Project ST5000: Early findings

Findings so far:

• The Benmar clutch relay draws 100 mA.  Plenty of headroom within the ST5000's spec of 2 amps.
• Yes, PWM* is used for the output in all operating modes.   When set up to drive a hydraulic pump, the duty cycle is higher, but still uses PWM
• When you press the +1 button (adjust the course 1°), the PWM duty cycle is about 10%.  There is no chance this will operate a relay coil.  The mechanical relays in the Benmar drive will need to be replaced.
• The PWM frequency is 48 Hz - well within the operating range (multiple kHz) of almost any solid state relay
• An H-bridge of 4 solid state DC relays can operate a reversing DC motor and will pass thru the PWM.
• Having soft start and low speed runs for small rudder movements will be a huge boon.  I welcome the PWM overlords. 
• Update:  I have ordered Allied Electronics part No. 70184710 as the MOV - it will shunt 20 amps at 58V, and cost a thundering $0.67.

There are no barriers to proceeding.   Next step:  get 4 suitable solid state relays and a big MOV (to quench the magnetic field collapse back currents - the motor is a very inductive load).

* PWM: an acronym standing for Pulse Width Modulation.  The DC power to the motor is not continuous, but rather is rapidly switched off and on.  The duty cycle is the fraction of the time that the power is on, and can vary from 0% (no power at all) to 100% (full power).  For a familiar example, your microwave uses PWM when you select anything less than full cook power.  When cooking at 80%, it will run the magnetron at full power for 8 seconds, and then turn it off for 2 seconds, repeating (you would measure a frequency of roughly 0.1 Hz).

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