I have a new electrical problem, I have two known good 120 amp alternators for my '85 both of them are reading high charging voltage. They run around 14.6 on the dash and 14.9 on a multimeter hooked to the alternator. I ran a good ground from the battery to the top mounting bolt and that made no difference, I'm not even sure if it is supposed to but I have learned a long time ago that grounds is the first thing to be checked on a C4. Could it be the battery? It starts right up every time and is showing 11.9 volts with just the key turned on. Any ideas?

 

Thank you, I never knew the temperature fact, I guess I don't get out enough, hahaha. I went into the search and found the same thing you told me basically. I am relieved because as I have said MANY times here, I hate electrical problems.

 

Yes it is temp dependent. How does it look after you get it hot.

 

To be honest, I didn't even look at it. I'll make a special effort to do that. Now I know that sounds lame but I had just got home from seeing a friend in the hospital and my thoughts were not on the alternator.

 

I am not sure "when" Temperature compensation while charging was adopted by GM and installed in the Corvettes. It is certainly the best way to help charge a flooded lead acid battery.Battery Temperature Compensation - Ample Power


www.amplepower.com/primer/temp/index.html
Be that as it may, Ample Power introduced the first alternator regulator that was temperature compensating in early 1987. The sensors were not very installation ...

 

I just spoke with my alternator rebuilding friend and he said that regulators used on automobile alternators did not offer Temperature Compensation until (he believes) the late 1980's probably more likely the early 1990's. This is a guy who has spent 40 years building alternators. The first mechanical point type regulator was introduced in 1963 but that did not have any sort of temperature compensation he told me. It was the simply the first "point type" regulator for an alternator. Up to that time cars were still using generators which produced 12 Vdc output. The newer style Pointless electronic regulator was put into service with GM in all their vehicles in 1973. But at that time they did not have temperature Compensation built into the regulators.

When asked about when "Temperature compensation" appeared he said it was probably in the early 1990's for GM. That would make sense as the technology was developed in 1987 and General Motors frequently lags along for a while before adopting new technology.

I guess I will ask for evidence that proves otherwise.

 

I found this bit of info here:

In 1933 I came upon the above scene as a student engineer assigned to work with Max Whiting in Industrial Engineering. We were having problems with holding constant voltage and with temperature compensation. My US patent 2014880, an improvement on the Teare-Whiting patent helped. The temperature compensation problem was solved by using a material having a negative temperature coefficient of electrical resistance. However our big problem was cost. Contacts with the automobile manufacturers had already indicated that our costs were too high to interest them.

 

Wow, I guess I really stirred the pot but it was not intentional. I am just sitting here quiet waiting to see how this turns out.

 

https://www.lifewire.com/high-amp-al...-damage-534775

 

HA, happens all the time here.

In a nutshell: A device needs amperage to operate, volts push the amps to the device. The higher the amp load on the system the lower the charging voltage will read. If AC, cooling fans, headlights are on the voltage will probably read in the mid to low 13's.

14.9 V @ the battery is a tad high suggest having the battery load tested it should hold 10.8 volts @ a 200 amp load for 15 seconds. If it fails the load test it is probably sulfating you need a new one.

To test for a sulfating battery: After the load test use a battery charger & charge @ 30 amps for 10 minutes & monitor the charging voltage. If the voltage exceeds 16V while charging the battery is sulfating it is headed south & will fail @ some point without warning = you need a new one.

Good luck

 

"Ihatebarfingdogs" The battery's physical temperature and it's internal resistance. Sometimes a good surface charge will do that as well.

When I am working with batteries I use a Electronic load that pulls the current out at a constant rate and measures how much power is in the battery. I only discharge them to 70% of their rated capacity and recharge them 110% each cycle. This allows me to see just how many amp hours the battery really has in it. I do this about five times to "Form" the battery and prepare it for a long hard life. I have tested batteries for so long that I know who tells the truth about their products and who does not. I even test the newer lithium Ion batteries and have had issues with people that over-state the capacity of their products. I also do this "Forming' on the batteries I use in my cars, boat and aircraft if they use a FLA battery as they will last longer. Some manufacturers "Form" their batteries in the factory, the cheaper ones do not as it cost time and money.

"Midnight 85" It is not your fault, you had a valid question. I would suggest you remove the battery clean it up and top off the electrolyte and then charge it out of the car (Or disconnected from the car, both + and - wires) until the battery stays at 14.4 or above after sitting for an hour. I suspect you have a "tired" battery that wants to be replaced. If both of your high amp alternators were showing a high charge I would go straight to the battery and look for the problem. I have a aftermarket single wire hi-amperage alternator with a built in regulator and it does a great job keeping my battery happy but I have never seen it go over 14.6 while charging. I monitor the battery voltage using a calibrated meter. When you installed your 120 amp alternators did you up-size the output wire? On my C3 I took a #4 flexible wire and ran it from the output of the alternator to my starter solenoid to allow it to have good solid access to my battery's Positive side. At least on a C4 the battery is closer to the alternator than on my 1968 C3 so the wiring doesn't have to be gigantic.

"Churchkey", you are offering good advice! When I test a battery starting a car I use a good multimeter like a Fluke which has a "Min-Max" function on it. You hook it on the battery and set it to record the high and low voltage of the battery and then start the car. If it drops below 10 volts I suggest a recharge first and then perform the test again, this time if it drops below 10 Vdc I replace the battery.

 

Thanks churchkey, I'll check this out tomorrow.

 

ctmcloskey, thank you, I will check this tomorrow. Battery is only 2 years old but that means nothing. Also, the 120 amp alt was factory on my car.