bad alternator????

hy everybody,, the other day i was running my 1983 944 and had to stop to put gas.. and when i try to restart my car,, the battery was dead,, so i boost it. When i was comming back home,, i see that the light of the battery was illuminated,, and with my tester i read 11.41v when the car is running,, so i think that is the alternator,,, BUT he just had a rebuilt job done!!!, oh yes in the same time a have change the ground strap of the engine who's attach to the body,, maybe its not the good strap??


thanks for your help

check connections, recheck strap, if there ok, altie?

Look for corosion on the cables them selves. If they are too nasty or corroded the battery won't charge right.

Alternator or regulator......
Lemme check the data and possibly help to x-shoot.

B right back

How to determine which is bad........
I was'nt able to find the answers that I was looking for... possibly someone will follow up and fill in where I really dont know what I'm talking about......

The alternator makes the juice...... the regulator determines how much juice is needed and controls the alternator. The regulator controls the alternator by turning on and off the current flowing through the field.

Now here's what I dont know.... whether the field current is always hot (+) and the regulator turns on and off the ground (-) -OR- if the regulator turns on and off the potential (+)(12V)

What I do when I know is to hot flash the alternator field for a short time to determine which is defective. I'll get to the alternator and essentially remove the regulator from the circuit. If for example I knew that the regulator turned on/off the voltage to the field as needed, I would disconnect the field wire from the alternator and connect a test lead from the alternator field terminal to the positive post of the battery. With the car running I would take a voltage reading at the battery and compare it to the battery voltage with the field test wire disconnected.

If with the field test wire connected I were getting 13 something volts (help me out here guys ... about 13.4V) and just flat 12 volts or less with the field cold (test wire disconnected) THAT TELLS ME THAT THE ALTERNATOR IS GOOD BUT THE REGULATOR IS NOT TURNING IT ON. <~~ oops,cap loc. If the field test wire does not affect the alternator performance .... then one of two things. A) the alternator is not worth its weight at this time, although it does help take up the slack in the A/C belt. -OR- B) possibly its the other type of system that the regulator switches the field by opening/closing the ground.

Happily I have not had to learn the porsche charging system as of yet for my own needs.

P.S. Dont drive around town with the test wire connected until your new regulator comes UPS.... you'll over volt and boil the battery.

Sometimes, and I dont know if this ever happen with Bosch... a regulator will stick closed and the alternator runs all the time. The battery overcharges, the electronics can be damaged, sometimes smoke. The pilot can manually control the field with a switch in flight until a practical time to land safely and have it repaired. He will watch the voltmeter (or she) and adjust both the load and cycle the alt field switch to basically manually keep electricity in the battery as needed.

Apologies for me getting long winded. I like airplanes too.

I hope this helps you understand the way the system works... and therefore you may be able to troubleshoot by trial and error. I offer this info with the best intentions but do urge you to utilize it at your own risk. If anybody can teach me something or save BlueBoy from following my bad advice.... Do so now in bold, capitol PRINT!

Have a great weekend!

Hi,
Presume you have checked up what the previous posters have mentioned. Usually battery light recieves two signals, high and low..via the ammeter.
Now one can determine what is high and low only with an accurate altmeter and one shoudl know what amperage is being generated. However since you have also mentioned a re-build altie (not a good idea for a sane amp reading), its very very possible that the copper windings or rotor brushes have given way.

Try this, start engine and let idle, open batter cap (if its not a sealed one) check to see if any section is not bubbling too much. Next if you have a hydrometer check for specific gravity around 1.26 and 1.28. If anywhere low, then certainly your battery will start to self ruin, no matter what juice or regulated amperage is supplied...the darn term-signal is sent back via the ammeter.
If at all the voltage supplied to battery is OVER 13.4 or appox 14.2 volts, forget it your batter is nearing its self ruined state.
Like an earlier poster has detailed, the voltage regulators job is to keep the OUTPUT voltage between 13.5 and 14. Now I can go on and on regarding Diodes and how they impact your AC/DC conversions and all the priniciples of elecetromagnetic induction, but dont want to bore the list

hope you can get to the bottom of your problem, if not fling the re-built altie back at the chap who fixed it

gluck

I like the advanced education......

Now I can go on and on regarding Diodes and how they impact your AC/DC conversions and all the priniciples of elecetromagnetic induction, but dont want to bore the list

I understood what you said, tell me more.

PS. One more post and I am regular.....