Relay for spotlights

[bigpapanoodle]

Looking to wire up some spotlights. Will this set up be correct?

 

[wheeto]

Looks good. Don't forget the - potentially two different - fuses in that setup, though.

 

[Taylortwocities]

You do not operate a relay by switching the earth on and off.
Surely the switch should be in the 12v line. Between 86 and 30.

 

[bigpapanoodle]

I have tried it and it works. Surely better not to have live wires coming into the driver/passenger side?

 

[Taylortwocities]

Yes it works.I’m not an auto electrician so switching (neutral) in house electrics is a no no. But look at your vehicle. Surely just about every circuit switches the live. Have a look at your horn, windscreen wipers, heater blower, EVERYTHING is switched live.
Maybe a petrol head can Comment?

 

[telectrix]

courtesy lights switch the negative.

 

[wheeto]

Yes it works.I’m not an auto electrician so switching (neutral) in house electrics is a no no. But look at your vehicle. Surely just about every circuit switches the live. Have a look at your horn, windscreen wipers, heater blower, EVERYTHING is switched live.
Maybe a petrol head can Comment?

Agreed, switching neutral is completely unacceptable in LV eg houses, where dangers around touch voltages exist.

In the automotive world, low side switching is super common especially in modern cars where most items are computer controlled. Generally this is for the following reasons:

1) N channel transistor switching is easier*.
2) fusing arrangements for low side switching are often more practical.

I'm sticking with my original answer of "it's fine, pay attention to the risks in this situation which relate to fusing, not which side is switched."

All the best,



*Long story.... Look up an electronics article on low side vs high side transistor switching if you're interested.

 

[bill01803]

I think a fuse might be a good idea

 

[James]

Agreed, switched ground for relays and other automotive items is quite normal and safe.

Some examples of such things being standard are
Door switches for lights (already mentioned)
Horn on most cars
Fan thermostat
Points on cars old enough to have them

 

[Taylortwocities]

Thanks. Every day’s a school day!

 

[James]

Thanks. Every day’s a school day!

Before cars had 314 different buttons on the steering wheel, there was one slip ring and brush behind the wheel that brought the ground wire from the horn to one terminal of the horn press switch.
The other terminal was simply grounded to the steering column.

 

[bigpapanoodle]

Thanks everyone for your input. I am aware that the horn works by grounding to earth but I guess with the high draw needed for the spotlights I am still wondering about using the ground to switch. More research on my part needed!

 

[James]

Switch is only powering the relay coil, tiny draw.

 

[Taylortwocities]

Thanks everyone for your input. I am aware that the horn works by grounding to earth but I guess with the high draw needed for the spotlights I am still wondering about using the ground to switch. More research on my part needed!

There’s minimal current passing through the switch, it’s only operating the relay. That is what the relay is for.
As above, you must have a fuse in the 12v feed to the relay. How big will depend on the load of the spotlights.

 

[bigpapanoodle]

I'm guessing the reasoning behind running a live to the dashboard is for when you wish to power a warning light for the switch.