Relay question

[Scouter]

I know this goes outside the range of home improvement, but pardon me.

I am trying to install fog lights on my vehicle, my state requires the lights go off when the high beams come on. Normally I would just trigger it off of the 12v high beam light with a standard 5-pin relay, but those things trigger off of 12v, this car isn't so kind. Instead of a high beam light it has a light assembly with parking, low, and high beams all inside (remember the Christmas lights, if one goes out they all go out? here if one goes out you have to replace the entire assembly). There is a single 12v that goes into the assembly, then there are three wires that come on when their individual lights need to come on...thing is, these wires carry 5.24v instead of 12v. Automotive relays don't come in 5v, at least none that I can find.

I did find a 5v triggered relay that is meant for a furnace, 5v triggers up to a 30a circuit. Got it today and tried it out...nada. I connected it up (VCC to +, GND to ground), the relay doesn't trigger. Thought maybe I got a bad relay, so I pulled out a switchable AC adapter (3.4vdc to 12vdc) and tried it, it triggered as soon as I switched the adapter to 4.5vdc. I think I have an idea what the problem is but don't want to mention it, I'd rather see if someone else comes up with the same idea, or if I'm totally wet.

This is a China item off of Amazon, came with no paperwork, so nothing I can provide other than what I already have.

[EricU]

It's a mechanical relay?
If it's mechanical, you might be pulling too much current off the 5v line.

[Scouter]

It's a mechanical relay?
If it's mechanical, you might be pulling too much current off the 5v line.

I don't know, there is nothing online that says one way or the other. I purchased it because it "looks" like an electronic relay (blue box) vs the clear or black boxes the mechanicals come in. But that's what I was thinking as well. It was only $3, so no big outlay. It came soldered on a PC board with screw contacts for the wires, which is why I went with it.

[jteneyck]

Instead of trying to find a 5 V relay, could you step up the voltage from 5V to 12V and then use a standard 12V relay?  

Link

John

[Snipe Hunter]

By any chance... did a higher trim level of your car come with fog-lights? If so, there may already be a relay socket for fog lamps and the wiring. You'd probably have to install a switch. There may also be a spot for that switch on your dash.

[Scouter]

Instead of trying to find a 5 V relay, could you step up the voltage from 5V to 12V and then use a standard 12V relay?  

Link

John

On a car? Not sure I can do that without compromising all of the computer systems.

[Scouter]

By any chance... did a higher trim level of your car come with fog-lights? If so, there may already be a relay socket for fog lamps and the wiring. You'd probably have to install a switch. There may also be a spot for that switch on your dash.

Yes, a higher level does come with fogs, but the switch for them is contained in the light control arm. The control arm I have doesn't include that as an option.

[Roly]

Yes, a higher level does come with fogs, but the switch for them is contained in the light control arm. The control arm I have doesn't include that as an option.

What vehicle is it ?  May help to figure out what the circuitry is. Those voltages sound like they are controlling a solid state switch that is being controlled by a computer. Roly

[jteneyck]

On a car? Not sure I can do that without compromising all of the computer systems.

I don't see how that would compromise any upstream computers.  But if there are downstream ones, then, yeah, that wouldn't work.   

John

[Scouter]

What vehicle  is it ?  May help to figure out what the circuitry is. Those voltages sound like they are controlling a solid state switch that is being controlled by a computer.  Roly

That's exactly what is happening. It's a Toy Rav4 Hybrid. The light housing is a single piece, if a bulb Goes out you have to replace the entire housing, not an individual bulb (LED). I found a SS relay that triggers off of 3vdc and can handle up to 15A (fogs only put out 4.83A each).