Alternator Q&A
 

Hello folks... Some basic questions from a guy with a long time pickup ownership (and repair) experience but a short list of brand experience (mostly Ford, one year of Chevrolet).

Is it normal for a 2001 Silverado (2500HD with the 6 liter) to see wild swings in amperage based upon engine RPM (as reported by the dashboard gauge as well as other examples given below)? Since I have acquired this pickup, I have seen that gauge go from below half to above half to about 75% of the gauge range. When I am at 2500+ RPM it generates far more than 14 volts, according to the gauge. When idling - in most conditions - the gauge shows less than half on the gauge, sometimes as low as about 25% on the gauge itself. The gauge changes constantly with engine RPM after about 10 seconds from starting.

In my previous truck ownership experience, this never happened. I rarely saw any fluctuation in the dashboard gauge.

I can verify that the alternator puts out far more amperage at 2500+ RPM compared to idle, or even compared to 2000 RPM. I can do this in an interesting way I will describe below:

I have a mobile two way radio installed in my pickup. It is a Kenwood. It offers two power levels. Either 25 or 65 watts. If the engine is idling at 700 RPM or so (according to the tach), I cannot use the radio on 65 watt mode. This was never an issue in my 1990 Ford F-150, which was the previous home of the radio. If I spool up to 2500+ RPM, I can transmit without issue. The gauge displays a wild swing in amperage increase prior to my attempt following my revving of the engine. At idle or even at 2000 RPM, I can only use the radio on 25 watt mode, no more.

Another way I can verify the increase in power is at night. I can see a significant improvement in headlight brightness as I increase my engine RPM until I get to about 2500 RPM. When idling or cruising down a hill in the dark, I am very unhappy with the headlamp brightness out here in the middle of nowhere backwater rural woodsville. If I am in the throttle some, I can see a pretty significant difference in headlamp brightness. I would think this would not only be unacceptable to Chevrolet owners, that it is just plain wrong.

I can use a multimeter and also see a significant swing in voltage supplied at various RPM levels. As low as 12.1 volts and as high as 14.9 have been shown on my meter during testing. I would think this was a poor result. However, without extensive Chevrolet experience, I want to ask you all what you think about this.

The vehicle battery was new when I purchased the pickup and seems to be functioning fine, including allowing me to use the radio at high power (65 watt) while the pickup is turned off.

I believe there is something wrong with the alternator - which is a Delphi. Specifically, I believe there is something amiss in the voltage regulator inside of the alternator. All the wiring is clean, free of corrosion or debris and is not an odd length of run, it all looks just right - including the connectors, as far as I can see it. I am planning on replacing the alternator with a new 130 amp unit, but before I just go do that, I wanted to know if you had any thoughts.

Thanks for your input, and I hope you all have a great day now...

Jason

the gauge on the instrument panel shows voltage not current.
It shouldn't swing around too much.


It will move around a bit based on accessories you have running, state of charge of the battery, engine RPM, etc.
Also keep in mind that the dash gauge is not a precision instrument. It's meant to give you a rough idea.
If you want to troubleshoot issues then use a multimeter or one of those digital gauges that plug into your cigar lighter.
I'm not sure what year GM implemented smart charging on these trucks, but voltage higher than 14V could be normal.

Swing by a battery dealer or auto parts door and ask for a free load test (battery + alternator should always be checked together)



every vehicle is a little different.

That's to be expected. More energy in = more energy out
https://cimg8.ibsrv.net/gimg/chevrol...580b5ef79a.jpg




How is it powered? 65W is really pushing it for a cigar lighter plug.


That shouldn't happen. There's something wrong with your charging system.




12.1V is definitely too low and means the battery is discharging.
Definitely have your truck load tested.

While you are at it, check the ground connections on the negative battery cable - make sure the mating surfaces are clean and tight.

Good Luck!

Good morning guys…

Thanks for the input here. I tried to keep it succinct in my original post, so didn’t detail every fact possible, I only hit the high spots. :)

I went ahead and replaced the alternator and I am not kidding you, this is a night and day difference. The vehicle has been running on a bad alternator for so long that I didn’t know it could even be possible. I think it is the most likely scenario that the voltage regulator was barely holding on.

Anyhow, I am really grateful for the help, and I can report that the entire situation has changed, including the dashboard gauge. It is essentially steady, showing only a needle width of difference for a hundred of a second.

As an aside, the old alternator weighs almost half of what the new unit weighs. I found that to be very interesting.

Have a blessed Sunday guys…


Jason