Alternator Question -- My light glows - Page 2

RoninLB · 07-20-2003, 08:24 AM

Hey Gentlemen...

yeah, it's a package deal when dealing with people.. but IMO, Loren is a no BS straight shooter.. and he's not the only guy like that around here.. and when the world is in high gear and a short move is only needed to do the task.. screw being polite, and being fully socially correct.. but I'm not a pro.. LOL.........Ron

david914 · 07-20-2003, 08:50 AM

Oh gosh, I wasn't very happy at all with Automotion at the time as you might imagine! Especially when you add the shipping delay from west coast to east coast into the equation. Took a couple of weeks to do what should have been a couple of hours! I got real good at R & R'ing the alternator though! This time, I ordered a new regulator from our host thinking that was most likely the problem. Of course, yesterday I discovered that the field diodes are bad. One is shorted and another is open. Both on the negative side. If I can find someone who will sell me just the diodes, I'll replace all six (three negative, three positive). If I can't get the diodes, I'll be stuck buying another rebuilt unit. If that's the case, hopefully I can get it done locally so I won't have to re-live my previous experience. The bearings look and feel like they're in great shape as they ought to be. The car doesn't have that many miles on it since it was installed.

david914 · 07-21-2003, 03:05 PM

OK, update. I called a local rebuilder this morning expressing an interest in purchasing new diodes for my alternator. He took the numbers that I got off the back of the housing and said they sounded like Paris-Rone numbers to him (hmmm, this is a good sign. the guy knows Porsche alternators!) Long story short, he called this afternoon and said he could get the rectifier assembly (or "horseshoe" as he called it) for $54. Not bad! I should have it in a couple of days. With any luck, I'll be back on the road by this weekend! I'll let you know.

Superman · 07-21-2003, 04:40 PM

I'm going to suggest something that has been suggested earlier. Just take the unit down to the trusted electric motor repair place and have them hand it back to you in a couple of days, rebuilt. Guaranteed. It's not expensive.

Also, many motor shops have spare parts lying around. That is, some parts are expensive because they rarely fail. So, a good used one off an old alternator can save you money.

Many of the folks here know much more about electrical theory than I do, but I did watch a guy rebuild alternators, during my work breaks, daily for a couple of years. There are many steps. The windings have to be checked for continuity. The little thingie needs to be turned in a lathe. The doohickeys have to be trimmed back down so they don't leak energy. Once finished, you have what is basically a new alternator. Not an old alternator with a new horseshoe.

McDaniel · 07-22-2003, 04:45 AM

Had the same problem on my restore. Drove us crazy, tried everything, new alternator, new VR, test, test, test. Finally
found corrosion under the insulation of the blue wires where
they connect to the VR. Replaced the spade connector, (a 6
cent part) and viola! Problem solved, light is on when started,
goes out at 2500 RPM as it is supposed to.
Hope this helps.

kpfoten · 07-23-2003, 08:12 AM

Will the Alt. light stay on if the battery is bad and not holding a charge?

304065 · 07-23-2003, 08:53 AM

Kris,

Short answer: no

Long answer: If your battery has shorted plates internally, that should be revealed in a load test. If the battery is strong enough to run the light, and you have verified that voltage is in fact getting all the way back to the D+/61 terminal on the alternator (and not shorting to ground somewhere along the way), then it should be strong enough to excite the field. If you rev up the engine and it doesn't go out, then your alternator is not putting 12v back into that circuit, which means a bad VR or bad diodes.

The scenario you are describing, a lit bulb with a junk, shorted battery that is essentially a straight-through to ground, would require a working battery to first light the bulb, then excite the circuit, then the battery would have to fail, resulting in current flowing backward through the D+/61 circuit into the shorted battery and to ground, thus lighting the bulb by current flow in the opposite direction. Impossible.

kpfoten · 07-23-2003, 11:16 AM

Thanks, John.

Stupid P-car question of the day: The system seems to be charging at 13.6-14v. Is there anything with the alternator diode problem that might ruin a new battery? I'd like to take a few spins in it before I take it back apart and get a new alternator...

Thanks,

david914 · 07-23-2003, 12:59 PM

Not unless your alternator is OVERcharging. If you haven't already, measure the voltage with the old battery in and the rev the engine up to ~3K. If your voltage stays below ~14 volts, you should be OK to put the new battery in for a spin around the block.

POZE · 06-18-2004, 09:42 AM

HELLO
my Alterntor on my Porsche 911t 1974 seems to be overcharging, the light goes dim when the engines on, when its reved up to maybe 3000rpm, its goes up to 18V on the voltmeter.

I replaced the reg today, but still the same.

Does this mean that my Alt is faulty and needs a rebuild etc? the earth is good, ive got the original earth strap from the alt to engine, and a seperate one direct to the neg on the battery.??

any help appreciated!

logician · 12-29-2004, 03:21 PM

Poze, did you ever figure out the problem with your alternator?

-Juan

POZE · 01-04-2005, 12:55 AM

HELLO
I fixed the problem in the end.

I had the Alt rebuilt for £50gbp.
The problem was still there. After thinking, i checked the dash light bulb, and had fitted a 12V 0.5W VW bulb, i changed this to the more powerful Porsche type bulb, and the light went out.

Simple error!

Cheers
poze