I now have lots of data on my charging problem - i just put the car on the battery charger at night and took the time to do some extended diagnostics.

The alternator doesn't seem to be able to carry a load. If the battery is fully charged and I don't have the lights on, no problem, the battery doesn't drain, and I get 13-14 volts out of the alternator (which I replaced the brush/regulator pack first thing).

However, driving with lights on, and after a while I notice the dash lights start to dim. Eventually the radio cuts out. Then I'll see voltages as low as 9V (probably lower, I haven't pushed it) with the car running. My brand new clamp ammeter shows 2.5-3 amperes on the positive battery cable. Revving the engine doesn't change anything.

The old brush pack didn't appear to be very worn - I've cleaned battery terminals etc., so does this mean worn slip rings in the alternator? This alternator is one I purchased about three years ago - it was a Bosch rebuilt unit from Van's. It always was rather odd in that when I first started the car the battery light would be on until I revved the engine a little, then it would go out, and I don't remember the original one doing that.

Anyway, if anyone has any ideas other than replacing the alternator, please let me know, thanks!

__________________
kalpol
79 280SE
82 Fiat Spider 2000
81 Fiat Brava
04 BMW R1150RT
96 Jeep Grand Cherokee

Take the alternator to a rebuild shop. They can test it, and if needed repair it.

A generic autoparts stores should be able to test it too.

Are you seeing the 9 volts at the alternator or at the battery?

If at the alternator, it may be bad. As the diodes heat up, they may be acting funny or there could be a high resistance (read bad) connection in the alternator.

If it's at the battery, you have a bad wire somewhere. Could be the output wire from the alternator to the battery (or junction block then battery), a bad ground from engine to chassis or from chassis to battery. Could even be from the ignition switch to the alternator.

Could even be loose or worn v-belts. They don't need to make noise to be slipping and it might get worse as it warms up.

Michael

__________________
Usta haves '69 250/8, '76 280C, 1971 250C 114.023, 1976 450SEL 116.033
Current have, 1983 300SD 126.120

As Michael said, check your belt tension and also perform an ohm check on your primary wires.

Jim

__________________
14 E250 BlueTEC black. 45k miles
95 E320 Cabriolet Emerald green 66k miles
94 E320 Cabriolet Emerald green 152k miles
85 300TD 4 spd man, euro bumpers and lights, 15" Pentas dark blue 274k miles

Alternator wiring harness leading to starter buried down under exhaust manifold on the 280SE could be cracked insulation toasted wires. One of my 123's had history of eating alternators - 3 of em over 2 yrs, finally replaced petrified stone alt wiring harness to solve the problem. As part of repair before discovering this i went nuts running engine to chassis grounds, even grounded the alternator mount.

I finally broke down and bought a Bosch remanufactured alternator. I examined the old one, and noticed the slip rings were highly scored, and that the new brushes I had installed were rather ground down - bits of carbon hanging around their edges. I didn't look at the new alternator to compare though..didn't think of it till after I installed it. I suppose I could get a dental mirror and have a look.

I also tested resistance between the alternator harness and battery clamps - everything came up zero except for the small black wire in the alternator plug to the negative battery post - it measured 6 ohms. (This was a pretty cursory test since I don't really know where everything goes.) The ground strap bolted to the alternator body tested zero between its terminator and the negative battery post as well.

I haven't started the car yet since the radiator is off being rebuilt and the oil and transmission cooler lines are disconnected, but I'll post measurements just as a comparison.

I'm just curious what would score the slip rings like that - heavy arcing, crap in the alternator (moisture maybe from the leaking radiator?), bad ...something?

__________________
kalpol
79 280SE
82 Fiat Spider 2000
81 Fiat Brava
04 BMW R1150RT
96 Jeep Grand Cherokee

bosch is the answer. It has solved many of my problems-they are like a god. But I know that the alt runs the car system as the battery is only used to start the car. I had the exact same problem in my 300 SEL. After I replaced the alt all was fixed. I bet that you will be just fine.

__________________

Timothy Evans
TimEvans35@gmail.com
CELL 310 990 6780


1985 380 SL
2010 CL 6.3 AMG
*2009 CL 550 Sport 4matic
New addition-1984 380 SE
Newest Edition 1986 300E AMG

Yes, but that's the thing...the alternator I just replaced was a Bosch rebuilt I put in about three years ago. I am worried something is eating my alternator.

However, they're cheap ($136 for the last one) and very easy to replace so I guess it's not that big a deal.

__________________
kalpol
79 280SE
82 Fiat Spider 2000
81 Fiat Brava
04 BMW R1150RT
96 Jeep Grand Cherokee

I just changed the alternator this past fall/winter...made a BIG difference in performance and light O/P from the headlights...and they didn't "dim" while "Fausta" was idling.

One test is to remove the "+" terminal from the battery...if the engine stops or lags down to nothing and then stops, it's your alternator.

BTW, Bosch is what I bought...beautiful running and quiet...that was ALSO the proof that the other unit was heading south.

Good luck.

__________________

M. G. Burg
'10 - Dakota SXT - Daily Ride / ≈ 172.5K
.'76 - 450SLC - 107.024.12 / < .89.20 K
..'77 - 280E - 123.033.12 / > 128.20 K
...'67 - El Camino - 283ci / > 207.00 K
....'75 - Yamaha - 650XS / < 21.00 K
.....'87 - G20 Sportvan / > 206.00 K
......'85 - 4WINNS 160 I.O. / 140hp
.......'74 - Honda CT70 / Real 125
.
“I didn’t really say everything I said.”
. . . . . . . . . . . . . . . . . . ~ Yogi Berra ~