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batteries and offroad lights

Discussion in 'Chevy Silverado Forum (GMC Sierra)' started by bigbuck493, Feb 16, 2014.

  1. TimTom64b

    TimTom64b Member 2 Years 500 Posts ROTM Winner Gold Member

    My alternator has been acting up... will be replacing soon. Hopefully that will take care of it.
  2. Jamm3r

    Jamm3r Member 1 Year 100 Posts

    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.
  3. Pikey

    Pikey Moderator Staff Member 2 Years ROTM Winner 1000 Posts

    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.
  4. bigbuck493

    bigbuck493 Member

    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
  5. Jamm3r

    Jamm3r Member 1 Year 100 Posts

    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.

    Who knows. Usually dealers are on your side if warranty problems come up. I'd be surprised if there were are problem.

    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.


    It'll save you a few amps, maybe enough, who knows.
  6. Flyinfool

    Flyinfool New Member

    If you used your defroster with the temperature above 32°F 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.

    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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