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When talking about electrical upgrades, a few posts talk about a direct grounding wire from the alternator case to the negative battery post.
What is the value added for this? The alternator is grounded to the engine block, the engine block is attached to the negative battery post by a cable.
If all the ground straps are in good shape, there is no advantage to adding a ground wire from the alternator. I think people erroneously believe that if an alternator produces 150 amps that it also needs to return 150 amps back to the battery negative post. You absolutely need a large gauge power wire coming out of the alternator, but not a separate large ground.
Thanks... I upgraded my battery cables to 3/0 welding cable about 2 years ago, keep coming across "you need to ground your alternator" posts... was wondering if I was missing something.
I learned decades ago that the charging circuit suffers integrity as the vehicle ages on some brands. In my world, I was a VW/Audi repair tech for my entire career and had to rebuild a lot of charge circuits on the older Gen 2 cars. The guage of the ware was two sizes too small, (Kind of like the Grinch who stole Christmas' heart. ).
Anyway..... what would happen is where I lived in Seattle, WA. the commuter traffic was simply too heavy for the engine to get up to speed and enable the alternator to keep up with demand. Cold, wet winter mornings and they are loafing along in stop and go traffic with the headlights, wipers, and heater on, it didn't take long for the battery to go dead. And when they jump it to get it started and bring the car in, everything is functioning correctly. Battery was new, alternator voltage was 14.25 at the output on the alternator and at the battery. But the voltage arriving at the battery would drop off to 13.5 or so if I turned on any accessories. Replacing the entire charge circuit, or simply installing a parallel wire from the alternator output post to the battery always fixed the issue. Adding the ground wire from the body of the alternator straight to the negative post of the battery always brought the charge voltage back up to where it's supposed to be. I never worried about installing a fuse in the circuit because the factory wiring harnesses in the early days didn't have one either.
FWIW, I added factory braided ground straps from junkyard vehicles from the motor to body and body to frame on my '97 E350. The original straps we OK because it's a CA vehicle. But these additional straps are there to carry the load from lights stereo, fan blowers etc. I also doubled-up the alternator power cable by adding another in parallel from a junkyard E350....so I'm not immune to overkill on this stuff.
When I replaced the battery cables, I got 50 feet of 1/2 inch braded grounding strap material, bunch of crimp on connectors and replaced all the grounding straps on the truck and added a couple more
When I installed a high output alternator to supply power for some accessories and the 5th wheel 4x 6v batteries, I felt the need to add a 4 gauge wire from the alternator case to the battery ground on the driver side. Was it needed? Maybe... I also added positive cables from the alternator B+ post to each of the batteries. I figured after almost 20 years of service (at the time) on the OEM cabling and the alternator output being 40A more than the OEM, it couldn't hurt.
I sometimes go a bit overkill with wiring though, as I did with my 5th wheel solar install pictured below.
the OEM grounding wires are fine, right up until they aren't.
Adding a heavy ground wire from the Engine block / Alternator base to the Battery negative
is just good Insurance, that way every thing will have a Common Ground Reference,
especially when that starter starts asking for more juice.
I had a 1951 Plymouth that was having starting problems.
Traced it down to the big heavy woven ground strap from the firewall to the engine block, it was corroded so bad, it fell apart when I tugged on it.
Adding a heavy ground wire from the Engine block / Alternator base to the Battery negative
is just good Insurance, that way every thing will have a Common Ground Reference,
especially when that starter starts asking for more juice.
But the alternator isn’t supplying any power during the high amp draw conditions of starting or Glow Plug activation. I actually see the additional ground wire to alternator as a potential for sending extra current through the case of the alternator (and regulator) if the main ground gets compromised. Sure, the power lead makes sense, but I just don’t get adding a ground wire to it.
But the alternator isn’t supplying any power during the high amp draw conditions of starting or Glow Plug activation. I actually see the additional ground wire to alternator as a potential for sending extra current through the case of the alternator (and regulator) if the main ground gets compromised. Sure, the power lead makes sense, but I just don’t get adding a ground wire to it.
Batteries located at the opposite end of a vehicle would benefit more on something like this.
But the alternator isn’t supplying any power during the high amp draw conditions of starting or Glow Plug activation. I actually see the additional ground wire to alternator as a potential for sending extra current through the case of the alternator (and regulator) if the main ground gets compromised. Sure, the power lead makes sense, but I just don’t get adding a ground wire to it.
I'm with stupid here. 😂 If the engine has good enough ground for the starter to function I don't believe a extra ground to the alternator is really needed. Grounds already there should be more then sufficient.
But the alternator isn’t supplying any power during the high amp draw conditions of starting or Glow Plug activation. I actually see the additional ground wire to alternator as a potential for sending extra current through the case of the alternator (and regulator) if the main ground gets compromised. Sure, the power lead makes sense, but I just don’t get adding a ground wire to it.
it DOES NOT have anything to do with the Alternator providing current.
and it will NOT damage the alternator.
the idea is to provide a backup Common Ground from the ENGINE BLOCK to the negative battery terminal on the Driver Side.
The alternator attachment bolts screw into the block, the alternator case is not part of the situation.
all it does, is ensure that the Starter can pull equal current from BOTH batteries.
a poor ground, causes all/most of the starter current to be pulled from the Passenger side battery.
Suppose I need to slide under the truck. Is the factory driver’s side battery ground wire not connected to the block?
On my old e99, both batts grounded to the same location on the lower block. On my current 02, I cannot recall if both batts terminated there (even though I did the alt upgrade thing back in December). In both trucks, there was enough stud length to add another ground wire (either from a negative batt terminal or the alt case).
And just to add to the discussion about extra grounds: awhile back I worked in a huge sawmill. The main piece of equipment was a 3-axis saw that relied heavily on sophiscated controls. After I started, I learned that the saw would have a "mind of its own" on random ocassions. Since it was my job to keep the plant running, I needed to figure out what the deal was, because it was getting worse. The mill was constructed in 1974 (I started in 2005), and like most heavy industrial facilities, a ground grid was put in before the slab(s) were poured. On a hunch we checked for stray voltage on the ground system. Sure enough, it was a mess (underground corrosion was getting the upper hand as it turned out). We cut a hole in the floor next to the big saw and drove a giant rod into the earth (amongst other remedial efforts). Problem solved. The take-away? Stray voltage (which is a form of bad ground) raises holy-old-heck on sensitive electronic control equipment - which normally runs at sub 50v DC by the way - just like the PCMs.
In regards to our 20+ year old rigs, connections will be compromised - even in the most arid conditions (my 02 was from AZ and one of the first things I did was clean all the ground points I could, and it needed it). Anything that can be done to keep electric current in its place will be in the best interest of minimizing/eliminating nuisance or intermittent problems. Or leading one down a false path of troubleshooting. Especially in these floating ground systems that are not truly grounded - to earth. Having done an alt upgrade on two of these things, including upgrading cable size and adding an extra block ground connection at the alt, my seat of the pants take is that starting is more spirited and my batteries got a season longer out of them than before the upgrade (on my 99, i havent had the 02 long enough to tell). And it may sound weird, but my lights seemed brighter. Is this all due to an extra ground? prob not entirely. But if one is going to up-size the alternator and red lines, doing the same (and more) on the black lines will ensure you dont introduce some wildcard problem that keeps your truck in the driveway instead of on the road.
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