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Old 05-04-2021, 21:58   #1
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Lithium Battery Terminals - Which Metal

I have some Lithium cells coming and I am going to use Grub Screws with washers and nuts to attach everything that needs attaching to the various terminals.



I was going to use stainless steel, but was wondering if this is a bad idea due to its conductivity? I am not sure I can get anything like i need in copper, so what are my options?
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Old 06-04-2021, 05:06   #2
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Re: Lithium Battery Terminals - Which Metal

Why grub screws [I'm not visualizing the application]?
What materials are the terminals made of?

Evidently, grub screws are available in Grade 660,, stainless steel, copper alloys [brass?], high tensile alloy steel, nickel alloys, titanium, Duplex & Super Duplex Stainless Steel etc
https://alloy-fasteners.com/grub-screw.html
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Old 06-04-2021, 06:57   #3
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Re: Lithium Battery Terminals - Which Metal

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Why grub screws [I'm not visualizing the application]?
What materials are the terminals made of?

Evidently, grub screws are available in Grade 660,, stainless steel, copper alloys [brass?], high tensile alloy steel, nickel alloys, titanium, Duplex & Super Duplex Stainless Steel etc
https://alloy-fasteners.com/grub-screw.html

Rather than screwing bolts into the lithium batteries, grub screws allow me to put the bus bars, BMS (motherboard sits directly onto the battery) and other connectors on and then use a washer & nut to bolt down tightly. Chatting to my local 12V shop, they told me that stainless will be fine, as the bolt/screw is not how the main current is connected.
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Old 06-04-2021, 07:15   #4
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Re: Lithium Battery Terminals - Which Metal

I was having a hard time along with Gord in visualizing this. You're using the grub screw to convert the terminal hole to a stud? Put your bus bars and connections over the new stud and then tighten with a nut/washer? Interesting approach, and one I might have to adopt. I like that the grub screw can be held in place with the hex key unlike a normal stud/threaded rod.

I suspect the terminals are alumin(i)um, I wonder if set/grub screws in the same material would be suitable? Certainly better conductivity, and maybe better avoidance of dissimilar metal corrosion, but strength? Would depend, I suppose, on the diameter.
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Old 06-04-2021, 07:49   #5
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Re: Lithium Battery Terminals - Which Metal

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Chatting to my local 12V shop, they told me that stainless will be fine, as the bolt/screw is not how the main current is connected.
Yeah, this is generally the case, since the bolt/screw is really just clamping the wire terminals to the battery terminals, and that's where the surface area connection is made. I suppose it's conceivable that your bolt on bms will alter that, but if it's designed for that style installation then it should probably have good connection.
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Old 06-04-2021, 11:24   #6
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Re: Lithium Battery Terminals - Which Metal

UFO,
I have stainless steel bolts on my cells and have had no problems. I have copper bus bars connecting the cells. I have not had any problems. As others and your 12v shop have mentioned the connection is mostly going to be from the terminal pad itself.

That being said be careful. Stainless does not conduct as well as copper or aluminum but it conducts. Use insulated tools. Even a small short can degrade a cell or cause more biological harm.

What are you using for cells?
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Old 07-04-2021, 06:41   #7
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Re: Lithium Battery Terminals - Which Metal

UFO,

Glad to hear your batteries are on their way!
My Victrons have stainless M8 bolts. Like others have mentioned, the connection is via the terminal "pad" not so much the bolt. Best of luck!
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Old 07-04-2021, 06:48   #8
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Re: Lithium Battery Terminals - Which Metal

The big problem with grub screws is that people first tighten the grub screws, then add busbars and terminals and then proceed to put the nut on and torque that down without using a hex wrench to prevent the grub screw turning, stripping out the terminal threads
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Old 07-04-2021, 20:04   #9
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Re: Lithium Battery Terminals - Which Metal

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UFO,

Glad to hear your batteries are on their way!
My Victrons have stainless M8 bolts. Like others have mentioned, the connection is via the terminal "pad" not so much the bolt. Best of luck!
This. Even though stainless is an incredibly poor conductor compared to copper or aluminum, the pad is doing the conducting, not so much the stud.

For this reason, I would make sure that your ring terminals touch the terminal pad. I wouldn't put a stainless hex nut or washer on the bottom of the stud underneath the ring terminals.
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Old 07-04-2021, 21:09   #10
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Re: Lithium Battery Terminals - Which Metal

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The big problem with grub screws is that people first tighten the grub screws, then add busbars and terminals and then proceed to put the nut on and torque that down without using a hex wrench to prevent the grub screw turning, stripping out the terminal threads

Yeah I figured that one out - I also don't want to force the grub screw through the bottom into the battery - Heard of this happening with some of the Chinese lithium cells.
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Old 07-04-2021, 21:10   #11
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Re: Lithium Battery Terminals - Which Metal

Thanks to everyone for all the info
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Old 08-04-2021, 21:25   #12
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Re: Lithium Battery Terminals - Which Metal

Quality lithium cells have one copper and one aluminium terminal because the anode and cathode plates are copper or aluminium, so no dissimilar metals problems occur under the cell lid where it can't be sorted. Quality lithium cells also have stainless helicoil inserts to reduce the risk of thread stripping and to better maintain the clamping pressure required to prevent the terminals and connections fretting and wearing material away causing the clamping pressure to be reduced.
Be sure to use a quality anti oxidisation compound such as Alminox to maintain that good connection between all the component surfaces.
Lithium cells operate in the 0.001v range when cell balancing is involved, unless all the contact faces are oxidation free and tightly clamped, any voltage variation will be the result of resistance and voltage across a resistor creates heat and this is the number 1 killer of lithium cells. Any heat generated at the cell terminal is fed straight into the the cell internal connection where the super thin plates are simply bolted to the terminal block .... heat will oxidise these ultra thin plates and that marks the beginning of the end for that cell. This is why cell top balance boards that use a resistor to burn off excess capacity rapidly kill the cells they were designed to protect.

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Old 08-04-2021, 23:54   #13
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Re: Lithium Battery Terminals - Which Metal

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Quality lithium cells have one copper and one aluminium terminal because the anode and cathode plates are copper or aluminium, so no dissimilar metals problems occur under the cell lid where it can't be sorted. Quality lithium cells also have stainless helicoil inserts to reduce the risk of thread stripping and to better maintain the clamping pressure required to prevent the terminals and connections fretting and wearing material away causing the clamping pressure to be reduced.
Be sure to use a quality anti oxidisation compound such as Alminox to maintain that good connection between all the component surfaces.
Lithium cells operate in the 0.001v range when cell balancing is involved, unless all the contact faces are oxidation free and tightly clamped, any voltage variation will be the result of resistance and voltage across a resistor creates heat and this is the number 1 killer of lithium cells. Any heat generated at the cell terminal is fed straight into the the cell internal connection where the super thin plates are simply bolted to the terminal block .... heat will oxidise these ultra thin plates and that marks the beginning of the end for that cell. This is why cell top balance boards that use a resistor to burn off excess capacity rapidly kill the cells they were designed to protect.

T1 Terry

Thanks for the heads up on the Alminox - Just ordered some
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