304 Stainless steel electrical contacts. Bad idea? - Page 1
Forum section: electronics / beginners

author: rickey1990
author_rank: Regular Contributor
timestamp: July 30, 2022, 09:27:25 pm
content: Hi, I am currently working on a project, That involves connecting 40/50A lugs to a PCB. I know there's tin plated copper board connectors. However I was looking trying to come up with cheaper methods.I remember in electronics class that Stainless steel shouldn't be used for battery connectors. Which this isnt however i went on a online calculator to see the power drop for 304 stainless. If I was to use M6 x 18mm square washer with a 1.5mm thickness as a pad for a lug.Work out the area for the 6mm hole and take that from the area of the 18mm square. It would leave me a area of a 19.4mm circle. Which I used for my wire size.Leaves me with these results. Would you say these are acceptable. Or should I really be using Brass or copper.Also wago also uses stainless steel in there connectors.

author: Benta
author_rank: Super Contributor
timestamp: July 30, 2022, 09:41:51 pm
content: Probably not the best idea, but explore it.Stainless is stainless because it builds an oxide layer on the surface by itself. Not because it doesn't corrode. it does, especially in contact with aluminium (galvanic corrosion).Oxide layers are bad for conductivity.

author: abquke
author_rank: Regular Contributor
timestamp: July 30, 2022, 09:48:58 pm
content: -As I understand it, Stainless is tricky for welders because it doesn't conduct heat quite as nicely as other steels which can affect material properties.-Steels are generally harder than the usual electronics metals so a battery contact can't dig into the material and have a surface to make electrical contact. On the contrary, the steel would scratch up the (likely) nickel plating of the battery.-Dissimilar metals + moisture + electricity usually equals badI'd say "try it and see", but I doubt it will qualify as a good idea.

author: MrAl
author_rank: Super Contributor
timestamp: July 30, 2022, 10:31:48 pm
content: Quote from: rickey1990 on July 30, 2022, 09:27:25 pmHi,If SS was good it would be widely used but instead they use gold plating because of the resistance to corrosion. Gold isnt as good a conductor as silver or copper but it's still used in a very thin layer and so the extra resistance does not matter as total resistance also depend on the length of the conductor and a thin plating is not very long.So with SS being much cheaper than gold but not used widely, i would think SS is not that good. It does depend on other things too though like the normal movement of the contacts. If they rub that could reduce the resistance.You also have to remember that it may be hard to test without doing a test that lasts for months. It may look good for the first week or two, but then after 6 months start to show signs of a problem with the contact resistance. You might be able to set up a custom test set that checks for this, but it will take patience and unfortunately it may act differently in a different applications. Flashlights seem to be a problem area even regular tin plating doesnt seem to hold up for long and needs to be cleaned. Maybe the humidity gets to it.The "long term tests" are always a problem area when you try to design your own stuff that is not normally done it takes time to know if something is going to work out well over months or years.If you are really intent on doing something like this though, maybe you could try to find some papers written on contact testing as sometimes they have tests developed for particular types of components. For transistors for example they elevate the temperature and increase voltages and then can extrapolate the spec's for long term normal use at normal temperatures and voltages.If you find out anything definitive maybe you can get back here and report the findings. Should be interesting.Oh BTW there is a company Air Electro that seems to claim SS has good properties for this maybe you can check with them.

author: rickey1990
author_rank: Regular Contributor
timestamp: July 30, 2022, 11:00:20 pm
content: Thankyou for all your comments. Well I will be making afew of them.. Also afew PCB manufacturers have 10 (10cmx10cm) boards for $5. Which is why I was looking at larger contacts. If I don't have to pay for the space, I might as well get the most out of my 10 by 10.I have decided on brass 6mm * 18mm round washers. Hopefully that will resolve some of the issues.brass can be more brittle , however 100 washers for £4 makes it a cheap fix.