Bert- I'm posting this to the list so people can see the resolution....
looks like it is pretty well figured out now.
The original relay has two coil windings, apparently. Note the ground
connection shown to the case and one side of what I think is a 'voltage'
coil, which is connected to the 61, generator light, connection. It
shows a second coil, which is apparently a 'current' coil from the 51 to
the 86 terminal. I'm not certain, but it looks like this coil may work
in opposition to the voltage coil, not allowing the aux battery to be
connected until the main battery charging current drops to a certain
level (maybe the 10V or so level?). The current coil would be a large
diameter wire with a few turns wound in the opposite direction to the
voltage coil. The changeover point for charging the aux battery could
be adjusted by the number of turns on the current coil. It looks as
though the dropout would happen when the engine is shut down.
The new relay will work fine as a 'disconnect', without the additional
coil. It won't have a current sensitive feature and will just
open/close to connect the aux based on whether the motor is running.
Take a look at the schematic- there are two diodes in this relay. They
are called 'snubber' diodes, and are used pretty often in industrial
relays and electric vehicles across the coil and/or load to limit what
is called 'inductive kickback' from switching loads (this keeps the
radio interference low). The diodes are like 'one-way valves' for
current (current passes from the positive voltage in the direction of
the little arrow, but not in the other direction). You MUST observe the
polarity marks on the relay, or it will not work. The diode across the
coil should not pass current except the kickback when the coil is
dropped out. The other one, connected to the terminal, is there to keep
you from frying the other diode if you do hook it up backwards, but it
will keep the relay from working if you do that (no current through the
coil). The polarity of the 30 to 87 connection does not matter one to
the main battery (B+) and one to the aux battery (+). The 85 should be
grounded, with 86 to the 61 terminal of the regulator.
Glen Hadley :<)>
On 3/16/2013 08:10, Bert Knupp wrote:
Battery isolation relay
Glen,
I think you've hit it correctly. Just for fun, I'll send you (a) the
VW shop bulletin pages, (b) a translation of the relevant paragraph,
and (c) the schematic from the isolation relay itself. Note that the
isolation relay has an ungrounded plastic case. If I'm reading your
reply correctly, I think you (and Gerald Livingston) have correctly
discerned how I need to do this.
The isolation relay that I have is a new Bosch 0 332 002 156. It is
not a standard continuous-duty automotive relay as others are
describing (with the standard 30-87 NO switch and 85-86 coil
terminals. It is sold specifically for use as a battery-isolation
relay (Batterie-Trennrelais), and is fairly pricey, leading me to
agree with your hunch that it is in fact a voltage-sensitive feature
that opens the contacts when the criterion voltage is reached.
For esthetics, I wish it were the old original 1969-vintage relay in a
metal can, but those are extremely hard to find nowadays. With some
exceptions, I've tried to keep everything on the Copbug
vintage-correct, right down to the fire extinguisher, 4m antenna and
"wanted" book.
Thanks a lot for your thinking and writing!
Bert
*From:*[email protected] [mailto:[email protected]]
*On Behalf Of *Glen Hadley
*Sent:* Saturday, March 16, 2013 7:26 AM
*To:* [email protected]
*Subject:* Re: [vintagvw] Battery isolation relay
With the batteries connected in parallel, they cannot have different
voltages (axiomatic- they are connected by a very low resistance wire,
and current will flow as needed to keep them at the same voltage).
The relay can't be triggered by a difference between the batteries.
This description makes me think very strongly that it is a voltage
sensitive relay, dropping out at about 10 volts, which could not be
replaced by a 'standard' relay like the one you have.
Glen Hadley
On 3/15/2013 14:37, Bert Knupp wrote:
As described in the factory's shop bulletin, the relay is
/actually/ supposed to open the circuit only when the potential
between battery #1 and ground drops below 10.0 volts, but keep
them connected in parallel so long as both battery #1 and battery
#2 hold 10 volts or better. In other words, the relay is
"triggered" by having a (pos+) feed to both coil terminals, one
from each battery. If one battery begins to run down, it creates
a difference in potential (voltage) between the two batteries,
opening the relay so #2 gets cut loose in order to stop it from
running down #1.
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