1997 850 NA - Aging 100A Alternator

Post by **xHeart** » 26 Dec 2016, 13:53

It appears to be the original VOLVO 100A alternator. It charges at 13.78-80V with running lights.
A year old battery at cold start was 12.20V.

Would you consider replacing ALTERNATOR for preventive maintenance?

Post by **tryingbe** » 26 Dec 2016, 14:05

With car running and everything turned on, what is the voltage between the positive of alternator and the positive of battery?

Post by **cn90** » 26 Dec 2016, 14:23

My experience with alternator is as follows:

1. The VR, being an electronic component, can last 50K or 250K. Completely unpredictable.

2. The 2 bearings (Front and Rear): they are usually noisy at 160K-200K range.
If you are skilled, then you can either:
a. Re-grease the bearings.
b. Install new bearings.

Post by **BEJinFbk** » 26 Dec 2016, 14:31

xHeart wrote:It appears to be the original VOLVO 100A alternator. It charges at 13.78-80V with running lights.
A year old battery at cold start was 12.20V.

Would you consider replacing ALTERNATOR for preventive maintenance?

Considering what passes for a "rebuilt" alternator at most parts houses these days? No.
The OEM is a very good unit. You may have a little voltage drop in the cables and the
test mentioned above is good PM data, but if it's not leaving you stranded, you're OK.

If you're truly concerned, find a good factory alternator from a JY car to keep on standby.
You can have it checked out by plenty of places off the car. I'd leave the one you have in
place unless you have a solid indication that it's failing. "If it ain't broke" applies here, IMHO.

If you're really concerned about a known good replacement, replace the spare's bearings
and voltage regulator. Most of the time, those are the only parts that wear out on these.

Again, be VERY cautious about "rebuilds"!

Post by **abscate** » 26 Dec 2016, 15:06

I think I still have two left in my parts stash from harvesting my mechanics cars

I rebuilt mine 10k ago, so no spare for me

beigg · Post by **beigg** » 26 Dec 2016, 16:13

as long as the windings are good, the alt is likely serviceable. I've had success in lucking out in finding a NOS Volvo OEM alternator at a fraction of the prices out there. Once installed, I rebuilt the original and put it on the shelf for future needs.

Post by **misha** » 27 Dec 2016, 13:46

xHeart wrote:It appears to be the original VOLVO 100A alternator. It charges at 13.78-80V with running lights.
A year old battery at cold start was 12.20V.

Would you consider replacing ALTERNATOR for preventive maintenance?

With lights,heating and rear defroster ON you should have at least 13.5v at idle,everything below that is not enough to properly recharge the battery.
Spec is 13.5-14.4v at idle.With all those consumers OFF you should have 14.0-14.4v at idle.

Battery at 12.2V after it sits overnight means that it's at 50%.I think that i allready post a "state of charge table" for you in some previous topic.

Post by **E Showell** » 27 Dec 2016, 14:12

Might consider replacing the voltage regulator if the brushes are super worn. Transpo makes a replacement regulator for the Bosh alternators that is a bolt on replacement. Generally available for somewhere around $55-60.

Post by **BEJinFbk** » 27 Dec 2016, 14:34

I think you guys are worrying a little too much about specifics.
With all due respect, it's more than just a numbers game.
When you start considering climate, driving habits and the
overall state of the car, there are just too many variables.

If it starts and runs consistently, the empirical evidence tells the tale.
If the OP was having some kind of charging system problem, I'd agree,
but it sounds fine to me. Why risk breaking things with unneeded work?

I'd also agree with checking out voltage drop on the cabling before jumping
into any other "fixes". Start with an engine running output check directly
at the alternator. You should ideally have the same at the battery.

Post by **xHeart** » 27 Dec 2016, 18:54

I did not have multimeter back when our V70XC engine would cutoff and come right back on. It hesitated infrequently during the drive -- 154,000+ miles. The symptom started after I had restored new battery, coils, spark-plugs, and air meter. Now 2 years on, all is good since installing one from a local rebuilder guy referred by a local Volvo mechanic -- life-time warranty.

Back to our 850 100A alternator, I do not have issue like V70XC.
The recharge reading today was 13.2x at idle with load -- running daylight, radio, trouble lights, windows going up and down, and heater blowing.

Your chart Misha.

Street parked, overnight temps are negative º. It cranks and engine starts effortlessly. Quick and responsive after engine is warmed up.