Aluminium Busbar Joint Corrosion

This stuff looks good...

http://www.sanchem.com/aSpecialE.html

Wow, that looks absolutely perfect. Thanks.

Just wondering if you should use a nylon/non-conductive bolt with non-conductive washers to avoid galvanic corrosion due to dissimilar materials.

Ah yes, thanks! I didn't even think of that. Although it'll be dry, galv corrosion between the bolt & Al will could possibly loosen the bolt over time. I'll do as you say and use Nylon washers and probably also wrap the bolt shanks in plumber's tape or something.

A 300 grade of stainless steel bolt and nut will work.

I agree with Ronseto. Use stainless steel hardware. That is commonly used in the electrical equipment industry for fastening of electrical connections.

This table is taken from: Atlas Steel Technical Note No. 7 "Galvanic Corrosion"

Guys, I still say that stainless steel and Al are NOT compatable. Check out the chart.

Zinc plated steel then.

Two things:

1. I'd use Cadmium plated hardware.

2. Oxices of Aluminum form very quickly, so have the compound ready and apply it as soon as possible after sanding and wiping with solvent.

OOPs: 3. things

3. DO NOT use plastic hardware to join the bars!!!!!!!!!Ever! Thermal cycling and cold flow will make the joint fail in short order.

Hi Lyn,

When you say use cadmium plated hardware, you don't mean actually cadmium plate the Al busbars do you? Cause I guess I could have that done.

But I suppose you mean the parts (eg cell tabs) attaching to the busbars?

Thanks,

Clint

No. Just use cad plated nuts and bolts to join the bars.

Cad and AL are close on the electromotive series. No corrosion because of dissimilar metals.

Ah, yes. I'm with you now. Now that you say it, surely galvanised would do fine - zinc is even closer than cadmium to Al 6061 on the galv chart and will be easy to come by. Thanks Lyn.

Oxices? wow that's obscure....Would this be the same as oxides?

Forgot to spellcheck.

And Ron, SS and Al are never a good match if ANY humidity is present. (Just my experience)

Absolutely positively DO NOT SAND the contact point, you want a mirror polish if you can manage it before you join the surfaces, rough surfaces will do nothing but trap debris/oxides and prevent proper cleaning. Clean well with a dilute Muriatic (Hydrochloric) acid before you apply the nooxid (does look like a good product)

You'll have to inspect regularly to make sure that corrosion isn't occurring.

Given the small size of the bus bar bolts may not be the best choice, using external clamps would probably be best, maybe a couple of very small bolt to prevent the plates from shifting but the main electrical soundness of the joint will depend on the pressure you can exert over as much of a contact area between the two bars as possible.

It may seem a bit overkill, but joints like this are the FIRST failure point in an electrical system like that and it's very important to do it right. There is no such thing as overkill.

HCl instead of sanding makes sense too. You have all been so helpful. Thank you.

It is a very good solution!!

Would add: use ALCLAD-6061 Bus bar,and instead of adding nooxid-only clean it and attach with external clamps from Aluminum/Stainless Steel Material

Umm, one question:

It seems that joining aluminium is quite problematic and some of the more knowlegable posters seem to suggest that you are almost guaranteed to have problems in the future with these joints, even if done correctly.

Since the bus bars are so small, does it not make sense to consider moving to copper busbars? I'm guessing that aluminium was chosen for weight saving but copper can be a smaller cross section for the rated current. And 50A can be carried in something far smaller in cross section than 15 x 3 mm.

You will have enough challenges with an electric vehicle without building in areas that will be problematic.

Jon.

Copper is a good option for you, but it could be it would end up too small to use, 50A would only need about 20mm2 worth of copper. If you are set on alu then I personally would tin plate it, depending upon the joint positions and size you could do it locally at the joints or just plate the full bar.

Out of interest is this the main battery busbar link? Have you considered the short circuit output and it's effect on the bar?

If our battery short circuits then there's going to be a lot of trouble other than melting busbars! Try exploding LiIon cells!

We have several safety circuits and fuses.

Nothing wrong with melting busbars.

You want to consider engineering in some fusable links.

Another great idea, I'll certainly be doing this. Thanks.

The main reason for using Al is cost. Although it's not that expensive, we're using a lot of it - over 30m.

Also, Al was easier to obtain than copper in those quantities and we're kind of in a rush!

Finally, I believe similar precautions need to be taken with copper. Although its oxides aren't as severe as Al, they're essentially similar.

Do not use this on electrical joints it is not conductive!!!

Thanks so much. This is really helpful!