Floor hatch: raising and lowering using a linear actuator

Thread Starter

MarkyMarkFunkyBunch

Joined Dec 31, 2021
6
hi all,

I am new to this forum looking for some help. First of all, though I understand some of it, I am quite out of my depth on this one.

I have a hatch in my floor which is currently manually operated using a cleaning cloth (yes, I know). In order to operate it, first a small piece needs to be taken out of the way (as it will otherwise block the movement of the hatch), then the hatch can be opened using said cleaning clotch. See the pictures 1 and 2. When I installed the hatch, the plan was to use a linear actuator (12VDC, 1A) to raise/lower it. In order to operate it, an up/down switch was installed in my main light group (see picture 3).

I've run into two issues I need to solve, where I am desperate for help. I've also attached my wiring diagram (apologies for any errors, not very good at it).

Issue 1:
The switch is only able to operate using 230V AC, whereas the actuator uses 12V DC. I've solved/jerryrigged this by wiring both the up and the down button to a separate power outlet. on each outlet, I use an AC adapter (for UP: 12VDC, 2A, for DOWN: 12VDC, 1.2A). When I connect either of the AC adapters to the actuator, everything works fine (in one direction). However, when I wire up both adapters (in opposite polarity to get both up and down movement), I do not have any movement (though some noise from the actuator). I believe I am shorting out the actuator.
How do I solve this?
I've looked at using single diodes, bridge rectifiers as well as a H-bridge, but my understanding of these are not good enough to implement a proper solution.

Issue 2:
I want to raise the small strip of wood out of the way using a servo motor prior to the main hatch moving. This I need to time that it moves before the main hatch rises on the UP movement and that it moves down again after the main hatch is lowered on the DOWN movement. For this I am considering a timed relay, but I am not sure how to wire these in this diagram.

Thanks for all the help, I really appreciated it! And all the best for 2022.

Marc
 

Attachments

eetech00

Joined Jun 8, 2013
3,154
hi all,

I am new to this forum looking for some help. First of all, though I understand some of it, I am quite out of my depth on this one.

I have a hatch in my floor which is currently manually operated using a cleaning cloth (yes, I know). In order to operate it, first a small piece needs to be taken out of the way (as it will otherwise block the movement of the hatch), then the hatch can be opened using said cleaning clotch. See the pictures 1 and 2. When I installed the hatch, the plan was to use a linear actuator (12VDC, 1A) to raise/lower it. In order to operate it, an up/down switch was installed in my main light group (see picture 3).

I've run into two issues I need to solve, where I am desperate for help. I've also attached my wiring diagram (apologies for any errors, not very good at it).

Issue 1:
The switch is only able to operate using 230V AC, whereas the actuator uses 12V DC. I've solved/jerryrigged this by wiring both the up and the down button to a separate power outlet. on each outlet, I use an AC adapter (for UP: 12VDC, 2A, for DOWN: 12VDC, 1.2A). When I connect either of the AC adapters to the actuator, everything works fine (in one direction). However, when I wire up both adapters (in opposite polarity to get both up and down movement), I do not have any movement (though some noise from the actuator). I believe I am shorting out the actuator.
How do I solve this?
I've looked at using single diodes, bridge rectifiers as well as a H-bridge, but my understanding of these are not good enough to implement a proper solution.

Issue 2:
I want to raise the small strip of wood out of the way using a servo motor prior to the main hatch moving. This I need to time that it moves before the main hatch rises on the UP movement and that it moves down again after the main hatch is lowered on the DOWN movement. For this I am considering a timed relay, but I am not sure how to wire these in this diagram.

Thanks for all the help, I really appreciated it! And all the best for 2022.

Marc
Might be able to use one AC adapter and switch the DC polarity using the up/down switches.
Do you have schematics of the switches? Or part numbers so we can look them up? Actuator part number?
 

Ya’akov

Joined Jan 27, 2019
5,663
Welcome to AAC.

It is a bit hard to follow what you are doing concerning the switches so in general terms the best way (absent more information) to do this would be to use a relay to reverse the polarity from up to down, or vice versa. The "normal" direction would be without the relay turned on, the reverse would have the relay on. It requires only one power supply, and will work perfectly.

On the wood strip, you propose an "open loop" system. That is, to depend on timing and not feedback. This is not very good because the wood may not move for some reason and the hatch will try to open anyway. Instead, I would use a limit switch that actually detects the wood in the open position, and enables the power supply to the actuator. If the wood is not up, the actuator won't run, if it is, it will run. This can be done in a complementary fashion disabling the wood movement when the hatch is open as well.
 

bassbindevil

Joined Jan 23, 2014
422
Not that you asked for an alternative approach, but... what if the hatch is raised by gas-filled struts like on a car hatchback, held closed by an electric latch? You close it by pushing down, or possibly by a small electric winch if it must be operated remotely.
 

Hymie

Joined Mar 30, 2018
1,081
Something else to consider in your design – should any component fail which results in the hatch being held in the down position, you need to have some release mechanism, otherwise you might be constructing your underground tomb.
 

Thread Starter

MarkyMarkFunkyBunch

Joined Dec 31, 2021
6
Thanks all for the good tips and advice.

@Yaakov: I am using the 230V AC switch to change polarity. This works insofar only one of the transformers is connected at a single time. My problem is when I connect both of the transformers simultaneously. When I press either the up or down position on the switch, nothing happens. It is not possible to press both the up and down simultaneously as this is mechanical not possible.
RE the wood strip: would I still not need a relay to time the opening of the strip/actuator? I've attached a diagram with all the stages, hope that clarifies it. What other info would you need?


@eetech00 : Thanks, that was my initial plan but that's when I found out that the switch only works on main. I've attached the wiring diagram
@LesJones : Thank you! This is definitely something I will give this a try.

@Hymie : Regarding the latch, this has been built already. And on the plus side, I would be locked out, not in ;)
@bassbindevil : Thanks, that might work were it not that the hatch is very heavy
@twohats : Thanks, this helps a lot. will probably come back with more questions.
 

Attachments

Ya’akov

Joined Jan 27, 2019
5,663
If I understand correctly, AC switches can give issues when on a DC circuit. The datasheet itself says it is rated for 10A 250V AC. If this does not matter, it can make things a lot easier indeed.
You are correct the ampacity ratings of switches are much lower for DC than AC, but a 10A AC switch should not have a problem with this project, particularly if you put appropriate snubbers on the relays involved to suppress arcing. I doubt your switches will have any problem switching the power to a small 12V relay, which is what they should be doing.

You can eliminate a lot of weirdness if you just use 12V throughout.
 

crutschow

Joined Mar 14, 2008
29,792
Below is the schematic of a basic H-bridge circuit using two SPDT relays with 12Vdc coils, and using one 12Vdc supply (V1).
The diodes are to prevent arcing and contact erosion at the switch and relay contacts from the relay coil and actuator motor inductances.
(Ignore the extra inputs on the switches as they are for simulation purposes).

Edit: You could also use two SPDT switches in place of the relays.
If you don't need a momentary switch, then a 3-way type wall-switch would work.


1641221383746.png
 
Last edited:

Ya’akov

Joined Jan 27, 2019
5,663
Below is the schematic of a basic H-bridge circuit using two SPDT relays with 12Vdc coils, and using one 12Vdc supply (V1).
The diodes are to prevent arcing and contact erosion at the switch and relay contacts from the relay coil and actuator motor inductances.
(Ignore the extra inputs on the switches as they are for simulation purposes).

Edit: You could also use two SPDT switches in place of the relays.
If you don't need a momentary switch, then a 3-way type wall-switch would work.


View attachment 256743
Since he has the separate floor board that must be opened first and closed last, he'll need to incorporate limit switch(es) to interrupt power in the open and close operations until the board is fully retracted or fully closed.
 

eetech00

Joined Jun 8, 2013
3,154
If I understand correctly, AC switches can give issues when on a DC circuit. The datasheet itself says it is rated for 10A 250V AC. If this does not matter, it can make things a lot easier indeed.
if you can use DC. then you could wire it this way.
But you'll have to add limit switches to ensure the wood in the proper position.


1641233891296.png

Edit: This won't work if switches are "momentary, center-off" type.
 
Last edited:

MisterBill2

Joined Jan 23, 2018
11,881
Thanks all for the good tips and advice.

@Yaakov: I am using the 230V AC switch to change polarity. This works insofar only one of the transformers is connected at a single time. My problem is when I connect both of the transformers simultaneously. When I press either the up or down position on the switch, nothing happens. It is not possible to press both the up and down simultaneously as this is mechanical not possible.
RE the wood strip: would I still not need a relay to time the opening of the strip/actuator? I've attached a diagram with all the stages, hope that clarifies it. What other info would you need?


@eetech00 : Thanks, that was my initial plan but that's when I found out that the switch only works on main. I've attached the wiring diagram
@LesJones : Thank you! This is definitely something I will give this a try.

@Hymie : Regarding the latch, this has been built already. And on the plus side, I would be locked out, not in ;)
@bassbindevil : Thanks, that might work were it not that the hatch is very heavy
@twohats : Thanks, this helps a lot. will probably come back with more questions.
If the problem is only when two supplies are connected in parallel but with the opposite polarity, attempting to be able to provide one or the opposite polarity to the load, the cause of the problem is very clear! Each supply presents a very low impedance to the reversed polarity. That is typical and probably impossible to avoid.
Fortunately an alternative approach is available:
The approach needed is to add a polarity reversing switch in the 12 volt line from the higher current rated supply, so that the linear actuator can be run in either direction. That switch will be a double pole Double Throw, two position maintained contact, switch, rated at over two amps capacity.
It will not be used for stopping and starting the actuator and thus it will not need to have a higher DC current rating. THat is because The ON/OFF control of the 230 volt mains would remain as it is, and the reversal switch will not ever be used while the supply is on. This is the solution.
The switch will need to be well marked as to raise and lower positions, and it will need to have an adequate current rating.
 
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MisterBill2

Joined Jan 23, 2018
11,881
If you use the scheme I suggested in post #16 then no snubbers are required because the switch is never making or breaking any current. AND it uses several fewer parts, and thus it will be much simpler to implement. Also, by never interrupting the current or starting the motor through the switch contacts, the switch will last a very long time.
A single swtch will cost much less than two relays. And iif you think wiring a single DPDT switch is complex, just try all of those relays and diodes.
 

Ya’akov

Joined Jan 27, 2019
5,663
If you use the scheme I suggested in post #16 then no snubbers are required because the switch is never making or breaking any current. AND it uses several fewer parts, and thus it will be much simpler to implement. Also, by never interrupting the current or starting the motor through the switch contacts, the switch will last a very long time.
A single swtch will cost much less than two relays. And iif you think wiring a single DPDT switch is complex, just try all of those relays and diodes.
Hey, @MisterBill2, you seem to have missed that the switches were one of the constraints of the project because they are part of an existing array, so the solution has to incorporate them.
 

MisterBill2

Joined Jan 23, 2018
11,881
Which switches? The mains switch? That would stay, at least one of them has to stay.OK, now I see I went back and looked at that picture more closely. So is another one of the buttons available? If not, the control can be achieved rather easily using a minor variation on the original scheme, EXCEPT that the switches will be switching DC. AND adding any diodes will prevent operation.

That scheme works like this: Both supplies are powered, and the positive of one is tied to the negative of the other, and that junction also ties to one wire from the actuator The other wire from the actuator connects to one side of both switches. The second side of one power supply goes to the open switch second terminal, the second side of the other power supply goes to the second terminal of the other switch. Thus one switch will supply a positive voltage and the other switch will supply a negative voltage. And if one of the other buttons is available that can be used to energize the two power modules.
As for a seperate means to remove that gap filler, that could be made to be part of the mechanical linkage.
 
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