Hello! Likely the simplest of questions for today but I have a 12v actuator that I need to operate with two different switches.

- Built in limit switches
- +/- open
- -/+ close

This is operating a 6000lb door to my decommissioned nuclear missile silo. Sometimes I wish I were joking.

I originally was going to use two DPDT switches, one inside and one outside to control it. But that is a terrible design b/c if one switch is left in either on position it will cause a major problem if the other switch is activated.

So the obvious question is, how do I wire this? If I need different switches or relays that's fine. I haven't started wiring it so can do whatever is best.

I have done google searches to no avail. Either I'm not searching for the right thing or this is more difficult than I thought.

Thank you in advance for any help.

GT

 

hi GT,
Welcome to AAC.
What current is the actuator drawing from the 12V supply.?
E

 

hi GT,
Welcome to AAC.
What current is the actuator drawing from the 12V supply.?
E

I’m currently using a car battery with a trickle charger so we can open and close the door even during a power outage.

If there is a more preferred method I’m open to that. Thank you.

GT

 

hi,
The way I read your first post,
To set the actuator to the Open position the voltage is applied in one direction, +V to Actuator Wire 'A' and the -V to the actuator wire 'B'.
and to set the actuator to Closed the supply to 'A' and 'B' is reversed.?

Do you want the ability to Open & Close from either switch, ie: the outer switch and inner switch.

How many amps from the battery.
Sorry so many questions, but I don't want to entomb you in a bunker!

E

 

Is a center biased off switch or an open and close button one either side of the door acceptable ? It would mean you would have to hold the switch / push button while the door was moving. This could be done without using relays. With the addition of some relays just a short push of the button could make the door travel the full way. Are the outputs of the limit swiches available external to the actuator ?

Les.

 

Is a center biased off switch or an open and close button one either side of the door acceptable ? It would mean you would have to hold the switch / push button while the door was moving. This could be done without using relays. With the addition of some relays just a short push of the button could make the door travel the full way. Are the outputs of the limit swiches available external to the actuator ?

Les.

That is correct; the actuator only has two wires so to open, apply power. To close, reverse polarity.

Yes, I’d like to open and close from either side.

I have another way in and out in case of emergency so no worries about being entombed.

The battery is a small tractor battery I had laying around so it’s probbaly 150 amps or so? I can get a different battery if needed.

The switches I have are center off. On/off/on but again can get different switches if needed.

Thanks again!

GT

 

One more try: how much current do you think the actuator draws when operating? Are you able to measure it?

If the actuator has limit switches and diodes built in, then a foolproof method is to use an impulse (latching) relay as a DPDT flipflop. The two switches reduce to a pair of SPST pushbuttons wired directly in parallel, in series with the relay coil and the battery. Whatever state the door is in (open or closed), momentarily pushing either button sends it to the other state.

ak

 

One more try: how much current do you think the actuator draws when operating? Are you able to measure it?

If the actuator has limit switches and diodes built in, then a foolproof method is to use a latching relay as a DPDT flipflop. The two switches reduce to a pair of SPST pushbuttons wired directly in parallel, in series with the relay coil and the battery. Whatever state the door is in (open or closed), pushing either button sends it to the other state.

ak

Sorry about that. 20a full load.

https://www.progressiveautomations.com/heavy-duty-linear-actuator

I have a meter so I think I could measure it.

GT

 

There is only one limit switch and I don't see any internal diodes, so this gets a bit more interesting. Also, 20 A is way above the rating for a Molex Mini-Fit pin, let alone a Jr pin.

Can you mount switches or sensors on the door or actuator?

ak

 

There is only one limit switch and I don't see any internal diodes, so this gets a bit more interesting. Also, 20 A is way above the rating for a Molex Mini-Fit pin, let alone a Jr pin.

Can you mount switches or sensors on the door or actuator?

ak

The actuator auto stops in full open or full closed. Not sure if that's considered one limit switch or two.

I could mount a switch on the door frame to indicate a closed or non-closed position. However, a switch on the full open position would be problematic. Its hard to explain but basically the door opens into an open space so there's no place that I could easily indicate full open. Plus, the door will be able to manually be opened beyond the distance that the actuator will release. I'd just disconnect the actuator to do this.

Your idea in a previous post with two SPST momentary switches and the DPDT relay. So with every push (from either side) the door would move the opposite direction, even if it was not fully open or full closed? If that's how it works it could work.

Eventually I'm going to probably do an Arudino setup with Wi-Fi app control but I don't need to do that anytime soon.

Thank you again for you help.

Anywhere near Arkansas? Just come visit and we'll get this done.

GT

 

Hope this doesn't complicate too much but I just remembered something else.

I have a red rotating light (like on a police car) and car horn that I'd like to turn on when the door is moving. I've watched War Games way too often.

GT

 

Another try at getting an aswer to one of the questions in post #5 Is it acceptable for the push button to be pressed for the whole time of the travel of the door ? I think AK's suggestion of a mechanical latching relay is better than the method I was thinking about which was an electricaly latching relay (One for each direction.) that was unlatched by the limit switches. As they are inside the actuator that solution is not possible. An alternative way to unlatch them could be a reed switch with a few turns of the power cable wrapped around it.

Les.

 

Another try at getting an aswer to one of the questions in post #5 Is it acceptable for the push button to be pressed for the whole time of the travel of the door ? I think AK's suggestion of a mechanical latching relay is better than the method I was thinking about which was an electricaly latching relay (One for each direction.) that was unlatched by the limit switches. As they are inside the actuator that solution is not possible. An alternative way to unlatch them could be a reed switch with a few turns of the power cable wrapped around it.

Les.

Sorry I missed another question. I promise I'm a better forum person than this.

Yes, its just fine to have a momentary switch pressed the entire time. Its actually much better for safety as well. In addition, there won't always be a reason to have the door open the entire distance if one person is entering / exiting.

I'll do some googling to see what an electrical / mechanical latching relay is.

Thanks!

GT

 

If you're sure the actuator shuts off in both directions, then the impulse relay should be able to do what you want.

Yes, its just fine to have a momentary switch pressed the entire time. Its actually much better for safety as well. In addition, there won't always be a reason to have the door open the entire distance if one person is entering / exiting.

This is doable with the impulse relay, but it means that the motor power is going through the pushbutton switches. They don't have to be push switches; a spring-loaded momentary toggle will have better contacts for this power level.

BTW, switches rated for 20 A DC are relatively rare. The vast majority of AC power switches are not, and will not last long in this application.

ak

 

I have confirmed that it will shut down in both directions.

I'm confused by the statement "the motor power is going through the pushbutton switches." Isn't the purpose of a relay to relieve the load on the switch?

And how do I get it to change directions? Or do I have one switch for open and one for close on each side?

Thanks again!

GT

 

I'm confused by the statement "the motor power is going through the pushbutton switches." Isn't the purpose of a relay to relieve the load on the switch?

Yes, but the idea of having the motor run only when a button is pressed changes things. In fact, now that I think it through, there is a critical question for this method:

If you want the motor to run only when the button is held down, and stop if the button is released in the middle of the actuator travel range, then what happens the next time the button is pressed:
a) actuator continues in the same direction
b) actuator reverses direction

And how do I get it to change directions? Or do I have one switch for open and one for close on each side

Direction changes are handled by the impulse relay. Each time its coil is pulsed, it changes the DC polarity to the motor.

ak

 

This https://forum.allaboutcircuits.com/...es-for-greenhouse-roof-window-control.134958/ thread is worthwhile looking at and so are threads about "chicken coop doors".

The basic control mechanism uses two relays that keep the actuator shorted when the relays are both engaged or both disengaged. This acts as a dynamic brake. For simplicities sake call them UP and DOWN.

The trickery comes in not using the actuator current in the limit switches. When the hatch is fully up, you don't want the up signal to pass, just the down signal. A diode does the trick here.

In the greenhouse thread, I discuss how to add OPEN/CLOSED and MOVING logic signals. So, you can get your strobe for moving too.

You can basically take your pick in terms of actuation and part of the problem is not drawing any quiescent current.

Up/Down push buttons that you hold is an option.

(on)-OFF-(on) is an option where () is momentary
ON-OFF-ON is also an option.

The latter 2 use a toggle switch.

Even push/push of a single button is an option with an impulse relay.

 

I'm wondering if I have just completely overthought this.

The problem with the DPDT switches I have is that they aren't momentary. So IF one of them is left on it messes up life for me.

However, what if I just used momentary switches (either DPDT or two momentary, one open one close) on each side. I'm not worried about the switches being activated by two different people on different sides.

So one of the two switches above with two relays, one open and one close would work right?

GT

 

Yep. With switches needed on both sides of the "door", your best bet would be momentary. The switches only need to be SPST.

one person trying to open the door and the other trying to close it would result in a "STOP". It should be easy to make the inside switch override the outside switch. It might be better if there is an open and close signal at the same time, the result is open. No fighting. Should still be doable with relays.

How long it takes to open might make a difference.

With a micro, you could make an interface like.

Push button at limit, goes in opposite direction.
Push button while moving, it stops. Push again, it continues in the same direction.
Double push the button while moving, it stops, waits a few seconds and then reverses direction.

 

This https://forum.allaboutcircuits.com/attachments/motor-limits-pdf.126710/ was the wierd diagram I came up with.

Vaa is motor power.
Goto A and Goto B are switches Push buttons in parallel in your case for Goto A and Goto B.
It does show +12 to activate the relays
@A and @B you get +12 there while your holding the button for goto A or Goto B respectively
The limit switches tell you that the door is closed or open and you get a light when it reaches the limit. In any event, the motor turns off.

Moving just rectifies the voltage across the motor, so it sees Vaa (motor voltage) minus two diode drops. That can go to your strobe.
It will strobe on open and strobe on close. If you wanted two you could use red and green strobes and diodes. red strobe for closing and green for opening or whatever.

RY1 and RY2 hold each side of the motor at ground when not energized. If they are both energized Vaa is applied to both sides of the motor, So if Vaa is applied to one side and Vaa on the other, Vaa-Vaa =0 V across the motor and the motor stops.