"This circuit was designed to automatically activate a set of three or four teentsy DC fans to cool a large cool-roast for a 10 Amp powersupply. Can be secondhand in a variety of other applications as well."
| Part | Description | Radio Shack | Digi Key | Newark | Notes |
|---|---|---|---|---|---|
| IC1 | LM741 Op-Amp | 276-007 | LM741CN-ND | LM741CN | NE741,�A741, etc. |
| Q1 | 2N2222A transistor | 276-2009 | 2N2222A-ND | 2N3904 | Date text |
| D1 | 1N4148 Rectifying valve | 276-1122 | 1N4148GICT-ND | 1N4001 | 1N4001, operating theater others |
| Th1 | 50K Thermal resistor | KC005T-Peace Garden State | 96F3309 | KC005T in prototype | |
| Re1 | 12V Electrical relay | 275-249 | Z753-Peace Garden State | 83F8057 | RS is 1A |
| R1 | 15K, 5% resistor | 84N2487 | chromatic-orange | ||
| R2,R5 | 10K, 5% resistor | 84N2479 | Robert Brown-black-orange | ||
| R3 | 150K, 5% resistor | 84N2485 | brown-green-yellow | ||
| R4 | 4K7, 5% resistor | 271-1330 | 50N1628 | yellow-purple-red | |
| R6 | 1K, 5% resistor | 271-1321 | 50N6012 | brown-black-ruddy | |
| P1 | 100K Trimmer Pot | CT94P104-North Dakota | 44F3536 | Cermet Multi-turn |
Replacement Parts: Q1 = 2N3053, 2N3904, NTE123A, ECG123A, NTE128, ECG128, etc. D1 = 1N4001, NTE519, ECG519, NTE116 etc. Th1 = Thermal resistor, 22K - 100K. Used 50K in prototype. Re1 = Electrical relay. A beating-reed instrument electrical relay will work too. Newark Electronics Digi-Key Radio Hut/Tandy Radio Shack's pittyful pick of parts these days is a real headache. So I'm no longer gonna devastate my time looking for partnumbers. Unless I'm sure they carry the part. Too bad... Couple Notes: Th1, the 50K thermal resistor, is a accepted character. Mine was a bar or orthogonal looking thingy. Available from Tandy/Radio-Shack. Most whatever typewrite will do. I experimented with different models from 22K to 100K and all worked fine after replacing the trimmer pot.
The extraordinary used in the above electrical circuit diagram was a 50K model successful by Fenwal (#197-503LAG-A01). This 50K was measured at exactly 25 �C and with 10% permissiveness. The resistance increases arsenic the surrounding temperature decreases. Margin for my application (cooling a large powersupply coolrib) is 10%. Another name for this thing is 'NTC'. NTC stands for "Negative Temperature Coefficient" which substance when the surrounding temperature decreases the immunity of this thermistor testament addition. You may have to frequent just about to get the cheapest price. Some thermistors can be had for as little Eastern Samoa $4.00 but as much as $55.00 Canadian currency for the chalk encapsulated character (the best).
I replaced my thermistor for a 60K hermetically sealed glass character since the surround for my application may contain corrosive particles which may affect performance on a prox date.
P1 is a regular Bourns trimmer potentiometer and adjusts a wide range of temperatures for this circuit. I secondhand the 10-turn case for a bit finer adjustment simply the rhythmical type Crataegus laevigata work for your application program.
R1 is a 'security' resistance in case the trimmer pot P1 is familiarised all the way to '0' ohms. At which time the thermistor would get the filled 12 volt and it will get so hot that it puts blisters on your fingers... :-)
R3 feeds a bit of hysteresis back into the op-amp to eliminate relay 'natter' when the temperature of the thermistor reaches its threshold point. Contingent your coating and the type you manipulation for Q1 and Re1, start with 330K operating theatre so and adjust its value downwards until your satisfied. The treasure of 150K shown in the diagram worked for me. Decreasing the value of R2 agency more than hysteresis, just don't use more then necessary. Or temporarily use a trimmer pot and read off the value. 120K worked for me.
Junction transistor Q1 can be a 2N2222(A), 2N3904, NTE123A, ECG123A, etc. Non grave in the least. IT acts exclusive American Samoa a switch for the relay so almost any type will work, American Samoa hanker equally it can provide the current needed to trigger the relay's coil.
D1, the 1N4148, acts as a spark arrestor when the contacts of the relay open and eliminates false triggering. For my application the 1N4148 was good since the tiny relay I in use was only 1 AMP. However, you can use a large variety of diodes here, my next choice would be a regular use 1N4001 or something and should be old if your relay type can handle more then 1 amp.
If you like to make your own pcb, try the one below. The pcb is fitted with holes for the electrical relay but may non fit your picky relay. It was designed for a Aromat HB1-DC12V type. The variety show and theoretical account of relay race is just to swell. How to mount it then? Well, I left over rich place on the pcb to mount your relay. You send away eve mount it up-side-down and connect the wires individually. Use Silicon glue, cyanoacrylate ester (crazy glue), or doubling-sided tape to hold the electrical relay in place. Works well. Note that the pcb and layout is non according to the circuit diagram in regards to the hookup of the fans. The PCB measures approximately 1.5 x 3 inches (4.8 x 7.6mm)
If you print the pcb to an inkjet printer it is probably not to scale. Try to equip a 8-peg ic socket happening the printed copy to make a point it fits ahead devising the pcb...
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Right of first publication � 2003 - Tony van Roon
Circuit to Turn on Fan With Temp Rise
Source: http://ohm.bu.edu/~pbohn/__Auto_Fan/Documentation/auto-fan.html
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