Hi,

I have a single axis joystick to operate the speed of a 24V DC motor. At center the joystick puts out 0V, at full forward it puts out +5V, and full back it puts out -5V. The motor controller uses the 0-5V signal for the speed of the motor. I can use a rectifier so that the controller always receives that 0-5V signal regardless of whether the joystick is being pushed forwards or backwards. My problem is operating the motor's direction contactor based off the positive or negative voltage. If positive, the contactor would engage and provide a direction for the motor, if negative the contactor would open and reverse the polarity on the motor. The contactor in this case has 2 N.O. positions and 2 N.C. positions. I need this contactor to open/close based off the polarity of the voltage signal coming out of the joystick. I have been trying to make this work with diodes but haven't come up with a way to provide the full voltage level the contactor's coil would need. Seems like there should be an easy way to do this, but I haven't come across it yet. See attached picture for schematics I am talking about.

 

Doesn't a single Schottky diode rectifier in series with the coil work?

 

Doesn't a single Schottky diode rectifier in series with the coil work?

But if the coil needed, say, 5V to operate, it would not get the full voltage through most of the joystick's range. Its analog, so across the full sweep of the joystick it will output a proportional voltage depending on how far forward/backward it is. A diode could apply voltage to the coil in one direction but might not be for the full rated voltage of the coil.

 

The hysteresis for a DC coil is quite wide, and should operate after the low drop of a Schottky,
Not an ideal solution to operate a relay with a voltage varied by a joystick
The ideal is a joystick with a N.O. SW contact.

 

The ideal is a joystick with a N.O. SW contact.

Like so.

 

Do You have to use a Contactor ?

Why not use a Full-Bridge-Motor Controller ?

How much Current does your Motor require ? ( Locked-Rotor-Amps ).

What does your "Motor-Controller" consist of ?

Do You have a Schematic-Diagram of your Motor-Controller ? ( please post it if You have one ).
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A full bridge controller would be better.
Does the joystick have a spring-return to centre? If so, you might find that it is exactly on the threshold of changing direction and the contactor is constantly changing state.

 

Do You have to use a Contactor ?

Why not use a Full-Bridge-Motor Controller ?

How much Current does your Motor require ? ( Locked-Rotor-Amps ).

What does your "Motor-Controller" consist of ?

Do You have a Schematic-Diagram of your Motor-Controller ? ( please post it if You have one ).
.
.
.

This is the controllers we want to use. It has a built in pot for speed control, or can receive a 0-5V signal for variable speed.

https://www.bodine-electric.com/pro...pwm-dc-motor-speed-control-open-chassis/0788/

 

If going ahead with that controller you may want to make use of the inhibit input, when reversing, this could be an 'At-zero-speed' detect switch on the motor.