Volks,
Thanks to everybody who chimed in on this one, especially Gerald and Glen. I'm going ahead with the installation (if it doesn't rain today) and I'll let you know the outcome. I'm optimistic. I left out another detail as I posed the problem: that I have a "coil-kicker" solenoid also installed to close off the direct connection from the battery to the starter when I turn the ignition key to Start. It shouldn't affect the installation of the battery isolation relay at all, aside from the space it takes up and the challenges in cable-routing. Thanks to all, Bert Knupp From: [email protected] [mailto:[email protected]] On Behalf Of Glen Hadley Sent: Sunday, March 17, 2013 6:52 AM To: [email protected] Subject: [vintagvw] Re: [off-list] Battery isolation relay 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: 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. -- 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]. 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