79 4 speed low miles. Battery gauge reads right at red line . Voltmeter reads 14.95 volts at battery and alternator stud. I replaced voltage regulator with no change. I have new battery. I cleaned all the grounds and still have 14.7 volts. Have checked and cleaned all connections, I bypassed the brown sensor wire and ran it direct to the battery same result 14.7 volts........ Any ideas what to do next.

 

My alternator output is 14.5 volts when running on my 79. Checked at output stud with a fluke meter. I have a newer style alt. CS130
your voltage looks good to me.

 

Drive it!
my 77 sits right up at the "Red line" of the volt gauge as well. Untill my fans kick on.
Sounds perfectly normal for a high output alternator.

 

I run 15.5 volts at alternator stud..
79 low mileage 4 speed

 

LOL...Mine was reading 38.5 volts at the stud and not charging the battery...The main wire had five splices in it, one splice was spliced twice...and this wire ran through the frame.... I'll trade ya!!!!

Drive it, mine is running 14.5 now....

60

 

What is the battery voltage on your multimeter with the engine off?

 

12.75 volts

 

12.7 - 12.8 is a perfectly charged battery. Once again, all sounds perfectly normal, Drive it.

 

The plug on the alternator with the two wires, red and brown. With the engine running using a voltmeter, positive lead to brown wire and negative lead to any metal ground, what voltage reading do you get?

 

15 volts is the max voltage out of the alternator. Unless the battery is very depleted, the charging voltage should be in the 13-14 volt range. Your 'sensing' wire going to the alternator (feed back from the battery to determine how it should regulate the voltage) is not communicating with the alternator.... bad connection at the alternator, broken wire, etc.

Running voltage that high (when not required) will shorten the life of your battery significantly.

 

Provide some details on the alternator? It sounds high for a stock type 10SI but could be normal for a performance alternator.



But the alternator has no clue what the battery charge level is, or when the battery voltage should be cranked higher to charge the battery. The alternator is dumb, it just tries to output the voltage the regulator is set for regardless of load or battery state of charge.

 

Not true. All modern alternators can sense the voltage level in the system....one way or the other. A car battery always being charged at 14.5 vdc will not have a long life.

Don't believe it? That would be YOUR problem.

 

Low mileage 79 stock original alternator with new voltage regulator. Battery voltage with volt meter 12.75v static. Running Red wire 14.78v Red field wire 14.69v Brown wire 14.75v

 

Sensing voltage and knowing the battery state of charge are two completely separate things. Of course the alternator has to sense the system voltage or else it couldn't regulate the system voltage.

The alternator in a C3 has NO circuitry that determines how charged the battery is which means it has NO mechanism to lower the voltage as the battery reaches full charge. The regulators that came in a C3 10SI have a stupidly simple circuit. Some resistors, transistors and a zener diode or two are about all that's in there. Just a stupidly simple analog regulator that varies the field current to maintain a constant output voltage. It certainly does not contain anything that regulates voltage based on battery charge.

The sensing wire also doesn't get anywhere close to connecting to the battery on a C3, It splices to the charging wire in the harness just downstream from the alternator.

You are confusing the basic 10SI with the newer alternators that have the onboard electronics actually dictating what the output should be. The electronics monitor the battery load and determine a state of charge and will cut-back the alternator output when possible mostly to save a little fuel.

So, if the alternator is setup to regulate at 14,7V then it is always going to output that voltage. If the battery is in jeopardy then some intervention needs to be done to fix the voltage because the alternator won't just magically lower it's output to save the battery.

Overall, good job with the attitude for someone who doesn't know what they are talking about.

 

Take a jumper and connect from the output stud to the red wire at the connector and see what happens. If the alternator lowers its output then you need to investigate the red wire further. If not, then it's just the way it is. The charging voltage has crept up over the years as battery technology improves.

 

on my 81 vette out put is 14.5

 

I jumped the two red wires no change in output voltage..

 

Scroll to the Power Train section Page 14
Regulator 13.8 to 14.8 volts at 85 degrees.
https://www.gmheritagecenter.com/doc...t-Corvette.pdf

 

Thanks for the info.

 

The voltage found in the main power wire (electrical harness) is used by the alternator to REGULATE its output voltage. The lower the voltage it detects, the higher the output voltage. If that were not the case, alternators wouldn't have REGULATORS built into them.
So, If your battery is fully changed and the alternator is sending 14.5-15.0 volts to it all the time, your battery will boil over and be "toast" in short order.