relays w/diodes

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seeker1

Member - Posts: 24

Joined: December 02, 2007

Location: Washington, United States

Posted: December 05, 2007 at 12:26 AM / IP Logged

I'm new to this. Tweaking a 96 mustang w/lights and remote start & control from an Audiovox aps998. In my research and installation I've ru accross relays with buit-in diodes between the 85th and 86th pin. Whats the purpose of this? If I understand right these are the coil contacts w/85 being the + contact and 86 the -. The diode setups I've seen have the cathode on 85 and the anode on 86. With 85 being the + side there wouldn't any current flow from 85 to 86 through the diode, it would go from 85 to 86 through the coil. And if there was a flow(I.E. hooked up backwards) wouldn't the current flow thru the coilanyway? Whats this diode blocking?

?????

Seeker1

Only the strong survive.

Eat the weak.

techman93

Silver - Posts: 591

Joined: October 28, 2006

Location: Pennsylvania, United States

Posted: December 05, 2007 at 12:54 AM / IP Logged

They put these diodes on starter kill relays and on relays where you want the coils to slowly go out of contact such to eliminate amplifier pop when you shut system off. It depends on what your using it for.

As I posted on Nov. 4, 2007

techman93 wrote:

When energizing the coil of a relay, polarity of the coil does not matter unless there is a diode across the coil. If a diode is not present, you may attach positive voltage to either terminal of the coil and negative voltage to the other, otherwise you must connect positive to the side of the coil that the cathode side (side with stripe) of the diode is connected and negative to side of the coil that the anode side of the diode is connected.

Diodes are most often used across the coil to provide a path for current when the current path to the relay is interrupted (i.e. switched off, coil no longer energized). This allows the coil field to collapse without the voltage spike that would otherwise be generated. The diode protects switch or relay contacts and other circuits that may be sensitive to voltage spikes. (JimR, contributor, install bay member)

The wire I'm test'n isn't doin' what it's supposed to be doin'... I am so glad I printed that tech sheet, with the wrong info.

Do it right the first time... or I might have to fix it for ya

seeker1

Member - Posts: 24

Joined: December 02, 2007

Location: Washington, United States

Posted: December 07, 2007 at 12:21 AM / IP Logged

techman93

Thanyou for the help.

Only the strong survive.

Eat the weak.

mobile1

Silver - Posts: 479

Joined: February 23, 2004

Location: United States

Posted: December 07, 2007 at 12:25 AM / IP Logged

a little clarification on what they are called.

Spike Supression relays or Relays with Spike Supression.

pcpackrat

Member - Posts: 5

Joined: May 07, 2006

Location: United States

Posted: December 07, 2007 at 9:54 PM / IP Logged

When a coil is energized it creates a magnetic field. When you disconnect power from the relay the magnetic field drops across the coil creating a reverse voltage on the terminals. Auto alarm and remote start systems use transistors to control the relay and that reverse voltage will destroy the transistor. The diode is a reverse protection for the driving transistor.

-PCP

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relays w/diodes

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