# Want to make a litte heater using an Aluminum Housed Wirewound Resistor 6.8 Ohm 50W

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#### Johanx2

I got a new project where I need a little heather to warm up a little space (3x3x2 feet). I have planned to use an Aluminum Housed Wirewound Resistor 50W 6.8 Ohm attached to a common cpu heatsink. I am looking the simplest way to control its temperature. What about using a 300w dimmer connected in serie with the power resistor and connected to 120V AC ? Will it work properly with AC current ? If it works, what value is better for the resistor ? is it ok at 6.8 ohm ? or what value is better ?

Sorry if my English sounds weird, :razz: its my second language. Thanks.

#### thylacine1975

##### Full Member level 6
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

Use heating bulb (chicken bulb), and stay safe

With this resistor you just playing with fire. You need more resistance for 110V/220V.

Or just by heater from thermoaccumulation oven or make it with kanthal wire (resistive wire for heater).

Use thermostat in that chamber.

Also you can use iron (for suit ironing) :

Or you can use soldering station heaters with thermostat :

Or you can use hot air soldering station heater with some forced air of fan (my recommendations) :

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#### Johanx2

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!

Thanks so much thylacine197! So I see I was too far from the correct resistance, I will keep all this in mind, 330 ohms.

@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!

#### tpetar

@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.

#### Johanx2

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.

I see, but tell me, should the thermostat be simple connected in serie with the iron (like a switch) ? And how can you set the temperature of a mechanical thermostat ? does it has a knob ?

#### tpetar

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.

#### Johanx2

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.

I understand, but tell me, the temperature I am looking for is (82 Fahrenheit degrees) I need it very stable, no less, no more, well just a minimum tolerance, maybe (80 F Min to 84 F Max). Could you recommend me a proper thermostat ?

Thanks a lot.

#### tpetar

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 ?

You can measure and monitor humidity also ?

#### Johanx2

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 ?

Yes, I am trying to make a terrarium. Hey, I just decided I am going to buy this cheap thermostat from ebay, it costs \$12 and I am sure it will satisfy all my needs. I did not know there was little devices like this.

#### tpetar

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.

Johanx2

### Johanx2

Points: 2

#### Johanx2

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.

Yes, snakes.

Let me show you what I just did. (see attached file) :-D The can and the soldering iron never gets too hot due to the copper and the fan. It is 40 watts, I am pretty sure it will give out the temp we are looking for. I have high temperature silicon, so i will put a little between the hole and the soldering. Thanks.

#### Attachments

• 2012-05-17 16-33-39.813.jpg
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#### tpetar

Yes better snakes in terrarium then in pockets. :-D I hope that you avoid putting a snake for a walk in your block. :-D

You make excelent job, you can make more copper wires inside to make better efficiency and transfer of heat.

---------- Post added at 01:51 ---------- Previous post was at 01:48 ----------

Make some metal bracket for fan, this silicon can melt and fan will fall off.

---------- Post added at 01:52 ---------- Previous post was at 01:51 ----------

And secure all holes from terrarium I think that your neibor dont want gabonica viper under theirs bads. :smile:

Put some fan protection. You can put this protections on both side of this device.

#### Johanx2

Yes, I had planned install to it some fan protections, I have many of those. I think there's no need to put more cooper since it does not get too hot (thanks to forced air, 12v fan at 9v) just the screw.

#### tpetar

Ok. You can perform some testing and experimenting.

I'm glad that you find solution.

Johanx2

Points: 2