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Voltage Regulator modification

5996 Views 5 Replies 3 Participants Last post by  gr_diver
Hello once again!

OPEL has mostly used Delco-Remy and Bosch alternators in the cars that this forum is about. I am going to focus on the latter (Bosch) and those with an internal voltage regulator, that many people (including me) use. In many cases, as I read on the web, it has been found that the BOSCH's alternator output voltage has been quite low at 13.8V, so under load it drops even more (OPEL (Haynes manual) describes that correct voltage should be 13.9-14.8V)

I came across this about a year ago.


I don't know how many of you are familiar with this mod, it is quite known and would say popular fix... I tested it, and shooted my voltage to 14.92V, TOO high, so I didn't use it as a permanent solution...

It is basically an easy fix, in short, one has to use a diode in the voltage regulator's ground "tongue", in order to "trick" the regulator that the volatge is about 0.5V lower than the actual, and thus have it increase it by such an amount, in most cases giving an output of about 14,5V.

I have been doing a bit of a research lately about voltage regulators, and read this article:


It says that those external electronic regulator found in cars and bikes are in fact adjustable, though one has to open the cover and locate a small 100 Ohms potentiometer (which the factory used for adjusting the unit and then sealed with a drop of paint), in oder to modify the output voltage.

Combining these two, would it be correct if I thought that by adding a potentiometer (100 Ohms as in the external regulators) instead of a diode as the first mod describes would result in having an adjustable voltage regulator? I mean, it's all about inserting a voltage drop in the ground path of the regulator, and such a pot can do it fine.

If I had a bench test power supply I would do the mod and post any results, but since I don't I am a bit cautious before attemting to mount such a modified unit in my alternator...

What do you guys think? Does it sound logical? Has anybody even tested this (I believe that there are smarter people, with more knowledge than me out there that may have though of it before...)?

Thanks in advance!
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Well, I have tried two different diodes (I kept a file of the results!!!), models:

a) 1N5402 which gave me a voltage drop of 0.38, and voltage from 13.95 to 14.92V,
b) BY255 hich gave me a voltage drop of 0.37, and voltage from 13.95 went to 14.89V

I tested these two, the first time I had mis-written the code "1N5402" with what I don't remember and the seller gave me that BY255 as a substitute for that forgotten code, the next day went back and bought the correct one, but I tried both...

Travis, maybe you can estimate what kind of a diode I need? That would make me more than happy, as I don't know much about electronics, and don't have anybody who knows to help me here that I live...
In addition, could adding a potentiometer instead of a diode work as a mod for adjusting a range of values (within the pot's specs) ?
Thanks man! That would be fantastic!!!! I really appreciate it!!!
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