For sale: Brass SOK terminal studs to replace M8 steel bolt.

[inspectorrgadget]

I created high-conductivity battery terminal studs for my SOK battery. I am willing to make more of them so others can get something better than a steel bolt to conduct electricity in their RV or solar setup.

The studs I made are metric M8 x 1.25 in high-conductivity brass.

Originally, my SOK-brand LiPoFe batteries used stock metric M8 x 1.25 bolts that threaded into the batteries. I feared that constantly removing and replacing the steel bolt into the alloy threaded hole might wear out the battery connection. So I converted to a studs-and-wing nuts arrangement in order to attach the cables to the batteries. In thousand of miles, the wing nuts have never come loose, and I don't need to go searching for a wrench each time I want to take the batteries out of my RV.

To enhance conductivity, decided to upgrade the battery studs to metric M8 brass. Because brass is a mixture of copper, iron, and often other metals (such as boron or nickle), most brass alloys do a better job of carrying current than do most types of steel. McMaster-Carr sold me a 1-meter long M8 threaded brass rod. One of the attributes listed in this rod's specifications is being electrically conductive:
https://www.mcmaster.com/90162a080/
Brass Threaded Rod
M8 x 1.25 mm Thread Size,
Item 90162A080.

I used a Skillsaw and a file to make four 1.5 inch-long studs for myself. Doing so took 6 inches off the 39-inch rod. Each of my studs is just under 1.5 inches long.

I have 33 inches of M8 threaded brass rod remaining, which I would sell to anyone who makes a decent offer for the leftover rod. Or, I could make 22 more pieces for any others out there who might also want some brass stud terminals for their SOK batteries.

I'd charge $3 bucks for a 1.5 inch stud, plus shipping.

If anyone is interested, DM me on this forum.

 

[Lilikoi_Heavy_Industries]

I have an inverter repair that I may be able to use these on--it sounds like a similar material to what a sheared lug was made out of... In fact there are probably a lot of uses for conductive M8 rod. Great idea and I will DM you if I end up going this route.

If this is similar material to that tinned brass inverter lug I sheared, you don't want to tighten them with a large socket wrench, their torque spec is very low. The way you're using them looks pretty safe, my inverter install manual called for a torque wrench though (12Nm). But it is the finest material for the job. It's a tier 1 inverter that is being repaired, where cheap inverters like wzrelb use stronger lugs that look/act like stainless.

 

[BentleyJ]

I believe its important that the information on this forum is true and accurate. So no disrespect, just the facts.
1) Brass is made from Copper and Zinc, Bronze is made from Copper and Tin. If Iron is present it is a trace impurity.
2) Please refer to this chart: https://www.tibtech.com/conductivite.php?lang=en_US Brass only has about 25% of the conductivity of Copper, it is better than steel and MUCH better than Stainless Steel. Perhaps this is what you meant by "high conductivity". Brass is a conductor, I wouldn't classify it as "good".

 

[timselectric]

This should be in the #diysolarmarketplace

 

[chrisski]

There is M8 copper rod that shows up on google searches for sale. I don't know if this is the same M110 hard copper I use for my bus bars, but copper would be a better conductor. With some of the tiny contact area on these cells, I can see why you'd want to squeeze every bit of conductivity out of it.

I'd nickel plate the stud prior to use.

 

[inspectorrgadget]

I was unaware there was a such a thing as "hard copper." I also explored various types of bronze to make a threaded rod that is better than steel. As often as I've unscrewed these battery terminals, I was worried the whatever M8 female thread is inside the battery would wear out from steel bolts going into it a bunch of times. I'd guess the female threads are some form of aluminum.

Finding M8 threaded rod or bolts in exotic alloys was rather tough. I could have ordered some, but then I'd wind up with 500 pieces. This brass rod is a lot easier to get. Thus far it has cost me about 70 bucks to make four pieces for myself, and but it I can spread those costs onto 22 more pieces it makes more sense, moneywise.

As for being posted in "marketplace", I might yet do that. Except, I am not really in the business of making these. I'm just trying to spread out my costs and let everyone else improve their connection over what the stock steel bolts do. Folks spent all sorts of money on giant 2/0 cables and such for their systems, only to route the final product (electricity) through a steel bolt. This threaded brass rod is an attainable improvement that anyone can do for themselves for 70 bucks on their own, or by getting them much cheaper through me.

There is M8 copper rod that shows up on google searches for sale. I don't know if this is the same M110 hard copper I use for my bus bars, but copper would be a better conductor. With some of the tiny contact area on these cells, I can see why you'd want to squeeze every bit of conductivity out of it.

I'd nickel plate the stud prior to use.

 

[inspectorrgadget]

I believe its important that the information on this forum is true and accurate. So no disrespect, just the facts.
1) Brass is made from Copper and Zinc, Bronze is made from Copper and Tin. If Iron is present it is a trace impurity.
2) Please refer to this chart: https://www.tibtech.com/conductivite.php?lang=en_US Brass only has about 25% of the conductivity of Copper, it is better than steel and MUCH better than Stainless Steel. Perhaps this is what you meant by "high conductivity". Brass is a conductor, I wouldn't classify it as "good".

Per the website where I bought it, it says: "These brass threaded rods are corrosion resistant in wet environments, electrically conductive, and nonmagnetic." It does not say to what degree they are conductive compare to copper. I believe the reason copper is not commonly used for threaded applications is how threads strip out quickly. My RV batteries are subject to a lot of vibration, and the electrical terminals get unscrewed quite lot. If going with a threaded copper stud atop a battery were a good idea, then you'd see lots of them. But one never sees such things.

If you can derive what the exact alloy and electric conductivity of this McMaster-Carr brass rod is, let me know. Perhaps you could get an M-8 steel rod, measure its electrical resistance, and let me know what it is. Then I'd measure the brass rod's resistance. Then we'd know for sure how much of an improvement this particular brass is over steel.

 

[timselectric]

It's a stud, just used for clamping force. It doesn't need to be conductive. Most studs are stainless steel, for non corrosion.

 

[inspectorrgadget]

I've obsessed over this whole issue of steel vs. other materials before. The whole "it's only clamping force" argument says that the little nickle-sized doughnut of conductive metal around the battery's threaded M8 hole is all that is available to carry the current. Whereas I say that if you can improve the electrical conductivity by switching to brass, then why not? You get the same clamping force, but also now have the entire stud running electrons down into all the female thread of the battery. In terms of overall surface area for electrons to go, there appears to be a lot more with a brass conductive rod vs. a steel bolt.

Steel has a conductivity ratio of only 3 to 15 percent, compared to copper. Brass has 28 percent the conductivity of steel

https://www.bluesea.com/resources/108/Electrical_Conductivity_of_Materials/

https://diysolarforum.com/threads/copper-tellurium-and-copper-sulphur-connectors.24336/

 

[timselectric]

If it helps you sleep at night. Go for it. There's no harm from it.

 

[rmaddy]

I'm at a real loss trying to understand the purpose of this modification. The stud provides no useful conductivity no matter what material you use. The wire lug barely touches the stud at all, if at all. All conductivity is between the flat bottom of the lug where it comes in contact with the metal ring around the stud. The stud is simply a mechanical means to ensure the wire lug makes good solid contact with the metal ring.

Or does this mod do something internally that I can't see in the photos such that it results in more current going to the metal ring?

Brass has 28 percent the conductivity of steel

You mean brass has 28 percent the conductivity of copper.

 

[Zwy]

First thing that comes to mind for me when mixing aluminum and brass is the two are incompatible and result is high galvanic corrosion. I know about it firsthand in my line of work. It does require moisture however for it to occur. Not probably an issue in many instances but for marine or RV use it could be a factor.

Second, a threaded connection should not be passing any current. The threads of any fastener are not perfect, this leads to varying current passing thru and basically a miniature welder in action. An example is to take a long bolt, screw a nut on the end and attach the ground clamp to just the nut. Begin welding on the bolt shaft and not the nut. The current passing thru the threads will lock that nut on tight if there is enough current/voltage or enough elapsed time for the "welding" to occur.

 

[inspectorrgadget]

First thing that comes to mind for me when mixing aluminum and brass is the two are incompatible and result is high galvanic corrosion. I know about it firsthand in my line of work. It does require moisture however for it to occur. Not probably an issue in many instances but for marine or RV use it could be a factor.

Second, a threaded connection should not be passing any current. The threads of any fastener are not perfect, this leads to varying current passing thru and basically a miniature welder in action. An example is to take a long bolt, screw a nut on the end and attach the ground clamp to just the nut. Begin welding on the bolt shaft and not the nut. The current passing thru the threads will lock that nut on tight if there is enough current/voltage or enough elapsed time for the "welding" to occur.

Famously, galvanic corrosion is worst between Iron and Aluminum. When postulating about how bad the corrosion between Brass and Aluminum could be, it's important to keep in mind that the stock male-threaded studs (as supplied by SOK) were steel. Could brass be any worse? As many know, it is the iron (FE)component of steel that reacts with Aluminum (AL). Since brass has a bit less FE, I'd suspect it's less subject to galvanic corrosion than steel.

I am not sure what kind of alloy SOK used for its female-threaded terminals. They might be aluminum, but I am not sure. It you were to examine practically any modern-day automotive engine made of an aluminum block, you will see that there are ample examples of a female thread into the aluminum block, with steel male threaded fasteners going into that block. I've taken apart 50-year old Volkswagen Bug engines which had steel threaded studs going into aluminum, most of which has zero signs of corrosion.

My RV setup has a total of 4 brass studs, which have been sitting in my SOK batteries since July. Recently I went to remove the battery terminals, and one of my brass studs unthreaded from the battery: I'm happy to report here was not the slightest sign of any corrosion.

If you want to geek-out about galvanic corrosion, I found this article:

https://www.fastenal.com/content/feds/pdf/Article%20-%20Corrosion.pdf

 

[Lilikoi_Heavy_Industries]

Second, a threaded connection should not be passing any current.

Cool story bro. Explain to me why my MultiPlus II inverter pos/neg battery lugs are made from tinned brass instead of stainless then.

Stainless would be MUCH MUCH stronger, but the tinned brass provides a lower resistance connection. You wouldn't need a torque wrench to install this inverter if they used stainless lugs.

But wait!!! threaded connections shouldn't be passing any current!!!

Victron must not know what they're doing, if they did, they would have used a stainless lug based on Zwy's comments?

What do you call the battery lugs in an inverter, if not a threaded connection?

Did you miss that the OP's use case also has the lug secured against a metal pad on the battery, it's not only touching the threads. Just like on my inverter.

The usage of "thread technology" (which you seem very against) doesn't mean that's the only path for the power.

 

[Zwy]

Cool story bro. Explain to me why my MultiPlus II inverter pos/neg battery lugs are made from tinned brass instead of stainless then.

Stainless would be MUCH MUCH stronger, but the tinned brass provides a lower resistance connection. You wouldn't need a torque wrench to install this inverter if they used stainless lugs.

But wait!!! threaded connections shouldn't be passing any current!!!

Victron must not know what they're doing, if they did, they would have used a stainless lug based on Zwy's comments?

What do you call the battery lugs in an inverter, if not a threaded connection?

Did you miss that the OP's use case also has the lug secured against a metal pad on the battery, it's not only touching the threads. Just like on my inverter.

The usage of "thread technology" (which you seem very against) doesn't mean that's the only path for the power.

I don't think you quite understand what was being explained. But ya, it's definitely a cool story as you put it.

Current thru the threads will cause the threads to weld together.

I did not state anything about current passing thru where two flat surfaces are clamped together by threads. Quite a difference there.

The OP was attempting to convey his brass thread was far superior to passing current. Quote from first post: "most brass alloys do a better job of carrying current than do most types of steel."

The threads should not be carrying current, the face of the battery terminal and the lug where to two meet should be carrying current.

I won't even get into expansion of brass compared to stainless when heated. It's called thermal coefficient, can you guess which one is higher. That's for another day, enough cool stories.

 

[Zwy]

Famously, galvanic corrosion is worst between Iron and Aluminum. When postulating about how bad the corrosion between Brass and Aluminum could be, it's important to keep in mind that the stock male-threaded studs (as supplied by SOK) were steel. Could brass be any worse? As many know, it is the iron (FE)component of steel that reacts with Aluminum (AL). Since brass has a bit less FE, I'd suspect it's less subject to galvanic corrosion than steel.

I used 304 stainless studs when I had cells with tapped threads.

If you want to geek-out about galvanic corrosion, I found this article:

https://www.fastenal.com/content/feds/pdf/Article%20-%20Corrosion.pdf

I have read it many times. You need to look at the chart on page 2. Top row lists different fastener metals ranging from Zinc/Galvl steel to Austenitic Stainless. In your case, the fastener is brass which is under Brasses, Coppers, Bronzes & Monel.

Next, go to second row down for Aluminum & Aluminum Alloys for Base Metal. Note the number is 3.

Go to bottom of chart, under Plating Compatibility Chart KEY:

3 The corrosion of the base metal is considerably increased by the fastener.

If that isn't clear, I'm sure we can discuss it more.