• SoftStart Clutch Controller
  • GDI SoftStart Clutch Controller

SoftStart Clutch Controller

GDI’s patented SoftStart Clutch controller smoothes and softens the engagement of electromagnetic clutches.  In some cases clutch engagement can be so harsh that it causes damage to the equipment.  Broken belts, sheared bolts and stalled engines can all be attributed to the jarring engagement of electromagnetic clutches.  Whether the goal is reduced impact on the equipment or the operator the SoftStart clutch controller is  the solution  for any applications using electromagnetic clutches.

Product Features


  • Closed loop control for consistent performance throughout the entire clutch life.
  • Precise current measurement for accurate and repeatable pull-in detection.
  • Closed loop PWM current control unaffected by charging system voltage.
  • One controller part number:
    · Radiometric RPM control automatically scales to RPM at time of engagement.
    · On-the-fly current calibration automatically adapts to different sized clutches.
  • Default to open loop control if RPM signal is unavailable
  • Optional fixed current calibration possible for special applications.
  • Optional open loop available (no tachometer feedback)
  • Short circuit protected
  • Load dump protected

How it works
Electromagnetic clutches inherently engage abruptly. For many applications with inertial loads, high stresses are produced, potentially shortening the life of components, bearings, mechanical mounts etc. The advantages of electromagnetic clutches are such that the stress problem has traditionally been tolerated by adding cost, either by over designing components, increasing enginesize, or simply accepting a higher failure rate.

The patented GDI SoftStart controller sensest he exact point at which the friction surfaces contact, then rapidly reduces the current to a level that allows the clutch so safely slip, but not release. Using engine RPM feedback, the patented controller adjusts the clutch current in a manner that drived the engine RPM to fit a desired profile.

Fields of Use

For Gas, Diesel, or Electric powered equipment; remove damaging jolt during clutch engagement; tachometer closed loop feedback (inductive or alternator input)


Problems solved by the SoftStart Clutch

  • Bolt Shear
  • Broken Belts
  • Link Breakage
  • Belt Screech
  • RPM Droop
  • Engine Stall
  • Operator Jolt
  • Mechanical Slam


GDI’s patented SoftStart Clutch Controller offers a simple solution to all of these issues!
Enhance the perception of value among users by making clutch engagement smooth and predictable.

  • Mechanical Life
    The SoftStart lessens forces to mechanical parts and improves the life of bolts, decks, brackets and other mechanical parts
  • Belt Life
    Reduce wear and breakage for belts and improve the quality & reputation oft he equipment
  • Engine Stall
    The SoftStart eliminates engine stalling and RPM droop by utilizing closed loop RPM monitoring while engaging the electric clutch
  • Mechanical Jolt
    Smooth engagement means less jolt tot he equipment and customers
  • Engine Cost Savings
    The SoftStart Clutch enables OEMs to reduce equipment engine size to save money

Technical Specifications


  • Operating Temperature Range: -40 to +70C
  • *Vibration: 20g’s @ 10 – 80 Hz SAE J-1378
  • *Shock: 55g’s SAE J-1378 (tested and passed to 150gs,, which is nearly 3 times the SAE specification)
  • *Humidity: 95% H SAE J-1378
  • *Salt Spray Test: MIL-STD-202G, Method 101E (5% NaCI @ 35C, 48 hrs)
  • *Dust: Unit is 100% encapsulated – dust can not enter
  • *Immersion: ASAE EP455 5.6 level 2
    Immerse controller in tap water at a temperature of 18C +/- 5C to a component top surface depth of 460mm. Orient in each of 3 orthogonal planes for 5 min in each plane. Upon removal, immediately subject to a cold soak of 019C for 30 min. Return to dry atmosphere of 25C for 60 Min. No impaired function, no water entry
  • Ultraviolet: GDI’s Q-Sun Xe-1- UV Chamber – 720 Hours
  • *Thermal Shock: Controller stabilized at 70°C for 30 minutes. Removed from oven and immediately immersed into 0°C water mixed with UV sensitive dye for a minimum of 5 minutes – repeated for a total of 10 cycles. Controller stabilized at -40°C for 30 minutes. Removed from chamber and immediately immersed into 25°C water mixed with UV sensitive dye for a minimum of 5 minutes – repeated for a total of 10 cycles. No functional failures or ingress of water.
  • *Chemical: ASAE EP455.5.8.2 chemicals brush exposure.
    Chemical test: Apply with a brush over the normally exposed surface area. Repeat once per day for three days. Check for impaired function or detrimental corrosion during the test and at the end of a 100 hour min interval following exposure to test condition. No defect from wiping the surface with the following chemicals at room temperature: engine oil, Transmission Fluid, Gasoline. Check Download Leaflet for more information.


Soft Start Clutch Controller

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