automotive grounding
automotive grounding
(OP)
I would like to bring up a discussion of automotive electrical systems. I am an EE and have recently started a career in the automotive industry for a newer company so I don't have any ideas to bounce off a more experienced automotive electrical guru. My question/concern is over using the chassis as the ground for electronics. This is to say, the main battery ground ties directly to the chassis. All grounds simply look for a good clean metal surface and the ground is tied there. This would not likely cause any problems. However, the industrial type vehicles we mfg have more than one power source with some sources having multiple batteries. I was drawing up a complete schematic and discovered that one source uses a chassis type grounding system and the other uses wires fed back to a common bus that connects to the other battery source ground. I would like to know thoughts/concerns/comments about any problems this may cause from an EMC standpoint. We have some systems that use microcontrollers but do not appear to have any problems. If anyone could comment on this or point to a source of information I would appreciate it. Thank you in advance.





RE: automotive grounding
I wonder why they ever called it chassis ground. (But thats another question). Surely its the return to the battery using the chassis as the return conductor.
As the car trundles along on its rubber wheels 12" or so
off the ground, who knows what the chassis voltage is.
As far as the electrics/electronics in the car it doesn't matter because the battery is strapped to the chassis so the
+ve connector is always going to be +12 (or so) with respect
to the chassis.
Now maybe, with two or more batteries they are do not share a common 'grounding' point. This may give rise to a difference in potential if the two devices used the same chassis as a return to different batteries.
Or then again maybe the devices attached to the second battery are more sensitive to noise, because (and I don't know if there are any studdies on this) how much does your car chassis ground change in voltage as you drive under power distribution lines.
Or then again it could be the old signal ground / chassis ground debate.
Anyhow just my 2ยข.
Any help ?, yes no let me know.
Regards
RE: automotive grounding
However, the standard chassis ground isn't all that fantastic either if done incorrectly. I have seen schemes that have several taps to the chassis at different points in the vehicle. This creates sub-ground circuits. If ground lug that your circuit is connected to draws signifigant current, then the voltage potential of your lug ("ground") increases. However, if you have several loads that will operate exclusively (i.e. only 1 out of 8 can be on at any one time), then this can contain your "ground" offset to these high-current loads.
To sum it up, one method isn't neccessarily better than the other. There are advantages to both methods, but a standard schematic will not allow you to chose which one is best suited to your application. Knowing where everything is physically located in the vehicle, coupled with constant attention to return current (most people forget that current flows through ground), will allow you to optimally design your grounding scheme.
Hope I haven't insulted anyone's intellegence!
Good luck and keep us posted!
RE: automotive grounding
RE: automotive grounding