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September 1999

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Subject:
From:
Seth Goodman <[log in to unmask]>
Reply To:
Seth Goodman <[log in to unmask]>
Date:
Thu, 2 Sep 1999 15:30:01 -0500
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text/plain
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text/plain (89 lines)
Sean,

I agree with John's answer.  Note that aluminum is a poor contact material
due to the formation of very hard oxides that have very high dielectric
strength.  In addition to the oxide inhibiting paste John refers to, you
might want to try a different surface treatment for the aluminum, such as
iriditing.  I use this routinely on aluminum chassis parts that have to mate
with RF gaskets.  I don't know about its long term resistance to oxide
formation, however.  Anyone care to comment?

Seth Goodman
Goodman Associates
7687 Leta Way
Verona, WI 53593-8631
Tel (608)833-9933
Fax (608)833-9966

> -----Original Message-----
> From: TechNet [mailto:[log in to unmask]]On Behalf Of Sean Hager
> Sent: August 30, 1999 4:24 PM
> To: [log in to unmask]
> Subject: [TN] Electro-mechanical connections for Power Applications
>
>
> Hi Group!
>
> I am currently having troubles with a terminal connections to the +5V
> output of a switching PS.  The current configuration basically consists of
> 0.5"x0.7"x0.060" aluminium bus bar (with hole for hardware),
> connected to 2
> 8guage stranded cables, via 2 8guage red ring lugs (tin/lead plated
> copper).  These are connected using 8-32 Screw and Hex nut w/ lock washer.
> This is my list of questions:
>
> Is the standard torque for this hardware type adequate for 50+ amp
> capacity?
>
> Do the ring lugs or bus bars require any preparation (cleaning, scoring,
> etc.) prior to assembly?
>
> Are there any special concerns with the dissimilar metals?
>
> How would you (or what standard would you use) to join this harness and
> terminal?
>
> I have seen a full 200mv across the bus bar/ring lug junction at [log in to unmask]
> There is no visible corrosion on either termination, and the hardware
> torque was approx. 15-20 kg-cm.  Generally this connection has been very
> reliable for about 5 years, lately we have seen a notable rate of low
> output on 5V attributed to "contact resistance" while loaded.  The
> manufacturer (Power Supply) has no hardware or installation guidelines.  I
> could best describe this as the "loose battery terminal effect"
> as compared
> to an automobile.  Is the solution realy as simple as clean and tighten?
>
> Thanks,
> Sean
>
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