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diy solar

Avoiding Galvanic Corrosion

Wow, so the Helicoll allowed you to increase torque from 32inch-lbs to over 100 and that reduced your computed IR by 22%!

Did you ever make measurements of contact resistance between lug and aluminum surface to estimate how much that changed?

Right now the 4nm or 35 in/lb for the M6 is under-rated due to the poor threads - see below as the stud themselves are good to 8nm or so. A M8 is then ~2.5x higher than that. In theory I should be able to torque them to around 150 in/lb but no need as 100 is plenty tight.


As for resistance my BMS, which computes this overall internal resistance per cell, went down by 22% on average once I reworked to use the helicoils and M8 studs. So this had a pretty significant impact.
 
Right now the 4nm or 35 in/lb for the M6 is under-rated due to the poor threads - see below as the stud themselves are good to 8nm or so. A M8 is then ~2.5x higher than that. In theory I should be able to torque them to around 150 in/lb but no need as 100 is plenty tight.
Oh, so you went with M8 Helicoil and M8 studs rather than M6?

How f do I’d you drill the holes?

As for resistance my BMS, which computes this overall internal resistance per cell, went down by 22% on average once I reworked to use the helicoils and M8 studs. So this had a pretty significant impact.
Yeah, especially since the ‘computed IR’ is a series combination of the actual cell IR (which doesn’t change with torque and has a spec of <0.25 mOhm) and the busbsr-to-terminal contact resistance (which will decrease with increased torque).

So if IRi + IRc decreased by 22% and IRi didn’t change, IRc had to change by >22%...
 
I would encourage you to think about what will happen when (not if) the fan fails. If that's ok for you then no problem ;)

Does the BMS contain a temperature sensor? (assuming attached to battery)

Manual reset thermostat in line with control of relay(s) used by BMS

More sophisticated: tach for fan, current sensor in motor drive to warn before failure. Redundant, hot swappable.

Other schemes: bimetalic or gas-charged tubes to open vents when hot, close when cold.

Simple backup: Wax holds vent shut against weight. If hot enough to melt, gravity opens and convection takes over.
 
Oh, so you went with M8 Helicoil and M8 studs rather than M6?

How f do I’d you drill the holes?

Yeah, especially since the ‘computed IR’ is a series combination of the actual cell IR (which doesn’t change with torque and has a spec of <0.25 mOhm) and the busbsr-to-terminal contact resistance (which will decrease with increased torque).

So if IRi + IRc decreased by 22% and IRi didn’t change, IRc had to change by >22%...

Yes, I went with helcoils to give me a usable 8mm * 1.25mm thread and put stainless 8mm studs into those threads which I mentioned way above :)

I did this as since I was putting in helicoils the 8mm made sense as my block-mons have a 8mm hole; and I use 5/16th lugs which are about 8mm. Both of those were a bit loose on the original 6mm fasteners.

I am pretty sure you can get 6mm thread helicoils if you want to stay with that size hardware.

And yes, as the BMS just measures the entire resistance as it can't isolate the contact from the internal that is a significant decrease.
 
What was the reason for this?
Still not sure (attempting to clarify). He may have merely been explaining how to remove and re-weld a grubscrew which has been welded in with JB Weld...

But the other way I could interpret what he wrote is that the bind with JB weld is stronger with increased cross-section...
 
JB weld is not welding. No process here is actual welding, its bonding. There is no reason to remove the remaining threads if you are just going to try epoxying in a stud.
 
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JB weld is not welding. No process here is actual welding, its bonding. There is no reason to remove the remaining threads if you are just going to try epoxying in a stud.
I thought about clarifying as I typed that, but figured you all would understand what I meant.

‘Re-weld’ as in ‘re-glue with JB Weld’...

If JB Weld will work just as well with remaining threads left in place, then he must have been explaining the process to remove and re-attach a grubscrew that had been secured with JB Weld and had to be removed (for whatever reason).
 
I thought about clarifying as I typed that, but figured you all would understand what I meant.

‘Re-weld’ as in ‘re-glue with JB Weld’...

If JB Weld will work just as well with remaining threads left in place, then he must have been explaining the process to remove and re-attach a grubscrew that had been secured with JB Weld and had to be removed (for whatever reason).
He was explaining a process that should break the bond so the grub screw could be removed. Nothing more, nothing less. Once the stud is removed then the hole could be drilled and tapped.
 
He was explaining a process that should break the bond so the grub screw could be removed. Nothing more, nothing less. Once the stud is removed then the hole could be drilled and tapped.
Yeah, I’ve (finally) figured out that was all he was talking about...
 
32 in/lb on the 6mm studs which was marginal as I mentioned as some stripped at that due to thread pull out. After with helicoil and 8mm stud 100 in/lb with no signs of pull out.

I get your thoughts on the co-planar contact and that the electron flow is from the flat terminal area to the bottom of the lug and this is correct if the fastener is a high resistance (due to low torque, needing thread lock or other goop on the threads). But remember electrons flow on the surface of the conductor. With the helicoils and 8mm stud you can use a nut on top that not only covers the entire top of the lug; but also had good torque to ensure a low resistance connection. So that 8mm stud up from the terminal block in the cell, through the lugs, and the nut on top, all contribute to more surface area and a contact that has lower resistance and more current capacity.

Consider most good quality plugs are "dual wipe" or "multi contact" for a reason - the more contact surface area the better - the electrons don't just flow on one side.

I wouldn't go over 80 (max 86) based on this: https://www.engineersedge.com/torque_table_sae.htm - and that class of aluminum is probably a lot stronger than the aluminum in the terminals of these cells.
 
I wouldn't go over 80 (max 86) based on this: https://www.engineersedge.com/torque_table_sae.htm - and that class of aluminum is probably a lot stronger than the aluminum in the terminals of these cells.
Why?

I have a M11 (7/16th) threads into the aluminum which according to your table is good to 228 in/lb.

I have M8 stainless studs into the M11 stainless threads of the helicoil which is good to 138 in/lb.

The 100 in/lb I am using is working perfectly fine, no pull out, no issues. I probably could go tighter but don't feel it's needed as the lugs/block-mons are nice and secure, load test to 2x max discharge rate shows no excessive heat, and it's all good. The only thing I am not happy with is the twist load put on the terminals by the 4/0 cable but working on a solution to that.
 
Why?

I have a M11 (7/16th) threads into the aluminum which according to your table is good to 228 in/lb.

I have M8 stainless studs into the M11 stainless threads of the helicoil which is good to 138 in/lb.

The 100 in/lb I am using is working perfectly fine, no pull out, no issues. I probably could go tighter but don't feel it's needed as the lugs/block-mons are nice and secure, load test to 2x max discharge rate shows no excessive heat, and it's all good. The only thing I am not happy with is the twist load put on the terminals by the 4/0 cable but working on a solution to that.

Oh, I thought it was M8 holes. Never-me-mind :)
 
Seems like a lifetime ago that I started this thread and got helpful advice like this.

It’s getting real now and so I am asking for some final suggestions before I buy my studs and get everything assembled.

Some updates on my end: my battery environment has a dirt floor which occassionally gets muddy during the rainy season, so not Marine, no salt, but worse than the typical basement or garage.

My main concern is avoiding any corrosion on the exposed threads of my grub screws. I’ll be locking them into place using either Loctite or JB Weld (more on that below) so I want to minimize the possibility of corrosion either between the exposed threads and the zinc-plated copper busbars and/or lugs, as well as any direct corrosion of the exposed threads from moist ambient air (such as white rust on zinc-plating).

I found these yellow-zinc-plated 6M grub screws and am thinking of going that route unless I need to worry about white rust:


This would translate to sealed yellow-zinc-to-Aluminum within the terminal (Loctite or JB Weld) followed by yellow-zinc-coated-steel to grey-zinc-plated-copper at the busbars/lugs with some exposed yellow-zinc-coated steel and grey-zinc-plated copper in the ambient air.

Reading about ‘white rust’ of zinc is the primary concern causing me pause on this solution, but that seems to be mainly caused by salt and I am miles from the nearest salt water.

So I’d appreciate any inputs as to whether this yellow-zinc-plated grubscrew solution should work well in my sometimes-moist environment or whether there are issues I am overlooking.

I’ve also tracked down some slotted aluminum grub screws but they are slotted rather than hex, likely pricey, and I’m concerned corrosion of the exposed aluminum threads may be at least as great as concern of corrosion of exposed zinc-plated steel threads (though I’d appreciate any comments).

And finally, while I steered away from stainless due to increased concerns of galvanic corrosion, between eliminating concerns of galvanic corrosion within the stud by sealing with Loctite or JB Weld and now being equally or more concerned about environmental corrosion (rust) of the exposed threads in my sometimes-moist environment, the stainless threads should be best for preventing any environmental corrosion, so I’d appreciate opinions as to whether stainless may actually be the best option for my sealed-stud in a sometimes-moist application...

A quick update on what has changed on my end since I first started this thread:

Loctite versus JB Weld: the upper 3 threads of all of my cells are worn after merely three gently by-hand (w/ screwdriver) insertions and removals of the bundled stainless steel bolts.

In addition, I used a newly-purchased torque-wrench to tighten 8 cells to 4Nm / 35inch-lbs and stripped the upper 3 threads from one terminal.

The bundled 6M bolts appear to be slightly undersized and I can thread a separately-purchased M6 bolt into pretty much the full 5 threads of to thus ‘stripped’ terminals (4-3/4).

The lower 2 threads of all 16 of my cells are pristine / untouched, including the stripped terminal.

So I’m hopeful that I will be able to get an M6 grubscrew threaded into the stripped terminal in a way that will hold and because of the wear on the upper 3 threads of all terminals, I’m considering to use JB Weld to permanently-install grub screws into all terminals.

If the only advantage to Loctite over JB Weld is that the grub screw can be removed if needed, I’m leaning towards deciding I want these grub screws to be permanently mounted, especially if JB Weld results in a stronger attachment than Loctite and/or if it provides a better environmental seal as far as preventing against the possibility of galvanic corrosion and/or ‘rust’ within the terminal.

Finally, I’m ready to seal my battery within an environmentally-controlled container (temperature control, pumping through dry cooling air from outside when needed) if that is the only way to operate without concern in my sometimes-moist environment.

For those of you with experience in harsher environments than mine and who understand all of the metallurgical issues of operating in a (fresh / non-salty) sometimes-moist environment, I greatly appreciate any inputs on what you would choose to do facing my particular situation...
This thread is about galvanic corrosion. While galvanic action promotes corrosion and determines which material is affected first, everything corrodes when the corrosion triangle is complete.
Metal, moisture, and oxygen are all that is needed. This is why a connector lubricant is so important. The oils in the lubricant form a barrier to prevent the moisture and oxygen from reaching the metal.
That being said, the mix of materials you are listing is a horror story in terms of galvanic reactions. If you think through the materials you have, the zinc plating on your screw is going to be the first attacked when (not if) moisture reaches your terminals. Once the 50 microinches of zinc is gone, you will have steel against your aluminum, so now, your aluminum terminal is the anode.
Up top, your tin plated bus bar resting against the steel screw and washer are the next to be consumed. At the same time, the bus bar tin will be attacking the contact face of the terminals. Depending on how thick that plating is, the copper is next. Along the way, the steel will also be corroding.

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. Replacing threads in a terminal with it is weaker than aluminum and will significantly increase contact resistance.

I hope you have good results with your setup, but if you are serious about preserving your terminals, I would consider eliminating the variety of metals making up your connections.
 
I hope you have good results with your setup, but if you are serious about preserving your terminals, I would consider eliminating the variety of metals making up your connections.

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.
 
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.
I guess I'm just a glutton for punishment. I keep recommending it and taking my lumps. ?
The connector lubricant is really important too.
 
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.

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.
 
The best solution i could come up with, was aluminium flanged studs. From there i wanted the best condictivity for the 'braided' busbars(for RV vibration mitigation) so opted for 'tinned' copper. To lock it down, i am using zinc plated flanged nyloc nuts, which should be fairly inert against the aluminium threads...thus if little corrosion, i hopeful of being able to remove the zinc nuts if absolutely necessary. I did put a minute layer of noalox between the terminal face and the flange underside, simply to minimise oxidation of the aluminium. I didnt put it between the upper flange surface and the tinned copper busbar connection as i had read it wasnt needed.
Dont know how good this will be, but it is what i have went will up till now.
 
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.
 
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