Hi all,
Just making a post for the archives pretty much here as it seems hard to find the information on. For the last several months I've been going through batteries like mad. After driving my car maybe 30 miles since the brand new battery was fully charged I put the charger on it and it wanted 3-4A which is pretty bad as that trickle charger generally goes slowly, so I know my car wasn't charging properly. Well I figured it was finally the time to order a new adjustable voltage regulator which is sold by TransPo. I called their closest distributor (found here) and told them what I wanted, it was very simple and very straightforward with an awesome price of $11.90. The part number for my 83 300D and probably many other mercedes alternators is IB372A. You can look up a different part number using their lookup menu located here, then clicking car application guide. There are two versions available one is a regulator which is set to 14.1V and the other, which I bought, is the adjustable kind which goes from factory voltage up to what most other cars on the road do.

Why get a higher voltage? Primarily it allows the battery to charge more completely and faster. My brushes were worn out anyway so I figured I could pay $15 for a regulator or I could pay the same price or less for an adjustable one, so why not? The regulator comes out with two screws, one can be a little of a task getting to but the other is cake. Perhaps I'll make a page for this.

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Jeff M.
Mercedes W123 DIY pages are now located here.
1983 / 1984 300D Sold
2000 CLK430 Cabriolet ~58k Sold
2005 Avalanche 4x4 ~66k

I revisited this thread and found the Transpo links dead.
BAD NEWS:
TRANSPO IS NO MORE!
here's the scoop: Early Warning for W124 Alternator Failure
Now the best alternative is just buy the PeachParts Bosch regulator, no need for adjustability anyhow!

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'95 E320 Wagon my favorite road car. '99 E300D wolf in sheeps body, '87 300D Sportline suspension, '79 300TD w/ 617.952 engine at 367,750 and counting!

THIS ~ As soon as you pay the extra $3 for a BOSCH branded voltage regulator your charging and dim lights issues with -vanish- .

Every non BOSCH branded V.R. I've tried (and I've tried a lot) never reaches the 14 volts, all BOSCH do right until the attery's at full charge .

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-Nate
1982 240D 408,XXX miles
Ignorance is the mother of suspicion and fear is the father

I did then what I knew how to do ~ now that I know better I do better

No issue with Transpo regulators in the past.
The beauty of the one I bought was it had an adjustment pot that you could set to any voltage 13.5 to 14.5 V (approx.) but yes Bosch seems the best bet now that Transpo made it difficult or impossible to buy. I would never buy a no-name regulator off the shelf in a Pep Boys or similar.

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'95 E320 Wagon my favorite road car. '99 E300D wolf in sheeps body, '87 300D Sportline suspension, '79 300TD w/ 617.952 engine at 367,750 and counting!

Or just get a 150a alternator off a modern post 2000 MB with a built in microprocessor controlled VR. Problem solved.

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CENSORED due to not family friendly words

This site has a mod that you can do to raise the charging voltage.
BOSCH Voltage regulator mod

In one of the Alternator threads one of our members did the above mod.

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84 300D, 82 Volvo 244Gl Diesel

I found this but don't know if the info is current: Adjustable Voltage Regulators for Bosch Alternators
Dave's Volvo Page - Volvo Adjustable Voltage Regulators

Looks like someone on ebay is also selling adjustable bosch type regulators-search = VR1 ADJUSTABLE BOSCH ALTERNATOR VOLTAGE REGULATOR IB373A 8020-1145A

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84 300D, 82 Volvo 244Gl Diesel

You could try here, they own Transpo and sell lots of other brands of parts.

Transpo Electronics

? Why make it so complicated ? .

I used to do the high ampere out put alternators but unless they had a BOSCH regulator they still charged under 14 VDC making it a wasted effort .

Just buy the right dang part and a spare for your glove box and FORGEDDABOUTI .

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-Nate
1982 240D 408,XXX miles
Ignorance is the mother of suspicion and fear is the father

I did then what I knew how to do ~ now that I know better I do better

Most of my vehicles measure 14.3 V when driving. I use a cigarette-lighter voltmeter. But, I think 13.5 V is enough to charge the battery, and anything over 15 V will "over-charge" it, which decomposes the water into H2 and O2.

The current output capability of the alternator is separate from the Vreg voltage set-point above, so the "wasted effort" comment of post #9 isn't quite true.

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1984 & 1985 CA 300D's
1964 & 65 Mopar's - Valiant, Dart, Newport
1996 & 2002 Chrysler minivans

Yes, it is true, I spent no small amount of time researching and beta testing this .

The stock 35A alternator is plenty unless you're adding serious current consumers .

The voltage, as you've checked is good as long as it goes above 14VDC above idle .

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-Nate
1982 240D 408,XXX miles
Ignorance is the mother of suspicion and fear is the father

I did then what I knew how to do ~ now that I know better I do better

Have not tried other brands, but I can vouch for the Bosch voltage regulators, I've installed a number of them in different vehicles and they are good stuff. Even the newest Made in India Bosch regulators are quite good.

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1998 E300 turbodiesel

America's Rights and Freedoms Are Not The Enemy!