Have you seen this happen to a bolt/nut before?

ebike11

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Hi guys
I had a weird thing happen today. I use long electric car cells as one of my packs. The tabs are not soldered together. I just use small nuts and bolts. Today i tried to start the bike and no power through my cycle analyst. The volt meter read 36V so i was wondering what was wrong. Then i started to disassemble when i seen this happen. The battery cell is fine. No leaks or damage but the bolt got totally zapped somehow.
Does anyone know what causes this?
Thanks!
https://s2.postimg.org/gde2vegbd/20170808_210940.jpg

https://s1.postimg.org/7tor9sa9r/20170808_210230.jpg

https://s1.postimg.org/4h8coqaqn/20170808_210222.jpg
 
Looks like the same thing that happens in old "fuse" style electrical panels in older homes. Arcing/Burning/Oxidization caused by poor contact...

The older fuse panels mostly had aluminum "rails" that carried power to all the fuses. The main issue with these older panels was that the fuses made VERY poor contact with the "rail" causing arcing and heating between the "rail" and the contact point on the fuse. This caused both surfaces to oxidize and "burn" to the point where the fuse would no longer make contact (or resistance between the two to be very high) causing the attached circuit to lose power.

Solution was to scrape or sand the oxidized/burnt material off of both surfaces (power OFF of course), apply dielectric grease to both surfaces, and reassemble tightly.

I recommend that you clean the surfaces with fine grit sand paper, apply dielectric grease to the surface and to a NEW replacement bolt/nut and reassemble.
You really should go through every wire, switch, and connector and inspect everything. Repair where needed and coat EVERY SINGLE contact in dielectric grease. Make sure everything is tight and secure!

Shouldn't have this problem ever again.

~Canabian
 
Thx for the reply! Yeah arcing sounds right. However the bolt and nut was still tight so the connection was still tight
 
It's corrosion. Specifically galvanic corrosion caused by interaction of dissimilar metals:

https://en.wikipedia.org/wiki/Galvanic_corrosion

I'm assuming copper wire with a non-corrosion-resistant metal, like plain steel.
 
Thats what I was getting at with the old fuse panels...

The bus bars were aluminum and the contacts on the fuses were usually brass or some other metal. This caused a galvanic reaction, as cal3thousand pointed out, which causes corrosion between the dis-similar metals making the contact between the two metals build up more and more resistance. If the current is high enough it then "jumps" past or burns through the corrosion.

The fix is as I said in my above post - Clean off the corrosion, apply dielectric grease, reassemble with new hardware.

Good Luck!
 
Copper and its alloys, as well as tin, zinc, steel, iron, aluminum and others are pretty notorious for this,... a matter of greater "nobility". LoL!

Due to that nobility issue, "code" typically required specific stainless connections to totally isolate copper from aluminum, etc., while still maintaining a solid electrical connection. 316 stainless being most noble unless you can afford gold, silver, platinum. Titanium may rank above that stainless and also be acceptable for use, although more costly.

It appears the nut and bolt was used for connection of the wire to the two base materials??? Your bolt and nut appear to be bronze? While as acceptable as stainless, there still should have been be a bronze "washer" separator to keep the copper wire OFF the dissimilar base metal, rather than between.

Remember,... to ISOLATE the less noble metals from one another. To attach less nobles together in contact with bronze or stainless does NOT solve the issue.
 
No the bolt and nut were originally silver color stainless steel i think..the result turned them brown haha..i replaced the bolt and nut with new ones...and your washer tip is useful.
The problem also is i attached a thin wire to the bolt and battery tabs and tightened everything. Thats were the metals mixed i guess. The wire is for monitoring the cell readout to make sure the cells are fairly balanced
 
This is not corrosion or galvanic action - it's overheating from a faulty connection.

The bolt appears discolored from overheating and seems to have residue from burning the insulating material. The heat also appears to have burned off the insulation on the balance lead as soon as it traveled out of the heatsinking safety of the aluminum battery tab.

bolt2.jpgboltWrap2.jpg

The first image shows the generally uniform discoloration from overheating, the burned balance lead insulation, and the burned-on plastic insulator on the bolt head. The second image shows what appears to have been some sort of moldable rubber tape used as a tab insulator that did not have the protective plastic film removed before application (?). The film appears melted where it contacted the bolt head.

The aluminum battery tabs are pliable and need to be clamped together with a rigid backing plate. Here small bolts were used which might give enough clamping area for the bike-sized currents that you require were it not for the balance lead installation. This construction technique has two major flaws:

  1. The connection is not tab-to-tab but instead goes through another metal (the balance lead). This introduces questions of the resistance of the intervening metal and the effects of pumping large current across a boundary of dissimilar metals.

  2. More importantly, since the tab metal is pliable, the contact area is reduced to the area of the balance lead times 2 (top and bottom) - not the entire area under the bolt head. The tab material under the bolt head/nut that is not in direct contact with the balance lead is not making suitable (if any) contact with the bolt head because there is no clamping force applied and the tab material is not rigid and easily deforms. The large area of tab under the bolt head is not really in play - only the tab material shadowed by the underlying balance lead is actually clamped. The means that virtually all the battery current is running side to side across the compressed balance lead which caused overheating.
You need to disassemble and clean the connection, then reassemble it using ring terminals for your balance leads so the force applied by the bolt is uniform across the surface and the tabs mate tab-to-tab with no intervening material. I would stack the bolt head, ring terminal, washer, tab, tab, washer, lock washer, nut. This should get mixed metals out of the equation, give a low resistance tab-to-tab electrical path, and squarely apply pressure area across the entire tab surface under the washers.
 
If there is a poor connection, that will lead to "arc-ing". Whenever there is a spark traveling through the air on a regular basis, there will be erosion as a result. I do not know if that is what is happening here, but...it is a "top-10" suspect to investigate...
 
ebike11 said:
No the bolt and nut were originally silver color stainless steel i think..the result turned them brown haha..i replaced the bolt and nut with new ones...and your washer tip is useful.
The problem also is i attached a thin wire to the bolt and battery tabs and tightened everything. Thats were the metals mixed i guess. The wire is for monitoring the cell readout to make sure the cells are fairly balanced
ya,.. it seems strange to some, that although such an affected mechanical connection can often pass voltage sufficiently, it fails miserably in passing current. And that's a lot of heat to discolor stainless so badly! Wow!

teklektik said:
This is not corrosion or galvanic action - it's overheating from a faulty connection.
If this occurred rather shortly after assembly, I'd agree that it's purely a faulty connection. Any increased resistance due to galvanic or corrosion usually builds over time, and then often suddenly fails with a sudden shift or change in environmental weather conditions.

teklektik said:
You need to disassemble and clean the connection, then reassemble it using ring terminals for your balance leads so the force applied by the bolt is uniform across the surface and the tabs mate tab-to-tab with no intervening material. I would stack the bolt head, ring terminal, washer, tab, tab, washer, lock washer, nut. This should get mixed metals out of the equation, give a low resistance tab-to-tab electrical path, and squarely apply pressure area across the entire tab surface under the washers.

AND this is exactly as I would suggest,.... with the addition of dielectric grease on mating surfaces. Be wise on the choice of ring terminal and the manner of attachment to your wire. THEN,.... monitor it closely for a time to assure that the right choices have been made.
 
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