Do I need a new alternator?

[markelectric]

I bought a newer ( 99 vs 95 ) suburban. Finally got to test drive it last night and noticed at an idle the headlights looked visibaly darker. At that time the voltmeter was near the red on the low side. When moving with the rpms up a bit the voltmeter would show 14 volts and the headlights were much whiter/brighter. I thought the alternator should have been more able to keep up at the lower rpms, especially since there were no other major power suckers on at that time. If this was 3 phase I would be in my zone but sometimes these automotive electrical things dont make too much sense. This burb also seems to be a harder starter but I think that is glow plugs. The voltmeter at cranking is every bit as high as at idle with the headlights on.
Your thoughts? Thanks

[NH2112]

I'd start by checking grounds, namely the engine to chassis and chassis to body.

[Dvldog 8793]

Another thing to do is slap a multimeter on the batteries and see how much of your voltage is getting to the batteries. It will also help you calibrate your volt gauge. Connectors, line loss ect... Also if you have weak batteries it will drain down the alternator at lower rpms. And as stated the ever present grounding problems.
Hope this helps ...
L8r
Conley

[tom.mcinerney]

If it sat a while before sale, the batts could be down , maybe sulfated a bit. Advice suggested above all relevant, I'd add that when sitting , esp with condensation, the connections can deteriorate.
I think our alternators are 3-phase , but the key things to be mindful of are :
I.) If a {output-rectifying} diode craps out , no one will know unless somebody puts an O-scope on it , and notes the missing pulse.
II.) The rotating field is energized by battery voltage thru brushes/sliprings via diode ... the brushes and/or sliprings wear out , and charging declines.
III.) The solid state regulators are fabricated from 'thick film' construction . These are like integrated circuits , but scaled up a million times , use like silk-screen ceramics, rather than doped crystalline silicon . These are quite rugged , but subject to occassional failure . With earlier electro-mechanical relays regulation had to be tailored to short-haul OR hiway driving ... most/many battery failures resulted from overcharging . The new regulators can adjust on the fly , but their output is strictly limited to avoid overcharging ... thus the marked relevance of connections mentioned in posts above [pun intended].

Many shops can do an 'output test' of charging system , sears used to be $14. These load down battery and test if alternator output rises to match.

Hot climates (and cold--extremes) are tuff on batts. When semiconductors are heated they conduct more readily. Thus the alternator's regulator cuts back on output when warm/hot. When ambient temp below 20*F they really crank , but the batteries can't really accept much charge when cold .

About ten years ago a local (second generation) auto-electric rebuilder commented that increasingly his new Delco parts were arriving from their manufacturing origin in China , and that the component quality was deplorable.

TDP member Damork has a few posts around here vouching for an an aftermarket alternator that worked well . Many routine rebuilt autoelectric parts are so poorly worked that they fail in less than 10K miles....That said , I usually deal with a local rebuilder that i can whine to if a problem arises . I think J Kennedy brings some experience to bear, as well.

Oh , yeah... the alternator output wire is a pigtail from the B+ batt cable ... it is a fusible link , they can deteriorate when on their way south....

[ 11-06-2005, 05:48 AM: Message edited by: tom mac 95 ]

[damork]

My 95 had 3 AC Delco alternators on it before I gave up and switched to the Duralast Gold brand sold by Autozone. I kept questioning myself if there was something I had missed such as bad batteries, cables, connections, etc., but the last time I had new batteries and knew something was wrong. Even had the belt squealing when the electrical system was under load.

I switched to the Duralast Gold about 35k ago and it has worked very well. It's a drop in replacement, voltage remains good at idle and under load, and they seem to be made very well. For what it is worth, my wife's truck and son's car also ended up with Duralast alternators and I have had the same good results.

As the autoparts market is always changing, you have to be vigilant as what may be good today may become junk tomorrow. The last I checked the Duralasts are still made in the USA and seem to be of high quality.

GM OEM replacement serpentine belts (at least for my truck) are now Dayco branded and in my opinion are absolute junk (only brand that flew apart in less than 15k miles when I was driving to work. GM's financial woes are forcing them to change, but that isn't limited to GM as several parts houses are cutting corners as well.

[ 11-06-2005, 01:28 PM: Message edited by: damork ]

[Dimsdale]

The Autozone near me will do free battery/alt output tests if you ask. Their alternator replacement even had the correct pulley size on it.