reversing polarity on 12 volt actuator

I need help designing a circuit to reverse polarity on a 12v actuator. The circuit will be started with a limit switch and from there needs to extend then retract automatically. I intend on having a timer on the circuit where I can control the time that its extended. I have looked at SGT Wookies H bridge design but don't think this is what I need. I am new at the design of circuits and not sure of what relays, diodes, 555, 556, etc. that I may need.

Why do you think Sgt Wookies' H-bridge is not what you need?

Where do I need to put the timer in the ciruit to adjust the length of time that the actuator stays extended? Will this circuit run its full cycle with the limit switch contacts closing and then opening?

tolarn said:

I need help designing a circuit to reverse polarity on a 12v actuator. The circuit will be started with a limit switch and from there needs to extend then retract automatically. I intend on having a timer on the circuit where I can control the time that its extended. I have looked at SGT Wookies H bridge design but don't think this is what I need. I am new at the design of circuits and not sure of what relays, diodes, 555, 556, etc. that I may need.

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For some help more exact details need to be posted.
What do you mean by starting with a limit switch?
Will the actuator be at its maximum travel when extended?
How long does the actuator need to be extended?
How much current does the actuator draw?

Have a look at this thread..... http://forum.allaboutcircuits.com/showthread.php?t=66786

By starting with a limit switch I mean that when the limit switch is triggered I need the circuit to start and run through its course until its triggered again. The actuator will travel to its max each time the limit switch is triggered. The time frame needs to be 0 - 10 seconds. I have need picked out a specific actuator yet. I do know that the length of travel will be 2-4 inches. I would like my power supply to be 12 volts and be powered by alkaline batteries. Is it possible that this circuit will work this way or will I need to get something similar to a sealed lead acid battery?

How do you intend to know when the actuator is fully extended? Internal limit within the actuator or external limit? There are a lot of unknowns at this point as to what you really want or have.

I'm considering using an actuator with internal switches. Which type will make the circuit work out better? As far as the materials needed I haven't purchased anything yet. I do have a few parts laying around but intend to buy all new materials when I start building my circuit. I would like the circuit to be simple as possible but would like to insure efficiency.

tolarn said:

By starting with a limit switch I mean that when the limit switch is triggered I need the circuit to start and run through its course until its triggered again. The actuator will travel to its max each time the limit switch is triggered. The time frame needs to be 0 - 10 seconds. I have need picked out a specific actuator yet. I do know that the length of travel will be 2-4 inches. I would like my power supply to be 12 volts and be powered by alkaline batteries. Is it possible that this circuit will work this way or will I need to get something similar to a sealed lead acid battery?

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How can we possibly give any advice about whether alkaline or sealed lead acid batteries will work. You haven't given any indication of what kind of current might be involved (even though that was specifically asked. I would think that the answer would be very different if the actuator is opening the door on a toaster oven versis lifting a two ton press so that a new peice of sheet metal can be slid in.

It would also be handy if you would answer MrChips' question and describe why you think that Sgt Wookie's H-Bridge circuit won't work in your application. If we know what you think its shortcomings are, then the better we can try to offer alternatives that don't share them.

If you will look at post #4 of the link I posted earlier, tell me what part of that will not work for you. The UP LIMIT and DOWN LIMIT devices are the ones that are built into the actuator. You could replace that terminology with EXTENDED LIMIT and RETRACTED LIMIT if UP and DOWN are confusing to you. Likewise for the UP and DOWN push buttons. Those two buttons would be replaced with momentary relay contacts that are controlled from the microprocessor or other device that you would use to start the process, control the time at extended position and command return.
The handle on my spoon may not be long enough for this.

The project I am working on is an automatic feeder the will be activated by the animal. Therefore the actuator will have a low current draw, it will probably one of the smallest (as far as strength and amp draw that I can find) actuators I can find. So from what you guys are telling me I can use momentary relay contacts controlled by a microprocessor I will be able to use SGT Wookies circuit. What type of microprocessor do I need?

An Arduino would do it.

This circuit should work great with the modifications you've provided. Where does the arduino fit into the circuit? Thanks for the help guys. Sorry for my lack of experience.

That information was previously provided.......

BillB3857 said:

If you will look at post #4 of the link I posted earlier, tell me what part of that will not work for you. The UP LIMIT and DOWN LIMIT devices are the ones that are built into the actuator. You could replace that terminology with EXTENDED LIMIT and RETRACTED LIMIT if UP and DOWN are confusing to you. Likewise for the UP and DOWN push buttons. Those two buttons would be replaced with momentary relay contacts that are controlled from the microprocessor or other device that you would use to start the process, control the time at extended position and command return.
The handle on my spoon may not be long enough for this.

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