Avoiding Galvanic Corrosion

[fafrd]

I’ve already completed my 90Ah 24V LFP battery using bundled copper busbars and stainless screws, but I’ve got to dissamble it to add the 8S wiring harness for a BattGO battery monitor, so I’m trying to understand whether I should do anything different to better protect against galvanic corrosion caused by dissimilar metals.

The battery will be used in a basement environment in the Bay Area so temps will be mild (50-70F) and humidity will be 65-75%.

Is copper-to-Aluminum, Stainless-to-Aluminum, or copper-to-stainless the mix that is of greatest concern in these conditions?

Is there any easy way using some sort of grease or another coating that I can reduce/avoid the possibility of galvanic corrosion?

How big of a concern is the possibility of galvanic corrosion using these standard LFP battery ‘kits’ in this relatively benign environment?

The battery is rated for 3500 cycles which amounts to close to 10 years cycling once per day - is corrosion likely to be an issue I’ll have to deal long before then and is there a cheap/easy way to avoid the issue for the lifetime of the battery?

 

[fafrd]

Did a bit of reading and it seems aluminum galvanic corrosion is the greatest concern, especially in contact with copper.

Didn’t see anything about stainless but aluminum screws/bolts are inexpensive enough that switching out the ‘kit’ stainless screws for aluminum seems a pretty straightforward way to get stainless out of the equation.

And for copper-to-aluminum interface, conductive zinc paste such as this seem like an easy way way to protect the surface of the aluminum contact terminal: https://www.acehardware.com/departm...brya_YICpJGqWuRQGPrhW9-g0JYGTIIBoC1VoQAvD_BwE

So what do those with more experience on the board say:

-will switching out stainless screws for aluminum screws and using anti-oxidation paste such as this address the concern of LFP galvanic corrosion?

-is the concern with galvanic corrosion on the surface of the aluminum contacts significant enough to justify the cost and complexity of this change?

 

[Hedges]

Aluminum is used in name-brand electrical terminals, but it is tin-plated aluminum. They are typically rated Cu-Al, compatible with both types of wire, and only for dry locations. I avoid aluminum as much as I can, but it is used for terminals in most of my breakers.

Stainless self-tapping screws or stainless screws and toothed washers are used to connect ground terminals to PV panels.

Compounds that exclude water would be beneficial.

Why is aluminum any part of your system? Is that what battery terminals are made of?

 

[fafrd]

Aluminum is used in name-brand electrical terminals, but it is tin-plated aluminum. They are typically rated Cu-Al, compatible with both types of wire, and only for dry locations. I avoid aluminum as much as I can, but it is used for terminals in most of my breakers.

Stainless self-tapping screws or stainless screws and toothed washers are used to connect ground terminals to PV panels.

Compounds that exclude water would be beneficial.

Why is aluminum any part of your system? Is that what battery terminals are made of?

Yes, the Aluminum I’m referring to is the terminals of my LiFePO4 cells. I’ll check the datasheet, but it looks like unplayed Aluminum and I’ve read in other threads on this forum that members are switching out the standard copper bus bars and stainless terminal screws for aluminum busbars and aluminum screws to avoid the possibility of galvanic corrosion.

You raise a good point about stainless to aluminum and copper to stainless being commonly used when grounding PV rails.

On the other hand, some galvanic corrosion when grounding PV panels is probably less of a concern that on a battery terminal. Between increased resistance on the contact to any specific cell or the bigger concern of the aluminum ‘threads’ degrading to the point they become stripped, avoiding galvanic corrosion on aluminum LFP battery terminals seems like a higher priority than avoiding a bit of corrosion on your PV array grounding over the ~20-year lifetime of the array.

 

[nosys70]

zinc is very soft and you can get is by the sheet, so applying a very thin sheet of tin between terminals and busbar will increase contact surface and protect against corrosion

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you can even use gold, very very thin sheet of gold is easily available for cheap

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[David Pocock]

For a marine installation I used 30mm studs stainless M6 studs and cemented them in the aluminium terminals with Loctite. That should stop moisture getting in to set up galvanic corrosion. I have copper, aluminium and stainless stacked on the same terminal so after burnishing all contact points I used a product in the UK called Ox-gard. This keeps also keeps out moisture but is itself a conductor and is said to be good between copper and aluminium.

 

[fafrd]

For a marine installation I used 30mm studs stainless M6 studs and cemented them in the aluminium terminals with Loctite. That should stop moisture getting in to set up galvanic corrosion. I have copper, aluminium and stainless stacked on the same terminal so after burnishing all contact points I used a product in the UK called Ox-gard. This keeps also keeps out moisture but is itself a conductor and is said to be good between copper and aluminium.

Interesting, thanks. So you permanently convert the aluminum femal thread to a stainless male thread by gluing-in with Loctite.

Then you coat the aluminum surface with Ox-guard before placing copper busbars on the post.

I understand the use of stainless for washers and nuts, but what is the second layer of Aluminum for?

Sounds like you have a great deal of experience in protecting against corrosion in a Marine environment, but would you have any thoughts as to whether those steps would be needed to avoid corrosion in a more benign basement environment?

The cheap and easy way to approach what you have done without investing in studs would be to apply Ox-guard to burnished kit parts and then stick to the standard stainless screw securing copper busbar onto aluminum post.

 

[fafrd]

zinc is very soft and you can get is by the sheet, so applying a very thin sheet of tin between terminals and busbar will increase contact surface and protect against corrosion

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you can even use gold, very very thin sheet of gold is easily available for cheap

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Good suggestions - thanks. Have you heard of anyone applying zinc or gold foil between aluminum terminal tops and copper busbars?

Between foil and a coating such as Ox-guard, is there an advantage to the foil (such as better conductivity)?

 

[nosys70]

I purchased gold for my busbar but i did not use it yet.
I will try with my next battery pack (8x280Ah)
for the first one i chemically tinned the copper and it gave a very good look.
but i think the tin layer is very thin, so you get the corrosion protection, but probably no increase in contact.
it is the easier and cheaper solution, you just need to dip the busbar into the mixture and wait less than1 min.
i will also purchase the tin foil, because the tin i got is a thick foil (i dissolved it in chloridric acid).
Gold is the best conductor and inoxidable, so you cannot be wrong.

 

[fafrd]

To recap the helpful suggestions that have been made on the thread, it sounds like galvanic corrosion between the surface of the aluminum terminals and copper busbars can be protected against using a coating like Ox-guard or zinc or gold foil.

And either Ox guard is also good-enough to protect against Stainless-to-Aluminum galvanic corrosion within the terminal threads or the female aluminum threads can be permanently converted to male stainless threads by gluing in a stainless post.

Using aluminum bolts seems like it is not worthwhile and so for my benign basement environment, the only question is whether degradation of the aluminum threads over ~10 years of lifetime is a high-enough concern to invest in Stainless posts or not.

Between Ox-guard and foil, and the fact that cleaning any corrosion off of the surface of the terminals and busbars if any should develope, it seems like avoiding (or recovering from) problems caused by galvanic corrosion on the aluminum terminals themselves is straightforward (and relatively inexpensive), so it is really the female aluminum threads that should be the focus of any real concern.

Does anyone know how the battery terminals used is large commercial solar farms are treated?

 

[Ampster]

I have been using NoAlox for 20 years and it is simple to apply. Apparently there are even better solutions but last time I organized my solar stuff, my electrical stuff and my battery stuff I discovered I had enough NoAlox for the foreseeable future so I will not be upgrading to the perfect product. I will put my NoAlox in my will for my son in law and my nephew.

 

[fafrd]

I purchased gold for my busbar but i did not use it yet.
I will try with my next battery pack (8x280Ah)
for the first one i chemically tinned the copper and it gave a very good look.
but i think the tin layer is very thin, so you get the corrosion protection, but probably no increase in contact.
i will also purchase the tin foil, because the tin i got is a thick foil (i dissolved it in chloridric acid).
Gold is the best conductor and inoxidable, so you cannot be wrong.

My next battery will also be a 8x280Ah, so I’ll be interested to follow in your footsteps...

What environment are your batteries being used in? I’m just trying to understand the source of the concern that lead you to chemically tin your copper in the first place.

Avoiding corrosion that degraded the aluminum threads is one concern (which may only apply in the case of harsh environments)( avoiding corrosion that decreases conductance between copper busbars and aluminum terminal surface is another.

I cleaned my copper busbars in a vinegar+salt solution before screwing them onto my terminals, but I’m wondering whether that is enough to maintain good conductance over time.

I suppose if you can measure resistance through the entire 8S series of cells from time-to-time, you can get an easy indication if terminal-to-busbar conductance has started to increase, but I’m still interested in what sources/threads have led members like you to be concerned about corrosion and to take the steps that you’ve taken...

 

[David Pocock]

Interesting, thanks. So you permanently convert the aluminum femal thread to a stainless male thread by gluing-in with Loctite.

Then you coat the aluminum surface with Ox-guard before placing copper busbars on the post.

I understand the use of stainless for washers and nuts, but what is the second layer of Aluminum for?

Sounds like you have a great deal of experience in protecting against corrosion in a Marine environment, but would you have any thoughts as to whether those steps would be needed to avoid corrosion in a more benign basement environment?

The cheap and easy way to approach what you have done without investing in studs would be to apply Ox-guard to burnished kit parts and then stick to the standard stainless screw securing copper busbar onto aluminum post.

Short stainless studs with an allen key head are not expensive. The problem with stainless machine screws is that they can allow damp into the terminal between aluminium and stainless although Ox-gard would be good there too. Loctite prevents that damp getting in. The allen key head means you can hold the stud steady with a key when tightening nuts. Those aluminium taps don't take a lot of use by the look of them and would be easy to strip so Loctite stabilises it. Sorry there is just the aluminium terminal rather than a second layer but if there is a washer needed in the stack then an aluminium washer would be good too.

I also used several layers of liquid insulation on the base of my aluminium cased cells (they are +vely charged). Every place the cells touch the case (and between them) there is a sheet of 0.5mm epoxy fibreglass. All blue wrapping (which is easily nicked exposing a hot aluminium case) has a covering of nylon mesh tape which binds the cells but also allows any heat to escape. And all electronic boards have several layers of Plastik-70 conformal coating.

 

[fafrd]

I have been using NoAlox for 20 years and it is simple to apply. Apparently there are even better solutions but last time I organized my solar stuff, my electrical stuff and my battery stuff I discovered I had enough NoAlox for the foreseeable future so I will not be upgrading to the perfect product. I will put my NoAlox in my will for my son in law and my nephew.

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?

 

[Hedges]

Yes, the Aluminum I’m referring to is the terminals of my LiFePO4 cells. I’ll check the datasheet, but it looks like unplayed Aluminum

Unplated aluminum is horrible stuff. Al2O3 or Al(OH)3 is an insulator, so would cause poor contact and excessive current/electromigration where it is broken and contact does occur. Self-tapping screws or toothed washers puncture the oxide and attempt to make a gas-tight seal. A busbar clamped to a flat aluminum surface should be a terrible contact.

Ask the vendor what surface treatment it has.

If not tin plated, "Alodine" is another electrically conductive possibility.

Chromate conversion coating - Wikipedia

en.wikipedia.org

 

[Hedges]

I cleaned my copper busbars in a vinegar+salt solution before screwing them onto my terminals, but I’m wondering whether that is enough to maintain good conductance over time.

Copper oxide is electrically conductive so it's not the problem. Aluminum is.

Certain mechanical arrangements of copper and tin-plated aluminum work, others do not. Aluminum setscrew through a aluminum sleeve (lugs) are used to connect either copper or aluminum wires to breakers and terminals. Copper lugs are only for copper wire.

So I wonder about the TCE (thermal coefficient of expansion) of stainless screws used to clamp aluminum busbars. I think they're fine for clamping copper. But the battery terminal they're clamping to needs a surface treatment so it doesn't oxidize.

 

[fafrd]

Short stainless studs with an allen key head are not expensive. The problem with stainless machine screws is that they can allow damp into the terminal between aluminium and stainless although Ox-gard would be good there too. Loctite prevents that damp getting in. The allen key head means you can hold the stud steady with a key when tightening nuts. Those aluminium taps don't take a lot of use by the look of them and would be easy to strip so Loctite stabilises it. Sorry there is just the aluminium terminals rather than a second layer but if there is a washer needed in the stack then aluminium washer would be good too.

If converting from Aluminum to Stainless using a stud, why would an aluminum washer be good - seems like it’s just more exposed aluminum that could have been avoided, another aluminum to copper interface to protect, and a stainless washer would have been better...

I also used several layers of liquid insulation on the base of my aluminium cased cells (they are +vely charged). Every place the cells touch the case (and between them) there is a sheet of 0.5mm epoxy fibreglass. All blue wrapping (which is easily nicked exposing a hot aluminium case) has a covering of nylon mesh tape which binds the cells but also allows any heat to escape. And all electronic boards have several layers of Plastik-70 conformal coating.

I’m new to this forum and don’t know the rules, but interested enough in stall of these inputs of yours to start a new thread if that would be considered more appropriate than straying off-topic here.

But until someone instructed me to that effect, I’m curios to you understand what battery size you have and what sustained discharge rates you are supporting that cause your aluminum case to get ‘hot’.

I’ve built my first battery but have not used it yet. My continuous discharge rate and my charging rate will be no higher than 0.3C, and from articles I’ve read, I assumed my battery should be running pretty cool at that level and I shoukdn’t really have any heat issues to worry about.

Appreciate understanding more about your experience in the area of LFP heat management (in this thread or another thread if that would be more appropriate).

 

[nosys70]

my batteries goes to cuba, not really at sea shore, but not too far.
humidity is very high all year long (above 80% most of the time) and you will hardly see a piece of iron that is not
totally rusted in few weeks.
So aluminium (with air+ salt it is just a nightmare) is excluded, copper is nice but needs protection.
i will try tin but tin is protecting only the copper, the alu posts of the battery are still an issue.
i will check for the battery with and without gold in time, but unfortuantely , the project just started so there is no data yet.
But as i said, you cannot go wrong with gold.

 

[David Pocock]

deleted

 

[fafrd]

Copper oxide is electrically conductive so it's not the problem. Aluminum is.

Certain mechanical arrangements of copper and tin-plated aluminum work, others do not. Aluminum setscrew through a aluminum sleeve (lugs) are used to connect either copper or aluminum wires to breakers and terminals. Copper lugs are only for copper wire.

So I wonder about the TCE (thermal coefficient of expansion) of stainless screws used to clamp aluminum busbars. I think they're fine for clamping copper. But the battery terminal they're clamping to needs a surface treatment so it doesn't oxidize.

I have the EVE datasheet and will read through it more carefully...

And another thought that comes to my mind as I read your post:

If investing in threaded posts to convert the female aluminum thread to a male thread, would an aluminum post be preferable to stainless?

Aluminum might be better for the within-terminal interface, but I suppose the exposed aluminum threads would need to be protected from oxidation and also would strip much more easily than stainless threads..,