aluminum oxide and connectivity question.

[funtech]

I'm designing an electrical device now, and I need to ensure good connectivity/conductivity.

The housing of my device is made of aluminum, and it also acts as the "ground." An automotive fuse (those plug type) is to be connected to this housing. My current design has a small notch in the housing where one of the legs of the fuse plugs into. Once plugged, the fuse will not be taken out unless it blows. I wonder if the aluminum surface in the notch will form oxide layer which will gradually lessen the connectivity. Should I worry about this?

Another option would be to somehow connect the fuse to a part made out of a different metal that doesn't oxide and connect this brass part to the aluminum housing via a screw/hole. Will this form better connectivity?

 

[IRstuff]

Housings should NEVER be used to conduct normal currents; they are to be used only for shielding and grounding of stray noise.

TTFN
faq731-376

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[MikeHalloran]

Speaking of shielding, aluminum is not effective against all fields. What you typically find in volume production is tin-plated or zinc-plated or nickel-plated steel, which can be much thinner than aluminum of similar stiffness.

Carrying operating current through the shell can present installation problems, because not all vehicles ground the same pole of the battery.

Even if it were permissible or wise to carry operating current through the shell, I can't think of a defensible reason for fusing that side of a circuit, so it doesn't matter how you attach the fuse to the shell; the fuse shouldn't be there.


Regarding the technical core of your actual question, the oxide layer on aluminum forms within seconds of exposing the actual aluminum surface, as in cutting a notch. So it's not possible to make a reliable electrical connection to aluminum by purely mechanical means.

It is possible to solder a wire or small tab to aluminum, by using a glass brush to abrade away the aluminum oxide while the joint area is kept submerged in molten solder, after which the pretinned wire or tab can be sunk into the solder pool. The process is slow and skill-intensive, and not at all the sort of thing you'd want to do in production.





Mike Halloran
Pembroke Pines, FL, USA

 

[VEBill]

It's unusual for one side of a fuse to be connected to ground. There are a class of faults where such an approach could result in the chassis becoming hot with power supply voltage (and presumably not fused). [Disclaimer: I'm reading between the lines and making assumptions, so forgive me if I'm off base. ]

One of these might be a better approach: