Heya Johanx2,
I've had to heat numerous small spaces (dog kennels/reptile enclosures/beer brewing setups) - the humble incandescant light bulb does a pretty good job simply and cheaply if the visible light isn't a problem
Your approach will certainly work OK though, but no - 6.8 ohms is much too low if you plan to use the 120V mains supply. The power dissapated within your resistor is given by:
P = V^2 / R, where V = RMS voltage of your AC supply (120V) and R is the resistance. At 6.8 ohms, P = 2118 Watts (which will lead to a spectacular failure
Solving for a (conservative) P = 40W then, R = 360 ohms. The nearest standard values are 330 & 390 ohms. With R = 330 ohms, P = 43.6 Watts. Perfect!
The physical temperature of the heatsink will be approximated by the heatsink's thermal resistance x P. Thermal resistance specifications seem to be (oddly) difficult to find for CPU heatsinks, but if we assume something pessimistic ~2 degreesC/Watt, your heatsink will hover ~80 degrees above ambient temperature. Just ensure you don't exceed the maximum operating temperature of your resistor - for aluminium housed resistors, this is typically ~250 degreesC - so you're probably pretty safe.
The light dimmer control will definitely work for you - have fun!
@tpetar, what a great idea you just gave me! If a buy a cheap/used iron, I will get a heater and even a heatsink! I can take apart the unit and just keep the main parts. Beautiful idea. Thanks so much. This forum is amazing!
Dont forget to use thermostat, and use two or three thermo protection, you can add thermo fuse.
Use at least one mechanical (bimetal) thermostat, additional you can use some thermostat with lcd and ds18B20 to measure temp and show data on some nice LCD.
**broken link removed**
Yes serial or if you whant to save it from current, you can use relay. This on pictures are made for particular temp, each of them.
On upper picture thise thermo fuses are up to 10A, if you need 20A then put two of them in parallel for the same temp level.
Then my friend digital to have small temp hysteresis.
Digital control of heater. Using digital DS18B20 or you can use analog LM35.
Measurement of temp will done over one sensor DS18B20 (better choice) or LM35 (or other) uC check temp data and control relay for heater. You can use solid state relay to eliminate sparks and noise.
You can even install temp logger, to monitor temp curve on long duration.
---------- Post added at 06:27 ---------- Previous post was at 06:19 ----------
Are you making some terrarium ?
---------- Post added at 06:34 ---------- Previous post was at 06:27 ----------
You say temp range 80F-84F this is 26,7C-28,9C
Did you plan and cooling also ?
Hehehe my friend, there is little nice things.
I think that on chinese writen "for safety reasons use only outside house / outdoor" :-D I just kiding.
Of course this can do the job, just check specification.
What goes into terrarium ? snakes ? :|
---------- Post added at 06:52 ---------- Previous post was at 06:47 ----------
Check temperature hysteresis range, and sensor precision.
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