Using 12v relay to switch ground

[Sfd295]

Hi all,

I'm attempting to switch two red/white Whelen dome lights that are ground side triggered (3SRCCDCR). I wired two standard N.O. Tyco 5 pin relays (one per color) like this:

Everything works, but the relays make a god awful noise when the system powers up with ignition. It's a loud buzzing noise about 1 sec long and then stops. The lights flash on for a split second during this time period, which bothers the hell out of me. Once it goes through this though the circuit works just fine. (EDIT: Forgot to mention the relays are triggered by +12V through a Core system which receives door open signals via CAN).

Any idea what's going on here? Is there a different relay I should use that won't make this noise and flash the output? I'm far from an expert on relays. Any help is appreciated!

Thanks,
DCL

 

[Jennifer Rose Towing]

As long as it is wired as shown you should be good. The noise the relay is making is it cycling at an insane speed. Common when wired improperly or bad ground. I would start by confirming you have the terminals in the rite place. Next, remove the positive trigger and use another positive wire (like from the cig plug) to activate the relay. If they work fine then its an input signal issue. If the issue stays then likely improper install or bad relay. Simple test to do, would love to know the result and can go from there

 

[JohnMarcson]

Stupid question; why make them ground side switched? Core should support turning them into positive. Is it a wiringing thing or a power up time issue?

As @Jennifer Rose Towing mentioned, the wiring seems fine, testit as she recommended. I used to drive an ambulance with a the aux rear brakes being the secondary flashers and it used ground to and a relay in some oddly complicated way. The relay would fail about once a year and two times a brand new one buzzed when powered up. We switched to Bosch only and it never did it again. I was told some relays have badly constructed coils essentially act like a primary transformer winding when powered this way.

 

[Sparky_911]

OP....I used the same relay set up in a freedom bar. I was using 4 Feniex dual color heads in place of some 400 heads. Had issues with buzz you discussed above everytime I started the truck, until I bought the Bosch relays.

 

[Sfd295]

Stupid question; why make them ground side switched? Core should support turning them into positive. Is it a wiringing thing or a power up time issue?

As @Jennifer Rose Towing mentioned, the wiring seems fine, testit as she recommended. I used to drive an ambulance with a the aux rear brakes being the secondary flashers and it used ground to and a relay in some oddly complicated way. The relay would fail about once a year and two times a brand new one buzzed when powered up. We switched to Bosch only and it never did it again. I was told some relays have badly constructed coils essentially act like a primary transformer winding when powered this way.

I'd love if they were high side switched but they require ground for the 'trigger' wires since they're dual color. One turns on white, the other red. The positive lead isn't switched. I haven't played with it but I know you can set a couple outputs on the Core to ground switched. They're currently occupied but I could always move stuff around. The lights are currently switched through an expansion module.

I rechecked the wiring and it's all good. I'll try the Bosch relays, I think I have a few laying around. I'll take a look at the ground too, but it's direct to a bus bar which is directly connected to the battery. I don't think it's the problem. Thanks for the suggestions.

 

[JohnMarcson]

I'd love if they were high side switched but they require ground for the 'trigger' wires since they're dual color. One turns on white, the other red. The positive lead isn't switched. I haven't played with it but I know you can set a couple outputs on the Core to ground switched. They're currently occupied but I could always move stuff around. The lights are currently switched through an expansion module.

I rechecked the wiring and it's all good. I'll try the Bosch relays, I think I have a few laying around. I'll take a look at the ground too, but it's direct to a bus bar which is directly connected to the battery. I don't think it's the problem. Thanks for the suggestions.

Makes sense. I tore apart a few relays I have here collecting dust and the build quality varied a lot more than I expected. I'd try the Bosch swap first.

 

[NoLimitSquads]

Hi all,

I'm attempting to switch two red/white Whelen dome lights that are ground side triggered (3SRCCDCR). I wired two standard N.O. Tyco 5 pin relays (one per color) like this:
View attachment 244698
Everything works, but the relays make a god awful noise when the system powers up with ignition. It's a loud buzzing noise about 1 sec long and then stops. The lights flash on for a split second during this time period, which bothers the hell out of me. Once it goes through this though the circuit works just fine. (EDIT: Forgot to mention the relays are triggered by +12V through a Core system which receives door open signals via CAN).

Any idea what's going on here? Is there a different relay I should use that won't make this noise and flash the output? I'm far from an expert on relays. Any help is appreciated!

Thanks,
DCL

If you find that your wiring is good, and your relays are good, set up an event. When ignition sense is on. Then create a timed virtual that is just longer than the length of time that you hear the buzzing. Make that virtual turn off the outputs to the relays. Have the event set that virtual to on.
What might be happening is on initial start up, your core might be leaking a small amount of voltage to those outputs, which isn’t enough to trigger the relay. Maybe turning the outputs off upon initial ignition startup will solve the problem.