Unknown reason why battery is dead

[raxley]

My truck didn't start yesterday, the batteries were showing about 9-1/2 volts. I charged it overnight, and today took it to O'Reilly's and they said my alternator was good (it's only about 2 years old and I replaced THAT dead alternator over the same concern, it was just dead one day.)
My batteries are only a couple of years old too, and they are decent quality brand both purchased at same time. My cables are pretty good (and have clean terminals)
Today, when starting it (after a charge) the alternator gauge needle took a while before it was at 12 volts, then it shot up and I knew it was charging. It acted differently than I remembered.
I'm wondering if my problem is really with the REGULATOR? Isn't the regulator part of the 'computer' (ECM) for the diesel engine?
In any case it seems to be working fine now.
Larry B has a alternator regulator that is internal, I guess it installs inside ONLY Denso alternators, it's $ 75 (https://fostertruck.com/collections...onversion-kit-for-dodge-cummins-89-2002-denso).
If I need to repair the alternator, I would really like to upgrade. The amps of my present alternator is around 135-150 and the alternator I was looking at was 240 amps, and at idle it's 170 amps. But if it's partially or fully the regulators 'fault' then I will still have the problem with a bigger (non internally regulated) alternator.
Another thing I was thinking of, is that with the hot weather lately, I've been running the AC all the time. I'm wondering if the fan and AC is taking more from my batteries than my alternator can keep up with.

 

[tomblue01]

Did OReilly's test both the batteries and the alternator, or just the alternator? Did they do a load test on the batteries, individually? 9.5V means battery death to me.
Is a "couple" two years, or 2-3, or 2-4? Consider a parasitic drain test if you feel the batteries died too early.
I see you're focused on the alternator, but I'd like to know more about the condition of your batteries. Would you electrically separate them; wait 30+ min [more is better!]; measure voltage for both of them?

 

[raxley]

Did OReilly's test both the batteries and the alternator, or just the alternator? Did they do a load test on the batteries, individually? 9.5V means battery death to me.
Is a "couple" two years, or 2-3, or 2-4? Consider a parasitic drain test if you feel the batteries died too early.
I see you're focused on the alternator, but I'd like to know more about the condition of your batteries. Would you electrically separate them; wait 30+ min [more is better!]; measure voltage for both of them?

I will do that later today after work.

 

[GAmes]

If all your drives are short range it could be the batteries are never fully charged. The fan doesn't pull any more power just because the AC is on. A 12 valve doesn't have an ECM. The voltage regulator is in the PCM. If it fails it doesn't come back. Are you sure you don't have excessive key off draw? I went to start mine about a year ago and the batteries were dead after the truck had been parked about 3 days. Using the disconnect one thing at a time method the culprit was my Kenwood radio.

 

[raxley]

Sorry for not getting back earlier to this conversation. I haven't had any problems with charging system except for that one time. I don't know what was different from any other day. I drive about an hour to and from work (2 hrs. a day) I run my ac a lot lately. I took apart all my terminals, cables and cleaned them and sprayed them with battery terminal protection (although haven't checked starter connection where big + cable attaches to starter, however about a year ago, I rebuilt the starter (foster truck parts, just about everything was replaced) and didn't notice anything bad. When I had done the terminal cleaning, I checked the battery voltage and it was 12.7 volts for both of them. I got the batteries about 2,3, or 4 years (max I think) ago. Usually I don't turn off radio, I listen to Spotify-I just pause the podcast on Spotify and go in the house for the day, so radio stays lighted every night, but I've never had problem before. The alternator is from Napa, it was a rebuild-I think that was 2-3 years ago.
I bought one of those cigarette lighter things for USB sockets and it has a digital voltage meter on it. When truck is running, it's about 13.2 volts I believe. Since I put it on truck a couple of days ago, it appears normal.
I only have one headlight right now, and ordered the sport light conversion and another wiring harness from Auto Electric Supply it was $275 and I'll use that with regular brighter halogens recommended by Stern Lighting. But that's not done yet.
I'm considering a bigger alternator, along with a bigger cables to and from alternator and batteries, ceautoelectricsupply.com had a good pre and post installation of same (although I will probably just buy wire to do it, not a kit-seems high in price)
Is 13.2 volts for my alternator at idle kind of low? Don't a lot of charging systems run around high 13 volts?
A google search says most 12V systems run around 13.5 to 14.5 volts, is this probably the problem? Can you put in a regulator that's independent of the ECM/PCM?

 

[GAmes]

You could put in an external regulator, but that would defeat the battery temp sensor that tells the PCM what voltage is needed. It is normal for voltage to show lower in the summer, a warm battery charges easier. Which reminds me. Have you checked the battery temp sensor? Specs are in the FSM.

 

[raxley]

You could put in an external regulator, but that would defeat the battery temp sensor that tells the PCM what voltage is needed. It is normal for voltage to show lower in the summer, a warm battery charges easier. Which reminds me. Have you checked the battery temp sensor? Specs are in the FSM.

So with the PCM, it enables variable voltage output from the alternator? I thought the voltage was the same, it was either on or off. I've looked up the external regulator kits (seems like a lot of Dodge conversion kits, this must happen a lot) and you can set the regulator voltage. Would you always want (for instance) 14.5V or some conditions it would be helpful for a different voltage?
How does the regulator know when to turn off voltage, or does it just go to waste when battery is fully charged?

 

[GAmes]

No, voltage is dependent on demand, actually amp draw, but you don't have an amp gauge. If the battery is fully charged and the draw is from a low amp appliance, like the radio, the voltage regulator acts accordingly. Nothing goes to "waste" because it isn't produced. Maybe this will help you. https://science.howstuffworks.com/environmental/energy/question501.htm

 

[DUtt]

bad diode in alternator, causing voltage leak down

 

[Bill Lins]

You could put in an external regulator, but that would defeat the battery temp sensor that tells the PCM what voltage is needed.

I'm running the regulator that mounts inside the rear cover of the alternator &, other than some static through the radio, I've had no problem at all- it works great.

 

[Road Dog]

So with the PCM, it enables variable voltage output from the alternator? I thought the voltage was the same, it was either on or off. I've looked up the external regulator kits (seems like a lot of Dodge conversion kits, this must happen a lot) and you can set the regulator voltage. Would you always want (for instance) 14.5V or some conditions it would be helpful for a different voltage?
How does the regulator know when to turn off voltage, or does it just go to waste when battery is fully charged?

The output from an alternator is 3-phase AC. The rectifier (diodes) convert this into DC and the regulator switches on and off to keep the voltage below [typically] 13.2 volts.
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There is a limit to how fast a battery can charge -- higher when it's near empty and much slower when it's nearly fully charged. Charge too fast and the battery heats up and the water boils off. The temperature sensor under the battery indicates when the battery is nearly charged and the PCM adjusts the voltage down to maintain the charge. It's tricky because all the vehicle electronics are drawing power too. Most regulators pick a voltage that trickle charges the battery so it will take a long time to bring the battery back to 100% if you left the lights on.

The regulator switches on and off thousands of times a second to keep the average voltage at 13.2V or whatever it's set to. If the voltage is too high the water will boil (really evaporate) away.