Where the lugs on the
EVE batteries are welded to the electrode is really tender. I've read a couple of other threads stating they've had issues with them coming off when tightening the bolts. - it's not just me being stupid.
disclaimer - I've been using tools for the last 53 years, my mom gave me a took kit when I was 7 and I've been messing things up since. I have a very good feel for "tight" and such. I'm also a machinist/fabricator so I can claim that I know what I'm doing, for the most part - including screw ups... (I like to call them teaching moments)
I had to disconnect the + lead of my 16S battery bank the other day. Reached up with the 10mm wrench (battery bank is over head), gave the 6mm bolt a turn and pop, the whole lug came off.
WTF?
THIS IS NOT GOOD!!!
Got on YouTube so I could get my certified battery repairman status and came across a couple of videos of people drilling and tapping the lug's base and reattaching it.
Easy enough. Well... kinda.
I screwed up (my typical action for a first try on darned near anything). Instead of using a drill press to control the drill depth as the bit broke through, dumbass me just grabbed a hand held drill and started in - carefully, but manually. Not smart.
The lugs are aluminum that appears to be cast over the copper electrode. The aluminum is nice and soft (easy to drill) and then it gets into the copper, which is much harder - well, springy. It doesn't flake out of the bit like aluminum, it strings instead and grabs the bit. I was waiting for the drill to break through and had plans of just being careful when I got there (can usually feel it as it breaks through) but was definitely surprised when it grabbed and plunged (and I know better...)
SPARK, SMOKE, SHIT!
Turns out that I shorted something out internally with the drill bit. Crap. I fixed the terminal and threw the battery back in the bank hoping it was going to play nicely with it's 15 friends but alas, no. I'd killed it. Time to order a new battery and do a bit of swearing.
Battery arrives yesterday. YAY. I pulled the disabled cell out of my bank and put the new one in place. As I'm tightening down the bus bar between the new battery and it's friend, pop, off comes the lug. SERIOUSLY??? More swearing. I'm absolutely blown away that it's popped the lug off at the weld. I did NOT ham fist the thing - I know better and have a good feel for this sort of stuff. The weld that holds the lug to the electrode is FREAKING TENDER!!!
Okay, time to fix this one - but I'm filled with more knowledge, i.e. DO NOT DO THIS BY HAND.
As I unscrewed the bus bar from the battery next to it, guess what - POP, off comes it's lug.
LOTS MORE SWEARING. May have even been one of those pissed off "stomp dances" that accompanied the swearing.
From my first mistake/repair attempt I've been able to discern that the lugs are not that thick and there's some sort of rubber mat underneath the lug, separating what ever's under it from the lug. (watched as many videos on the batteries as I could find trying to see if I could see any manufacturing videos - found a couple and yeah there's a protecting layer of rubbery something under the lugs - verified what came out on the drill bit - a thick gooey stuff).
I took very careful measurements from the top of the lug to the bottom of the hole I'd drilled and threaded in the dead battery. It's 5mm. The zip tie that I was using for depth measurement (because plastic won't conduct) actually went close to 20mm into the battery before hitting what ever it is under the gooey matting so I knew I had a little wiggle room.
I put the new battery in my mill and started taking itty bitty bites into the broken tab's lug. Right at 5mm it breaks through and touches that gooey mat.
Find the proper drill bit for a 6mm tap: M6 x 1 uses a #8 drill which is .199"/5.05mm in diam.
I was able to program my mill to do a 5mm deep, 5mm diameter hole in the lug. The end mill breaks through right at 5mm and no smoke or sparks accompany the break through this time (yay). The gooey mat also held the chips in place instead of letting them drop deeper into the battery. A small pair of tweezers was used to remove any spare pieces of metal left by the end mill. - and I'd coated the end mill in a thick grease to help capture as much of the stuff I was drilling out instead of letting it fall into the battery. (old trick, works well).
Greased up a 6 x 1.0 tap and started the threads into the hole - got about two turns worth of thread into the lug but was worried about the distance the snout of the end mill was penetrating into the battery. I needed to start the threads but didn't plan on using it to do the full threading cut. Didn't want to let the smoke out of this one so I switched to a 6 x 1.0 bottoming tap (once again, covered in thick grease to catch the chips) and very carefully tapped the hole through to 5mm deep.
To get as much clamping and surface area I machined a thick brass washer that fit in the lug's base. I placed the lug back on it's home (almost a snap fit), then the washer and then a 6 x 1.0 x 8mm bolt was used to hold everything together.
I repeated this on the other broken lug and now have two working batteries with bolt on lugs. I put them back into the rack and then VERY CAREFULLY tightened the bus bars and the battery's positive lead back in place. I used a wrench to hold the bus bar and lug while tightening the bolts.
So if you break a lug off of your battery it's not a total loss. Very carefully drill and tap and stick it back on.
btw, pic #3 is of my first attempt at repair (bad battery now) the corrosion is a result of spilling some of the liquid in the battery out - was unaware that they had it in them until I laid it on it's side. I was VERY careful not to touch/breath the stuff, as I don't know what it is and don't really want to find out if it has any side effects.
