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Tripping of Relay when operating with 8051

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Rahul Ahuja

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Hi
This is Rahul Ahuja

I am driving 0.5 hp 230VAC blower motor with 8051 using 10A relay. Everything is going ok but i am facing one problem. whenever relay gets ON it starts the motor but suddenly it resets the controller. I am using different power supply for controller and motor. Can any one tell why it is happening ????
 

Tahmid

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Make sure you use sufficient decoupling/bypassing.

Around the time the microcontroller is reset, measure the voltage from VDD to VSS. Probably the voltage drops, causing the controller to reset. This could be if the microcontroller power supply is run from the same line as the motor (probably is, from the same 230VAC supply).

Connect large capacitors from VDD to VSS and regulator input to ground (> 1000uF; try with 4700uF). "Isolate" the input of the regulator from the rectifier output by using a series diode.

Hope this helps.
Tahmid.
 

Tahmid

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Do the "isolation" as I mentioned before:



Connect the 12VDC supply to point A. Connect point B to the circuit wherever you had labelled "+12VDC". To minimize diode voltage drop, you should use a schottky diode. However, a regular diode shouldn't be a problem.

Hope this helps.
Tahmid.
 

Rahul Ahuja

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Point B will go into 7805 + supply, which will give +5vdc to controller??

Can i use this diode 1N4007 ???
 

Rahul Ahuja

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Can you please tell me which diode can i use ???




Do the "isolation" as I mentioned before:



Connect the 12VDC supply to point A. Connect point B to the circuit wherever you had labelled "+12VDC". To minimize diode voltage drop, you should use a schottky diode. However, a regular diode shouldn't be a problem.

Hope this helps.
Tahmid.
 

Tahmid

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Can you please tell me which diode can i use ???
You can use 1N4007 (or any of the 1N400X) if the current is <1A.
If current <3A, you can use any of the 1N540X.

Make sure you connected ULN2003 pin 8 to ground as it's a hidden pin in Proteus.
 
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sequel

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80series are not that ideal when it comes to driving inductive loads. this is as a result of their internal architecture where data/address has to make use of one path "von Neumann" Architecture. as this may result to error in terms of execution. the microcontroller may fetch wrongly when it is subjected to a strong EMI. so you have to be very careful when dealing with inductive loads; you will surely see the flaws of the 8051 micros!

so...
do a total isolation between the motor and the ground path of your circuit since it will not affect the operation of your design....as this will introduce noise looking at the power supply rails and thus will end up making the microcontroller to reset. also as suggested, do a proper power supply filtering.

ground the body of the crystal for a safer operation of the internal clock ciruit.
also increase the inductance of the ground by thickening the ground lines....if you have a vero board in your design then simply short unused copper line to the ground of your circuit.

above all you can shield your circuit from EMI generated by the motor....because this is a threat!

check out the image...

hope this helps
sequel...



- - - Updated - - -

80series are not that ideal when it comes to driving inductive loads. this is as a result of their internal architecture where data/address has to make use of one path "von Neumann" Architecture. as this may result to error in terms of execution. the microcontroller may fetch wrongly when it is subjected to a strong EMI. so you have to be very careful when dealing with inductive loads; you will surely see the flaws of the 8051 micros!

so...
do a total isolation between the motor and the ground path of your circuit since it will not affect the operation of your design....as this will introduce noise looking at the power supply rails and thus will end up making the microcontroller to reset. also as suggested, do a proper power supply filtering.

ground the body of the crystal for a safer operation of the internal clock ciruit.
also increase the inductance of the ground by thickening the ground lines....if you have a vero board in your design then simply short unused copper line to the ground of your circuit.

above all you can shield your circuit from EMI generated by the motor....because this is a threat!

check out the image...

hope this helps
sequel...

 

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