Alternator no charge - bench test regulator?
 

(US '84) My alternator suddenly stopped charging on my way home this evening. For reference it is a bosch 90A, 10 months old with 5k miles on it. Recently I had an issue with poor/no charge at idle with the blower and headlights on, otherwise it was working fine.

Here is what I found so far:
-alt belt was tight - no indication of slippage
- charge lamp works when key is on
- ~12v at battery (was driven home without alt so most likely why it is not 12.6)
- battery voltage @ alternator b+ connection
- ~10.5v at blue wire when disconnected with key on and all pod connections made (as per Wally's alternator circuit diagnostic method)
- removed alternator for inspection, found that the plastic guard over one of the voltage regulators connectors is melted/distorted but the wire is still intact, definitely not normal - alternator overheat? (Paris-Rhone Regulator)

So here's what I am wondering...
- is 10.5V at blue wire close enough to battery voltage for the alt to charge properly?
- since I have the voltage regulator removed, can I test it separately?

If possible I would prefer to buy a regulator rather than $130 on an entire alt.
Also this is my DD so I cannot afford too much down-time.

usually the brushes are worn but with a new alternator this should not happen.
However if the rebuild used a less than best Bosch regulator than this may be the issue.
I suggest to replace the regulator with a bosch unit,
also remove the engine ground cable on the right side of the block to chassis ,
if it has oil on it wash it in brake cleaner then clean the connecting points,
do the same for the battery ground,
and the 14 pin connector above the hot post as well as the hot post connections

Good suggestions. The current regulator is a Paris-Rhone according to the faded label. There is plenty of life left in the brushes. Slip rings look good.

Can I test the regulator to make sure it is bad? Where can I get a new bosch one (Pelican Parts has Valeo brand $65)

In the meantime I will clean engine & battery grounds + 14 pin connector as suggested. The hot post was cleaned and ox-gard applied fairly recently.

whoa if you have a PR regulator then you have a PR alternator,
please post a picture of the part you have,
front and back

>> Charge lamp works when key is on.

Does the lamp go out once the engine is running? Excitation comes through an internal diode once the alternator starts charging on its own. So if the light is out there's adequate voltage being generated to at least supply the field current.



>> 10.5 V at Blue wire disconnected

Depending on your meter, should be battery voltage when disconnected, key on. Modern meters should show full battery voltage. This is the excitation source for initial alternator light-off on start-up. Relates to question above too.


Stan brings up a good point about the brushes. With the regulator removed, brushes should be obviously long enough to reach the slip rings on the armature.

Cheapo "rebuilds" often just include cleaning and a new regulator/brush set/holder assy. The slip rings on the armature are a bit of work to replace, so cheapo rebuilders often try to skip this step if they are anything less than trashed. You can see the slip rings through the opening for the VR. If they are significantly worn or burned, you will miss out on alternator capacity. Perversely, a worn set of rings and bruhes is treated to higher excitation current, burning these parts even more quickly.

Here's some pics. On a second inspection there was an odd pattern on one of the slip rings (pictured).

Lamp does NOT go out with engine running - all warning lights stay lit, voltmeter reads 11 volts (usually reads 14 with engine running).

My meter is a fairly modern DVOM. AFAIK it is accurate. Will 10.5v be to low for the alt to charge properly?

Replacing any part on a Paris-Rhone alternator is a waste of time and money. On mine, after replacing the regulator, some diodes blew, after replacing them a stator winding burnt out, all in the space of a couple of years. Save yourself a lot of trouble and replace it with a different brand one now. Smiffy

According to the receipt the alternator has a lifetime warranty, is it worth taking it back?

the slip rings look good you could try swapping out the PR regulator,
OTOH you should also test the diodes before you swap in a new regulator.
If you put in a new regulator with a blown diode the alt will only make 13,4v not enough to keep the battery charged
Also if you have a warranty with the new alternator see if you can exchange it for another one.
Then make sure all of the other elex connections are good or the new part may also fail

You can eliminate the low excitation voltage as a possible problem by momentarily adding battery voltage directly to the field terminal with engine running. If it suddenly starts charging you can go after the problem with the wiring/etc im the car. If no change then the alternator is the problem.

Ah, thanks for the tip, I will definitely give that a try tonight. By field terminal you mean where the blue wire connects?

Do I need to remove the diodes to test them?

Yes on where the blue wire connects.

After the on-car test with full field, waste no more time diagnosing a lifetime-warranty part. Your disassembly if discovered will void the warranty. Take it back to the seller and let thgem test/replace if needed.

Alternator troubleshooting links:

http://www.nichols.nu/tip692.htm

http://www.nichols.nu/cat02.htm

Ok I just did the full-field test. With a multimeter reading 11.7v with the engine running, I fed power to the field connector on the alternator, voltage increased to 11.9v and rpms dropped slightly as if there was a load on the engine. Also did a voltage drop test across engine ground cable, battery ground strap, and alternator B+ to engine bay hot post - no voltage drop on either of the three. So is it safe to say the alternator is dead?

get a new alternaotr and check the hot post connection for the exciter circut before you run the new alt no need to fry it from a shorted wire

You may want to charge the battery so that the static terminal voltage is 12.2+ before doing any more testing on the car. The fact that the alternator kicked off when you strobed the field terminal says that it's doing something. I suspect that your run-down batttery is sucking more current than the alternator can make at idle speed, hense the rising but still-low terminal voltage. A deeply-discharged or old/worn out battery can make a good alternator look bad, and extended abuse can make it actually bad. But that's a tangent discussion. Focus on restoring the field circuit wiring. The current path runs through the 14-pin connector on the fenderwall by the jump post, and it's a very low-current circuit. A little bit or corrosion there will cause the low-voltage symptom you see on the alternator end of the exciter lead, so I'd start with a thorough cleaning of the 14-pin connector; it is probably due anyway. A soft brass toothbrush is a good way to get big stuff off the connector pins and the brass sockets. Then a good contact cleaner before reassembly. If you don't have the plastic cover for that area, get one to keep the rain and car-wash water out of the electric stuff there.

Well the car still starts as strong as it did when it had a full charge, but it is worth a try. The battery was hooked up to a charger this morning so it should be good. I will do one final test tomorrow and then it's off to Advance Auto for a replacement. Maybe someday I will do a higher output swap or get a Bosch from Napa if necessary.

Same results. Brought the alternator to Advance Auto for replacement, had them test it while I was there just to be 100% sure. They also had the same results, it put out a very small amount of voltage, nowhere near enough to charge the battery let alone run accessories. Sound like the voltage regulator? So they took the alternator as a core and I should get the new on on Tuesday (no charge - lifetime warranty). Also they gave me $73 store credit for some reason...?

I did a ton of searching on this a few months ago when my alternator crapped out. Similar symptoms. Would read 11-9-12V while revving engine and drop into 10.9 or so at idle.

I tried Dr Bobs suggestion as well because a bad battery can make a good alternator look bad as he says. new battery yielded same results.

The Bosch remans are a bit of a mystery. I have a Bosch reman (Bosch AL325X 90 Amp) that replaced the original Paris Rhone but its basically a Bosch reman of a Paris Rhone core. Your may still even have some of the Paris Rhone stickers or lableing on it - I think mine did.

What is unknown is whether or not it uses actual Bosch parts or if its just assembled by Bosch using Paris Rhone parts. In either case, when my old PR failed it was one of the diodes. The tester at Advance Autoparts should actually do a printout of the diagnosis that says if the failure is voltatge regulator, diodes, etc.

BTW there is another Bosch reman that fits our cars if you Google it which is the 90amp Bosch AL115X. I have not seen one but I have a hunch its the same one as the AL325X with different labeling. I'm curious which one you purchased.

In either case I swapped in a known good voltage regulator just to see if that was the issue and it wasn't - bad diode seemed to be the correct diagnosis at least on mine. Have had no issues since the install but I've talked to some people who are skeptical of the Bosch Paris Rhone remans, since no one really seems to know if the internals are really Bosch quality or just PR stuff assembled by Bosch.

This alternator is for Audi's. I've got one. It bolts up and works just fine but does not accept the vent shroud.

BTW - The true Bosch alternators have an easily-replaced regulator and brush assembly.

To the OP - It's probably a diode or two that has failed. A trip to an auto parts store with the unit would tell you if it works.

I got a Bosch-rebuilt Bosch alternator at Advance Auto.
Was about $150. Overnight delivery from their warehouse to the local store.

Also have 2 Delco cheapo rebuilds on the 2 USA cars.
Its a patch alternative for you.
One has run since March 08, about 25K miles.
No place for air hose though.

broken winding is a possiblity. you suck a rock in the vent line, or if you dont have a vent line, and that gets in the alternator and takes out a winding on one of the interal rotary coils.

So far so good - getting around 14.5V with engine running :thumbup:
Adjusted the voltmeter reading so it is now accurate with the engine running.
Also there was an issue with the charge warning lamp (actually I broke it by mistake :banghead:) so I swapped it with the fuel reserve lamp and put an LED in the fuel reserve's spot instead. After this repair (before installing the new alt) I got 12.2v at the battery and 11.6v at the blue wire. Time to drive!

BTW I took some pics of the alt before installation, this one says Valeo on it. It is a "Worldwide Rebuild" or something. The old alt had the 928 part # on the plastic cover over the rear alt bearing, the new one doesn't.