Soft start P-R yet anyone?

Dale Young

Senior Member
Joined
Aug 14, 2004
Messages
691
Location
Hopkinsville, Ky
Aircraft
Gyrobee, Grumman AA1-A
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70 hrs/gyro FW/ GOD only knows!!
Has anyone come up with plans for a soft start for an electric pre-rotator yet? (carbon pile,welding rod, or any other types)
 
The Monarch Butterfly I think uses a steel welding rod across the terminals of a solenoid. Maybe Chris Wilson can answer this question.
 
Yep!! It is a stainless steel welding rod on the Monarch. Shoot Tim you know what is going on just take care of Bud..... You Da Man :D

Fly SaFe,
Chris
 
DC control circuit

DC control circuit

I would think this would be a relatively simple DC control circuit. You will need an SCR of sufficient size to handle the full load current of the starter. Use a square wave generator / timer to control the pulse width and firing of the SCR. Some experimenting of the timer settings would be necessary to determine the correct pulse width and ramp up time. If you would like to put a feed back loop into the control it could be used to set the soft start time say form 0 to 100% RRPM in 90 seconds or what ever. More than likely just a low, medium and full speed setting would work for this application. Any technician from a reputable motor control company should be able to install / specify this application. Basically it works by turning the DC motor on and off at a very rapid rate of around 120 times per second for slow speed. At full speed it would stay on 100 % of the time. This is a standard device for controlling RPM in simple DC motor control circuits. For precise RPM and torque requirements the circuitry becomes more complex.
 
SCR's need to cross zero volts to turn off. In a DC circuit, as soon as you turned on the SCR, it would latch on. In a DC circuit, FET's are usually the component of choice. That's why I mentioned a PWM (Pulse Width Modulation) circuit. With electric vehicles becoming more common, heavy duty PWM controlers are also becoming more common. But I have a feeling that they aren't cheap.

Here's a few ideas that could be picked over https://www.discovercircuits.com/P/pwm.htm
 
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