Avoiding Galvanic Corrosion

[Solarfun4jim]

Wow, so these were aluminum M6 to M10 flanged adapters that you had custom milled - I’m impressed.

Since you’ve got that flange, no worries about piercing the bottom and sounds like you have had no issues unthreading the post when loosening the nuts (if anything, the opposite).

This is what Basen, Xuba and the other LiFePO4 cell resellers should have been bundling with their cells...

Where did you get the idea?

It was my own idea, to solve my main worry, of going into the cell, but it took some time to source someone to machine exactly what i wanted. Then after i had used then...i would modify if doing the same again.....put a hex on the flange, make it 5mm thick to get a key onto it and i would seal it in with the conductive epoxy, (suggested by 'filterguy') that way it is not a disaster if some squishes onto the flage when tightening it down.

 

[Solarfun4jim]

I think you are correct that those custom ones of his are aluminum .... but they do still add an extra contact point in series with the bus bar ....My bus bars are wider than the terminal top .... and I think his are also.
So, and extra physical contact point is added and there is less surface are for the bus bar.
If the flange size were larger that would help, also it might be possible to make up for the lost surface area by using a higher torque that the M10 will allow.

No, you cannot torque to higher than 4Nm, or else the stress goes on the underlying 6mm threads below the flange and above 8Nm, i sheared the stud.
I would definately increase the size of the flange area.

Edit....a stronger version of aluminium might help of course....but i just find everything aluminium needs more respect.

 

[Solarfun4jim]

I think you are correct that those custom ones of his are aluminum .... but they do still add an extra contact point in series with the bus bar ....My bus bars are wider than the terminal top .... and I think his are also.
So, and extra physical contact point is added and there is less surface are for the bus bar.
If the flange size were larger that would help, also it might be possible to make up for the lost surface area by using a higher torque that the M10 will allow.

I dont think you lose much contact area, since the current is also getting pushed through the more conductive stud material itself, to the nut above and then also transferred back to the topside of the tinned lug.

 

[Luthj]

Don't let perfect be the enemy of good.

Exactly, just use a liberal amount of quality silicone grease, coat all the surfaces, and check once a year for obvious corrosion. There are some folks who are taking their builds to the extreme. That's cool, but don't think its a requirement by any means.

The worst case scenario is a high resistance connection, which causes a high/low voltage disconnect or balance issue.

 

[Maast]

I'm not about to read 17 pages of this thread - but Noalox or any other anti-oxidant grease isnt to prevent 'corrosion' per se - it's primary purpose is to prevent aluminum from developing an high resistance oxidation layer, with a secondary effect is that it retards oxygen and water vapor in coming in contact with any metal - which would prevent copper oxidization and actual corrosion.

You do scrub all your aluminum-to-anything connections back to bright metal before connection don't you.

And for the record every single crimp I ever make, at work or at home has a antioxidant grease in it before I crimp, including hydraulically crimped connections as it may be gas-tight now, but it won't be after a few years of thermal cycling. The one exception to this is tinned-on-tinned connections, the tinning is VERY forgiving and more importantly doesnt develop a high resistance oxidation layer, at least not in anything less than geological time anyway.

 

[fafrd]

I'm not about to read 17 pages of this thread - but Noalox or any other anti-oxidant grease isnt to prevent 'corrosion' per se - it's primary purpose is to prevent aluminum from developing an high resistance oxidation layer, with a secondary effect is that it retards oxygen and water vapor in coming in contact with any metal - which would prevent copper oxidization and actual corrosion.

You do scrub all your aluminum-to-anything connections back to bright metal before connection don't you.

And for the record every single crimp I ever make, at work or at home has a antioxidant grease in it before I crimp, including hydraulically crimped connections as it may be gas-tight now, but it won't be after a few years of thermal cycling. The one exception to this is tinned-on-tinned connections, the tinning is VERY forgiving and more importantly doesnt develop a high resistance oxidation layer, at least not in anything less than geological time anyway.

So you would put antioxidant grease into a tinned copper 2/0 lug before using a hydraulic crimper to crimp 2/0 welders cable?

I ask because I’ve never crimped cable that big before and just bought a 10-ton hydraulic crimped to do exactly that...

 

[Hedges]

So you would put antioxidant grease into a tinned copper 2/0 lug before using a hydraulic crimper to crimp 2/0 welders cable?

I ask because I’ve never crimped cable that big before and just bought a 10-ton hydraulic crimped to do exactly that...

I did do that for 2 awg THHN which I crimped with a cheapie hydraulic crimper. (battery cables)
I'm also curious if that is better than bare copper "cold welded" (inside a tinned lug.)

 

[HRTKD]

I didn't put any goop inside my cable lugs. It never occured to me to do so. My thoughts on this are that a solid cold weld crimp onto a closed end lug, followed by heat shrink tubing (with adhesive) is as good as it gets. If you did it right, this is an air tight bond.

You could take this to an extreme and say that the insulation on the entire length of the wire needs to be removed so you can apply an antioxidant. This would, of course, be silly because the wires between the lugs don't need an antioxidant. And you would never get the insulation off in one piece, let alone get it back on. Yes, I'm being facetious here.

The goop could act as a lubricant, deteriorating the hold the lug has on the cable. This is my only objection. Well, that and it could make a mess as it comes out during crimping. Better wear eye protection!

If ABYC says to use it in lugs, that's a different matter.

 

[fafrd]

I didn't put any goop inside my cable lugs. It never occured to me to do so. My thoughts on this are that a solid cold weld crimp onto a closed end lug, followed by heat shrink tubing (with adhesive) is as good as it gets. If you did it right, this is an air tight bond.

You could take this to an extreme and say that the insulation on the entire length of the wire needs to be removed so you can apply an antioxidant. This would, of course, be silly because the wires between the lugs don't need an antioxidant. And you would never get the insulation off in one piece, let alone get it back on. Yes, I'm being facetious here.

The goop could act as a lubricant, deteriorating the hold the lug has on the cable. This is my only objection. Well, that and it could make a mess as it comes out during crimping. Better wear eye protection!

If ABYC says to use it in lugs, that's a different matter.

ABYC?

I’ll admit I had that same concern that lubricant could act to impede the quality of the electrical connection between copper wire and the tinned lug surface...

 

[Luthj]

When I was testing 2/0 lugs for severe service forklifts, we immersed various MFGs crimped lugs in acid, both new and after some time in service. With exception to poorly executed crimps (they kind that would fail a pull test), none showed any signs of liquid intrusion. This was with high strand count battery cable. I think the results would still hold for coarse strand cable.

 

[HRTKD]

ABYC?

I’ll admit I had that same concern that lubricant could act to impede the quality of the electrical connection between copper wire and the tinned lug surface...

American Boat and Yacht Council. They seem to be the gold standard for boating standards. If it's good enough for a boat, it'll work fine in an RV, though some of their standards are overkill for an RV. In our resources section I believe there is an older version of their standards document. It's very useful.

 

[Haugen]

Yes, that too.

But Haugen makes it sound like that alone won’t be enough (at least in a moist environment and given enough time)...

First things first.
I am, and always have been an advocate for using a connector lubricant on these terminals.
The misconception above is patently false and I don't appreciate you trying to put those words in my mouth.

Now that I’ve understood that even aluminum lugs are plated with copper or nickel and then tin, I’m realizing that avoiding dissimilar metals is essentially impossible with these cells.

In a warm dry environment, would you see major concerns as far as galvanic corrosion with tin-plated lugs secured onto the aluminum surface of the terminals using stainless grub screws (threaded posts) and brass nuts?

I don't know that I would use aluminium lugs.
You should switch to copper for the advantages of low conductor resistance.

What I HAVE said many times, is that the best place for the dissimilar metal change is where you can see it.
I won't be removing and reinstalling my bolts and bus bars just to check whether corrosion has set in.
That's why I recommend keeping everything aluminum through the bolts and bus bars using connector lubricant then attach copper lugs. (plated or not) Brass bolts might be a good idea at that connection.

 

[ArthurEld]

Should we be using something like Noalox inside aluminum crimp ring connectors?

 

[Haugen]

I was changing the converter in my camper to be able to install the lithium batteries. When I pulled the battery terminals off, there was a lot of corrosion.
It has only been about 6 months since I installed my battery cutoff switch. I installed gold plated terminals at that time to try to prevent corrosion. I'm not sure if I sprayed connector lubricant on these terminals.

I was surprised to see how much corrosion had already formed, but this is Florida. This is what happens when you connect steel, tin, gold, copper, and lead all in one connection and leave it in a camper.
I keep it plugged into shore power and let the A/C remove humidity while cooling it.

 

[Luthj]

Is that a flooded battery (I think I see removable caps)? If so the acid vapor/splash is known to cause corrosion on nearby metals.

I have used sealed batteries on fresh water boats many times, and corrosion like that is dramatically reduced. Untinned connectors still show some after a few years if there is condensing level moisture or splashing though.

 

[HRTKD]

@Luthj has it right. It's the vapor that's causing the corrosion, not necessarily the dissimilar metals. If the battery box isn't well vented it gets even worse.

 

[Maast]

Should we be using something like Noalox inside aluminum crimp ring connectors?

I've never seen an aluminum crimp ring connector, I think if they're silvery their universally tinned copper. If it's actually aluminum they you must absolutely use noalox or similar AND brush/sand the connector surfaces to bright metal. Noalox isnt anti-corrosion (though it does that too) its purpose is to prevent a high resistance oxidation layer from forming on aluminum.

Actually, if they're really aluminum I'd throw them away.

Aluminum is tricky, once a oxidation layer forms the connection goes high resistance and if there is enough amperage it'll heat up the connection - which makes the oxidation layer deeper, which makes the connection hotter etc etc etc until the connection melts. There are a few aluminum alloys that arent supposed to form an oxidation layer - but it isnt common.

In any case a hand crimped connector isnt a gas and watervapor tight crimp so you'd want to use sort of anti-oxidant grease to keep the copper wires from eventually developing a higher resistant oxidation layer - unless you're doing tinned-connector-on-tinned-wire crimps then you dont need it.

The only time I can see an argument for not greasing a crimp is with a hydraulic crimp using a thick-walled copper battery lug which is supposed to 'cold weld' the wire and connector barrel together - and even then I spooge my crimps.

You dont need much but you need some, on a boat it's absolutely mandatory.

 

[HRTKD]

I've never seen an aluminum crimp ring connector, I think if they're silvery their universally tinned copper.

Good catch on the aluminum ring connector. I missed that and thought, "What the heck does he need noalox in a ring terminal for?"

All my connectors are tinned copper.

Hey, in case nobody noticed it, TEMCo Industrial revamped their website. It's faster now with a new layout. It was really slow before the change.

 

[ArthurEld]

I've never seen an aluminum crimp ring connector, I think if they're silvery their universally tinned copper. If it's actually aluminum they you must absolutely use noalox or similar AND brush/sand the connector surfaces to bright metal. Noalox isnt anti-corrosion (though it does that too) its purpose is to prevent a high resistance oxidation layer from forming on aluminum.

Actually, if they're really aluminum I'd throw them away.

Thanks Maast. I assumed they were aluminum but I just checked and they are tinned copper.

 

[Haugen]

Is that a flooded battery (I think I see removable caps)? If so the acid vapor/splash is known to cause corrosion on nearby metals.

I have used sealed batteries on fresh water boats many times, and corrosion like that is dramatically reduced. Untinned connectors still show some after a few years if there is condensing level moisture or splashing though.

Yes. It is a flooded battery and sulfuric acid is definitely corrosive.

The camper hadn't moved in months, so there was no splashing. The battery is well vented which allows humidity in.

I'm not sure I can agree with you that the acid is the dominant factor. If you look closely, you will see that the lead and steel were not affected, but the tin and copper were. Note that all of the corrosion is green indicative of copper.

The tin and copper are the anodes compared to the steel and lead which are next to one another in the noble metal chart, but several steps above.

I won't argue that the sulfuric acid probably accelerated the process. Having gaseous acid instead of just moisture likely defeated the lubricant,but, this is definitely galvanic.