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QUESTION: I am trying to wire my own 12v linear actuator to a DPDT momentary switch that I have. That's the easy part. I want to know if there is a way (possibly relays?) that if I tap the switch in the up position, a constant flow of electricity will extend the actuator to it's full length before cutting the electricity supply. The same would go for if I tapped the switch in the down position. Almost similar to the way a garage door works. I want to keep this on the cheap side of things. Is this possible? If so, can you explain (maybe a wiring diagram to help?)

Thanks,
Kyle

ANSWER: You didn't say what actuator you are using. Many of them available, now days, have already taken into account that a shut off is needed and a limit switch is built into their mechanisms.  See this one, for example:

http://www.speedwaymotors.com/Spal-Linear-Actuator-12-Volt-Motor,7478.html?utm_m

And, you can find others.

Also, you can add your own contact switch that opens the circuit when the actuator reaches its end and trips the switch.  Here are some examples - but there are many, many types and sizes that can be purchased or made in a shop:

http://www.google.com/shopping/product/11701057107629867797?q=limit%20switch&hl=

Also, you can devise current switches that when the actuator reaches its end the current goes up and a transistor senses the overload and turns off the power.  Little more exotic and requirs some engineering but not complicated.

Maybe these ideas will get you going towards a solution.  If you need more, let me know the exact actuator and your application area.

Rgds.



---------- FOLLOW-UP ----------

QUESTION: Hello again,

Thanks for the quick response. It's not the cut-off that I'm interested in. The actuator I am using is a 12v 24" Linear actuator with built in limit switches at both ends of the shaft. What I am  wondering is how to devise a concept of how to keep the current going until the actuator is fully extended or retracted with only a quick press of the up/down momentary switch. I don't want to have to hold the switch in while the actuator extends/retracts. Is there a way to do this?

Answer
Yes,  same answer as before. But, you didn't give me the model number or source of your actuator.  Most of them nowdays have builtin limit switches.  See here for a typical solution:

http://static.speedwaymotors.com/images/charts/wiring_diagram.gif

And, you can purchase many types of limit switches that have built in switching to help you with the control mechanisms, etc.

http://static.speedwaymotors.com/pdf/910-64295%20SPAL.pdf

The whole business of actuators is a well developed business and there are many, many types of off the shelf and oem products for exactly what you want to do.  And, if you can find an already made solution it will, in the long run, cost you much less than engineering your own.

Your switch can be a detent switch which stays in one position; the limit switch turns off power.  Operation next time requires to move the switch back to neutral and start the cycle again.  Many of these oem type solutions are made for automotive and vehicular applications and have the same functional requirements as you are explaining.

all the best.  

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Electronics questions about AC, DC and digital theory.

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Graduate electrical engineer with over 40 years in electronic design, manufacturing, project organization and patent review. Experience in fields of industrial and consumer electronics (audio, video, acoustics, etc.)

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IEEE (Institute of Electrical and Electronics Engineers); Senior Life member AES (Audio Engineering Society), Fellow Life member

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BSEE University of North Dakota

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