Lights dimming, voltage sinking

[j91z28d1]

May I suggest something you'll likely ignore?
1. Have your ecm tuned (preferably, your ecm AND your tcm, in person / on site)
1a. Among the many other things that should normally be addressed by a tune to suit your particulars, have your four idle RpMs - Park/Neutral, & In Gear, with AC On, and with AC Off - raised by at least 100 RpM.

The extra RpMs at idle would likely have been enough to make even an OE alternator put out just enough extra juice.

there's a whole alternator section in the tune as well. lots of stuff in there that should over ride the idle settings when voltage falls because of load, some kinda boost mode.

 

[itschuck]

May I suggest something you'll likely ignore?
1. Have your ecm tuned (preferably, your ecm AND your tcm, in person / on site)
1a. Among the many other things that should normally be addressed by a tune to suit your particulars, have your four idle RpMs - Park/Neutral, & In Gear, with AC On, and with AC Off - raised by at least 100 RpM.

The extra RpMs at idle would likely have been enough to make even an OE alternator put out just enough extra juice.

Lol... ok I'm not ignoring you as a person, but likely wont do a custom tune for just this issue. Thanks tho!

 

[itschuck]

do you have an amp clamp to clip on the alt lead?

what kinda alternator did you install? I have a feeling it's not pulleyed or not putting out what you need at idle. you probably need at least 120amps at idle.. it might be time for the alternator upgrade iamdub did. newer style 6 pole.

No I sure don't. Its a tucson alternator unit that I installed.

 

[itschuck]

Did you upgrade the ground to the same size? A circuit it only as strong as its weakest link. You could use a 1,000A alternator and 4/0 for the charge cable and you'd still only be able to support what that factory 4 gauge ground will carry. I have 1/0 for my charging system- it'll fit through the RVC sensor with room to spare. Also, I have a ~1,000 watt Alpine that, according to dyno videos, should do 1,200-1,300 watts. A new battery (previous one was old and abused) greatly reduced my dimming lights and a 220A alternator showed further improvement. Now, the dimming is barely noticeable when I have the stereo cranked. A/C stays on max at all times here in Louisiana.

Having said all that, I think you have something wrong. I'd first upgrade the ground and verify all the terminations are clean so you can actually make full use of that new battery and 260A alternator.

I had not replaced the factory ground. Will do that today. I did go ahead and install a second battery and that has helped a lot. The volt meter on the dash will still dip when for example sitting at a light with the radio on and ac's both running, but the lights are not noticeably dimming anymore.

 

[itschuck]

You mention the radio, is it stock or customized?

With a stock truck none of these modifications are necessary. Alternator output does decrease when the battery has been charged to the satisfaction of the computer system. Look up the terms RVC for Regulated Voltage Control and EPM for Electronic Power Management with reference to GMC trucks.

https://www.gmupfitter.com/wp-content/uploads/2021/05/2011_LD_ElectricalPickupsChassisCabs_100813.pdf

The radio is an android tablet based touchscreen, that feeds a sundown audio audio 1200w amp, that provides a 1 ohm load to a set of dual 12's in the back.

I did go ahead and install a second battery and that has helped a lot. Next im replacing the factory grounds, make sure good surfaces, and match the 1/0 copper from the alternator. The new battery has 1/0 for + and - I think with this I should be completely resolved.

 

[swathdiver]

The radio is an android tablet based touchscreen, that feeds a sundown audio audio 1200w amp, that provides a 1 ohm load to a set of dual 12's in the back.

I did go ahead and install a second battery and that has helped a lot. Next im replacing the factory grounds, make sure good surfaces, and match the 1/0 copper from the alternator. The new battery has 1/0 for + and - I think with this I should be completely resolved.

Remember to replace the batteries in pairs. An old one will drag down the newer one.

 

[j91z28d1]

I found one of my trucks that I added electric fans to, that if you let it drop down to battery voltage at idle. I shorten the life of the battery a lot, like once a year. till I put a much smaller pulley on it and got the voltage up, the battery went back to 5 years ish. of course after that the alt died from it, but found a diesel one rust *** a direct swap. it was a larger case and charged at idle without over speeding. it's still on the truck all these years later.

the 2nd battery will help, but it's best to get it running on the alt at full load. a volt/dc amp clamp will help you know what's going on. a lot of these aftermarket alternators use the same size case/armature and just change diodes to up the current at high rpm, but they aren't a lot higher output at the low idle sleeps.