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Fading ground and buzzing relay help

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cberger62

Joined: May 09 2007
Posts: 5


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Post Fri May 18, 2007 7:58 pm

Here's the deal... I installed four cold cathode tubes in an '03 Dodge Ram. They are set up to come on with the dome light. Since Cathodes are not supposed to fade I used a relay thinking that when it saw less than 12volts it would turn off the cathodes. Everything is working but when the dome light starts to fade the relay buzzes and sounds horrible. Does anyone know how I can stop the relay from buzzing? Here is how the relay is wired.

Pin 30: fused positive constant (to battery)
Pin 85: ground signal from dome light
Pin 86: fused positive constant (to battery)
Pin 87: to red wire of cathode transformer.

Each transformer is grounded independently. Like I stated before, they work but the buzzing relay is killing the "cool" factor. Any help is appreciated.
kornholio788

Joined: May 02 2005
Posts: 9748
Location: Tosa, WI


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Post Fri May 18, 2007 8:06 pm

well i dont know off hand if your relay is wired right becuse i dont know the pins of a relay off the top of my head. But the thing that is "might" be is that the relay isnt liking the slowing fading voltage. Or it is a bad relay. I have never used a relay with something that faded so i dont know for sure. Dont quote me on this because it is just a guess. Some one will probably come in and correct me. But its my guess
cberger62

Joined: May 09 2007
Posts: 5


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Post Fri May 18, 2007 8:24 pm

The wiring instructions I used were the ones Phil posted in regards to ground switched dome light. I'm positive the wiring is correct because I checked it numerous times. I may try another relay but I don't know if it will help. Like you said, I don't think the relay is liking the fading voltage. Someone here has to be smarter than me. Help!
alienyoungjr

Joined: Apr 30 2004
Posts: 4654
Location: Texas


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Post Fri May 18, 2007 9:08 pm

I think it's the fading voltage that is making your relay buzz.
cberger62

Joined: May 09 2007
Posts: 5


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Post Fri May 18, 2007 9:18 pm

I think to too. So now how do I fix it?
alienyoungjr

Joined: Apr 30 2004
Posts: 4654
Location: Texas


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Post Sat May 19, 2007 5:54 am

you can use a capacitor. i'm not sure which one to use.
ImagoX

Joined: Aug 24 2006
Posts: 2124
Location: Columbus, Ohio


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Post Sat May 19, 2007 1:44 pm

The fading voltage is DEFINITELY making the relay buzz - the same thing happens on my car.

What I did to stop it was go to Michael's Crafts and get 4-5 sheets of black felt (12" squares or so). I wrapped the relay in multiple layers of the felt and secured it with black zip-ties, then stashed the unit as low as I could. You can still hear the buzz if you know what to listen for, but nobody that rides in my car or looks at it at shows notices now (I asked).
cberger62

Joined: May 09 2007
Posts: 5


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Post Sat May 19, 2007 5:39 pm

That's funny. I might give it a try though. Any other ideas?
Mav

Joined: Nov 26 2003
Posts: 2675
Location: So Cal


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Post Sun May 20, 2007 11:03 am

Try using a transister as a relay in addition to your relay. Have one of the legs on the transister on your power sense, one leg on constant power, and the third going to your relay for your cathodes. as long as the transistor detects power, it will feed a constant (rather than a fluctuating voltage) to your relay. The moment the voltage drops to 0 from your variable voltage output off the dome light, the transistor will cut power to the relay completely, rather than fading the voltage down.

Also, while your voltage may be variable to the light, the door switch that triggers the light on and off probably has a continuous voltage. Try tapping off of that switch instead.
cberger62

Joined: May 09 2007
Posts: 5


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Post Sun May 20, 2007 4:19 pm

Two questions. First, if I use a transistor how do I wire it up with the fading ground? The power is constant to the lights. The ground is what fades...

Second, if I use a door trigger would the lights only come on when that door is opened? Also, using a door trigger won't allow me to turn them on with the dome light switch.

Third, I'm getting frustrated.
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