Alternator drops out at low RPMs

[pitzel]

My alternator (CS130) stops charging at low RPMs, particularly when the engine is warmed up and on a hot day.  Idle is about 650rpm.  I personally rebuilt the unit with a brand new diode set, brushes, voltage regulator, and the "Iceberg alternator" housing (with extra fins for heat dissipation).

Was this "from the factory" behavior, or did the voltage regulators for the CS130 get modified over the years so they protect themselves from excess heat by simply refusing to excite the windings when the regulator was hot?  Presumably to extend their life to acceptable levels? 

Its not a problem for me as I rarely drive in rush hour stop and go traffic in hot weather, but it is slightly disconcerting to see the voltage down to battery voltage (ie: 12.4V) instead of the 13-14V.  Especially when, under such conditions, you have high electrical loading due to the cooling, AC condenser, and internal HVAC fans running full blast.  

Are there any smaller pullies available that would spin the alternator a bit faster under those low idle speed conditions?  

[55trucker]

My 1st impression is that the diode pack is at fault.

If the output falls off when at idle (under any circumstance) that would be an indicator of such an issue.

When you received the new diode pack did you check each diode to be sure they all passed current in only one direction & not the other?

[Cutlass350]

Fwiw, imho, GM/AC-Delco electronics used to make every other vehicle manufacturer look like bumbling kindergarteners.
 
Note, that I said "used to".

Yes, the CS130 alternator ended up being like so many other cost-minimized GM parts.
Imho, it's likely the voltage regulator.
Iirc, the CS130 went through "a few" iterations of voltage regulators.  My guess is that the regulators suffered from heat, poor design, and "wear" (electromigration).
My factory CS130 was one of the alternators that had "voltage surges/drops" "when it felt like it", at high rpms on the highway.  I would notice it in the lights.   That was with no AC, heat off, AC/heat on econ mode, no windshield wipers, stock radio at easy listening volume, etc.

When I did my "restoration" many years ago, I bought a new alternator directly from a GM dealer, and offered up old alternators to the Automotive Deity above , and hoped to get a newer alternator with the latest voltage regulator.
Thankfully, my offering to the Automotive Deity above seemed to work , and my new alternator has had a rock steady output, for now over 100K miles.

 

 

 

 

Edited September 22, 2019 by Cutlass350

[pitzel]

8 hours ago, 55trucker said:

My 1st impression is that the diode pack is at fault.

If the output falls off when at idle (under any circumstance) that would be an indicator of such an issue.

When you received the new diode pack did you check each diode to be sure they all passed current in only one direction & not the other?

A diode failure in a 3-phase to DC rectifier would cause noticeable ripple.  I had that happen with a previous alternator.  

I'm not convinced anything is actually wrong with my alternator -- I'm just wondering if, in the view of the astute people, there was an engineering change to the voltage regulators at some point in an effort to protect the systems from overheating during those high temperature, low RPM regimes, and thus improve reliability.  After all, there is somewhat of a double whammy -- the voltage regulator would have to go full field to produce voltage at a low RPM, yet the low RPM obviously draws a significantly reduced volume of cooling air over the circuitry.  

I do remember growing up the family having a H-Body with the CS-130 in the late 80s/early 90s, and having all sorts of problems with it early on.  Although now that I think of it, as time wore on, and it was replaced a few times, reliability did improve.  

BTW, when I say "stops charging", I don't get any indication on the dash other than my voltage drops.  The 'alternator' light or "check gauges" light does not come on... So I'm really just inclined to think that dropping out is just the engineered functionality of the voltage regulator/exciter.  When the RPM's are at driving speed, or the thing is cold, voltages are nice and high.  Up to 15V at -35C starts.  

5 hours ago, Cutlass350 said:

When I did my "restoration" many years ago, I bought a new alternator directly from a GM dealer, and offered up old alternators to the Automotive Deity above , and hoped to get a newer alternator with the latest voltage regulator.

Thankfully, my offering to the Automotive Deity above seemed to work , and my new alternator has had a rock steady output, for now over 100K miles.

Wow, you actually got 100k out of a CS-130?  That's amazing...   

Edited September 23, 2019 by pitzel

[55trucker]

28 minutes ago, pitzel said:

A diode failure in a 3-phase to DC rectifier would cause noticeable ripple.  I had that happen with a previous alternator.  

 

Depends on which of the 6 diodes would be to blame......if any of the negative diodes fails that will cause an a/c current to flow causing a *ripple*,

if one or more of the positive diodes is weak or goes open the voltage/current will drop. One will see that at idle with a voltmeter, raising the engine rpm to get the alternator to spin faster will raise the output masking the problem. The regulator limiting the output will not take effect until the alternators voltage output reaches the regulators designed built in setting 13.8-14v.

[Schurkey]

Subscribed.  This isn't something I've heard of before.

"I" would test for ripple, regulated voltage, full-field voltage and current.  I'd assure less than 1/4 volt of voltage drop between alternator + and battery +.  Also 1/4 volt or less of voltage drop on the ground side--battery - to alternator case or ground lug.

As a last resort, I'd replace the entire alternator (or at least the voltage regulator.)

[White93z34]

I seem to remember it being a relatively common complaint of the CS130 is lack of low rpm output, but I'd think it should be greater then 0.

Though the issue now is all the already marginal parts that came from the factory 25 years ago have been further "value engineered" to be even worse then new.