battery volt reg 85 190e
 

hey there, I think I drive my car less than most people on this forum, now that the weather is nicer I'm on two wheels. But when I do want to drive the cah, the battery is always dead. So I've been tinkering to see if I can't narrow in on the problem (the car will not start after say being left for four days). I started by fully charging the battery with a trickle charger. Then disconnected neg term and completed circuit with multimeter measuring current draw, basically none. I had done work before to find that central locking system was not working properly but that is long gone at this point. So no huge current draw with car off. Hook back neg term check voltage of battery 11.2. start car, engine running at idle for no more than one minute check voltage 11.2. have better half step on gas up to ~2k car's only been on for one minute check voltage: 11.2. So here are the questions. It seems like my alternator's not supplying enough juice. My car did stall on me one time when I sat in bad traffic and didn't move an inch for about forty minutes, which would suggest to me that unless this car is run at high rpm the alt can't keep up and the car is really only making it day by day because of the trickle charge. But this only happened once otherwise once the car starts, it always gets me where I want to go, I was under the impression that if your alt was bad you couldn't drive the car more than a mile or so before the battery would be completely spent. I have searched on this and see volt reg as something people replace when the alt is questioned but don't really know what it does, I know where it is and how to get it out, but not what it's real function is. What else can I do to confirm that it is a weak charging system other than measure voltages with car on and off? Someone suggested starting the car and removing the neg term to see if engine dies as diagnostic test of alt but there must be other ways too. any help would be great, thanks.

CDT

Your voltage is too low with and without the alternator running.

A properly charged battery should show a voltage of about 13.8V. The alternator should give a voltage of 14.5 to 15V when running.

Several things come to mind as possibilities.

1) Both the alternator and battery may be shot
2) The battery is OK but the alternator is not putting out enough
3) There is a common cause for such a low reading, eg a bad ground
4) The drive belt for the alternator is slipping
5) The battery is shot and is loading up the alternator badly
6) The idiot light in the dash has blown and is causing a malfunction in the alternator

When I last supected my alternator, my local Bosch agent bench checked it for free. Last time I bought a rebuilt alternator from my 190E I paid 38 GBP, say $55, from my Bosch agent.

The voltage regulator is a unit held into the back of the alternator with two screws. It included the brush assembly which is just as likely to give trouble as the VR.

thanks
 

one other tid bit on this. the battery is suspect. its only a year and a half old but when the car wont start (aka I know to hook up trickle charger) lately the trickle charger when hooked up to the dead battery will read 100% charged almost immediatly. I remember half a year ago that a dead battery would read 25% or 50% dead. so the battery is suspect. its a duralast, I just hate to trow money away without having a true diagnostic test to find the problem, shotgun approach to electrical system could get expensive. Last question, if a ground wire or strap were bad, wouldn't I see a current draw with the car off? Thanks for the help.

CDT

Try going back to to the supplier. A year and a half might be out of warranty, but a battery should last longer than that. A simple (and free!) load test should identify a truly dead battery. Running the battery completely flat will shorten its life considerably, however.
Nope. The ground wire is simply the final piece in the circuit. Typically, a bad connection increases the resistance in the circuit and reduces the voltage available to the appliance, including reducing the voltage to charge the battery