Hall effect relay questions.

[Marck]

I just bought a new car and we live out of town.  I want to put extra lights on the car and the law requires you to make sure they only operate when you have high beam on.  The next piece of this is that the car uses can bus to controll the lights and the car has automatic switching of high beam.

Toyota sell a loom that you can use to control extra lighting for about $200. And its quite a bit of messing around to install having to remove most of the plastics on the dash and bring cables into the cabin to install it all. 

The idea i am kicking around in my head is to use a Hall effect sensor clamped to the loom for the headlights to switch a relay to allow power supply to the additional light. 

I have done a little digging on Rs components and all the relays have a sense current of mA.  I would want this up around 5-10 amps.

So my questions for today are am i just better off paying the money for the factory loom or has my idea got a chance of working?  Its a fairly hot vibration filled dirty environment in an engine bay so the reliability of this idea dose worry me.  I know that with dc clamp meters that you sometimes have to demagnetise them to keep them working is this a consideration in this application of hall effect?

And if it will work will i find an affordable off the shelf product or is it something that would have to be made from scratch. 

As i type i feel like i am trying to find a complex answer to a simple problem.

Thanks
M




 

[Ian.M]

A hall sensor wont work round the whole loom if there is a ground return in the loom, or if the low beam is a similar wattage to the high beam.  You'd have to split out the individual high-beam wire from the controller to the bulb assembly (if its not integrated) and either sense current through it or voltage on it.  You'll also need to know the light technology if you want to  tap into the wire safely.

[Rerouter]

There will be a relay for the high beams, no electronics will be directly switching that circuit, find it, piggyback the relay coil wires to your own relay, and have that switch your lights.