Factory400
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Definitely - I am worried about that for sure.
I am fortunate enough to have the tools to repair a damaged thread if I go too far.
Copper washers and brass bolts or screws for battery terminals
- Thread starter sid the seagull
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I am fortunate enough to have the tools to repair a damaged thread if I go too far.
Bob B
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From that chart, it looks like stainless is the worst ... and that is what most of us have been using. Brass is in the middle and may be a good compromise between the hardness and the galvanic response.
Actually, it looks like the cheapest option .... zinc coated steel might be the best option.
Factory400
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I have been putting stainless STI type inserts into aluminum and using stainless fasteners in life-critical aerospace applications for a very long time. Admittedly, I never really researched the chemistry at all, but the engineers that specified these fasteners did. My particular cells have stainless inserts in the terminals which is far stronger than the bare aluminum in axial strength and also allows more mating cycles. Not sure if this is common or if I am just lucky.
So far, I have never seen any corrosion even in significantly corrosive environments. Stainless seems unlikely to be a problem in this application.
Now you tell me. I do still have stainless steel grub hubs. I wish you guys would make up your minds. I am just a poor EE. I skated through this stuff in school.
Read this.
Source of Belleville washers for 300kgf fixture?
I don't understand how two 70's in series equals 140. if they each compress to max at 70, then two in series will be flat at 70. The force doesn't divide, you just get more deflection before you reach 70. Two in parallel (back to back) equals 70 with twice the displacement. Two in series...
diysolarforum.com
I meant this one.
diysolarforum.com
I got 62 lb compression force with a 5/16" bolt and a finger tight nut.
Source of Belleville washers for 300kgf fixture?
I don't understand how two 70's in series equals 140. if they each compress to max at 70, then two in series will be flat at 70. The force doesn't divide, you just get more deflection before you reach 70. Two in parallel (back to back) equals 70 with twice the displacement. Two in series...
diysolarforum.com
I got 62 lb compression force with a 5/16" bolt and a finger tight nut.
Bob B
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I can't argue with your experience since even though I have an extensive background in electronics ....I am new to these type of factors that come into play with a DIY battery pack.
I am currently using stainless grub screws that can be held with a hex wrench while tightening the flange nut down on the bus bar. I am happy that this takes the twisting stress off the aluminum threads in the cell. I haven't used any of the thread lock that some have been using ... still trying to decide whether to keep this for my final setup.
I have noticed that if I remove the nut from the grub screw .... and then start removing the grub screw from the cell, it initially takes quite a bit of force to start the grub screw moving and I hear a "click" and the screw releases from the aluminum threads and comes out easy the rest of the way. I'm not sure what is causing the grub screw to seize a little with the aluminum thread.
This was after only having the pack put together for a couple of weeks.
Galvanic corrosion is different than what you are thinking. Aluminum oxide is a very poor conductor, your screws and bolts are not carrying the current, the surface where the busbar and the battery terminal meet carries the current. Galvanic corrosion is the chemical reaction when two dissimilar metals meet, basically any corrosion that would have occurred, will only occur on one of the metals. Basically it means the aluminium will corrode first and at a much higher rate. Aluminum oxide is the result, and it is terrible for an electrical connection, much worse than copper oxide. Just wipe some of the many and cheap compounds specifically designed for copper to aluminium on the terminal face, and the busbar. The stud and nut, don't worry about, they don't conduct current anyway. Basically you just put a very (and I stress very) thin layer on the terminal face and the part of the busbar to exclude oxygen and thus corrosion, the nice tight interface between the battery terminal and the busbar will squeeze and exclude oxygen and corrosion. Unless you get a lot of salt spray into the battery compartment, no problem. I doubt the corrosion of the screws will be a problem until long after the battery has reached end of life. It might weaken the mechanical connection given enough time, but we are talking decades in any environment I would put a battery.
Aaron_85
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You also must take into consideration the busbar-fastner compatibility as well, but the aluminum post on the cell being the hardest to replace, is the most important to worry about not ruining 
The paste is very important at stopping the oxygen getting in and starting the process.
you also reference charts like this, and the closer the metals are on the chart the lesser the effect is.
Maybe we need to start talking about using galvinised/zinc plated fastening hardware instead of stainless in/on our battery systems?
The paste is very important at stopping the oxygen getting in and starting the process.you also reference charts like this, and the closer the metals are on the chart the lesser the effect is.
Maybe we need to start talking about using galvinised/zinc plated fastening hardware instead of stainless in/on our battery systems?
Hedges
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Carbon Screws by Schmolke Carbon
Our carbon screws are manufactured in a highly specialised pressure extrusion procedure using only the best quality carbon.
www.schmolke-carbon.com
You also must take into consideration the busbar-fastner compatibility as well, but the aluminum post on the cell being the hardest to replace, is the most important to worry about not ruining
Maybe we need to start talking about using galvinised/zinc plated fastening hardware instead of stainless in/on our battery systems?
Most, if not all, of the anticorrosion compounds include zinc as a sacrificial element. As the chart you posted indicates, zinc would be the first thing to corrode. I would stick with copper or silver plated copper busbars, and stainless steel grub screws and nuts (either lock nuts, or a stainless lock washer). McMaster Carr has a great selection, very good prices, and fast shipping in my experience. I ordered a 6 foot long 110 copper busbar from them and it arrived next day (LA to Phoenix). It wasn't sent as next day shipping, but UPS was on the ball. Their biggest problem is not telling you how much shipping is until it ships and they charge your card, but the shipping is always very reasonable. I ordered 25mm stainless grub screws, washers and nordlock bolts as well as the busbar (comes with an assay certificate) for like $101. I didn't order the silver plated copper busbar because once cut and drilled, parts are no longer plated. Silver plated is like $10 extra.
My take on the problem: use aluminium studs, nuts and washers, and aluminium busbars. That way you only have the 2 connections to the loads to worry about galvanic corrosion and it's not on the expensive cells but on some cheap and easily replaceable busbars
Factory400
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Aluminum studs seem extremely weak for this sort of thing.My take on the problem: use aluminium studs, nuts and washers, and aluminium busbars. That way you only have the 2 connections to the loads to worry about galvanic corrosion and it's not on the expensive cells but on some cheap and easily replaceable busbars
Is galvanic corrosion a real problem that needs to be solved or a rare corner case in specific applications?
I see it as an advantage, if you break something it's likely to be the stud instead of the cell terminal
It is a real problem. Now, is it a problem here? hard to tell. Also, it depends on a lot of factors, main one being humidity. On a boat it'll definitely be a problem, and in a house in the desert it'll definitely not. For cases inbetween it's complicated.
Personally I'd say if it's in a house in a non-tropical area then it's fine. If it's in a tropical area, or in the basement, or in a vehicule I'd say it would be wise to take precautions against it. But that's only an educated guess, YMMV.
Factory400
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Interesting point.I see it as an advantage, if you break something it's likely to be the stud instead of the cell terminal
I am kinda thinking of a cracked aluminum stud while the system is under load - the resulting loose connection would become an inadvertent TIG welder with nothing to stop it. (have your cameras ready for the viral YouTube video!)
I will vote for the most mechanically sound fastener possible in this application.
So what would you advise for use in a basement at steady 65F year-round but humid during the rainy season (Bay Area)?I see it as an advantage, if you break something it's likely to be the stud instead of the cell terminal
It is a real problem. Now, is it a problem here? hard to tell. Also, it depends on a lot of factors, main one being humidity. On a boat it'll definitely be a problem, and in a house in the desert it'll definitely not. For cases inbetween it's complicated.
Personally I'd say if it's in a house in a non-tropical area then it's fine. If it's in a tropical area, or in the basement, or in a vehicule I'd say it would be wise to take precautions against it. But that's only an educated guess, YMMV.
Between stainless, brass, zinc-plated or aluminum and posts (grub screws?) or bolts, I’m a bit lost as to the most reasonable thing to do.
Also, as far as the zinc-based paste to use to protect the aluminum terminals from oxidation, I’ve understood that that is a good idea regardless of environment & fastener solution but a specific product recommendation would be appreciated (never used the stuff before).
Of course you're supposed to stay under the maximum recommended torque. Also, the same will happen with any more robust stud, you'll just strip the terminal threads instead of the stud. But I don't see how it can happen after your put the battery together, if it happens it'll be when you thighten the nuts.
Humid = galvanic corrosion can happen.
I would do as I said: aluminium for everything so no galvanic corrosion to worry on the cells terminals. Then for the two last busbars to the battery cables (who will most likely have copper lugs) I'd use either aluminium or copper bolts/nuts/washers (so only two dissimilar metals, no need to introduce a third one...) and dielectric grease. That's what I plan do on mine actually (basement, 15-20 °C).
Again, just my recommendations, feel free to implement only part or none of it if you don't like it
Does that mean if I keep the battery in a case warmed to ~25C throughout the wet season (winter) and only ventilate with 65F cellar air (or dry outside air) if/when temps rise up to high during the summer, I’ll have less/little to worry about as far as galvanic corrosion?
I’m already concerned my cells may not be charging properly at temps below 65F (because they were so cheap or whatever) so I’m considering keeping them within the recommended temperature range of 23-27C.
If another benefit of keeping the cells warm and dry is galvanic corrosion becomes a non-issue, that might be the straw that breaks this camel’s back (meaning I’ll take the plunge).
‘Everything’ including busbars (meaning go to aluminum busbars)?
From earlier inputs, I thought plated copper busbars addressed 90%+ of the galvanic corrosion concerns between aluminum terminals and copper busbars.
Aluminum busbars seem like a real PITA, especially since I’m considering switching to braided plated copper busbars to address concerns of mechanical stress during charge/discharge cycles (within a clamping fixture).
So I was planning on using plated copper for all connections to aluminum terminals (including connections to BMS and ANL fuse) and was trying to decide between bolt & nut options (stainless, brass, plated steel, aluminum; bolts or studs).
At either cellar temps of 65F & moist during winter or controlled temps of 25C and dry year-round, I’d appreciate your advice on which metal to use for studs and nuts securing plated busbars to aluminum terminals.
Thanks.
As I said, your recommendations start pushing me into the zone where I start thinking it may to be easier to keep my cells nice and cozy (warm and dry) rather that going to all that trouble to design them to be better able to withstand a harsher environment...Again, just my recommendations, feel free to implement only part or none of it if you don't like it
But I greatly appreciate your suggestions.
Probably, but then it would be best to not ventilate, just have a small few holes so things can equalize.
18 °C is totally fine, it's actually better than 25 from what I saw.
Yes.
Yes, plated copper will be fine
As said, feel free to mix and match the advices. I was just describing what I think is best, but of course "best" depends on your specific needs and what you want...
Basically the less dissimilar metals you have the better. For example if you start having zinc plated steel nuts, stainless studs, brass washers, copper busbars and aluminium terminals you'll have more problems no matter the environment...
No problem, I can see you use your brain cells so you'll probably chose a good solution and don't have problems, don't worry too much
Bob B
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It seems to me that there is somewhat of a juggling act to determine what is most important for a given installation.
I have been mulling over the various considerations and have NEARLY arrived at the conclusion that for my mobile environment, the durability of stainless studs and copper bus bars out weighs the galvanic corrosion risk. The risk of galvanic corrosion can be easily mitigated by the use of a noalox compount.
I am partially swayed by my bad experiences with aluminum wire in my house .... I can visualize .... correctly or not .... that constant vibration could cause displacement in the aluminum and cause poor connections over time.
I have been mulling over the various considerations and have NEARLY arrived at the conclusion that for my mobile environment, the durability of stainless studs and copper bus bars out weighs the galvanic corrosion risk. The risk of galvanic corrosion can be easily mitigated by the use of a noalox compount.
I am partially swayed by my bad experiences with aluminum wire in my house .... I can visualize .... correctly or not .... that constant vibration could cause displacement in the aluminum and cause poor connections over time.
Hedges
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My first concern regarding loosening of connections would be the stiff battery cables applying torque to the screws holding them.
I would look for either a geometry that didn't apply torque or a limber connection as mechanical strain relief.
Similar to what I see with "SMA" style RF connectors. If right-angle they loosen easily, but not if in-line.
I would look for either a geometry that didn't apply torque or a limber connection as mechanical strain relief.
Similar to what I see with "SMA" style RF connectors. If right-angle they loosen easily, but not if in-line.
Welcome to the engineering world: everything is a compromise ?
If I decide to go that route, the idea would be to use a heating pad to maintain at least 23C (or whatever) and use a fan, possibly connected to a vent/hose going outside, to blow in cool 65F air whenever temps climb past 27C (or whatever). There will only ever be ‘ventilation’ when the entire compartment starts approaching a danger zone (likely only because of sustained current draw).
I have one cell that appears to have taken significantly less charge to 3.65V at 18C but I only discovered that at the end of the capacity test.
Charged at 25C the cell actually delivered a hair over 280Ah, so now I need to circle back and repeat a test charging a 18C to understand whether the potential issue is ‘real.’
These grey market cells came so cheap, there is almost certainly something wrong with them.
EVE’s specification only shows 100% discharge performance at -25C and >= 70% discharge performance at -20C; nothing about charge performance at temps other than 25C+/-2C.
So charge performance at temps lower than 25C is completely unspecified.
On top of that, if a cell fails the >=70% discharge at -20C, this could easily be the reason EVE sells these cheap cells off through grey market resellers.
So I’m happy with how my cells perform at 23-27C but will remain cautious about assuming that performance translates blindly down to -8C without verifying first.
So one last question then:Yes.
Yes, plated copper will be fine
As said, feel free to mix and match the advices. I was just describing what I think is best, but of course "best" depends on your specific needs and what you want...
Basically the less dissimilar metals you have the better. For example if you start having zinc plated steel nuts, stainless studs, brass washers, copper busbars and aluminium terminals you'll have more problems no matter the environment...
If I’ve got plated copper busbars on aluminum studs, would plated steel studs, nuts and washers count as adding another dissimilar metal or does the ‘plating against plating’ mean plated steel will behave about as well as plated copper (which I am not interested in).
Taking your words at face value, with aluminum terminals and plated copper busbars, II should either go with aluminum hardware or plated copper hardware (from which I prefer the idea of aluminum).
Plated steel would be easiest and cheapest if that will work about as well...
No problem, I can see you use your brain cells so you'll probably chose a good solution and don't have problems, So don’t worry too much
Yeah, right. Between clamping fixtures, avoiding corrosion, assuring grey-market cells are well-matched and properly top-balanced, selecting the correct BMS for your application, and then all the complexity of wiring and charging systems and voltages, if you are not comfortable ‘worrying’, this is probably not the right hobby for you ?
The aluminum studs, nuts, and washers are not really good choices. Their purpose in this instance is to provide a firm physical connection between the battery terminal and the busbar. We already have problems with stripping the threads on the terminal, now we would just have additional problems with the threads on the studs and nuts, and easily deformed washers. Aluminum busbars would of course solve the problem of galvanic corrosion, however they would need to be substantially larger, and would just move the problem to wherever you decide to change from aluminum as a conductor to copper in the circuit. The stainless steel (or brass) in this isn't supposed to be carrying current anyway, as long as the connection lasts as long as the battery, we don't really care. I've also thought of using aluminum, but resistance is an enemy, and copper is a better conductor. Just my personal choice, but switching to copper as soon as possible when carrying current is my choice. Just my thoughts.My take on the problem: use aluminium studs, nuts and washers, and aluminium busbars. That way you only have the 2 connections to the loads to worry about galvanic corrosion and it's not on the expensive cells but on some cheap and easily replaceable busbars
You are 100% correct, everything in engineering is a compromise.
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So what hardware would you use to provide a ‘firm physical connection’ between an aluminum terminal and a plated copper busbar? Stainless, bronze or plated steel?