Hello Guys and Gals,

I have a question about best method to keep something warm in winter and outside temp in summer.

I am working on a 12vdc project where I need to keep a PVC or Metal box warm in winter.
In winter it hits -40c often which is way to cold for parts I am using in project.

So I purchased some PTC Heating plates that hit 80c I do not need box that hot.
That means I need to regulate power to the 12vdc PTC Heating plates based on temp.
I have 2 options in my head and dont know the best one to choose, so thats why I am asking here.
Option 1) Thermistor Relay Control Module where I can set a temp to cut out PTC heating plate.
Or
Option 2) something like a Heat Protector ST-22 Thermal Cut Off (but for DC when I find correct one.)

Thou project is outside it will be protected/shielded from snow, rain and sunlight.
The project box I have not chosen yet, but it will be sealed except for a small hole that will be there to let out pressure from temp changes.

So which would be my best option in your views, option 1) or option 2) ?


Thanks in advance
Sigma

 

For reliability and long life you want something without mechanical contacts, that instead uses a electronic switch, such as a solid-state relay.

I'm not sure about option 1 having contacts, but Option 2 does appear to have mechanical contacts.
Can you verify that?

 

What power level is this?

The power needed (and thus the power the temperature control has to control) will depend on the
heat needed. Which will depend on the surface area of the box and it's insulation (as well as wind etc).

Also what's your minimum temperature for inside?

PS: This isn't a 20 foot shipping container, right?

PPS: With enough thermal mass and insulation it could make it through the winter without a heater...

 

... another possibility:
thermostat board

 

For reliability and long life you want something without mechanical contacts, that instead uses a electronic switch, such as a solid-state relay.

I'm not sure about option 1 having contacts, but Option 2 does appear to have mechanical contacts.
Can you verify that?

Hello crutschow,

Thanks for fast reply to my questions.
Option 2) is mechanical from items I have seen as I have not found one yet in voltage I require.
Option 1) Is this part https://www.aliexpress.com/item/32839379012.html?spm=a2g0s.12269583.0.0.7f7b158eInUV4s

So I was leaning towards option one.

Thanks
Sigma

 

What power level is this?

The power needed (and thus the power the temperature control has to control) will depend on the
heat needed. Which will depend on the surface area of the box and it's insulation (as well as wind etc).

Also what's your minimum temperature for inside?

PS: This isn't a 20 foot shipping container, right?

PPS: With enough thermal mass and insulation it could make it through the winter without a heater...

Hello michael8,

Thanks for fast reply to my questions.

My project will all be 12vdc and all parts for it including relays, sensors and the rest.

The inside of box must remain at 15-30c except for summer as the parts can all take up to max 60c so heating will be off in summer.
Dont think there will be enough thermal mass to keep warm during cold winter at -40c for months.
There will be little to no wind and no chance for rain or snow or even sunlight to hit the box/enclosure.
Also no chance for flooding either by pipes or overland.

The box/enclosure will have various 12vdc relays (up to 6-12), power will be fed into box with external 12vdc (amps not calculated yet but I have from 1 amp up to 20amp on hand once final count is done and ready for power-up) Wires connecting components will be 18awg except for 12vdc low voltage low amp inputs on some of the relay boards.

And no it is not a shipping container/storage.


Thanks
Sigma

 

OK, the box isn't 20 ft x 8 ft x 8 f (shipping container). What size is it? This is needed to calculate the surface
area and suggest what the heat leakage might be. This will then lead to a possible power level.

Power to the relay coils will also add heat into the box -- can any heat from these be depended
on when it's cold outside?

I'm guessing metric since you used degree C. So say the box was 15 cm deep and 60 cm wide & high.
Surface area is then [front & back] 2*60*60, [sides] 4*60*15 total 10800 cm**2.

Your inside minimum temperature was 15C. Outside is -40C for a temperature difference of 55C.

Ok, now for some insulation (minimal). Let's assume an insulation value U value of 1 W/(m**2 * degree K) and
K and C degrees are the same size so:

10800 cm**2 /(10000 cm**2/m) -> 1.08 m**2

power watts = ((55 degree C ) * (1.08 m**2) ) * (1 W/(m**2 * degree C))

or about 60 watts of heat needed. Some of the heat could come from the circuitry if it was in operation (relay coils?).

https://en.wikipedia.org/wiki/RSI_(thermal_resistance)