alternator questions

[Joe]

The guy at the alternator shop said "the four diodes" in my alternator are shot.
Sounds like a '60s musical group.
He suggested I get a new alternator rather than rebuild this one.
I am wondering if there might be something external to the alternator that caused this to happen, and will fry a new alternator. Shows my electrickal naivete, probably.
Joe

[Cees Klumper]

A new alternator costs around $275 at SLS in Germany. You may want to check some sources for rebuilt parts in the US. I don't know whether there are rebuild sets one can order from someplace. Maybe Dan knows/sells these? I bought a distributor rebuild set from him a while ago.

[hands_aus]

Joe, there was a discussion paper about upgrading the alternator to a 55 Amp from a mid 70's car
if you want a copy let me know I will email it to you

Bob(Brisbane,Australia)

[rwmastel]

It's been said by experienced people that many of the parts in are cars are built to be rebuildable.  Things like alternators, distributors, starters, water pumps, fuel pumps, etc.  I don't have much electrical knowledge, so I can't help with the diode statement made by your alternator shop.

Rodd
1966 230SL Euro
1994 E420

[Joe]

I found a new one for $72 at this site: http://www.speedycarparts.com/
That price looks pretty good to me, and the shipping is free.
Yes, I've seen the article about upgrading from one from a mid '70s sedan with AC. Is the standard 230SL alternator inadequate?
I'd also really like to know if something external to the alternator can cause the diodes to burn out.
Thanks,
Joe

[Naj ✝︎]

Joe,
The only other items in the charging circuit are wires and regulator. These should be checked.You might find that the cost of parts of rebuilding your alternator yourself may be more than buying an exchange unit plus you get warranty with an exchange unit.
If you are going to upgrade, buy an alternator with internal regulator.That way you have tested alternator/regulator package.
Worth $0.02 cents?


naj
'Kloines Scheisserle'
65 230SL
68 280SL

[Ricardo]

I went to a local discount car parts place and traded my non-functioning alternator and about $100-125 cdn. for the exact same rebuilt alt.   I wonder if these alt. don't turn up on other cars as well as other model MB's.
No waiting had it the same day.
Richard V

[George Davis]

I found the following statement about diode failure:

"A common cause of diode failure in alternators is that the main negative loosens on the block or starter and the spikes blow things."

The same article (which was about marine charging systems) suggested adding a ground (negative) wire directly from the alternator case to the battery negative terminal.  I'd guess that isn't really necessary, but cleaning and tightening the engine-to-chassis ground connections may be a good idea.

Another thing that blows diodes is an open main positive circuit.  This can be accomplished (if destroying an alternator is your goal) by starting the engine then disconnecting the positive wire at the battery.  The alternator should provide enough electricity for the engine to keep running (for a while), but since there is no longer any place for the alternator's output to go, it fries the diodes pretty quickly.  Here again, cleaning and tightening all connections may be useful.

Last, once the new alt is in, there are some basic voltage checks that can be performed to be sure that the charging voltage is correct, to ensure that the voltage regulator is working properly.

George Davis
'69 280 SL Euro manual

[Bob G ✝︎]

I changed my alternator in febraury I had a 55 AMP and found it was off a 450SL the regulator was still connected. I went for the stock 35 amp Bosch rebuilt and replaced the regualtor car runs fine. I would like to locate the
little rubber buttie that goes on the end of the two wires that attach to the alternator does anyone have any spare I can buy?
Bob Geco

[Joe]

Thanks, George. Sounds like good information. I found the battery cables were loosely connected to the battery, and heavily corroded at the posts. I suspose it is possible one lost contact after the car was started at some time.
I'll check the grounds and clean up the battery connections.
Now I'd like to know if the stock 230SL alternator is adequate. Since at least one person has upgraded his, I am wondering if that upgrade to a 55- or 70-amp unit is considered a nice-to-do improvement, particularly for a non-air conditioned car. Now is the time to do it, since mine is shot.
I appreciate all the advice!
Joe

[Ricardo]

Joe
That might depend on your useage; if you have any auxiliary equipment that would add to your normal electric requirements such as stereo amplifiers, high output fog lights, A/C, or electric plug-ins that work off of the lighter socket like coffee pots etc. then it might be worth the extra few dollars. If your car is stock and everything is working right and you don't live in a cold climate (-30F)the stock alternator is more than adequate.
Richard V

[ja17]

Hello Recardo,
Yes you are correct. The same alternators were used in most of the same era Mercedes sedans. Although they are only 35 amps, I have never heard of anyone running out of power. I am sure that an upgrade to larger cannot hurt. However these cars were not "power" hungry by todays standars.
There was an early alternator which had terminals for wiring on the back of the units. The later alternator had a three pronged plug instead. Both  were used on the W113's and both were 35 amp. and used the same remote voltage regulator. Later Mercedes cars were loaded down with more electrical equipment and a 55 amp alternator became standard equipment. Features in the newer alternator was a removable alternator brush assembly and a different three pronged plug. Shortly afterward a later variation appeared with a new tiny voltage regulator attached to the alternator brush assembly on the alternator itself.

Joe Alexander
Blacklick, Ohio

[n/a]

Joe,

The alternator has 9 diodes, 6 power diodes and 3 field diodes.

I recently had battery charging problems. It turned out to be the alternator, who had a faulty field diode, the red warning light never went off completely, the battery died slowly. Also the mechanical Bosch regulator had burned in contacts. I had the alternator overhauled by a retired car electrician, and replaced the regulator with an electronic one : CAR GO nr. 130675. It's 1/3 of the height of the Bosch, the installation holes match, and I paid 35 Euro's.
I also have a 77 Ah battery since 5 years now, problem free till now, (1500 km's a year). The 35 amp alternator is fine for normal use.

Diodes can also get fried when welding is done on the car.  

Willy, 230 SL 1967 - 220 SEb 1965