I goofed up and did not remove the neg. battery cable when replacing a defective signal light bulb holder, and one of the three little posts broke off. I soldered it, and clumsily touched two of the posts together. That blew a fuse. Now that the battery has drained, I think it has done more damage than that. So now I think I will have to replace the alternator brushes. Or perhaps the voltage regulator. Or the entire alternator...
I have years of experience unbolting and replacing metal parts. I hate electrical work because I do not know my stuff. I do not know how to use a volt meter even. (I have rebuilt carbs and replaced all manner components but have always avoided this type of electrical work because I have friends who understand it better. However I must do this myself, because I am through being embarassed by not knowing this simple stuff, and those electrical whizzes are out of town). So, tomorrow I get into it.

Question: What is the best way to determine if my problem lies in the brushes, the voltage regulator, or if the alternator itself is completely shot?
What sort of readings should I see when I test things with the voltage tester (that I will go buy tomorrow)?

hmm, another intesting question. On my W126, i took it to three differant shops to have my alternator checked. MY battery checked out ok, and two of the shops passed my alternator as well. When i asked, the why does my battery not get recharged, they'd look at me with a dumbfounded look on their face. Finally, the third shop connected an amp meter(it may have been ohm also, i'm not sure), but it turns out that even though my voltage was ok, my regulator was causing my amps(or ohms i forget) to jump drastically. This wasn't allowing the battery to charge, thus my car wouldn't start. On my car the regulator was inside the alternator and my alternator bearings were going anyway, so i just replaced the entire alternator(actually the bearings locked up and then i didn't have a choice anymore )
good luck, im sure somone more knowledgeable will chime in shortly,
Ryan

__________________
83 300SD.......sold
96 integra SE....sold
99 a4 quattro....sold
2001 IS300.......sold
2002 330i.........current.
2004 highlander limited....current.

OK im confused. It sounds like you were working on a lamp socket somewhere on the car. I assume the ignition was off, and you blew a fuse. Im not sure how that happens unless the lights were on at the time you were doing the work. How does that relate to the alternator? Why would you assume that the alternator was involved or affected in any way? Whats the connection to the alternator here? Which fuse was blown.

If you could be more specific I might be able to help you.

__________________
I got too many cars!! Insurance eats me alive. Dave

78 Corvette Stingray - 3k
82 242 Turbo Volvo - Manual - 270k
86 300e 5 speed manual - 210k
87 420sel - 240k
89 560sl - 78k
91 420sel - 205k
91 560sel - 85k
94 GMC Suburban - 90k
97 Harley Davidson Heritage Softail - 25k
00 GMC Silverado 1 ton 30k

Ducati,

I agree with Dave and can tell you from personal experience that I have blown many a fuse without hurting the alternator, or the battery for that matter. I also do not see the connection between the event and the alternator. If you are having battery charging difficulties and they have just been noticed, you may have an alternator problem that is independent of the blown fuse.

There have been a number of recent threads here on the subject of voltage regulators, brushes and performance specs for alternators. Getting the alternator checked out correctly is more than just a voltage check, although if voltage is off the unit is clearly bad. Under no load conditions the voltage should be around 13.8 volts. At full load (lights, fans, etc. running but obviously not the glow plugs and starter) I cannot remember the value, but it is above 12 volts. If you meet both ends of the spectrum, you likely have an acceptable current output (amps).

The brushes are relatively easy to change, and can be found as separate items for a couple of dollars, or in a new voltage regularor assembly (easier, but costs closer to $40). The separate item repair requires some self motivation to take the old ones out, save some springs and manage to do some soldering, make a locking feature that keeps the brushes in the holder so the springs don't push them out, and so on. I have always opted for the new regulator.

If the alternator is not making the current rating, it likely needs to be rebuilt. I would opt for a rebuild from Fastlane or some other reputable supplier. Rebuilding an alternator is often viewed as no more than cleaning, repainting, pressing in new bearings, and installing a new voltage regulator. There is more to an honest rebuild, as it may need to be rewound, and likely needs a new rectifier section.

Hope this helps. Jim

__________________
Own:
1986 Euro 190E 2.3-16 (291,000 miles),
1998 E300D TurboDiesel, 231,000 miles -purchased with 45,000,
1988 300E 5-speed 252,000 miles,
1983 240D 4-speed, purchased w/136,000, now with 222,000 miles.
2009 ML320CDI Bluetec, 89,000 miles

Owned:
1971 220D (250,000 miles plus, sold to father-in-law),
1975 240D (245,000 miles - died of body rot),
1991 350SD (176,560 miles, weakest Benz I have owned),
1999 C230 Sport (45,400 miles),
1982 240D (321,000 miles, put to sleep)

Hi Ducati

A quick lesson on car electrics.

The colored wires to any item on the car carry + current to the item (radio, lights, whatever) Different colors and stripes to keep identity separate.

In order for the current to flow through the item and make it work, it needs to have a return path to the - terminal on the battery. In other words it needs to complete the circuit.

If this circuit does not get completed, the itemwill not work .

The way car makers and Bike makers complete this circuit (commonly called a "ground") to the - terminal on the battery, is by using the steel body of the car as a "wire", instead of running all these wires back to the - terminal. German cars usually use a brown color for the ground wire, and the rest of the world uses black. Sometimes you will see a neg (-) wire coming off of an item which gets screwed into the body somewhere else, or the item will use a mounting screw as a ground.

Anyway, I hope you can use this tutorial and if you know this stuff already, then good If not, then good

I have had luck with teaching people these basics with this tutorial of mine, and it helped them over this hurdle.

__________________
Ed
1981 300CD (Benzina)
1968 250 S (Gina) 266,000 miles!
1983 Alfa Romeo GTV6 (Guido)
1976 Jaguar XJS-saved a V-12 from the chevy curse, what a great engine!
1988 Cadillac Eldorado (better car than you might think!)
1988 Yamaha Venture (better than a Wing!)
1977 Suzuki GS750B
1976 Yamaha XS 650 (sold)
1991 Suzuki GSX1100G (Shafty Gixser)
1981 Yamaha VX920RH (Euro "Virago")
Solex Moped
1975 Dodge P/U camper


"Time spent in the company of a cat, a beer, and this forum, is not time wasted!"

In addition to the above, remember that you do not have to have a "short" to blow a fuse... a place in the circuit which creates too much resistance ,like a corroded wire/connector/frame will cause excess electrical flow and blow a fuse. When groups (based on the electrical diagram) of things start acting up all at once then these common ground points are the first places to check. There might be , for instance, five main grounds between the motor/frame,battery/motor,instruments/frame.You don't really 'check them' .... you take them apart and clean them and see if that cures the problem.For real security in dirty places it is nice to solder even solderless connections , done properly it pretty much eliminates any place for water/salt etc to reside in a hidden place like the wire/connector. Another cause of corrosion is simply the placement of two different metals together,, and soldering keeps the oxidizing influences out of there (wires copper/connector steel,etc ). Remember also that we moderns use 'ground' and 'negaive' interchangeably even though some cars used positive ground ( MGB's with dreaded Lucas Electrics for one example).
Personally I think when they invented electricity they should have made it visible, that would eliminate much of my problems using it.
An alternator needs to be checked by a trained machine....it can only make a certain amount of electricity at any given rpm depending on how it is made... there is an inverse relationship between the amps and volts it can make ... maxed on one means low on the other....good luck, Greg

I must disagree with Greg. When a connection creates too much resistance, like a corroded wire/connector the current is actually reduced. Lower resistance means more current and higher resistance means lower current. So if a connection creates too much resistance the current will decrease.

Ohms Law states that:

I=E/R which means Amps = Volts / Ohms

So your statement contradicts the laws of physics

Also I disagree with your statement :

"... there is an inverse relationship between the amps and volts it can make ... maxed on one means low on the other...."

A properly working alternator the voltage is regulated to 13.8 volts or something close to this value regardless of RPM - within limits of course. Its current capacity is determined by the size of the magnetic fields and magnetic components, diode capacity, and rotational speed. The current curve for an alternator increases with RPM reaching the max value at about 4000 RPM.

I agree with your statements about soldering connections. Most problems related to electronics are usually related to connections of some sort. And connectors are usually trouble. However soldering the pins in connectors is sometimes impossible without serious damage.

All the connectors I have seen in my MB's have silver plated contacts. A testament to the electrical engineers on the MB team.

__________________
I got too many cars!! Insurance eats me alive. Dave

78 Corvette Stingray - 3k
82 242 Turbo Volvo - Manual - 270k
86 300e 5 speed manual - 210k
87 420sel - 240k
89 560sl - 78k
91 420sel - 205k
91 560sel - 85k
94 GMC Suburban - 90k
97 Harley Davidson Heritage Softail - 25k
00 GMC Silverado 1 ton 30k

Greg, Dave

Curious thing about soldering connections.
Aston Martin::: One of the small, but significant things you pay for when buying one of these outrageously expensive machines is/are soldered connections! Perhaps they are heading off problems with their Lucas electrics in the very wet climate of the British Isles. This is a very expensive thing to do when making a mass produced automobile, but worth it in a small volume, hand made car like an Aston Martin.

Lucas Electrics. Joe Lucas; the man who invented darkness!:p

FWIW DEPARTMENT;

I should have fled in terror at the sorry sight of an abondoned 1976 Jaguar XJS, with no wheels! Just propped up on four peices of firewood tucked under the body... Whoo Boy.
Of course it didn't run, but someone had done up the interior recently and the body was perfect and everything was there. The silver paint was completely shot as you might expect, and the huge ignition distributor was dismantled and laying in bits in the rear jump seat. another Whoo Boy here.

The guy at the thrift store where it had been donated and subsequently vandalised said that it had run at one time and they had priced it at $4000. I looked at him like he was completely out of touch with reality, but he continued and allowed as to the sorry state of affairs in front of me that he would price it at $400.
$400 ?? Say now.This would be worth $400 bucks, even if to just turn the engine into a coffee table!

Well the really odd bit about this was, that my buddy had just given me 4 wheels w/ hub caps and trim rings to dispose of for him at my place of employment, because we recylce metals.
Yeah, you guessed it- Jaguar wheels Go figure.
Well, the coincidence was too much and the rest is history.

Why am I telling you this? Is it to explain why I am so stupid to purchase a car with Lucas electrics? With a Lucas distributor and Lucas fuel injection? and Lucas electronic ignition????

Well, as it turns out Every connection on the car had soldered connections! I couldn't believe it. And the highest quality large gauge wire I had ever seen in any car.
This caused a huge shift in my pre-conceptions about Jaguar.
Besides, everyone knows that V-12 Jags always get their engines changed for Chevys because they quit working for no apparent reason.

__________________
Ed
1981 300CD (Benzina)
1968 250 S (Gina) 266,000 miles!
1983 Alfa Romeo GTV6 (Guido)
1976 Jaguar XJS-saved a V-12 from the chevy curse, what a great engine!
1988 Cadillac Eldorado (better car than you might think!)
1988 Yamaha Venture (better than a Wing!)
1977 Suzuki GS750B
1976 Yamaha XS 650 (sold)
1991 Suzuki GSX1100G (Shafty Gixser)
1981 Yamaha VX920RH (Euro "Virago")
Solex Moped
1975 Dodge P/U camper


"Time spent in the company of a cat, a beer, and this forum, is not time wasted!"

Soldered connections are worth their weight in gold!

__________________
I got too many cars!! Insurance eats me alive. Dave

78 Corvette Stingray - 3k
82 242 Turbo Volvo - Manual - 270k
86 300e 5 speed manual - 210k
87 420sel - 240k
89 560sl - 78k
91 420sel - 205k
91 560sel - 85k
94 GMC Suburban - 90k
97 Harley Davidson Heritage Softail - 25k
00 GMC Silverado 1 ton 30k

So, Joe...did you keep the V12 in the car, or is it a coffee table?

Dave, yes I was playing a little loose with terminology for mental graphics reasons,,, since you corrected part of the statement, how about addressing the bigger part of the picture which I was trying to convey. That is: Can an increase in resistance due to corrosion cause a fuse to blow? If 'yes' how does it do that ? I don't know so I was portraying the only force I know that blows fuses as the culprit in this situation.... Rememeber I have already said I have problems with electricity....
I will have to wait to address the inverse relationship deal until I get my Petersens Hot Rod series book out... I am sure , if I read that , that that is where I read it.... Or, Was I using the wrong words for an inverse relationship somewhere here ? Correct that for me, if that was the case.... thanks, Greg

Greg,

Nothing in Nature is ever an "always" situation. In the case where a fuse is sized to protect some light duty components, say an 8 amp fuse, and you have corrosion on the connections of some part of that circuit, the circuit will draw more amps and can possibly blow the light duty fuse. You may have seen that in the past, and you will likely see it again.

The corrosion on the contacts looks exactly like some kind of load to the electrical system (greater resistance), and the wasted energy in the circuit produces heat. So, a line intended to draw under 8 amps can start drawing more than 8 amps and pop a fuse.

The power in a Diesel car battery (really any car battery) can easily pop any of the fuses in the lines (without damage to the battery or the system), and any extra load on any of the lines due to corroded connections will bring the line load closer to the fused limit by using up the engineered margin. In severe cases it is feasible the battery and alternator will droop in output Voltage from the 13.8 nominal no load condition but maintain around 12 Volts across the higher resistance connection, which can be dangerous. If it is dangerous it should drive the power demand of the line over the amperage limit of its fuse, causing it to pop before it does any other damage.
In a case where the corrosion is so bad that it is better simulated by an open circuit, next to no current will flow.

A case we have all experienced where corrosion drives the battery performance down is on the battery posts themselves, when they get so corroded the battery uses too much of its stored energy just pushing electrons across that layer of scuz between the terminal and the clamp to start the motor (Diesel engine turns too slow to start). When that is the problem, try touching the battery terminals after you have been cranking the starter motor for a while. I have done this on an outboard motor in a boat and changed the shape of my finger for a week or two.

Hope this helps. Jim

__________________
Own:
1986 Euro 190E 2.3-16 (291,000 miles),
1998 E300D TurboDiesel, 231,000 miles -purchased with 45,000,
1988 300E 5-speed 252,000 miles,
1983 240D 4-speed, purchased w/136,000, now with 222,000 miles.
2009 ML320CDI Bluetec, 89,000 miles

Owned:
1971 220D (250,000 miles plus, sold to father-in-law),
1975 240D (245,000 miles - died of body rot),
1991 350SD (176,560 miles, weakest Benz I have owned),
1999 C230 Sport (45,400 miles),
1982 240D (321,000 miles, put to sleep)

I haven't read all the responses but checking the brushes is quite simple. Remove the voltage regulator from the back of the alternator (2 screws). If the contact end of each brush is shiny and clean, they are okay, but who knows for how long. If one or both of the brushes has a dark dull coat on it, it's worn too short to make proper contact.

A voltage regulator is around $60 at the dealer and as little as $15 from FastLane. I understand that replacement brushes are available, but I haven't found any information on who sells them or what they cost.

Sixto
91 300SE ... recently 'deregulated' but quickly fixed
81 300SD

Thanks Jim, but I hope Dave does not see those two first paragraphs... because they seem very much like my statement "creates too much resistance ,like a corroded wire/connector/frame will cause excess electrical flow and blow a fuse. " LOL

Concerning my 'inverse relationship'.....
I have located that old Hot Rod Magizine tuning manual and it says ...

" A generator does not put out full voltage all the time. One of the characteristics of an automotive generator is that it cannot put out maximum voltage and maximum amperage at the same time. when it is putting out maximum current or amerage, the voltage fall to a comparatively low level. When the generator is putting out maximum voltage , there is practically no current flow at all. "

This is where I got the mental image of inverse relationship...
Perhaps this does not apply to alternators and remembering it is just showing the age of the cars I started out working on.... LOL..... Greg

Ouch...even I got confused in this discussion. Let me try to answer the original question.

1. Shorting the connector did not damage the alternator or battery because all lamp connectors are protected with fuses.

2. A simple check of the alternator can be done with a voltmeter. First, without the engine running, measure the voltage across the battery. Note the value.

3. Start the car and again check the voltage at the battery. If it is higher than in 2, the alternator is working. If the battery voltage with the engine running is the same or lower, the alternator is not charging. With our mercedes, this can be happening without the battery light coming on. The most likely cause of the problem is worn brushes on the alternator. You can replace the brushes alone, but you have to be able to solder to do it. You can also just change the voltage regulator. Either of these can be done without removing the alternator.

HTH

Joe