2013 Sierra Volt meter doesn't drop from 14+ volts as designed.

Discussion in 'Chevy Silverado Forum (GMC Sierra)' started by bigjer, Jul 12, 2013.

  1. stchman

    stchman Active Member 2 Years 1000 Posts

    So basically you're saying that the current electrical setup for GM vehicles is to lightly load the alternator (thus reducing some drag on the engine) and use the battery as a reserve to improve fuel economy? My thing with that is that the battery would eventually drain to a point where it would no longer be a reserve and the alternator would have to work really hard to charge it up.
  2. j cat

    j cat Epic Member 5+ Years 1000 Posts

    that is what I believe is going on. the battery MUST supply power to operate the electrical systems when going into power /fuel saving mode.

    now if this were a carb set up you do not have the higher electrical loads as we have now with more electrical components controlling/monitoring the vehicles operation.

    when the battery gets down in voltage the PCM must be turning the alternator back on and stays on until the alternator current drops off indicating the battery is charged .
  3. stchman

    stchman Active Member 2 Years 1000 Posts

    The alternator is driven by the serpentine belt. The alternator should be oblivious when AFM switches from V8 to V4.
  4. j cat

    j cat Epic Member 5+ Years 1000 Posts

    the alternator is driven mechanically by the belt, sure it is, However the alternator is electrically driven by the field voltage. the greater the field excitation [magnetism] the greater the charge and the PCM does control this field voltage which is a wire on the back or top of the alternator on the connector plug.

    so that is how the volts gauge goes up and down to reduce engine load at times that the GM engineers figured out would work until the warranty ends to increase MPG a few .
  5. RayVoy

    RayVoy Epic Member 5+ Years 5000 Posts

    Actually, let's call it "smart charging" (smart seems to be the catch prefix these days). Firstly, @j cat is right, heat is the killer of batteries.

    In the "old" system of charging, the alternator, using the internal regulator, kept the battery charged using 14.8 volts. On, or off. The regulator was either charging the battery with 14.8v (if it could), or it wasn't charging the battery.

    Three things are fact: electric load changes, temperature changes, and engine speed (alternator rpm) changes.

    The "smart" alternator, has the ability the change the charging voltage to match the electrical load. It also has the ability to change the charging rate to keep the battery in an 80%, or higher, state of charge.

    The whole idea is to keep the battery at an 80%, or higher, state of charge.
    The PCM can increase idle speed if the load is high and the state of charge falls below 80%.
    The PCM can change the charging voltage (maybe we only need 13.8 volts, not 14.8) and the duration, to keep the battery at an 80% state of charge.
    The PCM can turn off the charge if the temp is low (cold winter morning), reducing the spin load on the starter.
    After the start, the PCM can increase the charge voltage to quickly get the battery back to the 80% state.

    In doing all of this, the battery should run cooler, a cold engine should start easier and the reduced charging load on the engine should give better mpg.

    My 2 cents.
  6. tbplus10

    tbplus10 Epic Member Staff Member 5+ Years 5000 Posts Platinum Contributor

    You pretty much nailed it Ray, in older systems the voltage regulator controls whats coming out of the alternator, but the alternator load doesnt change much as far as drag on the engine, this new system in a sense allows the alternator to freewheel when it doesnt need to produce a lot of amps.
    Once the batterys charged load demand drops, turn off things like A/C, heater fan, radio, lights, load demand drops and remains low, theres no requirement to produce amps that arent used which is essentially what normsl alternators do.
    Drawbacks to this system are its controlled by the PCM which gives something new to troubleshoot or worry about failing.
    Advantages are it takes the alternator essentally offline when not required to produce power or as much power.
    This theory isnt new, ships and aircraft have been using this method for years when either max power is required or they want to go into fuel saving cruise mode. The difference in their systems is they manually select generators off-line or on line when a condition or situation dictates it.
  7. j cat

    j cat Epic Member 5+ Years 1000 Posts

    these are my opinions based on the components involved and over the years with training in electrical /electronic devices and what is best for a longer trouble free life. I maybe very wrong. the alternator and battery maybe a different design to handle this type of damaging cycling.

    just to point out something stated when the battery temp is very low like on a cold 20 deg f morning and you start your vehicle the alternator output is very high . 15 volts approx. the reason for this in a old design is to heat up the battery because a cold lead acid battery cannot charge. the high voltage wakes up the battery then after 15-20 min the battery can start to recover from the cold crank cycle.

    another comment. The battery does not supply any power when the engine is running with the old design. the sole purpose of the battery is for starting the engine and to get things going with the engine OFF.

    lead acid battery's must be fully charged at ALL TIMES , if not the batery will get internally damaged.

    so IF GM has changed these components in the design to handle what is going on now with these new vehicles I would be wrong. time will reveal this with I would expect more frequent battery and alternator replacements.
  8. RayVoy

    RayVoy Epic Member 5+ Years 5000 Posts

    Not for a second suggesting your view-point is wrong, like you, I also spent many years working in an environment where the lead acid battery was the life of the industry and I agree with everything you said about the lead acid battery. Salfation of the plates occurs during deep discharge and it requires a very high voltage/current to remove the salfate and return the liquid back into sulfuric acid.

    Deep discharge/recharge and the resulting heat will shorten the life of any lead acid battery.

    I wasn't taking sides, just presenting the current technology (be it good, or bad) being used by GM.
  9. j cat

    j cat Epic Member 5+ Years 1000 Posts

    one thing I have learned over the years is things do change . this maybe some GM engineering achievement . could also be a big flop at our expense .

    I understand what your saying with this . good info to get out there .

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