cline@aero.ARPA (Ken Cline) (11/01/85)
Every time I start my `78 Scirocco, the charging system idiot light comes on. Once the engine has been revved (to about 2300 RPM), however, the light turns off and stays off. While the light is on, my ammeter shows the battery discharging, and when it turns off the battery charges normally. VW will examine it for $35 an hour or so, but I'd like to fix the problem myself (if I can find it). Any ideas out there?
mpc@rayssd.UUCP (Manny P. Costa) (11/06/85)
> Every time I start my `78 Scirocco, the charging system idiot light > comes on. Once the engine has been revved (to about 2300 RPM), > however, the light turns off and stays off. While the light is on, > my ammeter shows the battery discharging, and when it turns off > the battery charges normally. VW will examine it for $35 an hour > or so, but I'd like to fix the problem myself (if I can find it). > Any ideas out there? This is just a shot in the dark but it worked for me. The fan belt that goes to the alternator was loose. Oh sure it turns the alternator, but it was slipping enough so that it wasn't turning the alternator fast enough to charge the system. Check it out. A fan belt may be the cheapest component of the charging system to replace.
tupper@wanginst.UUCP (John Tupper) (11/09/85)
> Every time I start my `78 Scirocco, the charging system idiot light > comes on. Once the engine has been revved (to about 2300 RPM), > however, the light turns off and stays off. While the light is on, > my ammeter shows the battery discharging, and when it turns off > the battery charges normally. VW will examine it for $35 an hour > or so, but I'd like to fix the problem myself (if I can find it). > Any ideas out there? I have experience with several vw's (rabbit, scriocco, jetta) and they all do this. VW's are just designed that way. -- John Tupper tupper@wanginst (Csnet) Wang Institute of Graduate Studies wanginst!tupper (UUCP) Tyng Road, Tyngsboro, MA 01879 (617) 649-9731
aliv@ur-tut.UUCP (William Simonds) (11/11/85)
I have an '80 VW rabbit and the same thing hapened to me. Upon investigation, Ifound it to be normal. When you start the car, the battery charges the coils of the alternator and runs the electrical system, thus the battery is being discharged. Once the engine is revved, the speed of the alternator spinning causes it to develop >12 volts. At this time, this voltage takes over the work that the battery was doing and begins to charge the battery. As long as the light comes on when you start the car and goes when the engine gets up to running speed, you are alright. If the speed needed to turn the light off is greater than normal operating speed, then I would expect either the belt is loose, or the brushes are bad (probably the belt). I hope this helps.
aliv@ur-tut.UUCP (William Simonds) (11/11/85)
Keywords:what happened? I don't know what happened to my last article, but I will repeat the lost paragraph. What I meant to say was that as long as the light comes on when you start the car and goes off when the engine gets up to normal running speed, you should have nothing to worry about. If this is not the case then there may be a problem with the belt or the alternator itself. Sorry for the mistake last time.
saf@bonnie.UUCP (Steve Falco) (11/13/85)
> I do not understand at all how it is possible > to generate current without this (stator lead) connected. > Anyway, theory or not something strange is going on. > If anybody out there knows the "truth", please let me know. I think with the wire disconnected you are making use of residual magnetism in the iron. Remember, you can build a gnerator with permanent magnets. Since the alternator components are made of soft iron, the residual magnetism is not great. Perhaps there is a magnetic feedback which builds with increased RPM. As a sidelight, the old-style generators had to be "polarized" when they were installed. This consisted of sending a DC current through the windings to set up a residual magnetic field. If you didn't do it, you would usually get no output. Sounds similar. BTW, don't ever try to polarize an alternator!!! The current can burn out the diodes. Plus it is unnecessary... Steve Falco