWH-25: 11" × 7" × 7"
MWH-50: 15" × 10" × 8"
MWH-80: 20" × 10" × 10"
Wire Type
75°C minimum