Avoiding Galvanic Corrosion

[David Pocock]

I'm not planning to charge or discharge at high C rates. All the precautions are because of use in a marine environment with salty air and sustained bumpiness. By 'hot', I mean live. The case is positively charged and the blue plastic covering is easily damaged and represents the absolute minimum of insulation in a static install but entirely inadequate (in my view) in a mobile installation. The problem with stainless is that it is a poor conductor. The stainless studs don't matter, they only hold the stack together but if a washer is needed in a stack then stainless may be better avoided in favour of an Ox-gard coated aluminium one.

 

[Hedges]

All the precautions are because of use in a marine environment with salty air and sustained bumpiness.

Then "pot" it. After using whatever inhibitors you like on the electrical contact surfaces, torque, let it sit/temperature cycle, torque again. Then clean with solvent, prime if appropriate, encapsulate the &#% aluminum and connections with something like silicone, urethane, parylene ...

 

[fafrd]

I'm not planning to charge or discharge at high C rates. All the precautions are because of use in a marine environment with salty air and sustained bumpiness. By 'hot', I mean live. The case is positively charged and the blue plastic covering is easily damaged and represents the absolute minimum of insulation in a static install but entirely inadequate (in my view) in a mobile installation.

Gotcha - thanks. As I packed my 8 cells against each other, hadn’t even occurred to me that the Aluminum case under the blue plastic was live...

I’ve got the entire battery in a plastic case and the cells secured well-enough that I should not need to worry about any damage to the blue coating. But I’ll keep these inputs on my for my next (280Ah 8S) LFP battery, which will be stationary.

 

[nosys70]

since prismatic are slightly "breathing" changing the geometry of the casing, you would suggest silicone, a rigid layer of expoxy would crack really fast. Plati dip could also fit. i think you can find it in spray version for rim protection

 

[fafrd]

I'm not planning to charge or discharge at high C rates. All the precautions are because of use in a marine environment with salty air and sustained bumpiness. By 'hot', I mean live. The case is positively charged and the blue plastic covering is easily damaged and represents the absolute minimum of insulation in a static install but entirely inadequate (in my view) in a mobile installation. The problem with stainless is that it is a poor conductor. The stainless studs don't matter, they only hold the stack together but if a washer is needed in a stack then stainless may be better avoided in favour of an Ox-gard coated aluminium one.

For a washer between the terminal and the busbar, I agree (though in general you should never use a washer there).

For a washer above the busbar, conductance is immaterial - a nylon washer would work just fine as far as conductance of the overall connection...

 

[David Pocock]

For a washer between the terminal and the busbar, I agree (though in general you should never use a washer there).

For a washer above the busbar, conductance is immaterial - a nylon washer would work just fine as far as conductance of the overall connection...

Probably, if you can rely on the stainless steel stud to terminal connection but stainless steel (poor conductor) coated liberally with Loctite (no conductor) ... hmm. I'd prefer to ensure that conductivity doesn't rely on the stud.

 

[fafrd]

since prismatic are slightly "breathing" changing the geometry of the casing, you would suggest silicone, a rigid layer of expoxy would crack really fast. Plati dip could also fit. i think you can find it in spray version for rim protection

Another OT post, but since the EVE datasheet only guarantees the maximum of 3500 cycles under pressure, I’m planning to use aluminum endplates squeezed together with 6 threaded rods to reduce/eliminate that breathing / swelling...

The only question I have is whether one is better off ‘top-balancing’ The force (meaning fill all cells to 100% SOC then use a torque wrench to apply the specified clamping force) or to ‘bottom-balance’ meaning drop all cells down near minimum SOC (minimum swelling), snug together the endplates to some safe low value, then monitor compression forces as the battery charged using a torque wrench and back off if they get too high...

 

[fafrd]

Probably, if you can rely on the stainless steel stud to terminal connection but stainless steel (poor conductor) coated liberally with Loctite (no conductor) ... hmm. I'd prefer to ensure that conductivity doesn't rely on the stud.

Easy calculation - surface area of the stud minus exposed sides in the case busbar is narrower...

I’d be slightly shocked if conductance of the threads is included by the manufacturer in their calculations...

At worst, they may assume 100% contact area with the terminal surface where most of the kit busbars contact well below 100% of that surface....

But even in that case, trying to compensate for that list conductance by relying on the threads seems much less prudent that just finding wider busbars.

 

[Ampster]

Are you comfortable that NoAlox would be fine for protecting against Stainless-to-Aluminum corrosion of the terminal threads?

And as far as any impact on conductance between terminals and busbars, I assume there is none (unmeasurable)?

Since I’ll be purchasing my own lifetime supply of NoAlox or whatever ‘better solutions’ exist today, would you have any products / names you suggest I check out before pulling the trigger?

NoAlox is for the Aluminum to Aluminum or the Copper to Aluminum electrical contacts to protect against corrosion. It is easy to find in the electrical section of a home center. As mentioned earlier those surfaces should be cleaned to eliminate existing Oxide before assembling. As far as better solutions @Haugen has some recommendations from his experience in aviation.

Stainless to Aluminum is an entirely different issue. In my case I used Permatex Red to keep my studs in place in the Aluminum terminals, Others have suggested that the Permatex will protect from some galavanic corrosion, I am in a dry environment and I have no need to remove the studs so if they become stuck it is not concern to me because the threads above the terminals is all I care about applying tension to the connectors.
If you are concerned about galvanic corrosion between Aluminum and Stainless bolts I used another Permatex product #80078 anti-sieze when assumbling my solar panel racking with Stainless fasteners. It resembles a product I used 35 years ago when rigging my sailboat. We often tapped the aluminum and threaded bolts directly into the mast or boom. It worked well in that harse salt air environment.

 

[fafrd]

NoAlox is for the Aluminum to Aluminum or the Copper to Aluminum electrical contacts to protect against corrosion. It is easy to find in the electrical section of a home center. As mentioned earlier those surfaces should be cleaned to eliminate existing Oxide before assembling. As far as better solutions @Haugen has some recommendations from his experience in aviation.

Stainless to Aluminum is an entirely different issue. In my case I used Permatex Red to keep my studs in place in the Aluminum terminals, Others have suggested that the Permatex will protect from some galavanic corrosion, I am in a dry environment and I have no need to remove the studs so if they become stuck it is not concern to me because the threads above the terminals is all I care about applying tension to the connectors.
If you are concerned about galvanic corrosion between Aluminum and Stainless bolts I used another Permatex product #80078 anti-sieze when assumbling my solar panel racking with Stainless fasteners. It resembles a product I used 35 years ago when rigging my sailboat. We often tapped the aluminum and threaded bolts directly into the mast or boom. It worked well in that harse salt air environment.

I’m trying to understand whether I need to be concerned (in my relatively benign basement environment).

Appreciate the heads-up about NoAlox (or an improved version) being useless for stainless-to-Aluminum corrosion.

So seems like the options are;

1/ Glue in a stainless post with Loctite

2/ Use some Permatex or #80078 on the stainless threads before screwing them in

3/ Nothing (just some NoAlox on the surface of the terminals).

Would be great to know how solar farms deal with their Aluminum battery terminals...

 

[fafrd]

I read carefully through the entire datasheet for the EVE LF280 (File No: LF280-72174 Version E Dated April 30th 2019).

The only references to the terminals state the following:

‘Remark: The pole is double aluminum pole structure.’

‘9.3.9 Connection a) Polishing the pole with abrasive paper before use, otherwise it would cause bad contact or failure.’

So it seems pretty clear that the terminals are unplated aluminum and oxidation of the surface is a problem (at least prior to assembly)...

Reading this, I think using NoAlox or foil (or both?) between terminal surface and busbars is pretty much of a no-brainer.

For the female aluminum threads, I believe the only real issue is whether the threads oxidize to the point they become stripped and unusable. Using some Permatex or equivalent is probably prudent insurance, but it sure would be useful to understand what practice is followed by battery manufacturrrs like Byd...

 

[fafrd]

Just found this: https://www.hunker.com/12502151/screws-compatible-with-aluminum

It states that stainless bolts will corrode aluminum threads, especially in a moist environment.

And it also suggests another solution which has not yet been proposed: use of zinc-plated carbon steel screws rather than stainless.

Zinc-plated screws are inexpensive and strong, so if I decide I need to do something about the standard stainless bolt + copper busbar ‘kit’ I will probably switch out the stainless bolts for zinc-plated bolts or perhaps threaded posts if I can find them.

 

[Luthj]

I have some experience with stainless fasteners on aluminum engines (boats typically). In a wet environment the galvanic corrosion takes a few years and can be significant. In freshwater it takes a bit longer. In dry environments this corrosion is dramatically slowed down.

A heavy bodied silicon grease (non drying, wide temp range) between the dissimilar metals is all that required in a dry environment. At least if you are expecting a 10 year life. Other purpose made anti oxidant grease products are commonly available, and are used extensively in grid electrical systems where aluminum is common. Any product that seals the interface to prevent easy access to oxygen will work.

I would not stack thin tin or anything else under the terminal if possible. That significantly increases contact resistance.

Another option is to have all the copper zinc plated. You can do this yourself, or just send the parts out to be plated.

 

[fafrd]

I have some experience with stainless fasteners on aluminum engines (boats typically). In a wet environment the galvanic corrosion takes a few years and can be significant. In freshwater it takes a bit longer. In dry environments this corrosion is dramatically slowed down.

Thanks - so sounds as though in a cellar environment you could consider doing nothing but that might be taking some risk of developing some corrosion before 10 years are up, right?

And as you state below, merely using a heavy-bodied antiox grease may be all that is needed to provide some additional protection / margin.

A heavy bodied silicon grease (non drying, wide temp range) between the dissimilar metals is all that required in a dry environment. At least if you are expecting a 10 year life. Other purpose made anti oxidant grease products are commonly available, and are used extensively in grid electrical systems where aluminum is common. Any product that seals the interface to prevent easy access to oxygen will work.

I would not stack thin tin or anything else under the terminal if possible. That significantly increases contact resistance.

Yeah, if using zinc or gold foil increases contact resistance at all, it’s probably not worth it. I assume the antiox grease would have little/no impact on contact resistance, correct?

Another option is to have all the copper zinc plated. You can do this yourself, or just send the parts out to be plated.

Well first, this discussion is making me want to check what screws were included in my kit. I’d assumed they are stainless but they might be zinc-plated - is there any easy way to check (even destructive since I’ve got spares)?

And second, am I correct that only the lower busbar needs to be zinc-plated? I’ve soldered my BMS sense wires onto my copper busbars and I suspect soldering onto zinc-plating is a no-no.

But if the lower of two busbars in contact with the aluminum terminal is zinc-plated, additional copper busbars including one with soldered sense wire can be added on top of the stack without causing any issue, right?

So zinc-plated screws/bolts and a lowermost zinc-plated busbar May be the best way to transition from the aluminum terminal to nickle-plated metal that will then be able to safely interface with copper, correct?

And if I was going to go the trouble of zinc-plated screws, a zinc-plated lower busbar, and a copper busbar (or zinc-plated busbar with an area of planting removed for soldering), would you still recommend the use antiox grease, or is it superfluous at that point?

 

[Haugen]

There is significant evidence that even "sealed" military grade connectors will have oxygen and moisture intrusion. This has brought down several F-16 fighter jets.
Like @Luthj said, moisture is a key ingredient in corrosion and salt accelerates it.
For my application, I am using all aluminum hardware for the connections to the cells. The main concern is having corrosion occur where you can't inspect and treat it. The absolute worst place would be the threads of your cells. BTW, aluminum is always the metal that is corroded first, except when zinc is involved.
Using a high quality connector lubricant will help. I would not consider NoAlOx high quality. It contains too many additional ingredients such as zinc. There are good spray on connector lubricants (like MIL-L-87177) that provide excellent coverage and ease of application. Once you have eliminated dissimilar metals that you cannot see, it's easy to inspect your terminals where aluminum meets copper twice a year and spray a little on as a preventative.

 

[Ampster]

But if the lower of two busbars in contact with the aluminum terminal is zinc-plated, additional copper busbars including one with soldered sense wire can be added on top of the stack without causing any issue, right?

The only issue I see is the different resistance between the sense wires and the terminal. Unless they are all stacked the same.

 

[Hedges]

I’d assumed they are stainless but they might be zinc-plated - is there any easy way to check (even destructive since I’ve got spares)?

 

[fafrd]

Zinc-coated bolts are

View attachment 20037

View attachment 20038

Zinc-plated steel is magnetic while stainless is not - thanks (and duh / head slap).

I’ll have to do some reaearch on how the acid conductance test works, but the magnet test is easy...

 

[fafrd]

The only issue I see is the different resistance between the sense wires and the terminal. Unless they are all stacked the same.

Well copper wire soldered onto a copper busbar is going to have about as little resistance as you can get (lower and more reliable than a lug connection).

Ann between a copper busbar and a matching zinc-plated busbar, if you don’t get good electrical contact over several square centimeters of contact area, zinc plating is more trouble than it is worth...

 

[fafrd]

There is significant evidence that even "sealed" military grade connectors will have oxygen and moisture intrusion. This has brought down several F-16 fighter jets.
Like @Luthj said, moisture is a key ingredient in corrosion and salt accelerates it.
[b{For my application, I am using all aluminum hardware for the connections to the cells.[/b] The main concern is having corrosion occur where you can't inspect and treat it. The absolute worst place would be the threads of your cells. BTW, aluminum is always the metal that is corroded first, except when zinc is involved.
Using a high quality connector lubricant will help. I would not consider NoAlOx high quality. It contains too many additional ingredients such as zinc. There are good spray on connector lubricants (like MIL-L-87177) that provide excellent coverage and ease of application. Once you have eliminated dissimilar metals that you cannot see, it's easy to inspect your terminals where aluminum meets copper twice a year and spray a little on as a preventative.

So just to be clear, you are using an aluminum threaded terminal lubricated with MIL-L-87177 (or equivalent) and then holding down copper busbars or aluminum busbars?

Once you go to an aluminum thread coming out of the terminal, any corrosion should be visible on the surface of the aluminum post in the cell. Whether using copper busbars or zinc-plated busbars, or aluminum busbars, maintainance should be straightforward.

Also, if corrosion within the threads of the post have been prevented and it’s only some surface corrosion that may eventually develop, until that corrosion causes an increase in resistance, nothing really need to be done about it - isn’t there an easy way to just measure full-battery resistance or single-cell resistance every 6 months to determine whether more extensive maintainance is needed rather than having to inspect all of the terminal surfaces every 6 months?