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Copper Capacitor Bank Rails

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Hon1nbo

Fri Jul 17 2009, 03:16PM

Registered Member #902 Joined: Sun Jul 15 2007, 08:17PM
Location: Pacific Northwest USA
Posts: 1042

Hey you guys,

I just got a bunch of 1/8" thick, 1" wide copper strips for my Capacitor Bank and I have a couple questions:

1) What is the best way to clean them for proper connections - can I at least polish them to make them look nice with something like Brasso, or will that be bad for electrical connections?

2) Should I use some kind of paste or extra hardware to ensure a good connection with the rails and the capacitor terminals? - I know that the surface area between them is what the current should flow through, rather than the screws...

3) I think I may have not been paying attention to this when I bought the copper: is C110 Copper good for these rails? It is listed as Oxygen Free...

aonomus

Fri Jul 17 2009, 03:58PM

Registered Member #1497 Joined: Thu May 22 2008, 05:24AM
Location: Toronto, Ontario, Canada
Posts: 801

For copper to * connections you should use a grease to prevent oxidation such as

although others have some conductive properties

For copper to copper connections if you can leave the connection permanent, solder them together.

As for cleaning sanding with a fine grit sandpaper (1200?) cleans them up to a nice shiny luster without losing too much copper. If it isn't terribly oxidized, use even finer sandpaper.

Proud Mary

Fri Jul 17 2009, 04:50PM

Registered Member #543 Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992

Don't use Brasso until after you have completely assembled the unit, as it leaves some kind of anti-oxidant coating on the copper to maintain its shine.

As for "oxygen free copper" - it is no more than a sales gimmick of the audio industry for selling costly inter-connects and loudspeaker cables.

klugesmith

Fri Jul 17 2009, 07:09PM

Registered Member #2099 Joined: Wed Apr 29 2009, 12:22AM
Location: Los Altos, California
Posts: 1716

DaJJHman wrote ...
3) I think I may have not been paying attention to this when I bought the copper: is C110 Copper good for these rails? It is listed as Oxygen Free...

Are you sure you don't have C11000? [edit: A co-worker who designs busbar parts says c11000 is a newer name for c110.]
Wikipedia and more respectable references say:
"C11000 - also known as Electrolytic-Tough-Pitch (ETP). This is the most common copper. It is universal for electrical applications. ETP has a minimum conductivity rating of 100% IACS and is required to be 99.9% pure. It has 0.02% to 0.04% oxygen content (typical). Most ETP sold today will meet or exceed the 101% IACS specification."

But I think conductivity differences between "coppers" is uncritical in most amateur pulse-discharge capacitor buses and railgun rails. For example, even if flattened copper plumbing pipe had a conductivity of only 50% IACS, the extra voltage drop and/or heating would still be quite negligible in those non-coil applications. Work it out! So if some harder copper alloy would reduce your rail erosion, it might be favorable in spite of some extra electrical resistance.

DaJJHman wrote ...
1) What is the best way to clean them for proper connections - can I at least polish them to make them look nice with something like Brasso, or will that be bad for electrical connections?

[edit] The aforementioned busbars, used for relatively low-voltage DC in our semiconductor manufacturing equipment, come from the fabricator with "bright tin plating". Keeps 'em looking nice, and has never caused us any electrical problems. For a DIY project I'd suggest tinning with solder, wiped smooth with a damp sponge or rag while molten, in bolted connection contact areas. The extra resistance compared to a dry or greased copper-to-copper interface will be negligible (work it out!)

Sulaiman

Sat Jul 18 2009, 07:00AM

Registered Member #162 Joined: Mon Feb 13 2006, 10:25AM
Location: United Kingdom
Posts: 3141

The finish of busbars is purely cosmetic
Copper is common for industrial busbars due to oxidation of aluminium
for capacitors aluminium is best as the capacitor terminals are usually made of aluminium
for most 4HVers the inductance of the bus is likely to to more of a limitation than the resistance.
The connection between the capacitor terminals and the bus bar is important
The only important part is the connection between capacitor terminal and busbar
Clean both surfaces and put the terminal in direct contact with the busbar
any spring washers etc. should be on the screw head side.
Don't over-tigten the screws as the thread in the aluminum terminals will strip
(how do I know this?

)
Grease etc. isn't required unless you're making a museum display piece.
My 2cents worth.

rp181

Sat Jul 18 2009, 07:42AM

Registered Member #1062 Joined: Tue Oct 16 2007, 02:01AM
Location:
Posts: 1529

make sure you use fine grit paper on the busbar and capacitor terminals before screwing it down. If you screw it tight, and don't remove it, you don't need grease. if you want a grease, look into kopr-shield.

Finn Hammer

Sat Jul 18 2009, 09:17AM

Registered Member #205 Joined: Sat Feb 18 2006, 11:59AM
Location: SkÃ¸rping, Denmark
Posts: 741

A solution of 1:10 of 35% hydrocloric acid cleans off the worst oxide on the copper.
After that, clean/polish with steel wool/soap sponge found under the kitchen sink (if you are a married man, or live with your mother)

.

This procedure results in a surface without directional scratches from grit.

Cheers, Finn Hammer

Hon1nbo

Sat Jul 18 2009, 04:29PM

Registered Member #902 Joined: Sun Jul 15 2007, 08:17PM
Location: Pacific Northwest USA
Posts: 1042

Finn Hammer wrote ...

A solution of 1:10 of 35% hydrocloric acid cleans off the worst oxide on the copper.
After that, clean/polish with steel wool/soap sponge found under the kitchen sink (if you are a married man, or live with your mother)

.

This procedure results in a surface without directional scratches from grit.

Cheers, Finn Hammer

I have used acid to clean copper before (muriatic, which is essentially 35% HCL) - but the problem with that is I have to be able to wash away the un-neutralized acid from the copper, and contain the runoff, etc - if I neutralize the acid present on the copper I have always seen heavy production of what I believe is Copper Carbonate, or possibly Cupric Chloride - I ended up etching the copper somewhat and had a lot of green tarnish

I am good with finishing metals with sandpaper, I even did the aluminum on my own car's rims! with wet-sanding, I don't end up with grit marks

just an FYI, the copper solution formed when I was using Muriatic Acid was actually usable for Plating Copper, very weakly, but noticeably...

Tesladownunder

Sat Jul 18 2009, 09:28PM

Registered Member #10 Joined: Thu Feb 02 2006, 09:45AM
Location: Bunbury, Australia
Posts: 1424

The important thing about busbars in this application is inductance not resistance which is only a minor component at 100kA in 30uS.
I estimated 600V across the busbar between 2 pulse caps, enough to give a small spark shower between them. Granted some of it was due to the heavy bolts but the caps inductance is relatively small.
Besides corrosion and black copper oxide electrical "burns" are a good look.

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aonomus

Sun Jul 19 2009, 12:10AM

Registered Member #1497 Joined: Thu May 22 2008, 05:24AM
Location: Toronto, Ontario, Canada
Posts: 801

Apparently another good way to clean off copper is to use lime juice and rising/wiping. I haven't tried this but I read it on a site that deals with copper flats for grounding.

Also for anyone that deals with flattened out copper pipe, the copper that they sell you at the hardware store has some sort of nasty oxidation/oil/varnish and printing on it that makes it hard to do anything. Wipe it down, then sand it and clean it off, then you can finally solder or make connections...

TDU is also right, resistance isn't much of an issue if you have a huge inductance in your layout. I used copper pipe bus bar that probably would melt under continuous duty, but for pulsed applications its just fine.

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