If you look close, you can see that the arcing between the bolthead and the washer disolved that washer (welding slugformed)
If you follow “the offgrid garage” on youptjoep, Andy often replaces these flimsy bolts and washers for a better quality type
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Thanks. As for the isolation. Yes. Heat shrink.
The SmartShunt is connected to that piece of copper. Right below the BMS. I use short spacers for the BMS and used a router to lower the shunt so that it fits below the copper plate.
The space that I have for everything is about 40 millimeter.
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Dirty or oxidized contact surfaces are often underestimated in such high current applications.
Blank copper will get an lite oxid layer if you touch it with you “sweaty” hands. This may play no role in standard AC applications, but if there are currents in the range of 100A or more this can be the result.
But unfortunately this topic is not handled very serious, not even by big youtube influencer.
I would always recommend to sand the surfaces, clean them eg. with alcohol, and maybe even add some cantact material like copper paste.
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In the new to be placed batterycable isolator, you can drill a 8,1mm hole trough the metal part and fit a m8 bolt/nut combination, use a spring-washer or a “veerschotel” washer.
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→ spring washer? Preferable A2 stainless steel.
There are no washer or spring washers delivered with the box to be installed on the busbar to terminal connections, would this be recommended? And I guess this is to prevent the bolt from getting lose, correct? Not because for improving the current flow?
Yes indeed. The busbars will get warm. If not hot. And then you also want spring washers. They ‘bite’ into the busbar. Good idea to use them.
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Here’s a picture of my BMS and the connections. In your case, I think (part of) the problem is that the flexible busbar was undersized. The busbar coming from the cell terminal to the BMS is twice the width of the busbar going from the BMS to the battery box terminal. The former shows no damage at all - it handled the current just fine.
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Great solution with regards to the cables. This was going through my mind as well as a possible solution. But what I don’t like that much is the single screw connection to the BMS and battery cell. This feels like the surface contact is smaller compared to the busbars I was using. What would be great if cable terminal/clamp/ring (not sure about the exact naming), with two holes are available on the marked. Or that you can make them somehow. Suggestions?
What is your view about the surface contact (mm2/cm2) in combination of 100A current?
I’ve seen some CAD model on grabcad, but haven’t found a vendor yet:
Maybe there:
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Rene,
You could use a copper plate. Something that I use as well, and put an M10 cable lug on it. Using a separate hole of course. Also. Make sure that the bolts are long enough. The JKBMS comes with short bolts.Those ain’t good enough.
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That is a good suggestion of course. Make a copper plate, two holes for the connection to the BMS, one hole for the connection with the cable using a cable eye (what is the english word?). Excellent idea. Thanks. I maybe go that route indeed.
Compression Cable lug.
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Ring Terminal - often used for smaller gauge wires?
Cable Lug
The problem with trying to use a cable lug with two holes is finding one that matches the BMS terminals exactly. The custom copper bar solution is probably easier/faster/cheaper.
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I’ve seen this with busbars made from plated steel where the cut is made using a sheering tool. The end of the busbar has a curve on it, and so no matter how much torque the bolt has, its going to have a tiny contact point.
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Looks almost like there was insulation (shrink tube) between the connection and all current went through the small bolt
Yes, based on the picture you would say, conclude that there was isolation between the two busbars, but that was absolutely not the case! See picture from the original installation.
And this is a picture of the negative terminal connection/installation of a new, 2nd, box. This looks good or …? Suggestions for improvements welcome.
I’m not (no longer) going to speculate about what it could have been. Let’s focus on preventing possible installation errors.
Clean surfaces.
Check terminal if it is flat.
You may need to remove burs from the machines holes. Called debur. The idea is to remove the edge at the end of the hole. Either from drilling of pressing a hole in it,
Triple check that absolutely nothing is in the way. Nothing crosses, or is in direct contact with the busbars.
Possibly add a nut and spring washer on the battery terminal bottom. Where the bolt is screwed in.
Torque the M6 with max 6Nm. If you suspect that the bolt is gone. Replace it.
By the way. What is that gold/brown residu on the battery terminal and the top of the busbar. Bolt head as well.
Where the bus bars have been lazer or cnc cut, often there are burrs on the edges that are not cleaned. I have seen in even in well known battery banks where even the little intercell bus bar connections have the issue. That is very likely the part of it if there wasn’t any insulation or other assembly issues (such as the curve if the bus bar lifting up a bit so the surface was not making full suramface contact) and choices there.
A hot connection (other than being undersized) is because of high resistance, which is a contact surface problem.