About Alternator Functioning

It's been a couple of weeks since I've posted anything.  It's been dead in the shop and nothing had sparked any ideas for a post until last week.  A Delco CS130 series alternator from the mid 1990's GM products came in with erratic charging problems and was overcharging.  It had a bad regulator, which is the part that controls the output of the alternator.  It was also a low quality rebuild from a parts store and probably wouldn't have failed if the rebuilding company had used a better quality regulator.

Anyway this sparked an idea for posting something about alternator functions, to help you diagnose your trouble.  Generally if an alternator is not charging on the vehicle, it could be any of the components.  Each manufacturer and model of alternator has it's own quirks and reasons they generally fail, so without knowing what your alternator is, it would take hours and hours of writing, that could fill a large book to cover all of what's out there.  There are however a few tell tail signs to look for when diagnosing your trouble that might help determine what's wrong.

If the alternator overcharges and is cooking the battery, or charges for a minute when you first start the vehicle when it's cold then quits, then it's most likely it's the regulator.  If the regulator internally has a loose ground it can also cause it to overcharge.  A totally non charging alternator can be the regulator but it's usually some other component.  Another component that can cause overcharging, but is very rare and usually will cause other alternator damage is a shorted rotor.  I've only come across a shorted rotor about four or five times in the 11 years I have been working on them.

If the alternator only charges intermittently, whether hot or cold and progressively gets worse, then it's probably the brushes worn out.  It can also be a loose connection either inside or outside the alternator.  Check to make sure all the wire connections are tight!  This is more common on Ford alternators and on Denso (Nippondenso) alternators that are used on Toyota and Chrysler products but can happen on other models.

Alternators that make a howling noise and may charge at a reduced rate, or not at all, usually has a bad rectifier.  A bad stator or a combination of both can also cause this condition.  This is more common on Delco alternators of the 80's and 90's GM vehicles.  (GM, isn't that now Government Motors?)

If the alternator is making a loud popping noise or roars like a waterfall, it will usually have bad bearings.  It could either be charging or not.  A squealing noise is generally not a bearing noise and is more than likely the belt slipping, due to either being worn, adjusted too loose or a weak tensioner.  The only exception to this is when the bearing shells or galls out, but it will usually lock up at that moment.  If the bearing comes apart and looses it's balls or rollers it will usually cause more expensive damage to the alternator and may be cheaper to just replace the entire unit, rather than fixing it.  Of course only a qualified rebuilder can only tell you if it's that bad!