Improving Contact Area on Welded Stud Pads

mcj7247

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I bought a 2mm flat bar of 99% pure copper on Amazon $17.99. I cut it to length to cross both terminals and then drilled 10mm holes so it is tight against the 10mm post and sits flat on the 13mm pad. I then used a washer and nut to tighten it down so I get contact with the 13mm pad, the 10mm post and the washer and nut on the post. I do not think you can get anymore contact then with this method and the copper conducts electric at a much higher efficiency.

When you say the "13mm pad" are you referring to the weld shoulder? l like your bussbar material with no slots, but I think I would prefer drilling a 6mm hole and mating to the flat 10mm pad as intended by the mfg.
 

Horsefly

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I bought a 2mm flat bar of 99% pure copper on Amazon $17.99. I cut it to length to cross both terminals and then drilled 10mm holes so it is tight against the 10mm post and sits flat on the 13mm pad. I then used a washer and nut to tighten it down so I get contact with the 13mm pad, the 10mm post and the washer and nut on the post. I do not think you can get anymore contact then with this method and the copper conducts electric at a much higher efficiency.

But... There isn't any "10mm post" on any of the welded studs we are talking about, right? The first pad below the stud is 11.11mm in diameter, according to what @Stepandwolf posted here. Seems like a 10mm hole would be the worst possible, since it would barely make contact with the 11.11mm pad, and it wouldn't fit down onto the 13mm weld shoulder.
 

mcj7247

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If your studs look like the ones [link="[URL]https://diysolarforum.com/threads/improving-contact-area-on-welded-stud-pads.26869/post-319290[/URL]"]Stepandwolf posted[/link], then without washers you have about 64mm^2 of surface area on the aluminum to connect your busbars to.

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.
Thank you for your feedback. I think the consensus is that the advantages of higher clamping force the M8 stud provides over the M6 stud aren't fully realized due to the torque limitation of the internal cell material. In addition, since my application doesn't require high current, the M6 welded stud is probably my best option.
 

mcj7247

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But... There isn't any "10mm post" on any of the welded studs we are talking about, right? The first pad below the stud is 11.11mm in diameter, according to what @Stepandwolf posted here. Seems like a 10mm hole would be the worst possible, since it would barely make contact with the 11.11mm pad, and it wouldn't fit down onto the 13mm weld shoulder.
I think he refers to the 10mm post as the same 11.11mm mounting pad in the pic.
 
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Donniesuits

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1631212157750.png

Sorry I am away so I can not get you a picture but using the one copied here. From the top down you have the threaded stud, followed by the first round ring (Yellow Dots), the second round ring (Red Dots) and finally the oval base.

The 2mm thick copper bar sits on the lowest ring (denoted with Red Dots) above the oval base. The drilled hole in the copper bar is tight to the next ring up, which is between the lower ring and the threaded stud shown with the Yellow dots. The washer and nut on the threaded stud clamps the copper down tight on the lowest ring (red Dots) as well as gives it another contact point.
 

Hedges

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I would drill the busbar to bear on the upper ring (Yellow Dots).
That way, bolt head and nut provide compression of busbar against contact area.
I would get 8mm thread, restrain busbar (not cell case) against rotation, and torque according to specs for such a bolt.
(I like to mash the hell out of a contact)

I would also use a moderately wide busbar, extending a bit past the stud. That way, current spreads radially outward from contact patch to reach cross-section of busbar.
 

Horsefly

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In my original post (I started this thread) I suggested some aluminum washers (actually, they are aluminum gaskets for Honda oil pan plugs). They have a inside diameter of 12mm, so a little larger than the top pad. The thickness seems pretty close to 2mm. I then put some Gardner Bender Ox-guard under and on top of the washer, then put my bus bars (with holes for M6 studs) on the stud. Tightening down the nut seems to do what @Hedges suggests in getting a good connection with the top pad, but also compresses the washer against the next level down (the weld shoulder). I haven't run any real high current tests, but I did run for 6 hours at 25A draw and there was no warming of the terminal threads or bus bars. My highest draw will be about 55A and even then for only 2.5 minutes at a time, so I think this will work well.
 

mcj7247

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In my original post (I started this thread) I suggested some aluminum washers (actually, they are aluminum gaskets for Honda oil pan plugs). They have a inside diameter of 12mm, so a little larger than the top pad. The thickness seems pretty close to 2mm. I then put some Gardner Bender Ox-guard under and on top of the washer, then put my bus bars (with holes for M6 studs) on the stud. Tightening down the nut seems to do what @Hedges suggests in getting a good connection with the top pad, but also compresses the washer against the next level down (the weld shoulder). I haven't run any real high current tests, but I did run for 6 hours at 25A draw and there was no warming of the terminal threads or bus bars. My highest draw will be about 55A and even then for only 2.5 minutes at a time, so I think this will work well.
I thought the M6 vs M8 stud conversation was within the range of the original thread and since you were part of that conversation, you were ok with it. I apologize if I hijacked your original thread @Horsefly. And based on the feedback, it seems you're M6 stud and a washer should enhance the contact surface area and add a safety layer for our lower current requirements.
 

Horsefly

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I thought the M6 vs M8 stud conversation was within the range of the original thread and since you were part of that conversation, you were ok with it. I apologize if I hijacked your original thread @Horsefly. And based on the feedback, it seems you're M6 stud and a washer should enhance the contact surface area and add a safety layer for our lower current requirements.
Wait! I wasn't feeling like anyone hijacked anything! Everything discussed here is perfectly fine as far as I'm concerned. After 8 pages of comments, I just wanted to make sure everyone knew that my originally posted idea seems to work well. Everything you have posted is good conversation to have.

I only started the thread. I don't own it! ;)
 

Donniesuits

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I would drill the busbar to bear on the upper ring (Yellow Dots).
That way, bolt head and nut provide compression of busbar against contact area.
I would get 8mm thread, restrain busbar (not cell case) against rotation, and torque according to specs for such a bolt.
(I like to mash the hell out of a contact)

I would also use a moderately wide busbar, extending a bit past the stud. That way, current spreads radially outward from contact patch to reach cross-section of busbar.
The Copper Bar is slightly higher than the ring with the yellow dots so I get great compression but I also get more surface area for electrical contact by using the larger ring on the battery terminal and the sides of the upper ring.

And to your point on a wide busbar I agree and the copper bar is wider than the busbar provided by the battery manufacturer.
 

Stepandwolf

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I bought a 2mm flat bar of 99% pure copper on Amazon $17.99. I cut it to length to cross both terminals and then drilled 10mm holes so it is tight against the 10mm post and sits flat on the 13mm pad. I then used a washer and nut to tighten it down so I get contact with the 13mm pad, the 10mm post and the washer and nut on the post. I do not think you can get anymore contact then with this method and the copper conducts electric at a much higher efficiency.

You aren't worried about oxidation? When using supplied busbars, they have the tinned exterior so you aren't getting copper to aluminum contact. In your case, it sounds like a lot of al/cu contact. Did you consider NOALOX?
 

Stepandwolf

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But... There isn't any "10mm post" on any of the welded studs we are talking about, right? The first pad below the stud is 11.11mm in diameter, according to what @Stepandwolf posted here. Seems like a 10mm hole would be the worst possible, since it would barely make contact with the 11.11mm pad, and it wouldn't fit down onto the 13mm weld shoulder.
Just to be clear, I was given the photo with the measurements. I think it is accurate for the battery it was an example of. Do we know the spec.s for Lt. Dan's washers? Suspect it was posted but I don't remember where.
 

Lt.Dan

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The washers i made have a .4375" hole for the 6mm stud, and a .5313" for the 8mm stud. They are surprisingly imperial and not metric.
 

rhino

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Sorry if this was asked already but has anyone actually experienced an issue with the small pads? I have a naive understanding that even if you are pulling 320A from a 48V battery bank you are only pulling ~20A from each cell which is what is going through those pads. Is that not correct?
 

Bob B

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Sorry if this was asked already but has anyone actually experienced an issue with the small pads? I have a naive understanding that even if you are pulling 320A from a 48V battery bank you are only pulling ~20A from each cell which is what is going through those pads. Is that not correct?
If the cells are in series ... all the current is going thru every cell. Each one may only be "supplying" a % of it, but all have the same current flow.
 

rhino

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If the cells are in series ... all the current is going thru every cell. Each one may only be "supplying" a % of it, but all have the same current flow.
Thanks for clarifying that for me :rolleyes:..For some reason was picturing parallel connections..
 

Horsefly

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You aren't worried about oxidation? When using supplied busbars, they have the tinned exterior so you aren't getting copper to aluminum contact. In your case, it sounds like a lot of al/cu contact. Did you consider NOALOX?
The risk of galvanic corrosion - which is what I believe you are talking about - depends on the environment. In the case of copper bus bars between aluminum terminal pads, if the place the battery is kept is in an arid climate, there is very little risk of any problem. Galvanic corrosion requires an electrolyte. A really good one is salty water. But in dry places (like the desert of Arizona or the dry high elevations of Colorado) there isn't much electrolyte. I still try to mostly use tinned copper, but I do have some untinned ring terminals in places. I've never seen any corrosion.
 
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