Avoiding Galvanic Corrosion

[fafrd]

I like it! Do I get any points for that?

I have the aluminum bolts, washers and bus bar stock on-hand, ready to go. I just need to find my motivation. It's around here somewhere.

Where did you find your aluminum bolts? Are they aluminum bolts or aluminum grub screws?

As I compound the issues of trying to affix stainless grubscrews into aluminum terminals with the possibility of stainless nuts galling into those stainless grub screws (degrading their threads and making disassembly less straightforward than expected), the idea of going all-aluminum is growing in appeal.

I’ve even asked about the possibility of using aluminum lugs with set screws.

These could be bolted down once and forever using aluminum bolts and nuts (or aluminum grub-screws if they exist) and then the copper or aluminum cable connections could be made (and easily dissassembled) using the set screws.

You could also bolt down an aluminum bus bar but

A/ disassembly requires unthreading the bolts (so threadbare within the soft terminal threads could be a concern) and

B/ a rigid busbar means that whatever fixturing solution you settle on for your 280Ah LiFePO4 cells, it can involve movement or require any flexibility of the connections.

Are setscrew connections to copper or aluminum cable a viable solution?

 

[HRTKD]

Aluminum bolts, not grub screws, from Amazon:

Amazon.com: Ochoos 50pcs/lot DIN933 Aluminium hex Bolt 6061 Aluminium Alloy Bolts M6 M8 M1015/20/25/30/35/40/50 - (Thread Diameter: M6, Length: 20mm): Home Improvement

Buy Ochoos 50pcs/lot DIN933 Aluminium hex Bolt 6061 Aluminium Alloy Bolts M6 M8 M1015/20/25/30/35/40/50 - (Thread Diameter: M6, Length: 20mm): Quick-Lock - Amazon.com ✓ FREE DELIVERY possible on eligible purchases

www.amazon.com

(Yes, I know the page says they are unavailable. I'm just letting you know where I got them. Very slow shipping also.)

I have searched and cannot find aluminum M6 grub screws. My Google Fu was lacking.

I considered using M6 threaded rod (cut to length by me), but the non-terminal end would still need something to grab onto. That seemed to be more work than it was worth. I do know this: I would never use a slotted end grub screw, but only because I know I'm a klutz and the screwdriver would slip out of the slot and cause something spectacular to happen.

 

[fafrd]

Aluminum bolts, not grub screws, from Amazon:

Amazon.com: Ochoos 50pcs/lot DIN933 Aluminium hex Bolt 6061 Aluminium Alloy Bolts M6 M8 M1015/20/25/30/35/40/50 - (Thread Diameter: M6, Length: 20mm): Home Improvement

Buy Ochoos 50pcs/lot DIN933 Aluminium hex Bolt 6061 Aluminium Alloy Bolts M6 M8 M1015/20/25/30/35/40/50 - (Thread Diameter: M6, Length: 20mm): Quick-Lock - Amazon.com ✓ FREE DELIVERY possible on eligible purchases

www.amazon.com

(Yes, I know the page says they are unavailable. I'm just letting you know where I got them. Very slow shipping also.)

I have searched and cannot find aluminum M6 grub screws. My Google Fu was lacking.

I considered using M6 threaded rod (cut to length by me), but the non-terminal end would still need something to grab onto. That seemed to be more work than it was worth. I do know this: I would never use a slotted end grub screw, but only because I know I'm a klutz and the screwdriver would slip out of the slot and cause something spectacular to happen.

Yeah, I’ve searched as well to no avail.

I suppose it is worth asking whether the soft aluminum threads in the terminals may wear less from unthreading aluminum bolts rather that stainless?

A long aluminum bolt with a nut can clamp down on a lug as effectively as a grubscrew so the only issue is that if/when disassembly of connections is required, that bolt will need to be unscrewed from the terminal threads...

Back to my question about aluminum lugs with set-screws, those could be tightened down by aluminum bolts + nuts once and for all time, so the aluminum but would never need to be removed (disassembly can be achieved by loosening the set screw...).

 

[HRTKD]

I suppose it is worth asking whether the soft aluminum threads in the terminals may wear less from unthreading aluminum bolts rather that stainless?

A long aluminum bolt with a nut can clamp down on a lug as effectively as a grubscrew so the only issue is that if/when disassembly of connections is required, that bolt will need to be unscrewed from the terminal threads...

Similar materials would hopefully wear less. It's also possible that the bolt will strip instead of the terminal.

I bought a variety of lengths of bolts, but I don't think they're long enough to use a nut on them, but that's an option.

 

[fafrd]

Similar materials would hopefully wear less. It's also possible that the bolt will strip instead of the terminal.

I bought a variety of lengths of bolts, but I don't think they're long enough to use a nut on them, but that's an option.

Yeah, you’d probably need 25mm bolts to have space for a nut, lock washer and washer..,

And if the bolt threads wear instead of the terminal threads that would be great. Someone pointed out that aluminum bolts are hardened versus the soft aluminum terminals these threads are tapped into..,

 

[Solarfun4jim]

another suggestion....
If you used the 'conductive epoxy' suggested by filterguy, then you could permanently secure 22mm M6 greenhouse bolts into the terminals, then simply cut off the square heads leaving approx 16mm exposed. Use aluminium lugs with tinned copper cables or tinned corrosion resistant copper lugs to improve conductivity???

Lot Of 10 Morris 90714 Dual Rated Aluminum Mechanical One Hole Lugs #2-#14 AWG | eBay
or
4 Ga. 5/16 Inch Stud Corrosion-Resistant Copper Lugs - 90 Degree - (Pack of 5) | eBay

Aluminium nuts...
M3 M4 M5 M6 M8 M10 M12 M16 Hexagon Full Nuts - ALUMINIUM Unanodised - Hex Metric | eBay

ps....remember the longer the leaverage of the stud, the more likely it will be stressed

 

[fafrd]

another suggestion....
If you used the 'conductive epoxy' suggested by filterguy, then you could permanently secure 22mm M6 greenhouse bolts into the terminals, then simply cut off the square heads leaving approx 16mm exposed. Use aluminium lugs with tinned copper cables or tinned corrosion resistant copper lugs to improve conductivity???

Lot Of 10 Morris 90714 Dual Rated Aluminum Mechanical One Hole Lugs #2-#14 AWG | eBay
or
4 Ga. 5/16 Inch Stud Corrosion-Resistant Copper Lugs - 90 Degree - (Pack of 5) | eBay

Aluminium nuts...
M3 M4 M5 M6 M8 M10 M12 M16 Hexagon Full Nuts - ALUMINIUM Unanodised - Hex Metric | eBay

ps....remember the longer the leaverage of the stud, the more likely it will be stressed

I’m really not worried about conductivity of the fastener - the conductivity I care about will be through the surface of the terminal (which is why it is important to have the lug cinched down with enough torque).

Cutting off bolt heads and relying on epoxy/fastener to prevent further rotation makes me nervous. If the epoxy doesn’t hold and the bolt continues to rotate as you cinch down the nut, it’ll pierce the thin shield at the bottom of the terminal and ruin the cell.

With a bolt head or even an Allen-head grubscrew, you can apply enough counter-torque to prevent that from happening...

 

[Solarfun4jim]

I’m really not worried about conductivity of the fastener - the conductivity I care about will be through the surface of the terminal (which is why it is important to have the lug cinched down with enough torque).

Cutting off bolt heads and relying on epoxy/fastener to prevent further rotation makes me nervous. If the epoxy doesn’t hold and the bolt continues to rotate as you cinch down the nut, it’ll pierce the thin shield at the bottom of the terminal and ruin the cell.

With a bolt head or even an Allen-head grubscrew, you can apply enough counter-torque to prevent that from happening...

I only had threadlocker, not epoxy and i could only use the tiniest amount, because i couldnt afford for it to squish up to the terminal face, but it secured the flange stud so securely, that when i used 8Nm torque to try and free it again(because i had noticed a tiny gap between the stud flange and the terminal face...carelessness), it sheared the stud. Are you intending to try and torque to 8Nm?
You on the other hand, by not using a flanged stud, can afford to apply more copious amount of securing bond and simply wipe clean the terminal face before it sets...so all your threads will be full of bond.

 

[fafrd]

I only had threadlocker, not epoxy and i could only use the tiniest amount, because i couldnt afford for it to squish up to the terminal face, but it secured the flange stud so securely, that when i used 8Nm torque to try and free it again(because i had noticed a tiny gap between the stud flange and the terminal face...carelessness), it sheared the stud. Are you intending to try and torque to 8Nm?
You on the other hand, by not using a flanged stud, can afford to apply more copious amount of securing bond and simply wipe clean the terminal face before it sets...so all your threads will be full of bond.

I’m not understanding.

‘Stud flange’ means the underside of the bolt head?

You had a space between the underside of the bolt head and the terminal face with a busbar or lug in between?

If you were using a bolt to clamp down on a busbar or lug, I understand why you’d have to remove it if it was improperly tightened (space allowing busbar/lug to move freely).

But if you were tightening a bolt directly onto the terminal face (with no busbar or lug in between the two), then I’m lost how you could use that to secure connections...

 

[fafrd]

I already said a long time ago I would use aluminium for everything up to the two main battery cables, but most members don't really like that solution for various reasons so I don't recommend it anymore.

This aluminum lugs are rated for 2:0 copper wire, meaning they should be able to handle 283A: https://www.gordonelectricsupply.co...eai-iIXQ9HJunhhZE-nywJ1UL2uqESUwaAi5VEALw_wcB

So what do you think about the idea of using a long aluminum bolt with nut,etc to lock the bolt with lug attached into the terminal with Loctite or JB Weld and then torque the lug down into the terminal surface with the nut?

The nut can be loosened if the angle of the lug needs to be adjusted but otherwise, short sections of 2/0 thick-stranded copper wire (not thin stranded welders wire) is used to form connections between cells by positioning in a pair of lugs and tightening down the set screws.

Is this a good solution to avoid galvanic corrosion and preserve the soft aluminum threads in the terminals by only using them once (and never unthreading them)?

The only dissimilar metal is the copper stranded wire in the aluminum lug, but I’ve got that combo used throughout my electrical panels...

 

[fafrd]

Worthwhile read on aluminum lugs: https://www.ecmweb.com/content/article/20892533/copper-or-aluminum-lugs-how-should-you-decide

As someone already pointed out, there are no all-aluminum lugs, only aluminum plated with nickel or copper and tin. All-aluminum lugs quickly oxidize.

Nore the comment about aluminum galling in aluminum.

And also note the comment about nuts stretching if torqued to high (resulting in a poor connection).

A lot to digest...

 

[Solarfun4jim]

I’m not understanding.

‘Stud flange’ means the underside of the bolt head?

You had a space between the underside of the bolt head and the terminal face with a busbar or lug in between?

If you were using a bolt to clamp down on a busbar or lug, I understand why you’d have to remove it if it was improperly tightened (space allowing busbar/lug to move freely).

But if you were tightening a bolt directly onto the terminal face (with no busbar or lug in between the two), then I’m lost how you could use that to secure connections...

Not quite... see my current arrangement below...

 

[noenegdod]

I'm sure everyone knows this, but JB Weld is an epoxy and is non-conductive. Using it on your threads increases the resistance from terminal to stud/bolt.

Have you tested the electrical conductivity of thread locker. Pretty sure its about the same as epoxy and claiming that "there is only a tiny amount" is pointless. There is only a tiny amount of space available in the threads for that tiny amount of thread locker to occupy and it will occupy basically all of it. In a threaded application, the points of contact between the male and female threads will still be there, the epoxy will simply fill the spaces in the threads in the location that were not touching anything. That said, loosing conductivity in the stud is basically immaterial under all but the highest loads. For me personally, even though my highest load will draw in excess of 500 amps, I have 4p4s so even at that load Im pulling 0.36C while they are rated for almost 3x that so loosing some conductivity through the stud is a nothing burger. Context is everything.

 

[Haugen]

But we've since learned these cells were supposed to have welded busbars. Not bolted.

Individual busbars and any motion means screws are likely to loosen.
A plastic structure securing the busbars together, preventing motion, could make it more reliable.

Coming up with a DIY welder (or access to a nearby laser welding service) might give the best results.

If your cells are properly compressed, there will be no motion of one cell relative to another.

The heat of welding bus bars on these cells would melt the plastic that is right up against the terminals. I don't believe that this is the intended method of attachment. Also, far too much care was put into preparing the terminals (chamfered, deburred, face machined flat) for them to be welded.

 

[noenegdod]

If your cells are properly compressed, there will be no motion of one cell relative to another.

The heat of welding bus bars on these cells would melt the plastic that is right up against the terminals. I don't believe that this is the intended method of attachment. Also, far too much care was put into preparing the terminals (chamfered, deburred, face machined flat) for them to be welded.

I do like your reply but for anyone using springs, there will still be relative motion between the terminals.

 

[cinergi]

If your cells are properly compressed, there will be no motion of one cell relative to another.

The heat of welding bus bars on these cells would melt the plastic that is right up against the terminals. I don't believe that this is the intended method of attachment. Also, far too much care was put into preparing the terminals (chamfered, deburred, face machined flat) for them to be welded.

Well, maybe if they're put in a fixture that doesn't expand and contract (such as a spring fixture). So "properly compressed" may be a misleading way to characterize it. I definitely see top-side movement in a spring-based fixture.

The welding in question is laser welding (no heat problem).

The cells are starting to be sold without threaded holes (some recent threads floating around here about that now). This, and the general weakness of M6 in these giant cells, is leading some to believe that the terminals *may* have been altered by someone other than the manufacturer.

 

[Hedges]

The heat of welding bus bars on these cells would melt the plastic that is right up against the terminals. I don't believe that this is the intended method of attachment. Also, far too much care was put into preparing the terminals (chamfered, deburred, face machined flat) for them to be welded.

The faster you weld, the less the thermal energy.
If they were meant to be bolted, I think they would have been drilled and tapped when the terminals were manufactured, not after the cell was finished.

Battery Pack Welding: Tips for Improving Tab-to-Terminal Connections

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Battery Pack Applications - Cylindrical, prismatic, pouch, ultra-capacitor

 

[Gazoo]

If your cells are properly compressed, there will be no motion of one cell relative to another.

Actually there is motion due to the fact the cells expand and contract. Even if the cells are mounted tight in a fixture with no springs there will be some motion. Compressing the cells too tight could shorten the cycle life and that's straight from the horses mouth, EVE. I don't see any way of avoiding some motion between the cells unless they are spaced far enough apart with a gap between them to avoid it.

 

[fafrd]

Not quite... see my current arrangement below...

View attachment 34966

OK, now I see. Do those M6-to-M10 flanged studs have a hex key at the top?

Where did you get them and how much did they cost?

 

[Solarfun4jim]

OK, now I see. Do those M6-to-M10 flanged studs have a hex key at the top?

Where did you get them and how much did they cost?

Mine didn't have a hex key at the top or a hex shape on the flange, but these were custom made, so you could specify that in your drawing. I was quoted approx £0.88each +vat if ordering 500. I only ordered 17, which cost a total including postage of £128, which made it very expensive. It is the machine setting that is the costly part.

A hex shape would have eliminated my problem of the stripped terminal completely, since i was having to double nut lock at the top to set my 4Nm torque. When i was subsequently 'breaking' the lock, i inadvertently released the 4Nm torque setting below un beknown to me. Of course, having set it with thread locker, it was then impossible for me to break it free and the stud itsel sheared. I'm not actually sure which grade aluminium was used, but you could specify this also. These can be machined out of many metals...see here below
Product overview - SB Cov Ltd (specialbolt.com)
in use....