Hi,
I am adding a 1200W buck converter before the fuse box on my car to add LEDs to every light source (stable 12V). It is an old car, so I have completely redone the harness with new wires, relays, fuse box etc.
I am grounding the battery, buck converter and every other electrical ground to the chassis. Will the 13v+ from the battery, and the stable 12v from the buck converter sharing the chassis as a ground cause any interferance with each other, or other problems? The starter gets its power directly from the battery, so it's the only reason why the battery ground is connected to chassis. I could run a cable directly to it if it would improve the setup.
Cheers,
Howard

 

Grounding the converter to the chassis should not be a problem.
But why do you feel it necessary to regulate the voltage to the LED? Typically they are quite tolerant of voltage variations.

 

I soldered 3mm LEDs to PCBs to get the exact light sources that I wanted. Just hoping to prolong the life of all the LED assemblies as I have put quite a lot of time into them. And the buck converter is a simple addition to the system for some peace of mind. You can get up to 14V from a car battery, which seems like a bit of a strain on the LEDs in the long run.

 

If you have a current limiting resistor in series with your LED's like they are supposed to have the difference in current between 12 volts and 14.4 volts is about 1 - 2 ma which is way below the threshold for severely diminishing the service life of an LED that is rated for say 20 ma service.

Also factor in the realistic run time of the LED's for the life of the vehicle and it's unlikely you will ever wear one out from run-time aging. Especially if it's an older vehicle that does not see hours of day in and day out driving use.

Also, why do you feel you need a 1200 watt converter to run a few watts of LED's? That makes even less sense.

 

the 1200W part is because I am running everything besides the starter motor through the converter since it is connected to the fuse box, so the fan draws a few amps, wiper, stereo etc.

 

What is the minimum input voltage for the converter?
Will it run at 12.6V input from the battery when the engine is not running?
Or don't you need anything to run when stopped?

 

You have now added a complex electronic device (buck converter) into a system that does not need it to function reliably. None of the LEDs, lights, fans or radio needs a regulated voltage to operate reliably. The mean time between failure for a resistor limited LED is much much longer then a 100 amp buck converter. If an LED stops working, it stops working. If the buck converter stops working, everything stops including your car.

Buck Converter = bad idea

 

the 1200W part is because I am running everything besides the starter motor through the converter since it is connected to the fuse box, so the fan draws a few amps, wiper, stereo etc.

That makes no sense at all being your vehicles electrical devices are designed to work in an environment where when the engine is running the system voltage is between 14 - 15 volts not 12.

To me this sounds like nothing more than over-engineering a solution to a problem that does not exist due to poor understandings of what is normal for the system to function in and at.

 

Fine, I will remove the buck converter, problem solved, thank you