0
\$\begingroup\$

I'm trying to mount AA terminal contacts in an anodised aluminium case. Given that the aluminium is anodised, does that mean it's not conductive and the contacts could directly make contact with it? If not, what's a good way to mount contacts on an anodised aluminium case?

Thanks

\$\endgroup\$
1
\$\begingroup\$

Coat the insides with scratch resistant isolation or fix the contacts such that they cannot touch the metal. Best option.

Anodisation in aluminium needs to be sealed to be reliable enough for real electric isolation. The anodisation layer can be punctured by sharp edges or worse: The chemicals inside a battery! Some electrolytes have a high or low enough pH or contain sufficient reactive Ions to take away the oxide layer, forming in some cases actually conducting wet-mass for a while. Since I assume you have no crystal ball to see if the batteries will ever leak, it's a decent risk. Anodisation may help retain the coating (due to surface roughness and/or porousness) and/or reduce the layer thickness requirement, depending on the chemical process used.

Many cheap-ish polymer coatings can handle these chemicals and light mechanical pressure, epoxy coatings would be good to a degree I'd expect. (<-- I'd expect... certainties come from spec- and/or datasheets.)

Of course in caps and such the anodisation works, because it's a thoroughly conditioned environment and the anodisation is done under very strictly controlled circumstances until all has been sealed in oil or plastic to prevent thermal cracking or mechanical damage. This is also one of many reasons a cap should not dry out. Dry cap != protected any more.

\$\endgroup\$
4
  • \$\begingroup\$ Thanks. So with epoxy costings, what should I look for I the spec to ensure that it's insulating? \$\endgroup\$
    – Kar
    Jun 30 '15 at 19:16
  • \$\begingroup\$ Also, are all scratch resistant coatings insulating? \$\endgroup\$
    – Kar
    Jun 30 '15 at 19:20
  • \$\begingroup\$ @Kar Well, a metallic-content coating would possibly be very strong, but not really insulating, of course. So no. You should look for dielectric strength, insulation resistance, or similar to find out how well it insulates. To find out if it prevents scratches a good hardness is required. Some resins are scratch resistant by self-healing but very soft, but these are usually more expensive than just very hard coatings. Like an affordable epoxy. Also layer thickness is a useful parameter. 100um at good hardness is better than 10um at slightly better hardness. \$\endgroup\$
    – Asmyldof
    Jun 30 '15 at 19:28
  • \$\begingroup\$ @Kar but for simple batteries with simple-battery weight I imagine almost any tough polymer like epoxy lacquer will give you a 99% chance of it being protected. Especially if the layer is more than 25micrometer. 100% is unlikely, 99.99% might be reachable. \$\endgroup\$
    – Asmyldof
    Jun 30 '15 at 19:30

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.