Rocky05 wrote:
thermorex wrote:
Rocky05 wrote:
[quote="papaindigo"]Most likely issue is alternator and/or alternator decoupler pulley. Check the latter at idle by looking down (may need grab a flashlight and remove plastic engine cover) the serp belt at the serp belt tensioner; if it's barely twitching decoupler is ok but if it's bouncing decoupler is bad and will eventually destroy tensioner. Otherwise have a good auto electric shop (best not start at Auto Zone as they have an incentive to "not" find a problem with their alternator) check alternator output which can be done on the vehicle.
Assuming you are buying "good" batteries (e.g. 800+CCA and a warranty period of 4+yrs) you should not be replacing them every 18 months. If you are getting 2yr warranty batteries then every 18 months is not unreasonable.
/side note. Has anyone ever experienced an alternator coupler fail in the open/ not charging position? Inquiring minds would like to know....
The decoupler name is a bit misleading. What happens is that the computer cuts the plus (the "energizer" wire for the alternator - the only thin wire that plugs on the top of the alternator - diesels have only one wire, gasolines have usually 2, the other one goes to the ignition coil) when charging is not needed, so alternator just spins without producing any electricity. When computer "senses" that charging is required, it powers back the energizer wire, which just creates a magnetic field in the alternator so the rotation of the rotor will produce electricity which will start charging the battery. When this happens, there will be a sudden mechanical resistance caused by turning the alternator rotor in an electromagnetic field -generated with the current from the energizer wire (which is not present when the energizer wire is not powered up), this is where the decoupler (which is purely mechanical - a spring and/or some clutches that is supposed to make that "shock" smoother) comes in place. So the decoupler, at least in theory, can't fail in "no charge" position since the decoupler does not turn on/off the charging, the energizer wire does that. Older charging systems had earth magnets which didn't need any energizer, they were always on, and turning the rotor in the stator that had earth, permanent magnets always produced electricity, you can't turn that off unless you stop turning the rotor.
As a side note, I am not sure how exactly the decoupler in the Crd is made, I think it's a combination of clutches (thus the red dust when the coupler goes bad) and some springs, but when it fails you won't miss it, sounds so bad that you'll definitely notice.
Oh, btw, don't mean to patronize you, just thought that a bit of detail won't hurt.
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Theromrex! LOL, I just saw this post! You and Papa give great explanations. BTW, I am an industrial electrician. I deal with many people that have no idea how electricity works. It is easier for me to dumb everything down, and give the simplest explanation possible. I just don't have that patience to write a dissertation on how an alternating current is converted into DC. Much less excitors or bridge rectifiers...
I just try to stick to the simplest determination of a problem and fix first. I usually work on multi-megawatt gensets, so please don't take my question of the coupler failing completely as an uninformed inquiry. The only diesel that I've been responsible for that is smaller than my CRD was a little hand crank start one cylinder diesel air compressor
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Great, that's why I added "don't mean to patronize you", my idea is that if this is "old news" for you, it could help somebody else. I'm not an electrician or a mechanic, I write software, but I'm curious enough about some things to determine myself digging for more info. Plus, electricity-wise, one of my best friends is an electrician, he answers all my questions and explains me lots of things.
The question is legit though, as to what makes the decoupler fail, and I'm still not 100% sure, but I'd say I'm 99% sure the cause would be clutch wear (I can't explain otherwise the all-known red dust that we notice when the decoupler goes bad) that leads to bearing wear. Maybe also that spring that's supposed to absorb the shock can also break... I should probably cut an old one to find out and post some pics...