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  1. #11

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    Quote Originally Posted by RayVoy View Post

    I'd suspect something else, the fuel pump shouldn't draw enough to dim the lights. Just cruising on the highway at an even 50 mph, the pump will run and stop to provide fuel, the lights probably don't dim under that condition.
    My alternator has been acting up... will be replacing soon. Hopefully that will take care of it.
    2009 Chevy Silverado 2500HDLT 6.0L w/ Towing Package, Dick Cepek GM8 Rims, Dick Cepek FC II 33X11.50R17,RKSport Ram-Air Hood(Functional), Lazer Lite Aluminum Tonneau Cover, Road Armor Stealth Bumper, PIAA Lighting, Diablo Trinity Tuner, Diablew Custom Tune, BullyDog Cold Air Intake, American Racing Headers w/highflow cats, Corsa Performance Sport Exhaust, Custom Striping, Black Bowties front and rear, Fuel Grille Inserts, Recon Headlights, Readylift Shocks, Readylift Upper Contol Arms, 2" Blocks in the Rear..

    Future Plans: HD Tie Rods, Under hood upgrades, Crower Camshaft and possibly electric fans.

  2. #12
    Jr. Engineer Jamm3r's Avatar
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    Quote Originally Posted by Pikey View Post
    you need to do some research before even considering a new alternator. Many of the new trucks have the alternator output controlled by the pcm. So, adding a larger alternator will net no results because the pcm will still call for the same voltage needed.
    Sorry, usually your posts are spot on but I gotta disagree with you there, Pikey.

    Sure, modern alternators are regulated by the PCM. We can agree on that. The PCM determines a target voltage based mainly on temperature (lower temps=higher voltage) but also informed by the PCM's guess of the battery's state of charge. This voltage is a limit. The alternator will try to deliver enough current to reach the limit.

    There are however a number of limitations intrinsic to the alternator on how much current it can deliver. The important one for this discussion is that the physics of the rotor and stator design will limit how much current -- how many amps -- the alternator can deliver at any particular RPM and at approximately 12 volts. For stock GM alternators, the pulley size is chosen so that the alternator can deliver around 60% of its rated current at engine idle, and 100% of its rated current at typical highway cruising RPMs.

    At higher RPMs the alternator is capable of delivering more than its rated current but will overheat and fail if it does so for very long. "Overwound" alternators -- hi-amp versions of the stock alternator in the stock case -- can handle higher currents, at high rpms, without failing. They have lower output at idle however as a result of compromises that have to be made to allow for room for heavier wire.

    So if you have a stock 105 amp alternator you'll get 60 amps at idle and if you have the stock lighting turned on and the A/C blowing cold you'll use all of that, and if you turn on those KC daylighters then the alternator won't be able to keep up no matter how hard the PCM tells it to work, and so the battery will discharge.

    As a result the answer is that you have to switch to a larger-frame alternator that has higher output capacity at idle, which is what I was recommending upthread. GM has used the AD244 in a variety of configurations -- snow plow and camper packages, diesel engines, police packages -- and it's a drop in fit (except for belt length) and works great. I have one in my Suburban and have the smaller CS-130 in my pickup so I know the difference and I know they are interchangeable provided that the connectors match (and there are adapter plugs out there if they do not).

    Look at your negative battery cable running off your battery. If it has black box attached to it then you have the system. That box is a hall effect sensor that tells the pcm how much current you are drawing at any one time. On my truck, with a new alt, battery, and all the grounds cleaned. I can roll up all four windows, my lights dim significantly for a second while the pcm tells the alternator to ramp up output. a few seconds later my lights are bright again even with all four windows activated.
    The sensor measures battery charge current, not alternator output current. It is used to adjust charging algorithms to maximize the useful life of the battery and limit the amount of electrolyte that gets "boiled" off.
    Minneapolis area - 1997 K2500 regular cab long bed + 8.5' Western Unimount plow + modified transmission + 2nd battery + modified camper charge circuit + 1971 Cayo camper -and- 2004 4x4 Suburban 2500 8.1 + Maxbrake controller + 2nd battery + modified trailer charge circuit + Reese receiver, pulls 30' Airstream trailer

  3. #13

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    Quote Originally Posted by Jamm3r View Post
    Sorry, usually your posts are spot on but I gotta disagree with you there, Pikey.

    Sure, modern alternators are regulated by the PCM. We can agree on that. The PCM determines a target voltage based mainly on temperature (lower temps=higher voltage) but also informed by the PCM's guess of the battery's state of charge. This voltage is a limit. The alternator will try to deliver enough current to reach the limit.

    There are however a number of limitations intrinsic to the alternator on how much current it can deliver. The important one for this discussion is that the physics of the rotor and stator design will limit how much current -- how many amps -- the alternator can deliver at any particular RPM and at approximately 12 volts. For stock GM alternators, the pulley size is chosen so that the alternator can deliver around 60% of its rated current at engine idle, and 100% of its rated current at typical highway cruising RPMs.

    At higher RPMs the alternator is capable of delivering more than its rated current but will overheat and fail if it does so for very long. "Overwound" alternators -- hi-amp versions of the stock alternator in the stock case -- can handle higher currents, at high rpms, without failing. They have lower output at idle however as a result of compromises that have to be made to allow for room for heavier wire.

    So if you have a stock 105 amp alternator you'll get 60 amps at idle and if you have the stock lighting turned on and the A/C blowing cold you'll use all of that, and if you turn on those KC daylighters then the alternator won't be able to keep up no matter how hard the PCM tells it to work, and so the battery will discharge.

    As a result the answer is that you have to switch to a larger-frame alternator that has higher output capacity at idle, which is what I was recommending upthread. GM has used the AD244 in a variety of configurations -- snow plow and camper packages, diesel engines, police packages -- and it's a drop in fit (except for belt length) and works great. I have one in my Suburban and have the smaller CS-130 in my pickup so I know the difference and I know they are interchangeable provided that the connectors match (and there are adapter plugs out there if they do not).



    The sensor measures battery charge current, not alternator output current. It is used to adjust charging algorithms to maximize the useful life of the battery and limit the amount of electrolyte that gets "boiled" off.
    Jamm3R thanks for the clarification. I did say that the op did need to do research about the subject. I was incorrect on my statement about there being no benefit. I don't know what I was thinking there.

    1995 Silverado 4x4
    6" BDS Suspension Lift-3" Body Lift-Add A Leaf in rear -Trailmaster SSV Shocks-Duel Steering Stabilizer Kit -AirAid Cold air intake-
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    2005 Yukon XL Jet Power Programmer, Bilstein Shocks, Bilstein rear springs, Helwig Anti-sway bars, EGR Window Visors, EGR Hood Shield, Denali Headlights, Headlight harness upgrade, GE NightHawk Bulbs, White Night Rear lighting system, Russell Braided SS brake lines, PowerStop Brake pads, PowerStop cross drilled and Slotted Rotors, http://www.gmtruckclub.com/forum/sho...5-GMC-Yukon-XL
    2002 Silverado ext cab 2wd (Sold)
    2003 Yukon XL (Totaled)

  4. #14

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    wait... question though... since iv had the truck i havent turned the A/c on yet haha. i either roll down the windows or my rear slide and the most ive done is switch on the recirculate button which isnt the same as the a/c lol and i mean i checked for the vyu and couldnt find it so i guess i have the emergency lighting package. idk if that makes a difference. i mean it has the name lighting in the package name so one might think its meant for a bunch of lights lol. but how much would the new alternator and pulley cost, could the dealer technically void my warranty installing it if i have any eletrical problems and lastly would a 100w offroad light kit be enough of a drop (60w all together) that i wouldnt have a problem with running the lights?

    - - - Updated - - -

    and if it helps im also getting an led third brake light and led tail lights with load resistors built in so ill be savin a little bit of energy there haha
    2010 Silverado, Z71 4x4, 5.3, ext. cab, 3.08's, undercover tonneau, 2.5" roughcountry front lift (with .75" rear block), Ranch hand summit bullnose front bumper, ranch hand legend rear bumper, flowmaster super 10 3" ci/co, corsa chrome double exhaust tip, dee zee bed mat, bed rug tailgate rug

  5. #15
    Jr. Engineer Jamm3r's Avatar
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    Quote Originally Posted by bigbuck493 View Post
    wait... question though... since iv had the truck i havent turned the A/c on yet haha. i either roll down the windows or my rear slide and the most ive done is switch on the recirculate button which isnt the same as the a/c lol and i mean i checked for the vyu and couldnt find it so i guess i have the emergency lighting package. idk if that makes a difference. i mean it has the name lighting in the package name so one might think its meant for a bunch of lights lol. but how much would the new alternator and pulley cost,
    Several hundred bucks depending on your tastes. Check the Nations Auto Electric web site for prices on various versions, or if you have a more competent local parts place who gets this stuff check with them.

    As an aside, there are dual alternator setups available that reflect the next level of this sort of thing. Not usually necessary for lights alone, but if you run a winch or an inverter it's worth considering at least.

    could the dealer technically void my warranty installing it if i have any eletrical problems
    Who knows. Usually dealers are on your side if warranty problems come up. I'd be surprised if there were are problem.

    and lastly would a 100w offroad light kit be enough of a drop (60w all together) that i wouldnt have a problem with running the lights?
    That's a valid question but it's hard to provide a straight answer.

    The thing is that it depends on what you're willing to put up with. Let me give you an example. I plow snow with my K2500 which has the small alternator, rated at 105 amps I think. Well it's fairly typical for me to have all the (stock) lights on and the defroster on when I'm plowing snow, and the hydraulic pump motor in the plow draws maybe 100 amps when it's running. So, when I hit the button on the control to make the plow go up or side to side, the electrical system drops to 11 volts or whatever because the alternator can't keep up. In situations where I'm moving the plow a lot and never running at speed, like plowing parking lots, the battery gradually gets more and more discharged. I'd like to replace the alternator but, well, $$$$, so it's down the list after a bunch of other things I'd like to do to the truck.

    So in your situation if you're really running trails at night and you're in a situation where you might run the lights 10, 15, 20 minutes at idle, because you're stuck in the mud or maybe because the guy ahead of you on the trail run is stuck in the mud, well, your battery will discharge. Maybe you're OK with that given the cost of an alternator, maybe not. Your call.


    and if it helps im also getting an led third brake light and led tail lights with load resistors built in so ill be savin a little bit of energy there haha
    It'll save you a few amps, maybe enough, who knows.

  6. #16

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    Quote Originally Posted by bigbuck493 View Post
    wait... question though... since iv had the truck i havent turned the A/c on yet haha.
    If you used your defroster with the temperature above 32F then you have been using the A/C. The A//C comes on with the defroster to dehumidify the air that is blowing at the windshield.

    Quote Originally Posted by bigbuck493 View Post
    and if it helps im also getting an led third brake light and led tail lights with load resistors built in so ill be savin a little bit of energy there haha
    LED bulbs with load resistors will not save any power. The sole purpose of the load resistor is to draw additional power so that amp draw stays the same as what it was with the original incandescent bulb. Load resistors are used so that the computer monitoring the amp draw will not see the reduced amp draw of the LED and indicate an out bulb.

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