Improving Contact Area on Welded Stud Pads

bryn

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Well, this smaller contact area has put my plans for using the on stud blue seas fuse blocks i have, on hold.

i'm currently using them on my current lithium single battery setup, but when i received my order of new stud blocks yesterday, i noticed that the mounting hole is 10.3mm :unsure:, so thats annoying as i planned on each 12 volt 304ah packs individually fused connected in parallel together via a 30mm x 4mm copper busbar (i plan on tinning the copper)

i'm guessing that these copper washers will be the only way to solve this issue, i prefer the on stud fuse blocks over running wire to a mounted fuse block

*EDIT*

I was in the workshop working on some cables, when i realised i have enough cooper busbar to make a new mount for the stud fuses. just a short busbar with a 6mm hole. sorted
 
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Martijn

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I grabbed this image from that other string. It shows that post diameter to be 11.11mm.
View attachment 60158
OK, so I read about the crushed washers idea and like it.

I just received my new cells from Amy, they look very fine ;)

The stud pads welded on my cells, have a circle around the stud, with 11mm diameter, the circle below that is 15,5mm. I'm trying to see how they're welded, there is residue on that 15,5mm pad. Seems like instead of welding around the post, they welded through it and then ground down the weld?

Here's a photo, hope you can make it out:
1640954130600.png
You can feel some small ridges with your nail, so that's not perfectly flat. This worries me, with regard to contact with a spacer crush ring and increased resistance. Are the studs strong enough to actually crush the ring properly? At what torque?

I don't use a busbar with a large slot, but ring lugs and (braided)cable between posts.

Then again... the circle around the 6mm post, has a surface area of:
pi * (11/2)^2 = 95mm2
but minus the 6mm post, which
pi * (6/2)^2 = 28mm2
ends up being 67mm2 for that small circle, which should work for about 200A, right?

Am I missing something? What would be the wise decision here?


Using a busbar current calculator, you can run a continuous 51A through that cross section with minimal temperature increase if both sides are aluminum. You can surge much higher than that, of course, but you should average 50A or less in the short terms (minutes). Note that if your busbars are copper, then your margin increases substantially - not just because the connection is lower resistance, but because the copper will soak up the heat and spread it out, increasing the speed it dissipates any heat generated at the connection. This will be somewhat offset by the reduced area of contact due to oval and slightly oversize holes in the busbar, but I expect the copper to more than make up for that.

So I don't believe you need to go to extra effort to increase the contact between the cell and the busbar. Make sure you use copper busbars, clean all oxidation off the terminal and busbar, use an appropriate antioxidant, and tighten to the recommended torque.

Well, now I'm confused. I found this busbar calculator ( https://www.electrical4u.net/calculator/busbar-current-calculator-online/ ) - a 50mm2 busbar can carry 60A according to this, while a copper 50mm2 cable can carry 150A according to various tables.

Why the difference?
 
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Lt.Dan

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OK, so I read about the crushed washers idea and like it.

I just received my new cells from Amy, they look very fine ;)

The stud pads welded on my cells, have a circle around the stud, with 11mm diameter, the circle below that is 15,5mm. I'm trying to see how they're welded, there is residue on that 15,5mm pad. Seems like instead of welding around the post, they welded through it and then ground down the weld?

Here's a photo, hope you can make it out:
View attachment 77757
You can feel some small ridges with your nail, so that's not perfectly flat. This worries me, with regard to contact with a spacer crush ring and increased resistance. Are the studs strong enough to actually crush the ring properly? At what torque?
This is the dilemma I had when I first made my batch of washers. See this pic of mine:

20210412_133427.jpg

Thats why I went with a 1000 series Aluminum, considered "Dead Soft" aluminum, which you can actually bend with your finger tips. Kind of amazing.

Once I torqued down the stud, I had no problem with it being flat and making good contact. As you can see here.
20210424_124040.jpg
 

Hedges

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ends up being 67mm2 for that small circle, which should work for about 200A, right?

Am I missing something? What would be the wise decision here?

Here's a chart that says 70 mm^2 aluminum insulated wire can carry 91A


But that is for a long wire, with heat escaping in two dimensions through insulation.
Your contact area is smaller than terminal or busbar cross section area, but zero length. It is just contact resistance, not resistance per unit length.
The heat will escape in three dimensions including lengthwise in the busbar and into the cell; from there it spreads out to the environment.

I think only resistance of the connection matters, not area itself. (Yes, area affects resistance, as does pressure. I think resistance is mostly proportional to force.)
 

Martijn

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This is the dilemma I had when I first made my batch of washers. See this pic of mine:



Thats why I went with a 1000 series Aluminum, considered "Dead Soft" aluminum, which you can actually bend with your finger tips. Kind of amazing.

Once I torqued down the stud, I had no problem with it being flat and making good contact. As you can see here.
Hello Dan,

Seems with mine they tried to flatten the weld, see photo, left (blue) still has a small ridge, on the right (red) it's quite flat. This is the bottom pard of the stud pad.

A spacer ring could surely increase the contact area, as long as the middle part is making contact too.

From your photo, you crushed the ring onto the weld? What torque did you use?

1641029626441.png
 
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Colonel.lp

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OK, so I read about the crushed washers idea and like it.

I just received my new cells from Amy, they look very fine ;)

The stud pads welded on my cells, have a circle around the stud, with 11mm diameter, the circle below that is 15,5mm. I'm trying to see how they're welded, there is residue on that 15,5mm pad. Seems like instead of welding around the post, they welded through it and then ground down the weld?

Here's a photo, hope you can make it out:
View attachment 77757
You can feel some small ridges with your nail, so that's not perfectly flat. This worries me, with regard to contact with a spacer crush ring and increased resistance. Are the studs strong enough to actually crush the ring properly? At what torque?

I don't use a busbar with a large slot, but ring lugs and (braided)cable between posts.

Then again... the circle around the 6mm post, has a surface area of:
pi * (11/2)^2 = 95mm2
but minus the 6mm post, which
pi * (6/2)^2 = 28mm2
ends up being 67mm2 for that small circle, which should work for about 200A, right?

Am I missing something? What would be the wise decision here?




Well, now I'm confused. I found this busbar calculator ( https://www.electrical4u.net/calculator/busbar-current-calculator-online/ ) - a 50mm2 busbar can carry 60A according to this, while a copper 50mm2 cable can carry 150A according to various tables.

Why the difference?
What current are you wanting the busbars to carry? According to Amy, these welded studs are rated at 200amps, rating is worked out very differently from cables. If you have seen the contact area in high power relays, you will know how small they can be. Unless you are wanting to draw 1C it's not really necessary, and if done wrong you may end up with less contact area.
 

Martijn

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What current are you wanting the busbars to carry? According to Amy, these welded studs are rated at 200amps, rating is worked out very differently from cables. If you have seen the contact area in high power relays, you will know how small they can be. Unless you are wanting to draw 1C it's not really necessary, and if done wrong you may end up with less contact area.
I think about 200A max, but mostly less (100-125A), so that should be OK then.
 

Alloy

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Welded studs was bad fix to keep production/sales going.

Everything may work 24/7 heated environment but I won't use welded studs in my RV.

I was going to order cells last week but I've put that on hold after learning that welded studs only have a 10-11mm diameter aluminum contact surface. Adding aluminum washer is another place for corrosion.

Corrosion pastes are a temporary solution as they contain water.

I see carbon paste being used. We never dragged carbon fiber or graphite on aluminum. Even if the alum wasn't scratch there'd be a corrosion line that would show up later. We always put isolation (plastic) sheet between Carbon Fiber and aluminum to prevent corrosion.
 

Horsefly

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Welded studs was bad fix to keep production/sales going.

Everything may work 24/7 heated environment but I won't use welded studs in my RV.

I was going to order cells last week but I've put that on hold after learning that welded studs only have a 10-11mm diameter aluminum contact surface. Adding aluminum washer is another place for corrosion.

Corrosion pastes are a temporary solution as they contain water.

I see carbon paste being used. We never dragged carbon fiber or graphite on aluminum. Even if the alum wasn't scratch there'd be a corrosion line that would show up later. We always put isolation (plastic) sheet between Carbon Fiber and aluminum to prevent corrosion.
There's lots of negativity there dude, and I'm not certain any of it is grounded in truth.

By "corrosion pastes" do you mean conductive anti-corrosion pastes? If so, I'd like to see where you get that they contain water. I've got regular OX-100B. I'm not sure what all is in it, but I know it has zinc and grease. Where I'm from, you can't really combine water with grease. Moreover, I have no idea why they would put water in there. MG847 seems to be better (costs more) and has synthetic oil, carbon black, and amorphous fumed silica. No water.

It sounds like you are looking for cells that do not use aluminum for the terminal pads. Good luck with that.

I don't know what your expertise is. Sounds like you've done something with aluminum, but clearly not for electrical properties (plastic?).

Sounds like you should stick with non-DIY systems.
 

S Davis

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Welded studs was bad fix to keep production/sales going.

Everything may work 24/7 heated environment but I won't use welded studs in my RV.

I was going to order cells last week but I've put that on hold after learning that welded studs only have a 10-11mm diameter aluminum contact surface. Adding aluminum washer is another place for corrosion.

Corrosion pastes are a temporary solution as they contain water.

I see carbon paste being used. We never dragged carbon fiber or graphite on aluminum. Even if the alum wasn't scratch there'd be a corrosion line that would show up later. We always put isolation (plastic) sheet between Carbon Fiber and aluminum to prevent corrosion.
The older version LF280N has a larger contact area.
 

Alloy

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There's lots of negativity there dude, and I'm not certain any of it is grounded in truth.

By "corrosion pastes" do you mean conductive anti-corrosion pastes? If so, I'd like to see where you get that they contain water. I've got regular OX-100B. I'm not sure what all is in it, but I know it has zinc and grease. Where I'm from, you can't really combine water with grease. Moreover, I have no idea why they would put water in there. MG847 seems to be better (costs more) and has synthetic oil, carbon black, and amorphous fumed silica. No water.

It sounds like you are looking for cells that do not use aluminum for the terminal pads. Good luck with that.

I don't know what your expertise is. Sounds like you've done something with aluminum, but clearly not for electrical properties (plastic?).

Sounds like you should stick with non-DIY systems.

My appologies but there's allot of assumptions being made.

Terminals are rated for 200A....for how long?

Does anyone know what the maximum contact resistance for the terminals is?

6mm (1/4") studs are suppose to be torqued to 6-8ft/lbs how much do they need to squash alum washers? To much torque will bend the bus bars upwards. Might not happen with 3/16" (5mm) copper bar but what about 1/16" (2mm) copper?

Has anyone loaded a bank up to the fused (400A) amperage of 12V bank built for a 3000W inverter and used a thermal camera to check the welded stud connections?

It is easy to mix grease with water. It goes white when it mixes with water. There's water proof grease but it's not 100%.

When we put systems together we never put bare copper with bare aluminum. One side always has to be nickle or tin plated.

The surface to surface contact area (not the width of the bus bar) needs to be a minimum of 5 times the cross section area of the buss bar.
A 2mm x 19mm bus bar is 38sq/mm x 5 = 190sq/mm
Area of the 11mm terminal is 95sq/mm. It's short 95sq/mm of contact area.
The original 16mm termnals were 201sq/mm.

The amount removed from the bars for the bolts or studs is not deducted because contact of the bolt/nut/washer makes up for it BUT!! ...the slot in the mfg. supplied bus bars looks to be 8mm or more. For a 6mm bolt/stud the hole should only be 3-10% larger so a max of 6.6mm.


Edit: I see this and I ask why change if it was working.
1641184484210.png
 

Horsefly

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Terminals are rated for 200A....for how long?
What does this mean? Does this imply that there is an expiration date on electrical connections? Can you point me to where this is?
Does anyone know what the maximum contact resistance for the terminals is?
As someone up thread explained, the resistance and its meaning is different for a terminal than for a length of wire. Let's turn this around: If you know the resistance of a terminal, show us mathematically how you would use it.
It is easy to mix grease with water. It goes white when it mixes with water. There's water proof grease but it's not 100%.
Like I said: Neither of the two anti-corrosion pasts say they have water. What is your proof that they do? Why would they put water in it?
Who is we? I asked you what your expertise is, but you didn't explain. Maybe if you did, I could give you some credibility.
The surface to surface contact area (not the width of the bus bar) needs to be a minimum of 5 times the cross section area of the buss bar.
Maybe I missed it, but is this an accepted fact? I hadn't heard it before.

The rest of your post is at least approximating math, but I don't get it (and I think I'm pretty good at math).

I'm not trying to beat you up, but... You are throwing out lots of stuff that isn't really accepted science, and you may be hurting your own ability to implement a good battery / battery bank. Calm down and take a look at it.
 

Hedges

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Edit: I see this and I ask why change if it was working.
View attachment 78113

We know everything that came before was a total kludge, including back-alley "machinists" drilling and tapping crooked hold in aluminum cell terminals. We understand the cells were meant to have laser-welded busbars forming packs.

This latest one looks pretty good. But I would only consider it actually good if the contact surface is plated.

If I'm throwing stuff out that you know isn't accepted science then please correct me.

I came across papers on bolt-together busbars, which I linked somewhere in the forum. Take-away was actual contact area is quite small, points here an there.
But I don't believe mating surface 5x busbar cross section is a requirement.
 

Hedges

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I've seen this 5x recommendation for mating bus bars to bus bars. I posted the article in this thread.

"The contact area (sc) must be at least 5 times the cross-section of the bar (Sb). Sc > 5 × Sb for main busbar continuity links"

"For branch busbars, the contact area can be smaller, complying with the condition Sc > 5 × Sb."
(What that says in words, it doesn't say with equation)

"For equipment connection plates, contact must be made over the whole surface of the plate for use at nominal current."
(Don't know that that means in terms of numbers)

If not 5x then what is acceptable for contact area and hole size?

The paper I found previously and linked in post below as disappeared. Take-away was actual area of contact was about 1% of overlap area clamped together.
That doesn't mean overlap area 1% as big would be OK. Those many points of contact spread apart lets current fan out from them into bulk material, "spreading resistance", not all crowded together in a small cross section.


I'm not sure what number to recommend, or what is generally accepted electrical design practice.
I think contact area of solid wire in a screw terminal, torqued to spec, is very small compared to its cross-section. Contact in a relay even smaller. In a mated connector relatively small.

For these battery terminals, my biggest concern is native aluminum oxide. After that, rotation causing loosening. Then clamping force, and finally area.
 
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