You're doing the drain test the wrong way. That test light trick worked years ago before the insane engineers put all the computers on the car, but no more. Today, with all the memory circuits in the multiple computers, the industry standard is a maximum of 35 milliamps. Chrysler says at that rate, a good, fully-charged battery will still be able to crank an engine fast enough to start after sitting for three weeks. Test lights need a lot more current than that to glow, so you could have an excessive current drain and never see it in the test light.
Since the mid '90s, the Engine Computer needs up to 20 minutes to go to "sleep" mode. Until then, it can draw up to three amps. Most digital volt / ohm / amp meters have an internal 2-amp fuse that will blow if it is on the 2-amp range. Also, if you start out on the ten-amp range, that usually requires moving the positive probe to a special jack. You can watch for 20 minutes until current drops to the normal "ignition off draw", (IOD) value which must be less than 35 milliamps, (.035A). The first problem is you need to switch to a lower range for more accuracy. That means unplugging the red lead and moving it to the common jack. You just opened the circuit, and that restarts the 20-minute counter. The computer wakes up and tries to draw three amps again. That blows the internal fuse.
Even if you did get past that problem and get a usable reading on the 2-amp range, you'll still need to switch to the 200ma range to get the needed accuracy. All volt - ohm meters use "break-before-make" switches which means as you turn the knob, it breaks the connection between the jack and the 2-amp circuitry, then it makes the connection to the 200ma circuitry. That tiny gap is enough to wake up the computer again.
What you have to do is remove the negative cable, like you did, then reconnect it with a small jumper wire. Now you can also connect the amp meter. It will read 0.00 amps because it is being bypassed by the jumper wire. After 20 minutes when the computer has gone to sleep, you can disconnect the jumper wire, then read the current on the meter. If you find you need to switch to a lower range, reconnect the jumper wire first, switch the meter, remove the jumper, then take the reading. As long as something is always connected between the battery's post and the cable clamp, once the computer has gone to sleep. It will stay that way.
You also have to fashion a way to open a door or window, if necessary, that doesn't tell the Body Computer you're there. A single interior light will draw half an amp. Most cars have multiple lights, so that can also blow the meter's fuse.
As a point of great value, removing the alternator for testing is never an acceptable way to do it. It takes over five horsepower to run a wimpy 55-amp alternator wide-open. At most, those in-store test benches have a one horsepower motor. All generators need three things to work; a wire, (coil of wire), a magnet, (we use an electromagnet), and most importantly, movement between them. Because of that needed movement, all generators are very inefficient at low speeds. All professional charging system testers require engine speed to be increased to 2,000 rpm for a few seconds for part of the test. Bench testers can't do that.
Since a bench tester can't run the alternator under full load, it can't accurately test for a failed diode. With one bad diode of the six, the most you'll be able to get for output current is exactly one-third of its rated current. The smallest of the two alternators for your car is a 140-amp unit. With a failed diode, you'll only be able to get around 45 amps during the full-load output current test. That is not enough to run the entire electrical system under all conditions. The battery will have to make up the difference until it slowly runs down over days or weeks. With such a large alternator, 45 amps could be enough to keep the engine cranking and the lights from dimming, but the battery may never become fully-charged except during long highway trips.
When a diode fails, you lose one of the three output phases, and that results in very high" ripple" voltage. Bench testers don't check for ripple voltage but all professional load testers do. A few list them with a specific voltage and those usually can make printouts. The most popular testers just show the ripple voltage from "low" to "high" on a relative bar chart. It's usually pretty obvious by looking at that chart when it's too high.
The last thing professional load testers measure is charging voltage. That is the one test you can do yourself, like you did, with a simple digital voltmeter. What you listed is perfect. The acceptable range is 13.75 to 14.75 volts. It's okay if it pops up a little higher once in a while. Since Chrysler developed the first electronic voltage regulator for 1970 models, they have all had temperature compensation built in. Charging a battery is a chemical reaction, and that occurs less efficiently at lower temperatures. Chrysler's voltage regulators increase charging voltage a few tenths of a volt in cold weather to help that charging process take place.
From what you've described, it sounds like you don't have a problem. I've been an electrical specialist since the early '70s, but I have never checked the battery voltage on any of my cars at the times you described, so I don't know what "normal" is. I do know that a computer drawing three amps for 20 minutes is comparable to leaving one head lamp bulb on for 15 minutes. That will remove the "surface charge" from the battery and make your reading a little lower. Your car is new enough that other things are taking place after you remove the ignition key. On my 2014 Ram truck, there's moving things taking place in the dash, sometimes ten or fifteen minutes after I stop the engine. What's important is you said the engine cranks fine the next morning. If you hadn't had the previous condition, you wouldn't even be working in this area or think there was a problem.
Tuesday, March 26th, 2019 AT 7:06 PM
