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Old 12-25-2002, 12:37 PM
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Installed a 143A alternator in my W124 (86-95 E-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 (and, it was the wrong diameter). 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 unit is rated at 143 amps, and connected 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 alternator output is slightly less when hot, than when cold.)

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 little 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! 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 HVAC 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 sap 2-5 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! 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:
http://www.w124performance.com/images/W124_stereo/

Only one of the photos would squeeze past the ShopForum 65k/800x600 size limit, so you'll need to click the link above to see the rest of them!


UPDATE: I have since upgraded to the 150A version, just for grins. I also have upgraded my '94 E500, and plan to upgrade my '93 300D as well. The larger alternators have been working perfectly for over 4 years now. It's also helpful with the factory afterglow system, and heated seats, both of which I added to my '87...

Attached Thumbnails
Installed a 143A alternator in my W124 (86-95 E-class) - with photos-alt_installed.jpg  
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1997 E420 - 155kmi (Bugeyes)
1994 E420 - 145kmi (Blondie)
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1992 400E - 189kmi (Stinky Dirty)
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Last edited by gsxr; 03-13-2008 at 10:14 AM.
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Old 11-17-2003, 09:29 PM
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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. 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:








HTH,
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Dave M.
Boise, ID

1997 E420 - 155kmi (Bugeyes)
1994 E420 - 145kmi (Blondie)
1993 500E - 193kmi (Lollipop)
1992 400E - 189kmi (Stinky Dirty)
Check out my website photos, documents, and movies!

Last edited by gsxr; 01-02-2009 at 01:01 PM.
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Old 11-17-2003, 10:08 PM
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So can you feel the horse power loss when driving? Does it effect fuel mileage? I am not about to spend 300 bucks for an alternator. I will go junk yarding and hopefully find a wrecked 'new benz'.

I am in need of a bigger alternator. My poor 55A alternator is actually doing pretty well with my subwoofer. The headlights will dim when it bumps at idle, so I keep it close to 1,000 rpm and the dimming stops.
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Old 11-17-2003, 10:19 PM
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blue car interior

wow - I can't believe the lengths you went to get a stereo into that blue MB!
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Old 11-17-2003, 10:26 PM
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dave,i had a question about your door panels...did you buy those pre-fab...or did you make them? and any idea how i could do something like that to a w126? im itching to put more speakers in my car,since i have 2 channels on one of my amps that isnt being used at all....i also need to look into getting one of those 200 amp alternators....the paper that came with my sub amp says it can draw in excess of 150 amps...im thinking my stock alt. isnt gonna cut the mustard for much longer
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Old 11-17-2003, 10:38 PM
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190D22 - I couldn't tell a difference in power loss with the big alternator, but I have 148hp, and you have less than half of that. So for you, it could be noticeable. But with a subwoofer amp, you don't have much choice! I'd get the big alternator and deal with the power loss (if any). If you read the original article, you'll see you can get a nice used 143A for under $100 shipped to your door. I wouldn't spend $300 on one either!

bodyart27 - Yeah - and I'm not done yet! I need to complete the amplifier & capacitor installation in the trunk, the 150A alternator install, the power distribution block at the battery, and the bandpass subwoofer enclosure. The photos you see are what's done so far. When it's complete, I'll post a report here - probably in the Car Audio section, though.

85drtysthbenz The door panels are from Jehnert Sound Design in Germany. Unfortunately, they don't make anything for the 126 chassis - only the 124, 129, 170, 202, 208, and 210 (as of last year anyway). I bought them because I did NOT want to dink around with custom fabrication. They're not cheap, but custom fab isn't either. A really GOOD high-end stereo shop can make custom MDF & fiberglass door panels for you that will work well, and look nearly stock, but plan on the cost being $200-$300 per door - and that's without speakers! I'd contact LaJolla audio first (post in Car Audio forum) and see if they have something for you. On the alternator, ummm, you have a problem. The high-output units only bolt on to engines with serpentine belts. Your OM617 has V-belts. So far, nobody has figured out how to make a serp-belt alternator bolt up to a V-belt engine. You'll be stuck having your stock unit re-wound at an electrical shop, which will help, but not be as good as the OE monsters (143/150A).


HTH,
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Dave M.
Boise, ID

1997 E420 - 155kmi (Bugeyes)
1994 E420 - 145kmi (Blondie)
1993 500E - 193kmi (Lollipop)
1992 400E - 189kmi (Stinky Dirty)
Check out my website photos, documents, and movies!
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Old 11-17-2003, 10:47 PM
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I was thinking the exact same thing... our engines are totally different animals (power wise). But, are (nearly) all mercedes alternators the same mounting style? I could just go with a smaller size than 143 but WAY bigger than 55!

Suggestions?
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Old 11-17-2003, 10:50 PM
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The short answer is that almost all alternators from 1984-present, with serpentine belts, should be interchangeable. That's NOT a guarantee though. It should be pretty easy to locate a 100-120A unit, almost anything from 1990-up with a V8 engine will have one of those. It's the 143/150A units where you need to be picky about the year & model. Honestly, it depends how serious your stereo is. If it will pull a LOT of current, I'd go for the 143A, with at least a 4 gauge cable to feed the amps in the trunk. Remember that without an electrical load (i.e., with the stereo off or at low volume), the alternator drag will be very low - almost no power loss compared to your stock unit. I would get 100A at minimum though...
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Dave M.
Boise, ID

1997 E420 - 155kmi (Bugeyes)
1994 E420 - 145kmi (Blondie)
1993 500E - 193kmi (Lollipop)
1992 400E - 189kmi (Stinky Dirty)
Check out my website photos, documents, and movies!
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Old 11-17-2003, 10:53 PM
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[. You'll be stuck having your stock unit re-wound at an electrical shop, which will help, but not be as good as the OE monsters (143/150A).


HTH, [/B][/QUOTE]

i wonder what kind of output i could get by having my stock alt rewound? i gotta do something before long...all this headlight dimming,even at half volume, is driving me crazy
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Old 11-18-2003, 10:35 AM
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Well, the largest V-belt alternator that I know of (stock) is 65A. A good shop can probably pump that up to 80-90A, I think. They're limited by the physical dimensions of the housing. Yours is probably either 55A or 65A, which is kinda small for any decent stereo. My stock 70A was pretty weak too. No idea on cost.
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Dave M.
Boise, ID

1997 E420 - 155kmi (Bugeyes)
1994 E420 - 145kmi (Blondie)
1993 500E - 193kmi (Lollipop)
1992 400E - 189kmi (Stinky Dirty)
Check out my website photos, documents, and movies!
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Old 11-18-2003, 05:49 PM
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I'm new here, have an 83 240D. The alt is dying I think. Only throwing about 12.9 volts even at around 2k rpm. I replaced the voltage regulator. Has anyone found a replacement bigger than stock or the 65 amp alt? I'd love to throw something in that could handle a amplifier or two
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Old 11-19-2003, 09:37 PM
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Well I have done voltage tests and it won't drop below 14.1 with the sub hitting its hardest. I can't remember if I had all my other stuff (headlights, fogs, heater blower, etc) on or not. I have only a 160 watt pioneer premier amp driving a 10" sub mounted in a properly tuned box. It hits hard inside my car, but it is not very loud outside the car.

A 100A or so alternator sounds good. 143A-150A sounds like overkill for my little 2.2 that runs like a 2.0.
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Old 11-19-2003, 11:07 PM
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If you're staying above 14 volts, that's fantastic. But you should test with "normal" accessories on - lights, heater fan, etc and see if it's the same. I'd shoot for a 110-120A alternator, those should be pretty easy to locate - and relatively cheap, too. My stock 70A was pretty weak with much load applied, especially at idle (read first post in this thread for all the gory details).
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Dave M.
Boise, ID

1997 E420 - 155kmi (Bugeyes)
1994 E420 - 145kmi (Blondie)
1993 500E - 193kmi (Lollipop)
1992 400E - 189kmi (Stinky Dirty)
Check out my website photos, documents, and movies!
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Old 11-19-2003, 11:59 PM
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A 90 amp VW alternator might be an interesting option for those with the v-belt system. Most VW's from the late '80's on up w/AC had 90 amp units IIRC.

I put a 65 amp VW alternator in my old 220 D to replace the wimpy 35 amp original alt. w/ external regulator-- worked great.

Good luck.
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Old 11-20-2003, 12:16 AM
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Zeitgeist - great idea! I didn't know it bolted up to the OM61x that easy. I upgraded my VW Dasher 55A alternator to a 90A unit from a later GLI, which was a big help. There was a 115A unit available also, I wonder if that would fit. It uses V-belt pulleys. I wonder if they'd line up with the OM617. That would be a GREAT solution for all the OM617 owners drooling over big alternators!!
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Dave M.
Boise, ID

1997 E420 - 155kmi (Bugeyes)
1994 E420 - 145kmi (Blondie)
1993 500E - 193kmi (Lollipop)
1992 400E - 189kmi (Stinky Dirty)
Check out my website photos, documents, and movies!
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