Charging problem

Hi,

This is a voltage issue but it is odd because it appears you have replaced the main culprits.

I am slightly concerned about the fact that you see 12 volts at times because an alternator should not allow it to drop below 13.5 - 14.

The purpose of the 12 volt battery is to just smooth out the voltage spikes that you get from the alternator while you are accelerating and decelerating.

Even though I am a little concerned about that, I think your real issue is most likely the battery cables themselves at this point. Have you ever tested the resistance of the cables or performed a voltage drop test?

I attached the procedure so you can try this and ensure your cables are able to deliver the voltage that the battery and alternator are producing.

https://www.2carpros.com/articles/everything-goes-dead-when-engine-is-cranked

Sounds good. Hopefully we get some results so we can at least move on or get it repaired. Thanks.

As a side note, Chrysler has a real long history of developing innovations that actually benefit the car owner, as opposed to GM and a few others that develop innovations that make them a lot of money. One of Chrysler's innovations was the "AC generator" first used in their 1960 models, and they copyrighted the term "alternator". GM didn't copy it until 1964. Chrysler also developed the electronic voltage regulator for 1970 models. GM copied it for 1972 models, but they put it inside their generator, as do most import manufacturers. This insures that when one part fails, you must buy both, meaning more than you need, unless you know how to diagnose the system and replace just what's defective. GM did the same thing with their "High-Energy Ignition, (HEI) system. It was a nice distributor, but at the time, no one knew how to diagnose it, so GM intended for it to be a drop-in unit replacement that needed no diagnosis. You bought every part in the ignition system, not just the one part that failed.

Charging a battery is a chemical reaction, and those take place faster as temperature goes up. To address that, Chrysler's first electronic voltage regulators had temperature compensation built in. That raised the target charging voltage a little in cold weather to help the battery charge. That is still done with the regulator in the Engine Computer, however, now the regulator has access to everything the computer knows. For example, the regulator can totally stop the alternator from working at wide-open-throttle when you might really need that five to ten horsepower used by the alternator. It can increase the alternator's output current when you turn on the rear defroster, rather than waiting for battery and system voltage to drop over time. It can anticipate the cycling on of the AC compressor and bump up charging voltage just in time to prevent the noticeable flicker of the lights caused by that sudden drain. If a load on the engine is causing coolant temperature to rise too high, it can cut back on the alternator to reduce the load on the engine.

Other manufacturers, mostly of imports, have tried doing the same thing, but when they hide the regulator inside their generators, they need additional wires running between it and the Engine Computer to share that data. Those extra circuits cause as much trouble as they solve.

Heat is always the deadly enemy of electronics, so the last place you'd want to stick a regulator, for reliability, is inside the generator where it sits right behind the radiator. In fact, most import failures are due to failed regulators, but since they're so involved to replace, you end up buying the entire generator Failure of Chrysler regulators has always been been very low. That doesn't mean they don't ever fail, but it is usually the last thing on the list of suspects. With the regulator inside the computer, about half of the charging system problems are related to the one wire that runs between the alternator and the computer, and the other half are for worn brushes inside the alternator. That doesn't leave much percentage for regulator failures. Guess I'll have to modify my numbers a little!

If you know about PLCs, you know much more than the average person. That will make this easier to explain.

The alternator develops three-phase output, and once rectified, the pulses of output voltage are pretty smooth, but it's the battery that really smooths out that "ripple" voltage. In my sad drawing, the ripple voltage is 0.5 volt, the difference between the 14.0 and 14.5 volts. As the battery ages, the lead flakes off the plates, and the ability to smooth that ripple voltage goes away, even though that battery can still crank the engine just fine. Now the question is what voltage is the regulator going to see and respond to? Suppose the target charging voltage is 14.4 volts. If the regulator sees the 14.0 volts on its sensing wire, it's going to try to bump up alternator output to get to 14.4 volts, but in so doing, at times the 14.5 volts might go a little higher before the regulator detects that and corrects for it. You'll see that as the head light brightness flickering. The same thing happens when people disconnect a battery cable thinking that's a way to tell if the alternator is working! (Don't ever do that).

This has been a real big problem with GM vehicles after they redesigned their generators for the '87 model year. They use the same common switching circuit that turns field current on and off about 400 times per second, but for some reason their generators develop huge harmful voltage spikes that can damage the internal diodes and regulator, and interfere with computer sensor signals. They even use three zener diodes of the six to try to short out those spikes. Once again it's the battery that dampens and absorbs those spikes, and once again, they lose their ability to do that as they age. It is real common for people to go through four to six replacement generators in the life of the vehicle. To reduce that number of repeat failures, always replace the battery at the same time, unless it is less than about two years old. The old battery will work fine in an '86 or older model.

I wasn't clear on the tests you did when you disconnected the battery cables. Did you have just one off at a time? If so, I suspect your confusion came from the unexpected voltage when the ignition switch was off. In fact, before the mid '90s there was still the "IOD", (ignition off-draw) circuit that maintained the memories in some of the computers. That was allowed to be up to 35 milliamps for most car models. By the mid to late '90s, a lot of cars have an Engine Computer that needs up to 20 minutes to go to "sleep mode" after the ignition switch is turned off. During that 20 minutes they can draw up to three amps. This makes the old conventional testing method for a battery drain obsolete. I can describe the procedure, if you need it, on how to do the testing as before, with an amp meter in series with one battery cable, but you need to short the meter with a jumper wire for that 20 minutes and any time you change ranges on the meter. Any momentary break in the circuit wakes the computer up again and restarts the 20-minute timer.

It appears you found part of the problem with the old battery, but there is still something going on with the cables causing an intermittent problem. The goal now is to get it to act up, then be careful to not disturb anything that could cause the electrical system to come back to life. We need to get under the hood with the voltmeter with the problem occurring so there is something to diagnose. A test light works better for this type of problem because it requires current flow through it to work. All you need is a tiny carbon track for the voltmeter to pick that up and incorrectly say there's a good circuit there.

When the problem is occurring, turn on the head lights so current is trying to flow. That will make the following procedure show up the bad connection more effectively. Start with the negative meter probe, or test light's ground clip, right on the battery's negative post, and the other probe on the positive post. You'll find 12.6 volts if the battery is good and fully-charged. Now move the negative probe from the post to that cable clamp. You should find the same voltage. Move the positive probe from that post to that cable clamp, and expect to see the same voltage. If the voltage drops when you move a probe from one point to the next, that is the point of the bad connection.

Move the negative probe to a paint-free point on the body sheet metal or exposed bolt head. This type of problem is caused by a loose or rusted connection of the smaller negative battery wire at the body perhaps two or three percent of the time.

Now move the positive probe by following the smaller battery positive wire to the under-hood fuse box, and put the probe on the wire's terminal where you're likely to still find 12.6 volts. Finally, move that probe to the stud that terminal is bolted to. This is where you're going to drop to near 0 volts most of the time. Clean that terminal, then be sure that nut is tight. This one connection has been the cause of most intermittent dead electrical systems on every brand of car.

The large positive battery cable is only for the starter motor. It's the smaller one that puts the battery in the circuit to smooth ripple voltage, so a poor connection there is like removing the battery while the engine is running. The result then would be the flickering lights. The regulator is seeing the changing ripple voltage and is trying to keep up with it. By the time is responds appropriately, the voltage has already changed again. The regulator will have a nervous breakdown trying to maintain system voltage.

Remember the type of problem you're looking for acts up because of the relatively high current flow through a less-than-perfect connection. If you plan on doing tests with an ohm meter, those never provide enough current to make the bad connection show. It's like standing on a garden hose and crushing it 99 percent closed. With the nozzle closed, you'll still have full pressure at the end, but there's no way you can get any water flow through it when the nozzle is opened. Opening the nozzle, or turning on the circuit, causes something to try to flow, and that is when the effects of the obstruction show up.

To say that a different way, the resistance is way too small to measure, but we can measure the results of that resistance, in this case, the drop in voltage.

Keep us updated on your progress.