diode across relay

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Reeceddogg

Copper - Posts: 329

Joined: September 23, 2002

Location: United States

Posted: April 20, 2005 at 4:35 PM / IP Logged

i recently rewired my headreast lcd to include a relay so they shut off automaticlly with the car but now when i turn the car on the get a voltage spike and i know this will eventually damage the screen. how would i use a diode on the relay to stop this

Relay wired:

85- ground

86- remote turn on

87- 12 volt constant

30- to screens

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Montrealler

Copper - Posts: 155

Joined: October 05, 2002

Location: Canada

Posted: April 20, 2005 at 7:57 PM / IP Logged

Install the diode to catch the back emf across the coil (pin 85 and 86 )

IT WILL SEEM STRANGE BUT DO THE FOLOWING

Put the diode Kathode(white stripe) at pin 86

Put the diode Anode (black side) at pin 85

When the coil stop to be energized sudenly the electromagnetic field wich is still present will go back in the coil an re-transformed into power

the diode will short the feedback pulse wich is always generated in the opposite polarity of the actual trigger of the relay.

This is why the diode seem to be install in reverse.

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joebiv318

Member - Posts: 46

Joined: May 03, 2005

Posted: May 03, 2005 at 9:53 PM / IP Logged

He said when he turns the car on he gets the spike. Not when he turns it off, does this matter?

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ff-mike

Copper - Posts: 199

Joined: November 15, 2004

Location: United States

Posted: June 13, 2005 at 4:29 PM / IP Logged

Good catch there joe

I would start with a noise filter on the output and see if that reduces the noise

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diode across relay

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