Bert,
Part number for the new Bosch part please?
Also, Let's think through your description of how this really works.
From you explanation of the original relay wiring that has only 4
terminals, I am not sure that it works the way you think it does.
On the original:
51 is the feed providing charging power to either of the two batteries(or
could it only be both at the same time!)
61 is ground when the generator is off(I am pretty sure)
and provides a small positive comparison voltage
when the car is charging(red light on or off comparison
to the battery charging state).
I am going to guess that when the charging system was "off" that
you could pull the equipment battery all the way down and it would charge
up after you restarted...andthat was about it.
On the other hand...I have never owned one ofthese of a bus with the dual
battery and don't know how it worked in a late model bus. My bet is that
both batteries got the same charging current after the engine was started,
but the equipment battery would give it's all and then that would be that
till you restarted the car.
Do you have a type2 manual with the same relay described in it? Seems
kinda weird that VW(or Bosch) would use different devices to do the same
thing for VW.
Send the part number! Bet I can find a reference diagram.
Cheers, dave
On Fri, 15 Mar 2013, Bert Knupp wrote:
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
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