Testing Voltage Regulator and Alternator

[Pawel66]

I found on this forum, in one of the old posts, a VR/alternator test, saying:
- measure voltage on D+ connector
- if the voltage is similar to the one on battery - VR is bad, alternator is ok
- if the voltage is significantly lower, alternator is bad

I have 13.4V on D+ and 14.1V on battery when the engine is running.

Any hint on what do I make out?

[WRe]

Hi Pawel,
if you want to test your alternator and voltage regulator I would:
1. Check all connections: At lot of faults occur because of bad, corroded connections espec. ground connections
2. Check charging current at battery in idle and higher rpms: Should be between 13,5 and 14,5V.
    If it's significant more than 14.5 your voltage regulator doesn't work.
    Maybe this could help: https://www.strichacht-forum.de/knowhow-v2/index.php?title=Reparatur_des_externen_LiMa-Reglers
    Alternative to electro-mechanical VR: Beru GER024 (~ 20€).
    If it's lower your alternator has a problem: belt tension, carbon brushes, diodes (charge control lamp glows during operation), ...
...WRe

[teahead]

Run the car, turn on all accessories (lights, radio, wiper, heater, AC) and measure voltage at battery.

Should be at least 13v.

[Pawel66]

Thank you both for your kind attention, comprehensive explanation and advise!

I have 14.1V across speeds on battery posts.

In the D+ test I have 13.4 vs. 14.1 - lower, but the alternjator lamp does not glow... truth is, the under dash courtesy lamp is blinking slightly at idle.

Will do the "teahead test".

[wayne R]

Pawel ,Hi ,i realize this was posted a while back, but thought i would,
let members know, about  this small dash  monitor that pushes into your
cigarette lighter socket,.
Its made by  Innova 3721, for memory about $15,can be purchased  from
many places,and although we as pagoda owners dont really need it, it works fantastic,
gives you the actual reading ,idling and cruising.Or kept in glove box, very handy.
Ask hundreds of  Porsche 911 owners that do not have voltage dials--lights up until 1987.
Critical for Porsche as when there alternator goes bad, it can start charging up to 16-17 volts
and blow the battery,which can cause a fire.
Photo from my 84 Porsche 911 , sold couple of years ago.

[Tyler S]

Here is a very good write up on theory, operation, and testing. Just remember that D+ is isolated from B+ (battery voltage) so a 1 volt differential is not unheard of. Varying state of charge in the battery, electrical load, and engine rpm all play a part in how the regulation is affected.

https://ratwell.com/technical/ChargingSystem.html

[Pawel66]

Thank you very much! great idea and great material!

One word on voltage regulator: when I tried a new Hella replacement - it did not keep charging voltage where it should be. It allowed 16-17V. A new Hella!

Makes me think you always should check a new VR.

NEW - Never Ever Worked.