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How to get rid of the noise coming from relay?

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bittware

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Hello experts,
My DC power supply features with an internal protection relay. When I use it for driving my DC motor in direction reversion phase, the power enters into protection state in a short time, meanwhile the protection relay inside the power issues an annoying noise. This noise results in the program running in the MCU to reset.
My question is:
Even if I stop the motor before reversion the power protection still exists, how to get rid of the noise coming from the protection relay inside of the power supply?
Thanks in advace!
 

klystron

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To remove the noise from the coil of a relay place a diode in a reverse bias mode accross the relay. Use a Shotcky diode for fast switching.
The noise is due to the back EMF of the coil. v = L* di/dt If the coil current is switched off di/dt is very big and v goes up to thousands of volts.

Added after 1 minutes:

To remove the noise from the coil of a relay place a diode in a reverse bias mode accross the relay. Use a Shotcky diode for fast switching.
The noise is due to the back EMF of the coil. v = L* di/dt If the coil current is switched off di/dt is very big and v goes up to thousands of volts.
 

nicleo

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bittware said:
My DC power supply features with an internal protection relay. When I use it for driving my DC motor in direction reversion phase, the power enters into protection state in a short time, meanwhile the protection relay inside the power issues an annoying noise. This noise results in the program running in the MCU to reset.
My question is:
Even if I stop the motor before reversion the power protection still exists, how to get rid of the noise coming from the protection relay inside of the power supply?
Your problem sounds very similar to the one I encountered before. In my system, I use circuit breaker. When I wanted to reverse the motor, the circuit breaker tripped. After we changed a higher rating circuit breaker, everything was OK.

The one I encountered:
Say LOWER rating circuit breaker is CBL.
Say HIGHER rating circuit breaker is CBH.
In my opinion, the 'starting' inrush current of the motor (3-phase induction motor) was lower than the rating of CBL, because we have no problem each time we started the motor.

Something weird... We did some experiments.

[EXP-A]
Say the motor was running at anti-clockwise (ACW) direction. Then, the motor was stopped until the rotor speed was ZERO rpm. After few seconds, we tried to start the motor in clockwise (CW) direction. However, the motor failed to start because the circuit breaker tripped.

[EXP-B]
Say the motor was running at anti-clockwise (ACW) direction. Then, the motor was stopped until the rotor speed was ZERO rpm. This time we waited for 1~3 minutes before we started the motor in CW direction. In this experiment, the circuit breaker would NOT trip.

So, we guess, the starting current during reverse in EXP-A must be higher than the rating of CBL. We said so because when CBH was used, the CBH would NOT trip. Also, we believed that the rating of CBL was just slightly higher than the starting current in EXP-B.

Then, we started to think why the starting current when the motor was reversed in EXP-A was higher than that in EXP-B. We suspected that when the motor stopped rotating, there's still some magnetic residue in the motor. If the motor was reversed after few seconds, the magnetic residue was still strong, and the therefore it needed extra starting current to overcome the 'cogging' torque due to the magnetic residue. After 1~3 minutes, the magnetic residue was weaken and therefore the 'cogging' torque also weaken.

May be someone coupld explain this better. Thanks.
 

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