Relays and Euro lights

Wed Jun 5 00:19:36 EDT 2002

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Bernie, comments inserted.
In a message dated 6/4/02 8:27:28 AM Central Daylight Time,
b.m.benz at writes:

>Welcome back, Scott.  Good to hear from you.

Love to nerd on 12v systems, 22 years of relays included....

>Sounds like you need to use better relays, or move from Chicago.  A 4 pin
>relay is not the best choice for this high current, two relay application,
>IMO.  Bosch and PB make a 5 pin cube relay specifically for this type app.
>in which there is a common input to two sets of 30A NO contacts and dual
>outputs, thus dividing the current between two sets of contacts and output

I don't think so Bernie.  IMU, the 5 pin 87/87 (dual line out) are connected
internally to each other, but the contact bridge between 30 and 87 is a
single contact NO. In other words, the 87 dual feed is AFTER the relay
contact. I don't show a "dual contact" 87-load relay application by any
vendor, the dual 87 (after the bridge) just avoids one having to stuff two
10/12 guage wires into a single contact.  If you show a dual contact bridge
SPST 5 pin relay, please share a part number.  I think you may be confusing
the SPDT relays using the 87 and 87a ports, which have two contacts.  Those
switch between 87 and 87a (dual points), they don't have a dual point jump
between 30 (feed) and 87 (load).  In the 87/a application, you EITHER have
contact on 87 (NO) or 87a (NC), not both.  And the 87 is considered the load
contact, with usually a double amp rating over the 87a.

I only show the 5 pin Bosch with dual 87 (single bridge/contact, dual 87
internally connected after the bridge) as 0332019150/151/155. ALL of these PN
have a single contact bridge between 30 and 87 and 2 x 87 load out.  What am
I missing here?

>This has great wiring advantages in that only one #12 wire need
>go into each socket connector.  In your enviroment maybe the relay cover
>needs to be replaced with a little silicone caulk.

This is NOT a recommended procedure by any relay manufacturer.  Extreme
environment, water and heat are a relay's worst enemy.  Avoiding that is
pretty easy in terms of concept, a lot more work in execution.  Hella lists
the following conditions that cause/increase failure rate of relays:
*  Burnt contacts
*  Burnt relay coils
* Oxidize connnection pins
*  Overloading
*  Wear and tear
* Corrosion

Given the above and the choice between underhood or in car.....

>In my 44s I've had my dual relays mounted on the frame member just behind
>the pass headlight, near where the jump post used to be (it's now airborne).
>No heat, no corrosion, no fuses, no problems, and wiring runs are as short
>as possible.  In the 89 chassis they are mounted on top of the pass strut

IME, working on numerous rally cars (some will remember the barrel super HD
relays with the top screw on fuse), you are compromising the half life of the
relay leaving in the engine compartment.  All anecdotes aside, there is no
question that any relay manufacturer would choose a well ventilated "inside"
application over any underhood.  Any well seasoned rallyist or offrorad guy
is just smiling.

my .02 arbitriaged thru the peso


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