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gsxr 12-25-2002 12:16 PM

Installed a 143A alternator in my W124 (86-95E-class) - with photos
Hi all,

This is not a "question" post, this is just a summary of what I did to my car, and thought it might help others as well. Due to large bulbs in my Euro lights and a hefty stereo planned, I needed more output. I picked up a 143A alternator from a 1998 S420 and experimented with it. I swapped my original pulley onto the 143A unit because the S420 pulley didn't stick out far enough. Otherwise it bolted right up - same mounting brackets, bolt spacing, everything. The new unit is larger and comes pretty close to the lower radiator hose but doesn't touch. So how does it perform? Read on:

I got the car fired up and tested the alternator output. Remember, my stock unit was 70A and had what appears to be two 10-gauge wires to the junction block near the battery. The new one is a 143A with a zero-gauge cable to a new distribution block and to the battery. I tested full load by turning on every electrical item I could, measured voltage with a Fluke 12 VOM, and current with a Fluke 36 DC clamp meter. All tests were done with a "hot" alternator, after driving the car at least 15 minutes with a decent load.

The stock unit could only cough up about 45 amps at idle, but did put out around 75amps maximum (revved up to ~2000 rpm). Voltage was poor... Never got higher than 13.6-13.7 volts even under light load or no load. Under moderate load it drifted down to lower 13's, and at peak load it went below 12 volts (!) as the alternator simply could not put out the power. :(

The 143A unit could put out roughly 100 amps at my ~600rpm idle speed, and appeared able to put out max current at barely above idle, not even 1000rpm! :D The highest load I could generate, including some current to charge the battery, was 125-130 amps. At 1000rpm, it put out the 130 amps and did so at 14.1 volts! And at idle, same thing, 14.1 volts (with a smaller load, under 100 amps.) The only time voltage dropped was with VERY high load at idle and I don't think I ever saw it go under 13 volts, and that was with an "artificial" load that is unlikely to occur in normal use.

My "normal" load is low beams (90Wx2) and ACC fan, plus whatever the chassis electrical stuff pulls (EDS, gauges, etc.) This appears to be roughly 40 amps, plus some current to charge the battery. The good news is, with my "normal" load I get a solid 14.1-14.2 volts, even at idle! VERY nice. I'd like the voltage a bit higher (14.4-14.6) but there is not an adjustable regulator available for the 143A unit (AFAIK). No big deal, I'm happy with the setup as-is. The stock unit badly needs an adjustable regulator, and I'd highly recommend one for those of you not interested in the full big-alt swap. Set it when stone cold to 14.6v or so, it will drop a bit as it gets hot, and you want to set the HIGHEST point.

The only down sides are extra weight and horsepower loss. The 70A unit weighs about 11.5 pounds, the 143A unit is 16.8 pounds. Not a big deal. But when you spin the shaft of the 70A unit, it feels light and spins easily. The 143A is MUCH heavier (massive) and definitely takes some extra crankshaft power to spin, even with no electrical load. I'd guess it could easily sap 3-5 HP more compared to the original. Still worth it, IMO.

Verdict: Would I do it again? Yes. I already bought another 143A unit & new pulley, and plan to install that on my other 1987 300D in a few months! :cool: For the record, a used 143A unit can be bought used for ~$75-125 or so. The donor car must be a 1996-1999 S or SL class with a V8 (SL500, S420, etc.) Others may work but I don't know what years & models, and most others are smaller (100-120A).

Photos of everything are here (nothing new from last time though):

I'll post a few photos below this, if I can find one small enough to squeak by the 65kB limit... :rolleyes:


gsxr 12-25-2002 12:17 PM

1 Attachment(s)
Here's a shot of the 143A installed, before the wires were connected:

gsxr 12-25-2002 12:21 PM

OK, well, the forum won't let me post any other photos because they are larger than 800x600, and I'm not going to re-size them all. Just click on the link below and see the photos for yourself:

:D :D


richbark 05-04-2003 04:01 PM

I have a 190e I want to upgrade the Alt on. My 65A is not working properly and since it needs to be replaced, I am thinking I may just install a high output Alt. It looks like you may have a 190e in your stable. Does it look like the 143A alt will fit in the 190 series?

I just got my car running great and now am starting my long list of custom upgrades (which includes a complete onboard LINUX based computer system). I will need more serious amperage to support my dream machine.

gsxr 05-04-2003 07:28 PM

Rich, assuming your 190E has a serpentine belt (which I believe it does), the alternator should bolt on. You will probably need to use the pulley from your old 65A but otherwise it should work. You'll need to beef up the cable to the battery, I'd use 4ga minimum (or a pair of 4ga), better yet use 2ga or 0ga. So far I've been really happy with my setup, I plan to install a second 143A on my other car too! :D :D

Good luck,

richbark 05-04-2003 09:35 PM

Thanks. I do have a serpentine belt and I will be on the hunt for a 143A tomorrow. I need to get this fixed ASAP (in fact I was thinking of buying a new 65A.. just to get the car useable.. but my wife said "no way..Fix it once only". I guess she is right. Thanks again.. I will post my results.

jcyuhn 05-05-2003 10:22 AM

What I *really* want to know is how Dave keeps those old diesel engines so clean. My 603 isn't bad, but it sure don't look like that!

- JimY

gsxr 05-05-2003 11:26 AM

Heh-heh.... thanks! :D :D Mostly just some engine cleaner from McParts, and a trip to the coin-op car wash to blast stuff off... more photos here:

:) :)

Limited Edition 07-29-2003 09:58 AM

Since Richbark has not posted his results yet, I will post mine. I installed a 143amp alternator in my 1993 190E 2.3. I got the alternator from Pat at Potomac German Auto.

The 190E originally had a 70amp alternator. I swapped pulleys and rotated the rear housing so the wiring would line up. It fits and works perfectly! I have not upgraded the cable to my battery yet, but it seems to be working fine for now.

I don't have any pictures yet or any power measurements but I will try to get those this week.

Thanks again for the research Dave!



gsxr 07-29-2003 11:41 AM

No problem, Don! Glad to hear it also works on a W201/M103 setup as well... :) :)

Limited Edition 07-29-2003 01:24 PM


Glad to hear it also works on a W201/M103 setup as well...
I have a M102 but it should work on a M103 with no problems also.

gsxr 07-29-2003 02:19 PM

Whoops - that's whay I get for typing a reply too early in the morning. ;) You sure do have the M102. Oooops! :eek:

gsxr 11-17-2003 09:27 PM

I got some photos of the 143A and 150A alternators side by side (click links below). Note that the 150A unit is slightly larger, and has a lot more venting in the case. Interestingly, the 150A is a half pound lighter, possibly due to the larger vents (16.25 lbs compared to 16.75). Also note the ratings on the nameplate. The 143A is rated 73-143A, the 150A is 90-150A. The first number is the alternator's rated output at ~1800rpm shaft speed, the second number is output at ~6000rpm shaft speed. That is NOT engine speed - you need to measure your crank pulley & alternator pulley diameter to translate that into engine RPM. On a side note, Bosch's website claims they now offer "Bosch Sport Compact High-Output Alternators" with outputs up to 200A, specifically designed for people like us with current-hungry ICE and Rallye lights. :D But I couldn't find a damned thing other than the press release, so I have no idea if they make a bolt-on 200A unit for our MB's.

Also: WorldPac now has the 143A and 150A alternators available. The 143A, with core (assuming you are upgrading and don't have a bad 143 to return), is ~$300. The 150A is closer to $400, which is nuts. Check with Rusty (800-741-5252, ***************) if you want a fresh rebuild. Or you can score a used one for $100-$150 if you check around enough.

Here's the photos:

mb123mercedes 11-18-2003 11:22 AM

Hi all.

Anyone know if it will fit a W123 diesel?


gsxr 11-18-2003 11:36 AM

I think this was posted earlier in the thread, but if not.... No. The big alternators fit MB engines with serpentine belts. So far, nobody has figured out a way to convert a late model alternator to the old V-belt engines. If you can do that, you'll have lots of people wanting to know how you did it! :D

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