Battery Relocation question

kenewagner

Registered User
I have had the battery in the trunk of my car for years. I also have had grounding problems for years to boot. This from Dave who has tuned the car many times. When I installed the battery I was told by many knowledgable people to just run a good ground to the body under the trunk, which I did. Now to what has me questioning that.

I am installing a 8,000 lb Mile Marker winch on my car trailer and chose not to be playing with a seperate battery to run the winch. My plan is to run a double cable, positive and negative to a two prong plug which will plug into a like socket at the rear of the truck. Positive cable to the trucks battery from the socket. I called Mile Marker Tech line and asked if I could ground to the frame of the truck in the rear rather than run a cable all the way forward. They said absolutely NOT. Said it would cause problems for the computer on the truck.

Question is

On the SC, is it possible that not running a ground cable all the way to the front can cause electrical grimlins? I know a lot of you will say "I have run like that, grounding to body in rear, for years with no problems" but it is it possible that the grounding path changes, once you move the battery to the rear, causing glitches to the computer?

I know through the years many ideas change about how things are done and just want to address this

Ken
 
I personally feel that as long as the connections are good, you should be able to mount the battery anywhere. And I know, however, wire is like a pipe line, so it could take more power to get the energy to a longer distance making it possible for gremlins. My mercedes and lincoln LS have batteries in the trunk from the factory. Im sure more will chime in being it is a good question.
 
I have done many battery relocations to the trunk or sometimes inside the cabin of the car. Whenever possible you should run a full lenth cable to ground the engine, this will preserve the ground loop. In some cases it isn't practical to do that. In those cases I'll find something of thicker metal close to the battery's new location, like a torque box instead of sheet metal to run the ground cable. Then run a cable from the front frame rail to the original engine ground.
 
Ken,

I would definitely say that grounding a trunk-mounted battery at the rear of the car could cause problems, especially in the electronics. The reason for this is because by doing so, the additional length of the frame/body of the car is introduced into every circuit that makes up the car's systems. You know how many weld joints, bolted connections, etc. that the electricity may have to pass through to finally complete the circuit when we're talking the entire length of the car! Small amounts of rust and dirt can more easily become parts of the circuit, which of course will eventually cause problems. There may be other issues too.

That being said, some places will be more dependable than others, but many places would probably work if you really want to ground it in the trunk area. But the best bet, is to ground the battery in the original place by running the ground cable from the trunk to the engine bay.
 
Ken:

Mine is grounded in the rear with no issues that I know of. I think it's bolted to the rear frame channel.
 
I would leave it grounded to the body of the car, but run a second cable from that point to the engine block. How is the ground cable attached to the body now ? Did you weld a stud on and use a nut to secure the ground cable ?

David
 
My trunk mounted battery is grounded to the frame rail and I've never had a problem either. Make sure you clean the connection points of all grease, dirt, and paint. A little dielectric grease on the bare metal will help prevent rust which would cause a problem. Beware of ground loops as they can cause some crazy problems. On our equipment we manufacture at work we specify to our customers to star point grounds, never daisy chain grounds, and to run only one ground to each part to avoid ground loops which can circulate noise, RF, and ESD. I've had "tech reps" tell me some pretty outlandishly stupid things in the past so I take everything they say with a grain of salt.
 
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Due the noise in an automotive electrical system, the ground path can be critical to the reliable operation of various systems susceptible to electrical noise. I'm not aware of any issues in our platform that would cause the battery ground point to be critical. The sensors the EEC would need to worry about are all pulled to the same ground potential in the wiring harness, so they self adjust to a ground moving around.

I could see an issue in newer vehicles that use a common data bus which relies on specific electrical properties for accurate timing of the data running through it.

After I had my trunk battery all wired up, I checked the ground potential and voltage drop at various locations around the chassis. I found nothing to concern me. Voltage drop from the back of the car to the front was about .02v at the fender relay.

That said, it isn't impossible for you to have issues due to how you wire up and ground your battery. But there is no particular reason why you would.
 
one more thought for you ken. If you go to a dyno again, what I suggest is two things. #1 - don't even bother going until you have the QH working, and know how to data log with it. You must get a data log when your car is having trouble. Make sure you are logging the battery voltage.

#2 - get a voltage meter and monitor the voltage at the front and rear of the car during your run. Tape the meters there and have someone watching the display.

See if what the meters show jives with what you are logging from the EEC-iv.

A mustang style (loaded dyno ) would be perfect for this kind of testing.
 
Ken,

I would definitely say that grounding a trunk-mounted battery at the rear of the car could cause problems, especially in the electronics. The reason for this is because by doing so, the additional length of the frame/body of the car is introduced into every circuit that makes up the car's systems. You know how many weld joints, bolted connections, etc. that the electricity may have to pass through to finally complete the circuit when we're talking the entire length of the car! Small amounts of rust and dirt can more easily become parts of the circuit, which of course will eventually cause problems. There may be other issues too.

That being said, some places will be more dependable than others, but many places would probably work if you really want to ground it in the trunk area. But the best bet, is to ground the battery in the original place by running the ground cable from the trunk to the engine bay.

Im sure there are those out there that have not experenced any problems grounding wise. I cant remember exactly when I started having the issues with tuning and whether it was about the same time I moved the battery, old age I guess or I have just move so far away from stock that who knows. I dont even remember where the original battery ground strap attaches to. I just know that my car doesnt tune and the consenses is ground problems. The existing ground is on the frame rail under the trunk and I have made sure the ground to the body is a good one. I am just going to run a cable up to the original location as soon as someone tells me where that is:rolleyes:

Ken
 
one more thought for you ken. If you go to a dyno again, what I suggest is two things. #1 - don't even bother going until you have the QH working, and know how to data log with it. You must get a data log when your car is having trouble. Make sure you are logging the battery voltage.

#2 - get a voltage meter and monitor the voltage at the front and rear of the car during your run. Tape the meters there and have someone watching the display.

See if what the meters show jives with what you are logging from the EEC-iv.

A mustang style (loaded dyno ) would be perfect for this kind of testing.

QH is working but just got the software downloaded before I went on vacation. The car is in my garage at home and with all the flooding and problems at my shop I havent played with it much. I hear what your saying though. Just got find some time to learn the QH

Ken
 
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Just run a heavy guage wire up to a insulated stud in the engine bay same side as the battery in the trunk. Then run wires from the stud to the frame rail, engine and body.
 
Just run a heavy guage wire up to a insulated stud or non insulated in the engine bay same side as the battery in the trunk. Then run wires from the stud to the frame rail, engine and body.
 
Just run a heavy guage wire up to a insulated stud in the engine bay same side as the battery in the trunk. Then run wires from the stud to the frame rail, engine and body.

Thats my plan for now. Think I will run a 10 at the shootout with a diffrent ground location:rolleyes::p Anyway I think it is worth a try and cant hurt anything

Ken
 
#2 - get a voltage meter and monitor the voltage at the front and rear of the car during your run. Tape the meters there and have someone watching the display.

See if what the meters show jives with what you are logging from the EEC-iv.

<-- Good suggestion :)
 
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