Thermostat controlled Roof

[heitjer]

I have a remote located greenhouse and have 12V solar power for my electrical needs. During our hot Texas summers I like to open the roof as soon as the temperature goes over a certain temperature. In the evenings or when the temperature goes below a lower threshold it should close again.

I thought I purchase one of the many Thermostats like this:
https://www.walmart.com/ip/Hunter-Heat-Cool-Just-Right-Digital-Thermostat/17248152
Basic function & mod (different requirement need) can be seen here:
https://www.youtube.com/watch?v=jnwJlApqoGc

I found a great circuit that works with a timer.
https://www.electronic-circuits-diagrams.com/forum/viewtopic.php?t=3520&postdays=0&postorder=asc&start=0

But this will not with my needs. When the temperature falls under the lower threshold the power goes out and my roof will not close. Here is the operational situation:

**broken link removed**

Any ideas on how I can solve this riddle?

 

[alec_t]

Not clear why the 'power goes out'. Is this because the solar power drops? If so, the answer is to have a back-up battery power supply which is kept charged by the solar power source when it is operational.

 

[heitjer]

alec,
sorry - I have not been clear on this.

The blue represents the temperature and the red line is the output from the Thermostat that I had linked. Typically the thermostats switch on a fan and that runs until the temperature has dropped below the threshold again.

So if I were to use a thermostat the power would be switched on until the temperature drops again. If this happens the roof would not close.

Does this makes more sense?

 

[KeepItSimpleStupid]

No, it still doesn't.

For one, I have no idea how the roof works. Power to open, power to close. Power to open, gravity to close, etc.

e.g. is it a simple contact closure that says open roof and when that contact is open the roof automatically closes?

We need to know something about the interface.

The thermostat is another thing entirely. The hysteresis of MOST HVAC thermostats are not programmable. In some thermostats they are.

A heat/cool Heat pump thermostat might work, but I couldn't get any information out of Honeywell and I havn't had the time to experiment. I wanted to know whether the reversing valve signal follows the heat/cool mode. The thermostat could save energy if the reversing valve signal was on only when say calling for cool.

There is a thermostat called "auto-changeover" that picks the heating and cooling modes. This type of thermostat usually has programmable hysteresis.

One of these days, I'll determine how the reversing valve contacts work.

 

[Boncuk]

Hi heitjer,

please check out UK garden centers. I used a cylinder with all fittings to be mounted to the green house frame and window.

That cylinder is filled with a special fluid which expands when it gets hot and opens the window. As temperature decreases the piston retracts to close the window.

Upper and lower trip points are adjustable in a wide range.

The device resembles a shock absorber for light type motorbikes and doesn't require any electric energy.

Boncuk

 

[alec_t]

Ordinary domestic room thermostats usually have a SPDT switch which clicks over (with ~1 deg C hysteresis) at a settable temp. Can't you use one of those to control an actuator?

 

[heitjer]

Great ideas

@KISS
The roof will be rolling open / close - almost like the this one:
https://www.youtube.com/watch?v=rmdNxjn6JAk

I am thinking about a motor to drive a pulley system on both sides. My motor comes from an old kids car (reversible).

@Boncuk
I looked at these and this is my fall back position. I do like the fact they they work reliably w/o power. But I like to open a larger roof line and not some small lightweight greenhouse panels.

@alec_t
I have not looked at simple components like this as I wanted to keep the easy setting interface of a thermostat for my wife.

 

[heitjer]

This would be perfect....

https://www.cyanogen.com/help/maxdome/Roll-Off_Roof_Controller_Installation.htm

...but too expensive!

 

[alec_t]

I wanted to keep the easy setting interface of a thermostat for my wife.

Hot stuff, eh?

 

[KeepItSimpleStupid]

www.homesecuritystore.com/p-643-mta-1-winland-temp-alert.aspx

 

[heitjer]

great find....

This TEMP ALERT seems to be the perfect fit, now I could use this with the following circuit to act as S6:

**broken link removed**