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I want to automatically open and close a door using a Linear Actuator on a timer?

I want to hook up a 12 volt linear actuator to a door hooked to a 110 volt timer with a plug on the bottom so when the timer turns the power on the plug will energize and the LA will open the door, and when the next set of pins on the timer come around it powers the plug again sending power to the LA again to close it, i obviously have to power the LA with a 110 v AC to 12 v dc converter, and most of the Linear Actuators have internal limit switches, so how can i revers the LA? Or do i need an AC Linear Actuator? The timer simply powers the plug on the bottom of it when the tab comes around and the next tab will be set to turn it off, in other words open in the morning and close at night, im thinking i need some switch with relays? any help would be apreciated.

robinthedark (author) 2 years ago
Ok, after looking at options in Grainger I got it,
So when the timer throws 110 v to the power supply that will thro 24 volt DC to a switching relay (every time power is interupted the relay switches contacs) so when the timer comes on it will retract the Linear Actuator and the limit will stop it, and then the timer will kick power on again thru the power supply switching contacs in the relay reversing polarity to the Linear Actuator
Grainger Alternating relay # 6CVF2 $24.00 bucks.

Thanks Guys,

Rob
orksecurity2 years ago
Reversing: If it's a DC motor, you generally just reverse the direction in which voltage is applied to it.

Having it start in alternating directions: Since power is off between the activations, the only "memory" you have in the system itself is the door position. But that's enough, with limit switches. Use one of the limit switches to control a DPTT relay (or a DPDT relay and a SPST relay). The relay should be set up so that one of the circuits it controls is a circuit that keeps it energized, so it acts as a latch (once on, always on until power is removed). The other pair of DPDT contacts is used like a DPDT switch to swap the connection on the motors -- wen energized, the relay causes the motor to run one direction, when not energized, the motor runs the other direction. Finally, take an input -- off one of the existing limit switches, or off a new switch you mount for the purpose -- which is also wired to power the relay's coil; this causes the relay to start up powered when power is applied _only_ when the door is pressed against that switch.

Should be easy enough to use those hints and turn them into a working system...

WARNING: As you've described it, there are no safety switches. If there's something between door and frame, the motor is going to do the best it can to push the door through that obstruction... damaging the door, the mechanism, and/or whatever is in the way. The classic safety precaution is to set up additional switches on the door or mechanism which notice if the door seems to be pushing back and cause it to reverse... but you'd also need to think about whether and when it should try again.
robinthedark (author)  orksecurity2 years ago
I was worried when I posted that someone was going to blow me right out of the water, you did a good job explaining it, I still have just a few toes left in the water but that’s about it.
Ok so this timer will go off, sending 110 v to the converter, sending 12 volts to the LA, opening the door, the limit switch in the LA will open stopping movement of the door, let’s stop there!, question, the timer is one from lowes/homedepot for watering lighting etc when the timer turns power on, it will stay on for about 15 min till the next pin swings around on the face and trips the power off, and when the timer comes around and comes back on at night it will again send 110 v to the converter sending 12 v to the relays reversing polarity of the motor??

Thanks for your patience; I’m not an electrician, although I did stay at a Holiday Express one time!!

Rob
Hmmm. Actually, you've just pointed out a flaw in my design. When the door hits the limit switch, that stops the door's motion in that direction. But now we've got that tripping the relate to reverse the motor, presumably operating the other circuit (and the other limit switch).... so the door would immediately start back.

We need a bit more sophistication. We need to keep the relay and door from switching to reverse until the power is cycled. Let me think for a bit to see if I can give you something Really Simple which achieves that.

(Others are welcome to chip in if you've got a good answer before I do. I'm trying to keep the design as self-evident as possible -- elevator logic rather than programming.)
No, you're doing great so far.

Me, I'd add a photoswitch....

Steve
robinthedark (author)  orksecurity2 years ago
Good thing you cant see the smoke comming out of my ears, but if i was to just use the timer to turn on the power and leave it on till dark and i came out of the power supply into a double pull double throw control relay, the relay should pull in with power thru the coil and stay pulled in, "opening the door" and then at night the timer would kick the power off switching the relay closing the door??
robinthedark (author)  orksecurity2 years ago
Yes, thanks, keep it simple if you can, remember Holiday inn Express!!!

Rob
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