Elec Question -Bus Frame DC Neg/Ground

[bevans6]

Studs on bus bars, or battery terminal fasteners, can have two different modes of design - compressive or conductive (or sometimes both).  Very often, if you look at the design, the stud or nut and washer is used in a purely compressive mode and only holds the electrical conductor or terminal in firm contact with the actual bus bar or terminal.  It's not being used to actually conduct the electrical current.  The marine type bus bar I bought is this way, it's a tinned copper bus bar with stainless fasteners.  I have a lot of batteries that have very similar terminals.  Other times the stud is also the conductor, and then you need to think about the use and the loads.  On race cars often the loads are infinitesimal but the need to have a corrosion free reliable connection is very high, so I can see using a stainless steel fitting for that purpose.  Never actually have, though.  I tend to bolt grounds to a tab welded onto the chassis, and home-run all the data signals.

This is the bus bar I bought:  http://bluesea.com/viewresource/74

Brian

[Sean]

Why do group 31 batteries always seem to come with stainless washers and nuts if they are so bad?  I believe the marine bus bars I have used are also stainless.

Most marine electrical hardware is not stainless.  What often look like stainless washers are actually plated brass or copper.  The plating is to minimize corrosion.

Stainless washers and nuts are fine on the very top of the connection, as I wrote extensively in the other thread, to mechanically secure it.  But you definitely do not want stainless as part of the current path.

Make sense?

-Sean
http://OurOdyssey.BlogSpot.com

[luvrbus]

I was told years ago copper is second to silver only in resistance and conductivity steel,nickel,and lead towards the bottom with lead being the worst what say you experts true or not

good luck

[Uglydog56]

Sean, while I freely admit that you know about 160 times as much about this as I do, I'm going to agree to disagree on this one.  While the mild steel or copper bolt may have better resistance initially, after 30 years of salt and road grime, that is not going to be the case.  I just finished disassembling my 56 chevy (my fourth), and I removed 90 percent of the bolts with a torch.  Having said that, I absolutely agree that any real loads need to go back to the battery.  My rule of thumb is 10ga or bigger goes to battery, small minor loads go to frame.  So maybe I never put any real current through the stainless bolts.  All my data on this is strictly empirical.

[bevans6]

I was told years ago copper is second to silver only in resistance and conductivity steel,nickel,and lead towards the bottom with lead being the worst what say you experts true or not

good luck

Here you go...

http://metaldetectingworld.com/conductive_order_metals.shtml

Short answer - you were told rightly...   

[belfert]

Why is gold so often used for contacts when both silver and copper are more conductive and WAY less expensive?  Is it because copper and silver will oxidize or tarnish?

[Sean]

Why is gold so often used for contacts when both silver and copper are more conductive and WAY less expensive?  Is it because copper and silver will oxidize or tarnish?

Solid gold is rarely used for contacts.

The reason many contacts are gold-plated, particularly in aerospace and other critical applications, is that gold does not corrode or oxidize, unlike copper and silver.  So when you have a mechanical contact between components (as opposed to, say, soldered), with gold you will not have the potential for a layer of oxide adding resistance to the circuit, or worse, opening it entirely.  The very small penalty in increased resistance of the thin plating of gold is a worthwhile trade-off.

-Sean
http://OurOdyssey.BlogSpot.com

[Sean]

I was told years ago copper is second to silver only in resistance and conductivity steel,nickel,and lead towards the bottom with lead being the worst what say you experts true or not

Actually, stainless steel, with a resistivity of 720 nano-ohm-meters (nΩm) is a good deal less conductive than lead, with a resistivity of 208 nΩm.  IOTW, the resistance of, say, a stainless washer would be about three and a half times the resistance of the same size lead washer, if there were such a thing.  Lead is only very slightly worse than carbon steel at 180 nΩm.

By contrast, copper has a resistivity of just 17.1 nΩm, less than a tenth that of carbon steel.  Some other metals commonly used for electrical connections or components:

Silver, 15.9 nΩm
Aluminum, 26.5 nΩm
Brass, 64 nΩm
Nickel, 69.3 nΩm (commonly used to plate copper washers in marine and similar applications)
Solder, 150 nΩm

Lead, by the way, is not generally used for mechanical electrical connections, with the sole exception of battery terminals.  The reason for its use here is quite simple, though -- the battery plates themselves are made of lead, and the terminal is merely a casting extension of part of the lead plate assembly.  Lead is also a component of many electrical solders, although the advent of RoHS has all but eliminated it, and this is to depress the melting point.  Other metals included in the solder help to give it better conductivity than lead alone.

-Sean
http://OurOdyssey.BlogSpot.com