Ground resistance?

Electricity is much like an algebra equation, what you do to one side you must do to the other. The lower the resistance on the ground return the better. Most installers never actually check the ground return resistance, they assume that because it is the biggest piece of metal it is the best. In actuality though it may be the worst. The only way to know for sure is to check it.

Most ground returns through the frame of a vehicle or sheetmetal in almost all new vehicles have a degree of resistance on the ground return. This is due to impurities in the metal, glues together unibody panels, crappy tack welds, paint, rust etc. It is not the size of the metal used for the ground return, it is the resistance in the ground return that is important.

With a high resistance in the ground return you can expect power supply problems with an amplifier, this includes but is not limited to noise, excessive heat output, low power output, failure of the power supply. As a general rule if the ground return resistance is above .5 ohm and it cannot be made lower by uprgrading the ground to frame at the battery, altering the ground point from the electronics (like an amp), a solid clean ground point, then it is best to wire directly to the battery. Usually a piece of OFC high current ground wire has far less resistance in it than the ground return of most but not all vehicles. I have found GM to be the worst as far as high resistances go and now my installers check every vehicle and inform the customer, this way the customer makes the decision on to spend the extra $ for proper grounding or doing it the assumed proper way with a nice short ground. Either way will work if the time is taken to check which way to go properly first.

Question for Rob@Forbidden, how much do you know about car starters relating to good/bad ground, and what effects that would have on that, Reason why I'm asking is I had a 1996 Honda civic, wierdest thing it would do, which would be that the car starter would become unresponsive and stay running!  We checked all the wiring, changed ground points, switched modules about 5 times, and just came back last week.  Finally used my brain and checked the resistance for the ground, which came out to 75.6 M ohms, and ran a ground wire for the car starter to the battery.  If all goes well, should work fine.  I heard through the grapevine through an installer in Vancouver that Hondas from the years 1992 to 1998 tend to have bad grounds in the vehicle, especially when hooking up aftermarket product.  The resistance by the way for the new ground was about .4 to .6 ohms.  This I'm assuming by your statement is a better ground? 

"Usually a piece of OFC high current ground wire has far less resistance in it than the ground return of most but not all vehicles. "     When you say this, you mean run from the amp directly to the battery?  What does OFC mean?  Not to sound dumb but not huge into car audio, just DC electronics.

While I am not a mechanic at all and never will profess to be one, my mechanic friend has run into the same problem before. It seems that the solenoid has a problem of getting stuck and when coupled with the high reistance stays open. He solved the problem by running the ground direct to the battery as well.

OFC = Oxygen Free Copper wire

Yes, running from amp to battery

Surprising, mechanics and electroincs usually don't mix, not an insult by any means to your friend, but most mechanics don't know jack about the electronics.  But thanks for the help on this one Rob.  Wierd stuff though when you don't have a proper ground, especially with car starters.  First time I got baffled by that let me tell ya!  Car still running even with ignition off, hmmm.............  That would puzzle the best of people.

Surprising, mechanics and electroincs usually don't mix!!!!!!!

I think that you need to re think what you said there. You must have not ever looked at a car if you made a statment like that. What do you think cars run on you must not have a clue. EVERY CAR ON THE ROAD HAS ELECTRONCS IN THEM AND THE ONLY WAY THEY RUN IS IF THEY ALL WORK SURPRISING THAT THERE IS SO MANY CARS ON THE ROAD IF WE DONT MIX WITH THE ELECTRONICS????? 

 Hey, didn't you know?.. Car mechanicing is easy.. the only reason people even bring their cars into the shop is '... well, I'd do it myself, but I don't have the time'..

 That's ok.. my vehicles run good. I did have to redo some wiring from the hack that installed the alarm/remote start on the one car, but that's no surprise..  there are hacks in every profession.

 It used to bother me, and sure, sometimes on a bad day it still might, but the way I look at it is that because I can work on my own stuff I've saved I don't know how much, and it's enabled me to have some really cool stuff that, if I had to pay for the work, I'd never been able to afford.

 I was driving a Lexus 430 over the weekend.. neat car. among other things, if you have the ignition key in your pocket the vehicle will detect this and unlock the door when you approach, and when you get in the car you'll be able to turn the ignition switch (without the key in it) and the car will start.

 I don't know if this system is available aftermarket.. it'd be neat.

 Regards,

 Jim

sparkie wrote:

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What you are after is a zero voltage potential for a ground.

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