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HiFiNutNut 2nd March 2012 09:36 AM

Aluminium flat or not in PSU?
I have been using aluminium flat to connect screw mount reservoir capacitors in my power amplifier power supply. I prefer aluminium flat as it is clean and tindy with far less soldering to do. Conductivity is excellent given the thickness and width of the aluminium flat.

However, I have just looked up aluminium in Wikipedia, and found that aluminium when exposed in air forms a thin layer of aluminium oxide in a fraction of a second.

I am wondering if contact resistance is high with aluminium due to oxidation and whether it is a good idea or not to use aluminium flat or not.

Juergen Knoop 2nd March 2012 11:23 AM

usually this is fine, you might want to use toothed washers to be on the safe side...

epicyclic 2nd March 2012 12:04 PM

Clean the mating surfaces with a fine abrasive and connect together asap . I have seen plank like bus bar joints filed through a layer of vasaline to inhibit the oxidation , the surfaces then cleaned with more vasaline and the joint made and checked with a moving mirror galvanometer , but thats a bit extreme as they were going to carry hundreds of Amperes.

HiFiNutNut 2nd March 2012 09:59 PM

Thanks for your input.

My worry is that from the Wikipedia site it says that the oxidation occurs within a fraction of a second (in pS) and it is all done.

In theory, the oxide reduces conductivity. In reality, the multimeter does not show resistance. But then I can't trust the multimeter because it does not have the resolution.

I guess the safest way to do it is that the connection to the PCB is directly connected to the last cap's screw terminal, rather than on the aluminium flat. The small resistance between the caps probably does not matter.

simon7000 2nd March 2012 10:03 PM

Most computer grade capacitors have aluminum screw terminals! Yes the oxide forms fast but that is thin and a good toothed lockwasher has been worked for 40+ years in many pieces of gear!

HiFiNutNut 3rd March 2012 12:38 AM

Great. I will keep the aluminium flat and will look for toothed lockwashers.

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