Thermostatic control of a linear actuator

robertazachary

Joined Jan 28, 2014
3
My friends who purport to know cannot tell me how to operate a linear actuator with two limit switches using a thermostat. I hope to open green house vents with this. The problem seems to be that the thermostat is in a constant on or off. I, of course, don't know much about electronics. If someone knows or can point me in the right direction, I would appreciate it.

GopherT

Joined Nov 23, 2012
8,012
I proport to know too. However, without knowing your background, the details of the window, the details of the linear actuator, the degree your heart is set on using said linear actuator instead of a normal motor and gearbox, you budget, the time you are willing to invest in learning electronics (if any), and your reluctance to buying a commercially available mechanism among other things, I am not willing to start describing how to design your project to help you complete your task.

I believe the previous sentence was one of the longer, yet nearly grammatically correct, sentences I have ever written.

Nykolas

Joined Aug 27, 2013
115
I think there was a comma missing! E

#12

robertazachary

Joined Jan 28, 2014
3
I am an English major/teacher and that was a great sentence. I decided to go this route because the rack&pinion type of openers are very expensive. I tried to finds some from old warehouse window operators with no luck. Those using wax cylinders seemed fine until I was told I would have to replace the wax every couple of years at $100 a pop. My vents are 26" by 12' and weigh about 40 pounds. I came across some 24V dc actuators at Surpluscenter.com for only$45. That price is what is actually driving this quest. In the short term, I am afraid that learning electronics right now probably wouldn't work as I spend my spare time caring for my elderly mother. In the longer term, maybe. I was hoping to pass the information to my "purporting to know" friends to perhaps stimulate their interest. Thanks for the reply, I am encouraged that you think there is a way!

#12

Joined Nov 30, 2010
18,223
Did you say 26 inches by 12 feet?
You are going to have to do something about sagging.

I'll go get a drawing. BRB.

tracecom

Joined Apr 16, 2010
3,944
I think there was a comma missing! E
No, but there is a missing "r."

robertazachary

Joined Jan 28, 2014
3
The vents are built on 3/4" square aluminum tubing with 1/8 wall. The skin is 28 guage
corrugated sheet metal. It is on the north side and so does not need to transmit light.

#12

Joined Nov 30, 2010
18,223
Lacking some information, and assuming the thermostat can carry enough power for the motor (not likely), this is the basic concept. Fill in some information to get specific changes necessary.

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inwo

Joined Nov 7, 2013
2,419
Do yourself a favor and get an ac actuator with built in limits.

Then you can connect it directly to a fan thermostat. (Sometimes called a barn thermostat) No other controls needed.

They are designed to do just what is needed for your project.

Line voltage, NO/NC, and a wide range or adjustable differential.

I'll look at Surplus Center and see what they have.

inwo

Joined Nov 7, 2013
2,419
Is it this one?
http://www.surpluscenter.com/Brands/VistaMounts/24-VDC-18-STROKE-LINEAR-ACTUATOR-5-1785.axd

If DC is what you have, then you will need appropriate power supply, control relays, and someone who can follow #12's diagram.

On the plus side it can be done with a standard low voltage thermostat, with a little modification.

Rather than a posting frenzy, I'll edit with new info.

Here is a 2 stage thermostat that can reverse a dc motor @3deg differential, by nature of it having 2 SPDT contacts.
http://www.ebay.com/itm/PENN-CONTRO...030?pt=LH_DefaultDomain_0&hash=item4d0a765546

And the specs for an A28.
http://cgproducts.johnsoncontrols.com/MET_PDF/996238.PDF

To allow for others input.

Or you can use 2 A19s. One for open and one for close.

Last edited:

#12

Joined Nov 30, 2010
18,223
If DC is what you have, then you will need appropriate power supply, control relays, and someone who can follow #12's diagram.
Am I that difficult?

If thermostat = open
and close limit = closed
motor gets power from the right side of the drawing through the DPDT switches in K1 until the close limit switch opens.

If thermostat = closed
and open limit = closed
K1 is activated and motor gets power from the left side of the drawing through the contacts in the DPDT relay until the open limit switch opens.

Yes, every single part does something important. One mistake reading it and you're lost. It will work with AC power. It will probably need a relay or two as current boosters. That depends on whether the thermostat is a 15 amp Klixon or a 1 amp wall thermostat, and it depends on the current needs of the motor. It's a basic chicken coop design. Modifications available.

inwo

Joined Nov 7, 2013
2,419
Absolutely not!
Very clear to me.
That's how I'd do it.

Things don't always read as intended. Sorry!
It was a factual statement as to what he needs.
In reference to OP statement.

" I, of course, don't know much about electronics."

Prompting, my search for a simple solution with no relays.

#12

Joined Nov 30, 2010
18,223
Everybody sees a different way to do it, based on their experience and the contents of their junk box. That's why dozens of us help Other People. Somebody usually hits the combination that the Original Poster can understand.

GopherT

Joined Nov 23, 2012
8,012
Am I that difficult?
You? I am not sure. But your drawings are fine.

#12