Relay Buzzing

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bellsracer

Silver - Posts: 703

Joined: January 14, 2006

Location: United States

Posted: June 02, 2009 at 7:40 PM / IP Logged

I have a 03 Saturn ION with an overhead installed on the roof. However, the overhead did not support negative trigger for the dome light. I used a relay to switch the polarity going into the trigger.

It works fine now, but now the relay buzzes every time the dome light turns off. How do I get rid of the buzz?

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i am an idiot

Platinum - Posts: 13,667

This member consistently provides reliable information

Joined: September 21, 2006

Location: Louisiana, United States

Posted: June 02, 2009 at 7:51 PM / IP Logged

The relay is chattering as the domelight dims. This will not hurt anything. You could try wrapping the relay with Dynamat or some other sound deadening material. The motor assembly in a Bosch relay is huge as far as relays go. You may try one of these from radio shack, it will be MUCH QUIETER than what you are using.

http://www.radioshack.com/product/index.jsp?productid=2062482

Ween

Platinum - Posts: 1,364

Joined: August 01, 2004

Location: Illinois, United States

Posted: June 02, 2009 at 8:24 PM / IP Logged

hi,

A diode (1N4001 or equiv) and capacitor(1000uFor so, at least 16V) should do the trick. Capacitor across the coil of the relay you added, pay attention to polarity of course. Diode in series on the domelight lead from the vehicle then to the coil of said relay. Should allow the relay to turn off a little more abruptly.

hope this helps,

hotwaterwizard

Silver - Posts: 1,350

Joined: December 11, 2003

Location: California, United States

Posted: June 05, 2009 at 8:14 AM / IP Logged

Ween wrote:

hi,

hope this helps,

This is what I would do too with a couple more ideas.

Do not run the positive and negitive wires together. The EMF from one wire can bleed into the other.

Add a 1uF capacitor in series with the positive lead of the Relay. Put the + twards the Relay (if you use a bipolar you don't have to worry about polarity).

John DeRosa (Hotwaterwizard)

Stockton California

When in doubt, try it out !

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i am an idiot

Platinum - Posts: 13,667

Joined: September 21, 2006

Location: Louisiana, United States

Posted: June 05, 2009 at 3:15 PM / IP Logged

In series?

KPierson

Platinum - Posts: 3,527

Joined: April 14, 2005

Location: Ohio, United States

Posted: June 05, 2009 at 4:46 PM / IP Logged

A reed relay will be silent - http://www.radioshack.com/product/index.jsp?productid=2062479

Kevin Pierson

dualsport

Silver - Posts: 983

Joined: September 27, 2005

Location: United States

Posted: June 05, 2009 at 7:37 PM / IP Logged

Is the dome light putting out a pulsed dc waveform to do the dimming by changing the duty cycle?

You could verify this is the case by disconnecting the load from your relay, only connecting the coil, and seeing if you get the same buzzing.

The diode and cap suggested by Ween would be something to try if that's the situation. That should smooth out the pulses to keep it from cycling on and off. A buzzing relay generally should be avoided as it's bad for the contacts, shortening the lifespan of the thing.

If the diode and cap isn't enough to smooth it out, adding a buffered transistor driver would do it, at the cost of added complexity-

i am an idiot

Platinum - Posts: 13,667

Joined: September 21, 2006

Location: Louisiana, United States

Posted: June 05, 2009 at 8:56 PM / IP Logged

The contacts of a chattering relay are damaged in high current situations. He is using the relay to convert the polarity and power the domelight on the roof of the vehicle. Not seeing the contacts being damaged from the 1/2 amp of current.

dualsport

Silver - Posts: 983

Joined: September 27, 2005

Location: United States

Posted: June 05, 2009 at 9:17 PM / IP Logged

Unless the chattering is necessary like in a mechanical horn, there's really no benefit to leaving it that way when it's easily corrected.

Instead of simply muffling it, why not have it just go click once instead of bzzzzzing every time the door closes?

KPierson

Platinum - Posts: 3,527

Joined: April 14, 2005

Location: Ohio, United States

Posted: June 06, 2009 at 6:31 AM / IP Logged

Since there is mechanical movement inside the relay the contacts will be rated for a minium amount of cycles before they wear out. The chatter will reduce the life span of the relay, regardless of the current going through the contacts, but typically the rated cycles is so high that the relay should still outlast the car.

There are multiple ways to look at this - you can make it more complicated and actually fix the problem, or you can keep it simple and hide the fact that there is a problem. Me, personally, on something so trivial, I would just throw a reed relay in there - quick and easy and it will no longer be an annoyance.

Kevin Pierson

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