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sorry for my english, I am from Indonesia.

I try to make a (car) relay active - switch on, if the motor/fan is working normal, so when the fan is out, not working or broken, automaticly the relay is off. enter image description here

But it is not working.

Can someone please help?

Edited Transistor NPN 2N3055

Motor 12 Vdc / 3 A

Car Relay Hela 12V

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    \$\begingroup\$ Please explain how you believe your current circuit should work. \$\endgroup\$ – Ignacio Vazquez-Abrams Jan 7 '16 at 9:23
  • \$\begingroup\$ What fault conditions on the motor are you trying to detect? \$\endgroup\$ – Icy Jan 7 '16 at 9:25
  • \$\begingroup\$ As long as the motor works fine, the relay should still on. \$\endgroup\$ – Herbrata Moeljo Jan 7 '16 at 9:29
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    \$\begingroup\$ 'not working' could be seized - high current; open circuit - zero current; disconnected load - low current + possibly lots of other conditions. \$\endgroup\$ – Icy Jan 7 '16 at 9:33
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    \$\begingroup\$ so you require base current of 3.75mA (150/40) - and you have sized 270R resistor to give 10mA at 3A motor current. If this is rated current typical operating current will be much lower perhaps less than 1A - try using 1 or 2 Ohm resistor instead of 270R - the BD139 can take 1.5A of base current - and this will also give a reduced voltage drop on the motor at full torque. \$\endgroup\$ – Icy Jan 7 '16 at 10:01
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You are not thinking this through. Using your circuit configuration

schematic

simulate this circuit – Schematic created using CircuitLab

Start by assuming the motor is drawing 3 A, and the relay coil is drawing 150 mA. Then the transistor collector current is also drawing 150 mA. Because the transistor should be acting as a switch, its base current should be in the range of 1/10 to 1/20 the collector current, or about 10 mA. Then the voltage across RSENSE should be $$V_{RSENSE} = 0.7 + I_b \times RBASE$$ For a 47 ohm RBASE, this works out to $$V_{RSENSE} = 0.7 + .01 \times 47 = 0.7 + .47 = 1.17\text{ volts}$$ and the power dissipated in RSENSE $$P = i VSENSE= 3\times1.17 = 3.5\text{ watts}$$ so you'll need RSENSE to be at least 3.5 watts, and a 5-watt resistor would be a reasonable choice.

Note that, whatever you do, RSENSE will need to dissipate a lot of power. This is because the voltage across RSENSE must be higher than the 0.7 volts needed to turn on the transistor. Operating with no safety margin, such a 0.7 volts at 3 amps will dissipate 3 times 0.7, or 2.1 watts. This would require a 0 ohm base resistor, and this would not remotely be a good idea. In your edited circuit, the reason it's not working is that RSENSE is only providing about 0.6 volts, and needs to be about 0.4 ohms in order to develop enough voltage across RBASE to drive the transistor (you can do this quickly by adding another 0.2 ohm resistor in series). Note that both resistors should be at least 2 watt units.

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You need to do a bit of work .First you should protect the BD139 from inductive kicks by say placing a 33V 1W zener across C and E .You may have popped the BD139 already.The 1 ohm resister could dissipate 9 watt and waste 3V if your motor pulls 3A.This is no good .Use a much lower value resister .Now the motor will operate normally and the circuit wont blow up .If you implement AC coupling by say a capacitor you will be able to detect whether the motor is rotating or not .All DC motors draw a DC current that has a significant AC component that is in sync with the rotation of the machine .If you place a scope across the resistor which could now be 100 milliohm you will see the waveform and devise a circuit to detect it .I published a circuit that detected fan fail on brushless DC fans.Your motor is different so your circuit will be different.

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