Automatic Chicken door opener

[HansW]

Hi all,
this is my first post in this forum. I have searched for my topic, but didn't find the answer I was looking for.
I have a linear actuator 12VDC with internal limit switches. Apply power, the actuator will move in one direction until it hit's the internal limit switch, reverse polarity and the actuator moves the other direction until it hit's the internal limit switch. I bought a electronic timer to turn on and off for the actuator at certain times and I bought a DPDT relay from Radio Shack to deal with reversing the polarity. Here comes my problem:
I need a latching relay to tie in with the coil connectors of the DPDT relay, because somehow I need to be able to automatically reverse the polarity every time power is made available by the timer, and as far as I can tell from research on the internet a latching relay will remember the state it is in every time power is applied.
What kind of (reasonable) latching relay would work for me? How would I wire the whole thing together to make it work?
I don't know much about reading electronic schematics, so it would have to be pretty simple for me to understand it.
Thank you for any help,
Hans

 

[cowboybob]

What are the outputs of the timer?

1. For instance, ON for a period of time and then OFF for a similar period of time (continuous)
or
2. ON (or OFF) for a brief moment at every period of time (pulsed).

 

[HansW]

It would be like your point one. On for one minute continuously (in the morning), then off. On again for one minute continuously (in the evening), then off. Twice on per 24 hour period for one minute.

Thank you!

 

[cowboybob]

OK. Though I'm still visualizing the sequence.

Will the timer be ON for the entire duration of the actuator's transition? Or just a portion? (In other words, how long does it take the actuator to complete one cycle).

Do you know how the actuator motor and limit switches are wired? If not, can you give me a Brand and Model #?

Reason I ask is that I'm not yet convinced you need a latching relay.

 

[HansW]

Will the timer be ON for the entire duration of the actuator's transition? Or just a portion? (In other words, how long does it take the actuator to complete one cycle).
It takes the actuator roughly 30 seconds to travel the entire distance, and yes the timer is ON for the entire duration and a little beyond.

Do you know how the actuator motor and limit switches are wired? If not, can you give me a Brand and Model #?
No, I don't know how they are wired. The model # is PA-02 with 14 inches of stroke from https://progressiveautomations.com.
As far as the actuator goes, I can keep it powered for as long as I want it will turn off after full travel is achieved. It will only travel in the other direction once I reverse polarity.
Thank you!

 

[cowboybob]

HansW,

It might be simpler and cheaper to get a timer that has a 12hr ON followed by a 12hr OFF function like this one. You might be able to find something cheaper or more readily available somewhere else)

It would power the DPDT relay for 12hrs and the de-power it for 12hrs, thereby switching the actuator polarity on that schedule.

Keeping the relay powered for that length of time won't be a problem (as a frequent customer of radio shack here, I don't know of any of them that aren't rated for continuous power on conditions).

I can give you the wiring diagram for hooking up all the components for this project, if you like.

 

[HansW]

cowboybob,
thank you for the great idea with leaving the power on for 12 hours ON/OFF with the DPDT relay. I would have never thought of this. I can accomplish that I think with the current electronic timer I have. Maybe if it is not too much trouble you could show me a wiring diagram, that would be awesome.
However, I do have a concern and a question. What if there is a power failure? Why is it so hard to do it with a latching relay? Or is that the completely wrong approach?
Thank you.

 

[cowboybob]

Another relay just unnecessarily complicates the system, is all. Essentially, the timer is doing the part of the latch relay.

As for a power failure, without a UPS for the battery and timer, you'll have to manually restart/recalibrate the system. No other choice, really, that I can think of.

You might want to consider some manner of manual override for the door itself.

We could also add a momentary switch to re-cycle the actuator to the position appropriate for the time of day.

Here's a schematic:

View attachment 63084

Hope this helps.

 

[HansW]

Thank you very much for the schematic.

I don't want to push it, but I do would like to ask:
1) Would you be able to draw a schematic including a latching relay and the type of latching relay to use if in fact it would work?
2) Or as an alternative I have two of these timers **broken link removed** could I make it happen what I want to do with two timers? One timer opens the door the other closes the door? If so how would I connect that?

Thank you for your patients.

 

[cowboybob]

Perhaps it will help to explain how the circuit I gave you works.

The timer/relay "unit" is the equivalent of a "latching relay". By definition, a latching relay is a device that, with the appropriate stimulus (a 12 hour ON signal from the timer, followed by a 12 hour OFF signal), toggles between two states: one (or more) contact group(s) of the DPDT relay are closed (ON), while the other(s) are open (OFF). Then, with the reverse stimulus, the opposite is true.

The timer/relay "unit", in such a configuration as depicted, performs that function.

So, in essence, what you are asking for is a "latching, latching" circuit, for which I do not perceive a need, if I have understood your task.

Below are examples of the two "states" the circuit has:

The Forward rotation state of the DPDT relay with the current path:

View attachment 63099

and the Reverse rotation state:

View attachment 63100

Here is the manufacturer's wiring diagram for a rocker switch hook-up (you would substitute the Timer/ DPDT unit for the switch). Note also that the battery polarity is reversed from my diagram. This has NO EFFECT, however, on functionality other than motor rotation direction. Change the battery leads as necessary to achieve the correct motor direction for your system.

View attachment 63102

 

[HansW]

cowboybob,
thank you so very much for going the extra mile to explain. Pictures do tell a thousand words.
One last question: What type of fuse would be appropriate for this kind of application (as with my initial task I'm clueless? Perhaps something I can pick up from radio shack?
Thank you very much!

 

[cowboybob]

HansW,

I could not find, anywhere (especially from the manufacturer) , how much current the actuator you have draws (and if they did, it would be for a "no-load" situation).

Perhaps whoever sold you the item can tell you, or direct you to a source of info.

And the load you put on the actuator could substantially alter (increase) the "no-load" draw.

Whatever that "full-load" current draw is, my suggestion is to add 50% to that number and use a fuse of that size (if they don't tell you the exact size needed for your application).

Radio Shack may or may not have the size fuse you need.

 

[HansW]

cowboybob,
thank you so very much for all the help you provided for me.
Hans

 

[cowboybob]

You're welcome, Hans.

CBB

 

[HansW]

cowboybob or anyone else,
I hooked it up as you suggested, and it worked fine. However, I had already a power failure and that messes things up plus there is always the thought in the back of my mind that I can't trust it. As I mentioned earlier I have a second timer and after studying a while I came up with a circuit that I think would work. However, I'm back feeding when the second timer is activated. So I think I need a diode to prohibit the back feed, what I have no clue what diode to get.
A) Could you see if my circuit with two timers would work?
B) If yes, what diode would I need to get? (preferably Radio Shack, or ebay)

If I can hook it up as shown, then power is only supplied for one minute at a time, so the chances of getting a power outage during that time is minimal.

I hope my drawing makes sense.

View attachment 63502

 

[alec_t]

I'm back feeding when the second timer is activated.

I don't see how. If the timers are simply time-controlled switches which are normally volts-free (i.e. no switch contact is internally connected to either V+ or V-) then can't you simply parallel the switches and dispense with any diode?
If the diode shown is forward biased it only serves to drop the voltage slightly; if it is reverse biased it prevents the left time-switch from delivering power to the relay.

 

[HansW]

When Timer 1 turns on the coil and the common are energized, all is well and everything works as expected. When timer 2 turns on (timer 1 is of course off) it energizes the coil as well which I can't have, that's why I thought to put a diode at the place shown to prohibit the coil from being energized. Hope that makes sense!
Thank you, Hans

 

[cowboybob]

Hans,

Can you describe the power failure to us?

For instance, what is losing power? The timer? The relay circuit? Both?

If the timer isn't battery operated, then:

As for a power failure, without a UPS for the battery and timer, you'll have to manually restart/recalibrate the system. No other choice, really, that I can think of.

(My emphasis).

CBB

 

[HansW]

I'll try to get back sometime later. Thank you, Hans

 

[alec_t]

When timer 2 turns on (timer 1 is of course off) it energizes the coil as well which I can't have

Ah, I see where you're going now.

I think this problem with timers and power failures is why other coop door opener designs (as featured in other threads on this site) use a light-sensor instead of a timer to actuate the mechanism.