Is the alternator going bad?

[Deezul1]

Its doing wierd stuff. A while back whike towing the RV the volt meter went up to about 15. 5 or 16 volts so I turned on all the electrical stuff I could to bring it back down to 14 and after a while I shut all that stuff off and the gauge was normal again. This went on and off like that for about 2 hours while running down the highway and then hasnt done it since. Now when I start the first time in the morning the batteries sound weak and the voltage is about 10 volts after start up and stays that way for about 30-45 seconds and then jumps up to normal voltage. The grid heater cycle is very different than this low voltage and slow to start charging problem. It only does this on the first start of the day. TIA

John

 

[Whitmore]

John, when you get time get the truck running and then disconnect the positive from both of your batteries and if the alternator is doing its job then it will support all functions.

I dont know about our alternators for sure but most are equipted with 2 sets of diaods in them and it is possibl e to loose half of your charging power which will give a slow death to your batteries ??? Kevin

 

[Uncle Joe]

NO NO NO..... DO NOT DISCONECT THE + WITH VEHECLE RUNNING!!!!!!

that trick was good in 1978 when there were no computers to fry rith the voltage spike,never happened to me but i whould hate to find out how much $$ the ecm is... ..... joe

 

[illflem]

Take your rig to an auto parts that will give your batteries a free load test. When battery cells short you can get some strange things happening. No big deal to disconnect the batteries with the engine running on a 12 valve but it will tell you little.

 

[BK]

Yes have your batteries checked... but you've seen this voltage come and go in what sounds like a short time. Something intermitant?



Your alternator should not go to 16Vdc.

If it does in a steady and long term manor, it is the fault of the regulator.

If the alternator does produce that high of a voltage it will fry your batteries due to over charging.



Since you've seen it come and go and not a steady output of 16Vdc. Check all connection, including cleaning your battery terminals. ( I'm not sure how the Ram's volt meter will act if the batteries have a bad connection, in theory if the meter had the bandwidth, it can read the peak voltage of the alternator when the output of the voltmeter is not filtered or "smoothed" to an RMS level by the batteries).

Check grounds. If you have to, remove ground screws and clean the washers, lugs and points of contact.



If you were to loose some diodes, yes your charging would be weak, but all that means is that if there is enough head room in the other windings, and you finally see your voltmeter back up to 14Vdc (providing it's accurate), it will just take longer to charge. . that is the alternator can supply enough current to heat up the grids. . if it cant your voltmeter wont be up at 14vdc.



If you have a DVM, just check your gauge.

When the gauge went to 16, did any other gauge read strange? Did the headlights or interior lights get brighter?



Bob

 

[Deezul1]

The 16 volt thing only happened the one session and has not happened again. The charging system seems to be fine all day long and works as it is supposed to, it just seems lazy on the first start of the day and wont give a charge indication for 30 seconds or so and in fact has a very low volt reading right after starting and then starts to charge normally. Its not the cycling low voltage of the grid heater, just stays at 10 volts until the alternater starts charging then you see the grid heaters cycle.

 

[Lsfarm]

Alternator?

Get your batteries load tested. If they are the original ones or over 4 years old, they are suspect.



But DON'T disconnect both batteries while the engine is running!! You will be playing 'Russian Roulette' with all the onboard computers!!



The voltage regulators 'look' for a voltage from the battery to tell if the battery is charged, if the voltage is low, the alternator will increase voltage to charge the battery. When you disconnect the batteries, the regulator senses zero voltage, and the alternator gives it all it can, which can be a significant voltage spike.



BK mentions clean your battery terminals, if there is resistance across dirty, corroded terminals, the regulator again senses low voltage, and will try to charge at a higher voltage.



Maybe the voltage regulators in our trucks are better designed to protect the system from voltage spikes than I am describing, but I wouldn't gamble on it.



Hope this helps, Greg L

 

[BK]

So the 16V happened just that one season. .

And you have sluggish starting. .



Batteries are most defenitly not happy. or possibly their connections... I'll type out my thoughts here to a conclusion. .



The slow charging or softness of your alternator bugs me too, since it's only at 10v for longer than your used to.



It does sound as suggested above that some of the windings maynot be contributing to the charging current, causing a lower than required output current.



The regulator controlls the exiting current of the alternator. It does it's best to keep 14Vdc at the battiers. If it see's that voltage lower than 14Vdc it will increase the exitation current and cause a greater current output to try and drag the batteries up. once the battiers start coming up in terminal voltage, the exitation current is reduced proportionatly. If the current output is low because one of the windings or it's diodes arent happy you will not realize the original current output from the alternator.



So besides age. . I'm guess that 16Vdc didnt do your batteries any justice and it sounds as if the 16Vdc possibly was the cough of a winding or diodes taking a dump in the alternator.



This though, assumes that all connections are well. If any have high resistance, your cranking will be slughish.



Since I'm not sure how the Rams voltage requlator would act with bad connections at the battery, I'm not sure... but basic theory would say that if the connections to the battery terminals had high resistance, that would cause the voltmeter to come up to 14Vdc rather quick, since the voltmeter not ---directly connected-- to the battery terminals. The voltmeter is connected the wiring that comes off of the battery lug connected to the battery terminal.





So it seems we are back to bad batteries and a not so happy alternator.



Oh my , thats a GM trait... I remember working on 80 GMs... when ever an alternator went it ate the batteries and I've seen a GM loss a battery and eat the alternator. It was a must to replace them in sets.





BTW, speaking of good battery health... FYI..... all the crude on top of your battery is conductive and is discharging your battery as the truck sits there and that crude helps cause the terminals to corrode quicker and worse.

 

[fest3er]

The PCM contains the voltage regulator (VR); DC must be quite sure it'll last to put it there.



Any number of things could cause a large voltage increase or drop:

- faulty ignition lowering voltage to the PCM

- faulty alternator fuse (140A) causing low voltage reaching the

system

- loose/corroded connections on the alternator

- faulty/loose/flakey battery temp sensor causing PCM to think

the outside temp is lower than it is

- bad PCM connections

- shorted wiring



I would suggest checking the easy things first: the alternator connections. If the + field connector is loose, low charging voltage could result. If the - field connector or the ground connector is loose, higher voltage could result. If the B+ is loose, it would require more voltage to get the desired current though to the battery. If the ground between the alternator and the rest of the truck is faulty, higher-than-expected voltages could result.



If the battery temp sensor is loose or corroded, the PCM could think it's real cold outside and charge the batteries at a higher voltage. (Presumably this is to rapid-charge them after some amount of intake heater grid usage when it's frigid out. )



A voltmeter would be very useful in tracing the problem. The voltage between two ground points or two B+ points should be quite close to zero. If you see a significant voltage, you have a bad connection that needs to be repaired.



Good luck!

Fest3er

 

[Deezul1]

Thanks guys, this gives me some things to check out and hopefully find something simple. The Batteries are 2 years old and load checked ok so hopefully its something loose. I cleaned terminals about 2 months ago but will do it again.

 

[BK]

Another story of a surprise failure that might help...



one thing else to look for that I found on a Ford explorer..... the factory battery wire to lug connection was faulty.



The lug is molded around that bare wire. . I guess the wire was never cleaned correctly and the molded lead never took well to the wire. After a few years the corrosion set in... and they kept replacing alternators and regulators and starters and batteries...

Went around the horn a few times for over a year...



The wire-battery lug assembly looked good from the outside, the voltage drop across it was very very high when I measured it during cranking the engine.



Good luck,,let us know what your find...



Bob

 

[PLaFrombois]

I've had the same problem recently with the battery gauge down to "10" or so after start-up, then it will return to normal after driving awile. I noticed this since my pre-heaters are being used for a longer period because of the cold weather. I was concerned about having a bad alternator or batteries. I went in for a recall and had 5 star check the problem. Their reply "this is a normal condition at lower RPMS when the cylinder preheaters turn on thay will fluctuate the gauge reading-No problem at this time. " Are they correct in their findings?

Thanks

Paul

 

[BK]

At lower rpm's your alterntator does not produce the current it's rated at. I know all my "parts" are just fine and I did see my voltmeter take dives at idle when the engine isnt warm.



Even if I'm not watching the voltmeter, I can see it in the headlights.

 

[Deezul1]

Thanks to all who replied I checked everything out and came to the same conclusion as posted by PLaFrombois. The 10 volt reading is due to grid heaters warming up and the slow start on the charging cycle is also from the heaters and thats why it was only on the first start in the morning. So much to learn on Diesels thats different from gassers. The high voltage reading has never happened again so I guess I was looking for trouble where there wasnt any.

Thanks Everybody for the help

John