# Need Help with Polarity Reversing switch

#### Redbuljunkie

Joined Aug 10, 2009
4
I am trying to find out how i can make a dc linear actuator reverse direction at an adjustable rate. Basically making it go up and down at a adjustable rate of speed. I do not know if need to use some sort of relay system or where to start exactly. I have looked into some motor reversing circuits but i dont quite grasp the concept of how the circuits are designed. If you guys can help at all i would be extremely thankful!

#### jj_alukkas

Joined Jan 8, 2009
753
Do you need a simple continous oscillator that keeps on going forward and backward with speed adjust?

#### Redbuljunkie

Joined Aug 10, 2009
4
yes, thats exactly what i need actually.

#### Redbuljunkie

Joined Aug 10, 2009
4
Ok, so I'm going to use a simple flip flop type circuit. So the first stage of the switch will push the actuator up, but the second stage needs to have polarity reversed to the actuator to drive it back down again. how do i go about this?

#### KMoffett

Joined Dec 19, 2007
2,903
Does your linear actuator have built in limit switches?

Ken

#### jj_alukkas

Joined Jan 8, 2009
753
You can build this using 2 ways. Electrically or complete electronically.
For an ideal motor/actuator controller, people use limit switches to make it solid and fail proof. If you have one integrated, you can use it, otherwise you will need to add 2 of them. Without limit switches, such a project would be a stupid timer project which sometimes even damages the motor or devices driving due to inaccurate timing.

Building electronically, can be done using flipflops, but for pure electronics, you need to also add an H-bridge to drive the motor as a logic IC cannot drive it.

Building electrically, simply uses 2 relays and 2 limit switches for accurate cycling. You can modify the motor power line and add a PWM to vary its speed. This should not affect the relay's power. This is an example.

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#### KMoffett

Joined Dec 19, 2007
2,903
The down side of my circuit was that it switches polarity on a motor at full speed. Probably not a good thing for the motor. Attached is another version. Relay3, C1, and Relay4 form a monostable that's triggered each time the polarity is switched. It briefly switches off power to the motor and shunts in a braking resistor.

This was all just to play with relays. A solid state version would be cleaner for most people to implement.

Ken

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#### jj_alukkas

Joined Jan 8, 2009
753
The down side of my circuit was that it switches polarity on a motor at full speed. Probably not a good thing for the motor. Attached is another version. Relay3, C1, and Relay4 form a monostable that's triggered each time the polarity is switched. It briefly switches off power to the motor and shunts in a braking resistor.

This was all just to play with relays. A solid state version would be cleaner for most people to implement.
Thats great Ken... Great circuit..
Solid state version is clean, but arent mechanical one's easier to build??

#### KMoffett

Joined Dec 19, 2007
2,903
I think that depends mostly on your skill level with the hardware. I just like to playing with relays. It's sort of a challenge, like building a control system with nothing but the simplest components.

Oh, the "REED RELAY"s are just any small relays, big enough to switch the big relays.

Ken

#### Redbuljunkie

Joined Aug 10, 2009
4
I will use the H bridge in conjunction with the flip flop. What I'm not sure of is if i can use the output signal from the flip flop for the input signal of H bridge without having to cut down on power? Sorry, I am new to this but i really appreciate all the help I have received already. You guys are great

#### KMoffett

Joined Dec 19, 2007
2,903
Redbuljunkie,

Can you post a schematic of the circuit you are planning on using?

ken