What is this thing? In the engine bay - 1972 W115 240D

[j-galap]

Hi folks,

Cleaning up in the engine bay yesterday, I followed a cable to find something not plugged in (and the plug all nicely melted).

See imagine:



I have no idea what it is. Any ideas? My car functions just fine without it...!

Thanks

[nordfisch]

Hi,
this is an external regulator for the generator.

Later generators have an internal regulator and don't need this part.

Regards
Norbert

[j-galap]

Ah, generator you mean alternator I assume? The alternator on my car is pretty new so perhaps that explains it.

I think I'll remove entirely then! Keep things tidy

[tyl604]

No, the term is generator - which all cars used to have. They were replaced with an alternator - different product.

[Diseasel300]

Originally Posted by tyl604

No, the term is generator - which all cars used to have. They were replaced with an alternator - different product.

A generator is a DC machine with a commutator. They fell out of use in the 1950s. Alternators (which produce AC voltage that's converted to DC voltage through a diode bridge) took their place and have a pair of slip rings instead of a commutator. It was once common for them to have an external regulator, Ford kept them through the 1980s. They are *NOT* a "generator" though.

[Frank Reiner]

A few gratuitous words on the matter of electrical generation.

Both of the devices ("generators" & "alternators") found in automobiles that provide electrical energy are energy conversion devices; mechanical energy is converted to electrical by the device. That process of conversion we commonly refer to as "generating".

Within the current carrying windings of both devices the current alternates in polarity from positive to negative. Hence, internally, both are alternating current (AC) generators, aka "alternators".

To produce an output of direct current (DC) that is usable in the automobile, the internal AC must be rectified to DC. It is the method of rectification that differentiates a "generator" from an "alternator". [Internally both are generators, and both are alternators.]

In the device which we call a "generator" the magnetic fields are stationary and the current carrying windings rotate. The AC in the rotating windings is rectified to DC by the interrupted contacts of the brushes on the segments of the commutator. A segment of positive sign is always presented at one brush, and a segment of negative sign at the other brush. In 180 degrees of rotation, a segment changes sign from + to -, and then back to + in the next 180.

In the device referred to as an "alternator", the magnetic field rotates, and the current carrying windings are stationary. The AC generated in the windings is rectified to DC by diodes which allow current of + sign to pass, but block current of - sign.

[Maximan1]

Originally Posted by Diseasel300

A generator is a DC machine with a commutator. They fell out of use in the 1950s.

I had an original generator in my '73 VW bug, and an original generator in my '65 Rambler. They were definitely still being used after the 1950s.

[BWhitmore]

I believe Chrysler introduced the alternator in 1960 and GM in 1962. My dad ordered a new 1962 Pontiac and was able to have access to the GM assembly plant in South Gate, CA. He witnessed the car being built and the installation of the alternator.

[Idle]

Given the vintage of the car and the previous owners it is bound to have had....

It looks like someone needed an alternator but didn't want to spend the money for a new one. But they had a generator and a voltage regulator and found the the generator would fit. Hence the addition of the regulator needed to make the generator work with the car.

Then, someone else owned the car and decided to put the thing back right and just blew off removing the regulator. Or perhaps the first 'solution' didn't work so well and melted down the plug. Then they owner would have to have sprung for an alternator anyway.

In any case this is not something that came that way from the factory. I mean, it is a Mercedes. You can order almost anything you want and maybe someone was too old school to want one of them new fangled alternator thingies.

In any case an interesting question. The good part is you don't need to worry about it.

And I bet if you removed it and found a Bosch part number on it you would find it came from a Volkswagen.

[gmog220d]

I'm digging this thread up because the original question was never quite answered. I also wish to add additional information I recently discovered which may help others who own cars that use the same 55 amp alternators (Bosch AL-80-X).

That "thing" mounted to the RH side of j-galap's engine compartment is (was) a external voltage regulator (VR) used in conjunction with the 55 amp alternator that came with '74 240Ds. This was an upgrade from the 35 amp alternator that came with '73 and earlier W115 220Ds, which also had external VRs. The external VR only came with earlier W115 240Ds. Have a look at this page in our sponsor's online catalog:

https://www.pelicanparts.com/catalog/SuperCat/3195/MBZ_3195_ELCHRG_pg1.htm#item4

Note that both internal and external VRs are offered. There is a chassis number break corresponding to numbers 056705 and 056706.

My '74 240D came with the external VR setup. My car's VR went bad recently, and I replaced it, but not with another external VR. I instead chose to replace it with the internal type VR associated with later cars. I simply replaced the brush holder attached to the alternator with the new style "short brush" VR purchased from our sponsor (Bosch). It works fine, and simplified my car's engine compartment a bit. Here's what the brush holder I removed from my car's alternator looks like:



So apparently what happened to j-galap's car is the alternator was replaced with the standard Bosch AL-80-X replacement listed for the car. Those alternators come with the internal VR so there was no need to use the external VR.

I also want to add that during my research into whether or not I could install a internal VR in my car's alternator I found a pretty useful web page. The page is part of a Volvo 240 related web site, but those cars and others used the same 55 amp alternator. The owner of this page sells adjustable output VRs, both external and internal, that might come in handy. There's a a lot of valuable information about alternators in general on that page, and I found the confirmation I needed before ordering the internal VR for my car.

https://www.240turbo.com/AdjustableVoltage.html#externalregonly

Cheers!

[Idle]

I asked a friend to look at this and he said his 1972 220d had this voltage regulator and it was still hooked up. So apparently he must have the old style alternator as well.

[t walgamuth]

Alternators were first introduced as standard equipment on a production car by the Chrysler Corporation on the Valiant in 1960...wikipedia.