Failed voltage regulator ...
Thread Starter
Rennlist Member
Joined: Oct 2003
Posts: 7,210
Likes: 17
From: Nova Scotia
Failed voltage regulator ...
There is a certainty at some point in 993 life that one will twist the key to start the car .... and be greeted with a grrrr ... clackity clicking of the starter solenoid: usual causes are a flat battery, or a dying starter.
My life was cheered by such an event a few days ago - battery was nearly flat (11.6v). As it was 4 years old, and with snow in the forecast, it was easy to conclude that the cold weather finished off the battery - wrong! The battery charged up onernight to a steady 12.6v, and the car started at the first touch.
No dash icons lit up indicating an alternator issue ...... so I almost drove off, thinking that I had left a trunk light or something similar on - which drained the battery: in a fleeting moment of doubt, I metered the battery with engine running- only to find battery voltage: NOT the normal 14V of a healthy alternator.
Long story, short version - pulled the alternator, and swapped in a fresh voltage regulator/brush set; now pumping out a healthy 14V @ 2000RPM ( 13.2V at idle, as I have the RS pulley hub = slower alternator speed).
It is often quoted that failed voltage regs allow the charge voltage to skyrocket uncontrolled - say, ~18V: enough to boil a battery dry, and lead to a hydrogen explosion event. Well, they can fail in the other direction too - and this is a case in point.
So what is the point of this post - simply this: when the flat battery event occurs, get the car restarted by whatever means, and do some voltage checks prior to buying a new battery - or new alternator for that matter: the Bosch alternator is pretty robust - more so than the $25 regulator. Replacing the reg. is the smallest part of the job if the alt. has to be removed anyway - so, it is a worthwhile step vs buying a different alt.
My life was cheered by such an event a few days ago - battery was nearly flat (11.6v). As it was 4 years old, and with snow in the forecast, it was easy to conclude that the cold weather finished off the battery - wrong! The battery charged up onernight to a steady 12.6v, and the car started at the first touch.
No dash icons lit up indicating an alternator issue ...... so I almost drove off, thinking that I had left a trunk light or something similar on - which drained the battery: in a fleeting moment of doubt, I metered the battery with engine running- only to find battery voltage: NOT the normal 14V of a healthy alternator.
Long story, short version - pulled the alternator, and swapped in a fresh voltage regulator/brush set; now pumping out a healthy 14V @ 2000RPM ( 13.2V at idle, as I have the RS pulley hub = slower alternator speed).
It is often quoted that failed voltage regs allow the charge voltage to skyrocket uncontrolled - say, ~18V: enough to boil a battery dry, and lead to a hydrogen explosion event. Well, they can fail in the other direction too - and this is a case in point.
So what is the point of this post - simply this: when the flat battery event occurs, get the car restarted by whatever means, and do some voltage checks prior to buying a new battery - or new alternator for that matter: the Bosch alternator is pretty robust - more so than the $25 regulator. Replacing the reg. is the smallest part of the job if the alt. has to be removed anyway - so, it is a worthwhile step vs buying a different alt.
Rennlist Member
Joined: Sep 2009
Posts: 8,679
Likes: 785
From: Canada & the Alps
Install a voltmeter that is connected directly to the battery so that you know what is going on at all times. 
