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  #31  
Old 03-13-2008, 05:29 PM
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Quote:
Originally Posted by iwrock View Post
The back of the stock alternator has plugs on it, not terminals... Do I just rerun new wires?
I have detailed photos of the new wires I ran, see the links in the first couple of posts. Use 4 gauge (or two 8 gauge in parallel) as a minimum for 143-150A.

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  #32  
Old 03-13-2008, 05:30 PM
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I forgot about that aux fan....in the summer when it comes on at idle in traffic it drags my voltage from 14 down to 12.5! And I don't even have A/C! I'd like to fix my A/C someday....so a bigger alternator is a must in all cases....I should have done it when I needed a new one but I did not have time to sit and re-wire the car nor search for a good priced 115A+ unit.
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  #33  
Old 03-13-2008, 05:49 PM
Craig
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Originally Posted by gsxr View Post
Even with a bone stock vehicle, some of us don't like yellow headlights at idle, for example with the AC on high and the auxiliary fan running, on a hot summer night. Every 1980's MB I've owned with a stock alternator (and no additional loads) does this.
OK, both my cars' lights are fine at idle with everything turned on, but I also don't have "off-road only" lights, a "pimp-my-ride" stereo, or any WVO crap. I do have a post-glow relay and relatively new batteries.

If you need extra electrical power for some reason, have a ball. I was just wondering why you thought it was necessary.
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  #34  
Old 03-13-2008, 05:52 PM
Craig
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Originally Posted by pawoSD View Post
I forgot about that aux fan....in the summer when it comes on at idle in traffic it drags my voltage from 14 down to 12.5!
That does not sound right, you may have a problem with that fan. I would take a look before you toast something.
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  #35  
Old 03-13-2008, 05:59 PM
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Originally Posted by Craig View Post
OK, both my cars' lights are fine at idle with everything turned on, but I also don't have "off-road only" lights, a "pimp-my-ride" stereo, or any WVO crap.
That depends how you define "fine". With a hot engine & alternator, and no loads turned on, check battery voltage. Probably 13.6v, give or take a few tenths. Which is not a problem. Now turn on the headlights, AC on max, and in force the electric auxiliary fan on (which runs most of the time with the AC in the summer). I'll wager a trunkful of WVO crap that the voltage will have dropped well below 13 volts. Wipers, rear defrost, radio, etc would add to it. This is normal behavior for a stock 55-70A alternator used on the 1980's models.

Some people may not notice it in the headlights, others do... with the load present, and at idle (stop light/sign), the lights will brighten noticeably when the engine is revved. Might not be as visible in the city, with lots of ambient street light. What pawoSD reported is typical, if you have a volt meter inside the car, so you can monitor it.

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  #36  
Old 03-13-2008, 06:07 PM
Craig
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OK, I still think you have a solution in search of a problem, but if you think it somehow helps you; go for it. I'm good with the stock system. There is no real downside to installing a bigger alternator, just your time/money.

BTW, I still think pawoSD should take a look at the current draw of that fan.
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  #37  
Old 03-13-2008, 06:10 PM
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It only does if its been running at idle for a while. It spins freely and runs strong. They use a lot of juice!
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  #38  
Old 03-13-2008, 06:13 PM
Craig
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Originally Posted by pawoSD View Post
It only does if its been running at idle for a while. It spins freely and runs strong. They use a lot of juice!
OK, that just sounds like a big voltage drop for one fan. If it's spinning freely it's probably not drawing more current than normal.
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  #39  
Old 03-13-2008, 06:37 PM
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The aux fan typically pulls 12-15 amps, and is fused at 16A. Often those fuses show signs of heat damage after a few years. If the car is already using 20-25A, an extra 15A load pushes the stock alternator past the limit of it's idle output (which is only 35-40A at idle). Remember, the alternator rating is typically at 2000rpm (engine RPM). The older alternators will typically put out about half the rated current at idle. The newer, high-output ones are more like two thirds rated current.
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  #40  
Old 03-13-2008, 07:03 PM
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OK, 12-15 amps sounds like a lot of current for that fan (thats almost 1/4 HP), but I've never checked myself. If it does pull that much it would cause a voltage dip.
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  #41  
Old 03-13-2008, 07:09 PM
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I agree wholehartedly with GSXR. I bought my '91 TE4matic at a time when I had an '85 quattro and '85 Jetta, both had 90a alternators (stock). The new Mercedes was the only one that would idle at low voltage, to the extent that the rear-window defogger and seat heaters would shut off when idling at a light or in slow traffic, the quattro would happily power the heated seats and rear-window defogger. The weak alternator did finally give up, around 90,000miles, where the quattro alternator was still original when I sold it with just over 200,000miles.

The alternators are weak.

The second thing that happens with the low output at idle is that you are drawing from the battery. Look at what affects the capacity and life-expectancy of a lead-acid battery. It has a set number of cycles, the deeper the cycle the less of them you get. every time the car is idling and fans etc. are drawing from the battery, that's a discharge-charge cycle albeit a minimal one. More important is the proper charging. You MUST charge a battery properly, every time, to maintain full capacity. Shallow charges and multiple cycles without proper charging will degrade the capacity of the battery as the battery's plates grow dendrites and have sulfated patches that do not recover. The lead-sulfate also sluffs off and ends up in the bottom of the battery, it can endure vibration and shock best when fully-charged.

Anyway, charging a lead-acid 6-cell battery is best over 13.4v (at the battery) regardless of the current necessary to maintain it. Some manufacturers believe in a 14.3v equalization to fully boil the sulfates from the plates and expose useful lead. The more incomplete charge cycles, the more sulfates, and eventually the more irreversable damage.

In short, it is important to properly charge a battery, 13v doesn't do it, and if it is interrupted and discharging every time you hit a stop sign, you're killing your battery. For this reason, I felt it necessary to upgrade to a charging system at least adequate for a VW of the same era: the 90a Bosch. 65a is a joke.

btw, thanks G for posting this DIY, we do appreciate it. Is the 150a an ML part (looks like it says "2001 ML" in paint marker)?
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Last edited by babymog; 03-13-2008 at 07:22 PM.
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  #42  
Old 03-13-2008, 07:47 PM
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Excellent writeup, Jeff... all your technical points about batteries & charging are spot-on.

There are a number of donors for the 143A and 150A units, basically from late 90's and early 2000's models with M119, M120, and M113 engines. But be careful past about 2002-2004, the alternators changed somewhere in that time frame to a newer electronic 2-wire regulator, which I'm not sure is compatible with our older 1-wire setups.

Anyway, I have a spreadsheet with more info, which may help those in search of a 143A or 150A unit. Click here for the Excel version, or those without Office, click here for a PDF version. It's out of date, I need to update the info on there. Most used units are in the $75-$125 range, btw.

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  #43  
Old 03-13-2008, 08:46 PM
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This is the 90a Bosch gleaned from a '92 190E 2.3. Looked like a new replacement, so it was worth the $20. Ring-terminal B+ instead of the spade-terminal on the original '87 65a Bosch. Roughly 11.5lbs.
Attached Thumbnails
Installed a 143A alternator in my W124 (86-95 E-class) - with photos-90abosch.jpg  
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  #44  
Old 03-14-2008, 06:19 PM
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I did the 143/150A swap a while back in my SDL and 300SEL, nice upgrade for sure.
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  #45  
Old 07-08-2008, 05:21 PM
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B+ D+ and W terminals

I used the B+ and D+ terminals on the new alternator, left the W terminal open.

Do you know what the W terminal is?

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