The 24 Hours of Lemons Forums → Lemons Tech → Battery relocation
The stock negative terminal has connections to the body, frame, and engine block. If we move the battery to the back, do I need to run a negative all the way back to the block or can I get away with cables from the battery to the frame and body, then block to frame?
or can I get away with cables from the battery to the frame and body, then block to frame?
Yes. These braided ground straps work well: https://www.delcity.net/store/Ground-St … a0QAvD_BwE
I will make on minor disagreement here. If you have an FI system seriously sensitive to to clean grounds you are going to have to do some work. Or if you have a GM with a finicky starter, don't do a little braid...make it a giant cable that bolts to the same bolt as your primary negative.
I will say we did none of this for years but the 3800 in the Dustbuster is constantly an issue so we ran the ground straight to a case bolt and then to the "frame". Granted, this solved little or none of the issues but it had to be tried.
I will make on minor disagreement here. If you have an FI system seriously sensitive to to clean grounds you are going to have to do some work. Or if you have a GM with a finicky starter, don't do a little braid...make it a giant cable that bolts to the same bolt as your primary negative.
I will say we did none of this for years but the 3800 in the Dustbuster is constantly an issue so we ran the ground straight to a case bolt and then to the "frame". Granted, this solved little or none of the issues but it had to be tried.
/agree
You would good, solid grounds.
+1 on good grounds making a massive difference. There is no perfect answer here.
Underhood you need to look where the stock grounds go and see if there were things with fairly direct battery grounds. In my Fox moving the battery to the interior with a short 2ga ground worked fine. Did the same on the Golf and ran a whole race with weird electrical issues (ie gauges working intermittently at speed but fine in the pits). Ran a full 2ga battery cable from the negative pole on the battery to a stud on the firewall and then 2ga from there to the stock ground cable (and also maintained the original chassis ground I had made) and magically everything worked perfect.
You can't go wrong with too much ground.
But to counter my own statement...we did away with 11'ty-billion micro ground wires on the Saturn with absolutely 0 issues. Big lug to the pan, jumper to the block...done
yes more or less - will go from battery to something solid. near the new battery location. like a frame rail or some other substantial component of the car. watch out for things like rear sub frames that are often rubber mounted. then take your stock grounds (the side that went to the battery post and attach them to a substantial component of the car.
If BOF, ground to the frame, if unibody, ground to anything that's remotely structural (seat belt mounting points are great, for example). For the last build, we welded an upside down bolt to thicker metal in the unibody, and it made a good ground stud. Drilling a hole in a spreader plate and welding a nut on the underside is also good - if your roll cage can't give you a good ground, you have a problem that has nothing to do with electricity.
Grounding the motor is often already done in a convenient way from the factory. On Nissans the battery cable goes to chassis first, then engine; all you do is clip off the battery-to-chassis part and put a lug on the clipped end. Battery cable is ready and engine ground is undisturbed.
You want a nice contact surface, so clean until you get legit bare metal. Use real actual cable lugs, those aren't expensive and you can 'crimp' them using a sledge hammer just fine. Cover final result with dielectric grease or paint to keep rust and corrosion out. If your ground attachment points are good and positive cable is of a correct size, you'll have no problems starting anything including a diesel.
BTW, on an EFI car, all you really care about is that your sensor and ECU grounds are all ending up at the same point (on a Sentra it's the engine block). Having multiple ground paths can create problems, even if your ground paths *appear* to have near-zero resistance. Other things, like fans, lights, and battery, can be grounded straight to the chassis, as they aren't sensitive to minute voltage differences - so you can ground your fan and lights right to the radiator support, and not bother running the ground back to a common point like the factory does. They do it for *other* reasons, mostly ease of assembly.
Also, pro tip: using a skinnier, stiffer thick-strand cable from Home Depot for battery-to-kill-switch works, and It'll have better properties vs battery cable. Then you can use an off-the-shelf battery cable to run from kill switch to the starter, so no need to order a 50 foot roll of battery cable to do your wiring.
I third/fourth the comment about improving grounds. I did was the OP suggested (stock battery cable to chassis and then multiple ground wires from the relocated battery to the chassis).
I found that I also needed a solid ground from the battery to the starter ground to enable reliable starting.
This wasn't that big a deal as my relocation was only to the passenger side footwell (it was a short additional run).
I didn't trust rust to conduct electricity from back there all the way up to there. So, I ran AWG 1, (both red and black,) up through the floorboard and then through the firewall with these big, fat, "military spec" pass-throughs. Terminated positive and negative at the same places the factory used.
Starter actually spins with more vigor now!
Chose AWG #1 because it was double the size of AWG #4, the factory cabling. That much of a size increase probably wasn't needed, but the added length required a size increase of some sort, and since the stock cables would get warm after a difficult start up, a large increase was not a tough call.
Any other circuits I've added take ground and power from this electrical backbone bypassing the factory harness. I DON'T use the body for ground on any new circuits. The pass-throughs make easy places to tap off for both powering fuse boxes and grounding blocks.
Ground is equally as important as power. Treat it the same way.
We relocated our battery to the trunk. Used 00 gauge cable from a pick-n-pull BMW for the positive terminal. Grounded the negative terminal to the body with the cable used to ground to the body in the OE configuration. However, we had a couple of issues that may or may not have been impacted by the relocation so to ensure that our relays all function well during the next race, I plan to run a dedicated cable to connect the ground side of my terminal blocks directly to the battery. If you're running the power cable from the front of your car to the rear, you may as well run a negative post cable as well.
The 24 Hours of Lemons Forums → Lemons Tech → Battery relocation