Hello guys. I’ve noticed the last few days when the weather is very hot and my ac is running. I’m getting the battery light coming on. Any one have any input ? Thx

 

NYC, do you seem to notice the light when the car is at idle at say a light or do you notice it more when at highway speed at say 2000 RPM? If it is at idle, I would say that is somewhat normal as you are pulling a lot of power with a low engine RPM. What you have to remember is that the alternator is rated for 130 amps output, but that occurs once the engine RPMs come up. At idle, you may only be able to output say 70 amps and you can actually overload the alternator for a few moments. That is why your car has a battery. It makes up the difference during those moments. I would do a quick check of your battery cables just to make sure. But I seem to recall that you replaced your cables a few years ago, so, you should be good. But, you never know.

 

It’s at highway speeds Thermo. And I haven’t ever changed out the battery cables.

 

Maybe you have corrosion somewhere on the cable-connection surfaces between alternator and battery, which still allow current-flow to a certain degree, but below the degree, which was design-intend...

 

I’ll take a look at the connections and some pictures tomorrow and let u guys know Whas up. Thx

 

Battery cables can corrode under the plastic insulation skin of the cables, so you don't always see a failing cable.
After 19 years.....probably worth replacing them with some suitable readily available after market ones to rule that common issue out of your scenario.

 

Drove today for over 2 hours. No ac on. No battery light at all

 

NYC, this seems to be pointing me in the direction of the cable either from the alternator and the starter or the starter to battery. With the A/C off, you are pulling far less power from the alternator. This is less current. Therefore, your "high resistance" (we are only talking like 0.5 ohms or less which is not really measurable by a normal multimeter) is not playing a factor in what the alternator can output. now, you want to have fun, try doing the same drive under the same temps, but this time turn on the rear defroster and the passenger seat heater. Maybe even drive with your headlights on. See what the battery light does then.

Just to maybe help make it make more sense, there is the first rule of electricity which is current = voltage / resistance. If you rearrange it, voltage = current x resistance. In this case, the voltage is going to be what is dropped by the high resistance connection. So, lets make a few assumptions: current draw is 80 amps, your resistance in the wire is 0.25 ohms. So, plugging that into the equation, 80 amps x 0.25 ohms is 20 volts. So, to get even 10 volts to the battery, your alternator would have to output 30 volts (10 volts reaching the battery and the 20 volts being dropped by the high resistance). Now, this is probably a bit extreme thinking about it because if you think about power then (power = voltage x current), you are looking at 20V x 80 amps, or 1600 watts. That would have the point of resistance becoming very hot, if not catching surrounding things on fire. This just goes to show how even a very small resistance can become a big deal. This is why I tell people to use an IR camera or IR thermometer to find these spots.

YOu may get lucky and you don't need new cables. It could be that you simply have some corrosion on a connection. Tell me you don't have rust on your car after all these years. Something as simple as taking apart the connection, wire brushing the surfaces back to shiny silver may be all that it takes to fix your issue.

 

Thx guys. Haven’t had a chance to look at the connections yet. But just wanna add that the battery is kinda old. I believe I bought it in January 2021. I’ll check what the date sticker on the battery is also. But I’m pretty sure it’s what I said. Never had a problem starting the car also. Just some more info for you guys. Thx

 

NYCJag2006, the battery will start the car even if it is about to fail. What I noticed as the age of the battery got up there, the car took a few more revolutions to start. With a new battery, you will see the car start pretty much as soon as you turn the key (it makes 1, maybe 2 revolutions than starts). Where, with an older car, you may crank it for say 2 seconds before it will catch. In that time, the motor has gone around 4-5 times. I know that doesn't seem like much, but it is a small thing to watch for to get an idea of how your battery is doing.

 

I’d suggest taking the car to a service enter to have the electrical system check out.

 

Heres what you do remove the battery and the box now look on the transmission you will see the ground connector ground wire attached there to a 10mm bolt remove the bolt and sand the lead and the surface and clean up the bolt .Now look where the fuse box is and look down and you will see a 13mm bolt with the other ground lead is attached to and do the same.problem solved

 

Have an appointment to get the cat checked next Tuesday. I’ll keep u guys updated. Side note. Drove again yesterday for over an hour. No ac on. No battery light on.

 

Drove again today. Ac on. Headlights off. No battery light

 

NYCJAG, from the sounds of things, your problem is not associated (atleast directly) with any one load in the car. The issue is that it is based on a combined load. I had a car that had a similar problem. Now, this happened to be a 1979 Dodge Colt. You turn on the headlights, all is good. Turn off the headlights, turn on the radio, all is good. You turn on the radio and headlights and the whole electrical system inside the car would go bonkers (temp gauges would peg, gas gauge to empty, dash lights would fade out, etc). After much cussing by my dad and myself because we could not figure out the issue, I decided that I was going for broke and I pretty much turned on every electrical item in the car. Much to my surprise, a bright white light appeared in the engine bay right behind the carb. Knowing that there was no light bulb there, I was curious what it was. It turned out to be a ground wire the diameter of a pencil glowing white hot. In short, it had started to corrode and made a high resistance point in the wiring. I tell the story to relate how strange things can happen with cars. In your case, I would be looking at those ground points mentioned above (easy to access things that may fix the car). In your case, it may take a bit more current than my story, but just the A/C, all is good, A/C and the headlights, too much after a period of time. This is where I would say to clean those points mentioned and then do a "stress test" by driving at night with the A/C on, headlights, turn on the rear defroster, maybe a seat warmer and then see what the car does. If you see that the battery light comes on, then you know you need to touch something else. But, if the light doesn't come on, tada, you are fixed.

 

had a similar problem and replaced the alternator, which didnt cure the problem.

Take the car for a half hour to one hour ride if you can. Now pop the hood and with a temp gauge check the temp of both the positive and negative clamp at the battery. If one is significantly hotter than the other at least replace that one cable. On mine. the pos cable was 134 degrees and the neg was over 200 degrees, so yes you will know the bad one. on mine it was the neg so i added a few more negs from the engine to the chassis and the battery to the chassis.

Further insult to injury, i think the replacement alternator is now acting up

 

I had a similar issue with battery light occasionally coming on, but the alternator voltage being fine and the battery testing ok. A lot of folks say it's usually the positive battery cable, so as a cheap solution I ran a generic 3ft 6ga cable with 5/16" lugs from the alternator to the positive terminal on the battery to supplement the original cable. I haven't had the battery light since, so this ended up being an easy fix for me. The alternator bolt was a little tricky to get to, I think removed the air box and used a couple of long extensions.

I also got a cheap USB charger that plugs into the cigarette lighter that shows battery voltage, so if the battery light ever did come on again I'll be able to just flip open the ashtray and to confirm that the alternator is still functioning as intended.

 

Battery light has been on intermittently since I bought my 2005 six months ago. Our guy just changed out the positive battery cable - he thinks this will address it!