55 OR 65 AMP Alternator? - PeachParts Mercedes-Benz Forum

shear2001 · #1 04-13-2004, 09:33 AM

I have a 85 300TDT and the off the shelf alternator that I replaced over a year ago is on its way out. I plan on getting a Bosch rebuild this time. Does anyone know if I should chose a 55 or 65 AMP? Thanks

Gurkha · #2 04-13-2004, 10:08 AM

Unless you plan to install heavy load draining electronics like amps, multiple high powered headlights etc. I see no reason to put the extra load on the engine with a higher power alternator.

TonyFromWestOz · #3 04-14-2004, 09:44 AM

Quote:

Originally posted by Gurkha
Unless you plan to install heavy load draining electronics like amps, multiple high powered headlights etc. I see no reason to put the extra load on the engine with a higher power alternator.

There should be no more load, for a given output current, whether you have a 40A or 100A alternator, other than the inertia of the rotating components.
The greater output current will allow faster battery recharge and/or greater loading on the 12V system.
If you use extra current, it will load the motor to that extent, plus the losses in the alternator.
eg. the difference in engine loading of a 55A alternator (@15V = 825W) and a 65A alternator (@15V = 975W) is 150W (less than 1/4 HP), at maximum alternator output.
There will be negligible difference in engine loading if the same power is drawn from the alternator ie a 65A alternator delivering 55A.

jbaj007 · #4 04-14-2004, 12:54 PM

I replaced a 55amp alternator on my 300SD a while ago with a rebuilt Bosch 80 amp unit from a 560SEL even though it was a tight fit. I have never been happier

(well... at least with electric systems).

With rear defroster, windshield washers, high beams, stereo and other sundry stuff on at the same time, I could always tell I was at the edge of having adequate recharging capacity. Dimming of lights, slower cranking, that kind of stuff.

With the larger alternator, adjustable regulator (13.8-14.4v.) and a voltmeter to keep tabs (sort of) on it, I feel more "secure".

Since you have to replace it anyway, and the 65 amp. is a drop in, I know I'd go 65 w/o a question.

81Wagon · #5 04-14-2004, 12:55 PM

For those of us who might need even more than 65A in our 123's, has anyone come up with a simple way to do it? I hear you can't just drop in a higher amp alternator from a later model Mercedes because the belts are different...?

I've seen people suggest getting the alternator rewound to put out more power, but I've also heard that carries a risk of overheating the alternator...

jbaj007 · #6 04-14-2004, 01:22 PM

The belts were different (v-belt vs. serpentine) on my swap. I just used the old pulley on the new alternator. Mine was a 126 (1984 300SD) though, not a 123, and there were some slight space issues with the belt adjuster having enough room. Slightly longer belts (by 35mm I believe?) helped.

Oh....and I had to make up a new little harness from the alternator to the connector block (easy).

dieseldiehard · #7 04-14-2004, 01:25 PM

I doubt if rewinding an alternator will give you anything worthwhile, it may reduce life as a result too. The diodes have to be sized to increase the current rating also, and there are not a lot of options with the Bosch alternators that have cases sized to fit the W123/126 cars.
The largest alternator that will fit the 123 is the AL69X. If you >really< wanted to go high current, fitting a Leece Neville would be the way to go but where to put it is the problem.
Nice thing about the W124 chassis is it allows using Bosch 115 or 143 Amp alternators, with the right pulley. These are the serpentine belts that are incompatible with the V-belt type.
DDH

Mr Goodfahrt · #8 04-14-2004, 06:58 PM

According to the guys at repairflix.com the alternator off a 1991-93 Saab 900 2.1 will fit with same bolts. The only concern is you must modify the connector and belts will have a little less adjustment room but still enough to work. The Bosch number is AL129X.

This is a 115 Amp alternator.

BTW, I have not personally tried this but I may this summer.

81Wagon · #9 04-14-2004, 07:27 PM

Says Mr Goodfahrt:

Quote:

According to the guys at repairflix.com the alternator off a 1991-93 Saab 900 2.1 will fit with same bolts.

Dude, you rule!

Bosch 65A alternator (AL117X):

Bosch 115A alternator (AL129X):

Obviously it's impossible to tell exact dimensions from a couple of pics, but it sure looks like a perfect match! As far as the size/shape/mount is concerned, at least. Any differences in the connections shouldn't be hard to adapt to.

Fastlane has it... too bad there's no chance of redeeming the core charge

. I might try this in just a few weeks...

shear2001 · #10 04-14-2004, 11:24 PM

I had'nt read my email when I purchased the 55Amp. I now wish I had went for the 65 Amp. I purchased the Bosch this time and not an off the shelf aftermarket. It lasted approx. 1 1/2 years.Hope this one gives me better longevity. If I remember correctly, installation was no picnic!!Oh well, thanks for all input.

dieseldiehard · #11 04-15-2004, 12:36 PM

This is revolutionary info!
I had never heard of an alternative (except the AL69X).
It looks like Bosch uses the 115 Amp core and made a version for SAAB with the same housing basically (except the back side looks like it has more openings for better airflow).
A big "Thank you" to Mr. Goodfahrt and 81wagon for the posts, and to repairflix.com for the concept.
Now there will be a run on these cores at the junk yards I presume.
FWIW, HGV says his stock alternator in a W124 wagon has something like 300K miles on it! I never heard of such life. In the W123 chassis they seem to fail at a fraction of that. I know one thing, changing the alternator in a W124 is a lot of work, like ten times more work that any W123 I ever worked on!
DDH

MBDFahrer · #12 04-15-2004, 12:48 PM

I had my alternator done on the 87 300D. It didn't seem hard cause it was 3 people (amateur mechanic me, amateur mechanic friend, ASE Certified friend's dad

watching and confirming most of the time) 45 minutes to do the swap.

Mr Goodfahrt · #13 04-15-2004, 12:55 PM

The www.repairflix.com video was extremely helpful with tips on this - defenitely worth the price. Especially about how to remove the old one. I think mine is definitely ready for replacement. I swapped out the voltage regulator and still only getting 12.2 max. Guess I'm running on the battery mostly...

I am checking yards in the Baltimore/Washington area for the AL129X. If anyone else finds one around please let me know. If I find one, I will do a newbie walk through on how I make out (will be authentic since it will be my 1st one ever).

gsxr · #14 04-20-2004, 05:26 PM

I had been under the impression that the early V-belt pulley (say, for OM61x engines) does NOT work properly with the later alternators that came with serpentine belt pulleys. You mean you got this to work? With the stock V-belt adjuster, brackets, and all that jazz? Any photos? This is the first I've heard of anyone actually doing it!! I thought the early pulleys were "keyed" where the late (serp) pulleys are taper fit only.

I upgraded my little 70A stock unit with a 150A unit in my 1987 300D, which is a piece of cake, since both have serpentine belts and the pulleys swap perfectly. Photos are here:

http://www.meimann.com/images/mercedes/W124_stereo/white_87/
and
http://www.meimann.com/images/mercedes/W124_stereo/blue_87/

dieseldiehard · #15 04-20-2004, 06:59 PM

The last W123 alternator I installed was a rebuilt (AL80X?) with twin pulley and I was surprised that it did not require a key, no keyway even!
The earlier version I removed used a single pulley and required a key (returned it sans-pulley~)
Dave, I never got that big 115 A alternator for my W124, the seller must have decided that he needed it (like the neutral feedback I left him) I wanted to upgrade the car but now that its done I'll live with the stock alternator. The big SAAB (129X) alternator has a V-pulley on it, its not a serpentine. I am now looking for one of them whenever I scrounge.
DDH