Thread: Grounding question

Grounding to the same ground point is generally considered a good idea. Make sure that ground point is a *good* ground point with a good return path to the battery.

I've heard both ways on the battery - yes and no, but in practice I've seen many installs where people ground directly to the battery and haven't had any issues. Where you may find a problem is if you have equipment this is NOT directly connected to the battery and is grounded to the chassis. If the ground connection is a higher resistance than your battery connection, it is that differential that creates the opportunity for a ground loop.

As always, make sure you fuse the battery connection within a foot of the positive terminal to protect the battery if the cable accidentally grounds, and fuse again near your equipment to protect the equipment. Check the FAQs in the nav bar for more info and also visit the FAQ Emporium forum for additional FAQs in the sticky section.

Thanks for your response Bugbyte. The way you describe the cause of ground loops makes good sense, and I recently did read something to that effect.

Perhaps a good compromise on the two different ways to do it, is to connect all my (trunk) component grounds to the same grounding point to which the battery is directly connected.

My plan as it is right now is to have a small distribution block for the (+) leads (all properly fused, and properly fused at the battery as well).

I do have some experience in DC work, as I've done a lot to my 28' sailboat. However, I'm very unclear on what can cause audio interference in an automobile. If the ground loop (caused by differential resistance as you described) is the only real concern, I think I should have a good grasp on how to approach and at least diagnose if something goes wrong.

Thanks again, and any more comments are also welcome.

Best,
Jake

But long grounds can themselves be troublesome...
Usually grounds are to the chassis/body etc (rather than from the front to the rear (battery) via cable) UNLESS that causes problems.
IE - single-point grounds are used to overcome problems like noise from ground loops etc. (But power grounds are often separate from signal grounds with only a single interconnection...)


As to grounding at the battery - it is usually the vehicle chassis/body that is ground. Strictly speaking, it is the alternator body hence the engine block etc.
But that assumes the alternator is supplying the power, hence the alternator is "absolute ground".
When the battery supplies the load, the battery -ve is absolute ground. This occurs whenever the alternator is unable to supply the full power required - eg, when cranking; during BIG amplifier outputs; switching transients (turning on headlights etc); or reduced RPM etc.

Hence it depends on the system. Big audio will have a local (second) battery which is the ground & supply for the amplifiers.
Standard setups will use chassis/body/engine ground.


The voltage difference between all the above ground points is the resistance between them times the current through that resistive path.


And even with big amps or winches etc, the ground us usually taken from a nearby body/chassis point since it may be too difficult to mount many or big cables to the battery. It should be inconsequential since the battery- to chassis/body cable should be the heaviest and shortest you can use - hence "negligible" resistance. (And that chassis/body point being for "common grounds" if needed.)

what they said..

the main reason everyone grounds to the car instead of the battery is because it is usually a very long run back to the battery, and that can cause problems with the electronics needing to 'push' the power down the line, causing heat, and premature-failure..

Originally Posted by OldSpark

As to grounding at the battery - it is usually the vehicle chassis/body that is ground. Strictly speaking, it is the alternator body hence the engine block etc.
But that assumes the alternator is supplying the power, hence the alternator is "absolute ground".

Ah, that makes sense. Thanks, OS!