Variable output Alternator's on Newer Gen GM Vehicles

[badstang123 10+ year member]

I recently purchased a 2009 Avalanche. I worked for GM previously and am aware that on the vehicle I have, GM is now using a variable output alternator. These alternators reduce output when the system is fully charged in order to aid with fuel consumption. If the alternator is working less it has less drag on the engine thus improving gas mileage (I'm sure it's minuscule but that is why they did it. I read this off of some literature on GM Technical Assistance website available to me in the our service department).

That is the background and here is the problem. As I have seen on many other vehicle similar to mine it's almost as if the alternator output adjusts kind of at random. I don't really notice any specific pattern it follows. When I first start the car it is over 14 volts then after driving a few miles it will go to around 13 volts most of the time and intermittently read around 14 volts exactly. The problem I see is that instead of running at 14.4 volts or so like a normal vehicle would while driving, the voltage will drop down to somewhere around 13 volts most of the time I'm driving. There are times when I have the headlights, fog lights, and system on (At high volumes) and it will remain near 13 volts instead of the alternator spiking up like you would expect under load.

Finally here is my question. Has anyone seen or heard of a way to bypass this type of system? Is there a way to get maximum output from the alternator at all times?

Here is the why. My lights will dim when the subs hit even while driving at speed. I'm putting out a peak watts of approx. 1550 with speakers and subs combined (That is peak measured with a multi-meter on 1K and 50hz sine waves). I ran 0 gauge wire from the battery to a distribution block near both amps. I then ran two separate four gauge positive runs to a Crossfire VR1000D and a VR404 (75 x 2 @ 3 ohms front and 50 watts @ 4 ohms on rear speakers). Both amps were grounded using 4 gauge wire to the chassis under the amps. I then measure ohms of resistance from the battery on the positive side to the distribution block and it's about .2 or .3 ohms. My resistance from the battery on the negative side to the ground points on the amps and amps themselves is also about .2 or .3 ohms. From what I can tell my means of power and ground seem relatively solid.

The factory battery to block ground is pretty hefty as is the factory alternator wire. The factory chassis ground is very small, so I already ran a new 4 gauge chassis ground. I plan to complete "The Big Three" in it's entirety but want to know if anyone has any other experience with these types of alternator systems that I should take into consideration and factor into this process. I know this was long but thank you for taking the time to read it.

Best Regards

- Justin -

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[jdawg 5,000+ posts]

http://www.missinglinkaudio.com/index.html

i beleive the stock alts are pulse width modulated

 

[18inchjeepin 10+ year member]

finding a replacement alt sucks, i have the same thing

 

[roarzorz 10+ year member]

I went through all this when trying to compete with my Yukon and hated it. I even went as far as to install a 2nd alternator that wasn't computer controlled and then the computer hated it & would spaz out. Eventually I just gave up with the truck and now compete with my Explorer. I've spoken with Chris @ MLA and he says that their module will fix the issue but I don't need it anymore so I haven't tried it.

 

[badstang123 10+ year member]

Thank you for the input guys. Looks like I'll need to make a phone call and get some information. Their site doesn't seem to have details on the new stuff.

One last question though. There is an extra location under the hood for a secondary battery but there is not one installed. Do you think if I wired that in so it was operating at all times the vehicle was on it would be beneficial with the dimming at least?

 

[loopkiller 10+ year member]

Thank you for the input guys. Looks like I'll need to make a phone call and get some information. Their site doesn't seem to have details on the new stuff.
One last question though. There is an extra location under the hood for a secondary battery but there is not one installed. Do you think if I wired that in so it was operating at all times the vehicle was on it would be beneficial with the dimming at least?

That depends on how low your voltage is dropping. If you are dropping below 12.6v, then yes anther battery in front may help. If you added another battery closer to the amps, that would give you more benefit since it will be closer to the load.

 

[98HOEONSIXEZ 10+ year member]

yeah give chris at mla a call, i can almost promise you it will take care of your problem.I have a older tahoe but before i had his module i had 3 ohio gens on7 group 31s and idling,jammin full tilt my voltage would go from 13.8 or so down to like 10.5 volts. .not good.i purchased the switchable module from 14.8 to 15.3 and with mine set on 14.8...startup it goes to about 15.3 and then after warm up my voltage at my amps read 14.8-14.9. anyways now i can jam it full tilt at idle and it never goes below 14 volts.. ..VERY IMPRESSIVE.i have a video of this too if i can find it ill show it too you.. .but yeah you wont be dissapointed with mla. .its the shit