Volks, I need some help. Various VW models over the years have used dual-battery systems: campers, sound trucks, fire engines, and police cars to name a few. The two batteries are connected via an isolation relay (in German it's a "Batterie-Trennrelais"). The idea is to permit both batteries to charge from the generator or alternator, but to "uncouple" the #2 equipment battery when the voltage drops below 11 volts, making sure that the #1 or starting battery doesn't get pulled down by the equipment. For example, in the police cars, it allowed the car to sit working an accident with the blue light, flashers and radio running but the engine off. If the available voltage dropped below 11 volts, the starting battery would disconnect so the car could start when done.
So I'm recreating the Copbug's two-battery system. I've mounted the #2 battery under the left rear seat and found a 75-amp Bosch isolation relay on-line. The problem: the four terminals on the new Bosch relay don't match the four terminals on the VW factory bulletin for police-car wiring. I'm usually pretty good at logicking-through circuits, but I'm stumped here. The factory bulletin shows an isolation relay with four terminals: 51, 61, 86 and 87. 61 comes from the 61 terminal on the voltage regulator. Skinny wire. 51 comes from the B+ terminal on the voltage regulator. Fat wire. 86 goes out to the #1 (starting) battery (+). Fat wire. 87 goes out to the #2 (equipment) battery (+). Fat wire. The new isolation relay comes with four terminals also: 85-, 86+, 30 and 87. The 30-to-87 circuit seems to be the switch that opens and closes. The 85-to-85 circuit seems to be the coil activation. The 87 and 51 terminals are high-amp screw terminals. The 85 and 86 terminals are low-amp Faston slip-on tabs. But I can't figure what's what. Can anybody help me? How do I hook up the new relay to do the job? I've written to Bosch, but I won't hold my breath. The last time I asked them for help, the reply came 5 months later - and they said they didn't have information on the old equipment. Aargh! Bert Knupp in Music City USA -- Visit the VintagVW archives at http://mail-archive.com/[email protected] --- You received this message because you are subscribed to the Google Groups "VintagVW - Air Cooled Volkswagen Discussion List" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To post to this group, send email to [email protected]. Visit this group at http://groups.google.com/group/vintagvw?hl=en. For more options, visit https://groups.google.com/groups/opt_out.
