# Pulsed DC output for auto starter motor

#### DavidS1966

Joined May 29, 2016
2
I have built a 12 vdc powered winch to help launch RC sailplanes. Currently the power is applied by tapping a foot controlled switch which in turn acts to pulse the automobile starter motor which powers the winch. A constant ON would cause excessive strain on the wings of the sailplanes and they would most likely "pancake". The foot controlled switch activates a dc solenoid, which in turn handles the load from the battery to the motor. I would appreciate any advice on how to incorporate an adjustable pulsed signal, so a constant press of the foot switch would yield a pulsed control output to the solenoid. I would like to be able to either increase or decrease the speed of the pulse while in use to facilitate the required torque to get the sailplane safely launched.

#### crutschow

Joined Mar 14, 2008
30,097
How fast do want to pulse the solenoid and how long is the pulse?
That likely could be done with a one or two 555 timers with a MOSFET to power the solenoid.
Do you know how much current the solenoid takes or what its resistance is?

#### DavidS1966

Joined May 29, 2016
2
How fast do want to pulse the solenoid and how long is the pulse?
That likely could be done with a one or two 555 timers with a MOSFET to power the solenoid.
Do you know how much current the solenoid takes or what its resistance is?
The speed of the pulsing will be approximately how fast you can use your foot to activate the switch. As far as the resistance, I will have to get back to you, but it is a standard Ford type starter solenoid. I figure the 555 or better yet an Arduino, would have to turn on a transistor or MOSFET, which would in turn carry the load to the solenoid. Not sure about any diode protection across the load terminals however.

#### crutschow

Joined Mar 14, 2008
30,097
The speed of the pulsing will be approximately how fast you can use your foot to activate the switch.
So is that about 50% on and 50% off, at perhaps a couple pulses a second?
I figure the 555 or better yet an Arduino
If you are familiar with an Arduino, that would work fine.
But it may be more difficult to adjust the pulse speed/duty-cycle in the field than with a 555.
The speed of the pulsing will be approximately how fast you can use your foot to activate the switch. As far as the resistance, I will have to get back to you, but it is a standard Ford type starter solenoid. I figure the 555 or better yet an Arduino, would have to turn on a transistor or MOSFET, which would in turn carry the load to the solenoid. Not sure about any diode protection across the load terminals however.
The load probably doesn't need it if it's worked okay so far, but the transistor/MOSFET will need diode protection from the solenoid coil inductance.