Inconsistant voltage

[shepherd92683]

I suggest that you take a close look at the factory negative cable for the hall effect clamp I speak of. If you have ground cables that do not pass through this clamp, that could explain your problems.

I have searched for info on this and get nothing that helps. Is there anymore detail on where it is or anything that would be helpful in telling if my vehicle has one?

[shepherd92683]

2. If you have an '08, it should be a PCM/RVC controlled alt right? Try this for me, next time it starts to drop in voltage while driving, turn your headlights on, not just the DRL, but use the rotary knob on the column to turn the lights on.

I tried this. It didn't seem to have any consistent effect. More often than not it would make the voltage kind of stabilize then after a few minutes, it would go up .4-.8 but not every time. I also tried turning the a/c on and off to see how it reacted and it was a -.1 or -.2 when turned on and immediately back up when off. My next task is moving my ground on my rear battery to the frame. That will wait til its not over 100 degrees out and I've not worked a 12-13 hr day. Haha

[shepherd92683]

Could it be that my 2 batteries are not sharing a common ground is what's causing it? One on the chassis and one on the frame?

[kandiman71874]

I suggest that you take a close look at the factory negative cable for the hall effect clamp I speak of. If you have ground cables that do not pass through this clamp, that could explain your problems.

I have searched for info on this and get nothing that helps. Is there anymore detail on where it is or anything that would be helpful in telling if my vehicle has one?

it looks like a plastic encased magnet that is around the battery cable up by the battery. you cant miss the damn thing.

[shepherd92683]

I ran the ground through the hall effect clamp

It peaked at 14.4 momentarily and then slowly dropped. This was the steady voltage result after initial start up.

This is driving me crazy!

No I dont have a VM-1, yes I wish I could replace the Stinger and yes the Stinger is calibrated as accurate as can be lol

[Karkov]

That's the sensor. You should have a ground running straight from alt to first batt, then connect all other batts negatives to the first batt, even if you go one by one by one. DO NOT add any additional grounds or ground things to frame or body. The sensor senses how much current is going through that ground wire so when you add grounds it doesn't know to have the alt ramp up output power. Essentially you want that sensor to read the negative side of everything in vehicle.

I ran ground from alt through sensor to first batt, then another from first batt to second, then to third etc. Then grounded amps to batts negative. If you do anything different you could, and most likely WILL see voltage issues.

[shepherd92683]

DO NOT add any additional grounds or ground things to frame or body.

Not looking to argue here, but that is part of a big 3 upgrade. I cant see why I wouldnt want to do that, but I ultimately need help in my situation so I am here to get any and all info to help. I also am not doing a run of 1/0 to my rear battery. With the amount of power I would ever run, I dont see the benefit of it.

One thing that is strange to me is I ran these wires (big 3) well over a year ago and instantly noticed a 1v increase. Only as of the last few months have I noticed the voltage issues. The only thing I can imagine is like Karkov said and the alt is not ramping up to output more power. But why is that happening out of nowhere? It used to run 13.2-14v all day at full tilt.

[Karkov]

Can't do a full big 3 with that sensor. Why voltage changed now I have no idea. What size do you have to your rear battery now? i don't care what size you run to back lol.

the reason for not wanting additional grounds is because you want that sensor to read all current so that your alt runs to keep up with demand 1:1 and not have things getting current through other grounds instead thus having your alt putting out only 60% (give or take of course) of what it actually should.

Big 3 isn't a cure all that everyone do do in every vehicle. 2005 and newer GM vehicles with the sensor can't just do the regular big 3 and call it a day.

I really can't help you with your problem, I only know about that sensor thing. If I was you I would remove all grounds (just unbolt one end of themhave wire in place not touching anything) and see what voltage then does. If your voltage is crap either alt is going bad,or battery is not holding charge well. have you ever topped off your batteries over night?

[shepherd92683]

As a test, I did undo the run from the batt - to the frame and no change. I have 1/0 on everything in the vehicle. I have topped off my battery's overnight. I have a Battery Tender Plus to do that with but I do need to do that again here soon. If this is a common issue on GM vehicles, surely there is a thread somewhere on SMD about it. I dont think I would be the first person to have this problem. If there is a different method of doing the big 3 than what is conventional, I'd like to know. I think my next effort will be removing my ground connection from my rear battery so see what happens. Thanks for the help Karkov.

[shepherd92683]

After removing power to my rear battery, the voltage stayed .3 higher. Would that mean that there is a weak link in the rear ground? I still need to move that ground point as I mentioned earlier. Need to get a couple 1/0 ring terms before I can do that though. If both batteries are grounded to different locations, can that affect the voltage in a bad way?