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Topic: How do I prevent video interference caused by electric motors (Read 7661 times) previous topic - next topic

David82

I have an analog camera signal, the power for the camera, and a dc motor which is activated by a switch and all share the same ground. When the motor is activated, the video feed blanks out for a second. I tried putting a capacitor on the + - rail but that didn't do anything. What can be added to this circuit to prevent the video signal from being interfered with?


In the illustration below, when the switch/button is pressed, the lcd screen blanks out because some sort of interference is being caused but the presence of the electric motor. This interference happens when the motor is switched on and under load AND when again when it is switched off but not while it is on! I can't change the wiring but I can add something to the circuit to filter out the interference somehow. What can be added to this circuit to prevent the video signal from being interfered with?


zoomkat

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I can't change the wiring but I can add something to the circuit to filter out the interference somehow. What can be added to this circuit to prevent the video signal from being interfered with?


If you can't change the wiring, then try using a larger power supply. 
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David82

what is actually happening to cause the interference (besides the motor being activated)? I don't think the video camera is losing power. It seems that the signal is being corrupted temporarily.

LarryD

The way you have it in your schematic isn't the same as how you have it wired up!

Grumpy_Mike

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what is actually happening to cause the interference

Current flowing in a conductor when it has a fast rise time radiates radio frequency energy. As a current pulse has an infinite number of harmonics it radiates a broad band interference signal.

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can't change the wiring

So you are probably stuffed.
However, you can try and cut down the interference by reducing the rise time in the motors by using capacitors close up to the motor contacts. You could change the motor type so that it does not have a commutator circuit breaker or you could attempt to minimise the disruptive effect of the interference in your video circuits by increasing supply decoupling. The "larger supply" solution works because it is a lower impedance supply and so less prone to picking up the signal.
However curing the problem at source is often a much better strategy.

David82

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Current flowing in a conductor when it has a fast rise time radiates radio frequency energy.

Can't I shield against it with a faraday cage of some sort?

Grumpy_Mike

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Can't I shield against it with a faraday cage of some sort?

No. You have to get the signals in and out and that breaks the cage effect.

Your wiring is bad if you could improve that it would help matters. Use a star ground wiring system not what you have at the moment.

zoomkat

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I don't think the video camera is losing power. It seems that the signal is being corrupted temporarily.


What is your power supply? If the motor starting current is high, it may cause the voltage to dip low until the motor comes up to speed.
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David82


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I don't think the video camera is losing power. It seems that the signal is being corrupted temporarily.


What is your power supply? If the motor starting current is high, it may cause the voltage to dip low until the motor comes up to speed.
If that was the case, the giant capacitor I tried to fix it with would've had some effect I would think.

David82

Applying a charged capacitor to the circuit will also cause the same temporary interference. What does that mean?

zoomkat

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If that was the case, the giant capacitor I tried to fix it with would've had some effect I would think.


Not really. The motor start can still pull the voltage low with a capacitor. Depending on the motor, the motor starting current can be several amps. So what is your power supply?
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David82

It's a 90W computer power supply and the motor is a power door lock actuator.

Grumpy_Mike

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Applying a charged capacitor to the circuit will also cause the same temporary interference. What does that mean?

It means you do not have any idea about fault finding.

Stop asking the same question and start reading the answers.

David82

I added a second, 12v power supply to the camera's power just to see what effect it might have. It shopped it from completely blacking out but there was still a little bit of interference. So basically it improved it but didn't solve it. Of course I can't use that in the final design but does that give any clues as to what needs to be added to fix the problem?

Grumpy_Mike

If you are not going to read the answers then I am not going to tell you again.
Good night.

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