A123 AMP20 tab surface preparation ???

[John in CR]

It's time to put my AMP20's in packs, and my plan for connection is to fold each pair of tabs over twice, flatten, and then crimp. Unlike a plain aluminum sheet the tabs show no signs of oxidation. Is that because there is some coating, or are the tabs an alloy that isn't reactive to air? Do I need to prepare the tab surfaces since I'm not welding or soldering the tab faces together? I plan to draw 300-400A peaks through the packs I'm making, so I need solid low resistance connections.

 

[999zip999]

JD has the most experience with tab folding. I wonder how his packs are holding up ? And at what amps ? I have mine bolted together and wouldn't use above 100 amps and fill comfortable. How big a pack ?

 

[John in CR]

How big a pack ?

39s...Actually a 26s pack (parallels to mutual advantage with 22s lipo) in series with a 13s pack.

 

[arkmundi]

At 300-400A, I'd definitely bolt them. You want to maximize the surface connection. I haven't heard before of any need to prepare the surface. My packs are still holding up well without. Interested in the theoretical limits of these cells. What controller are you using? You may want to read the A123 Battery Handling Guidelines which wb9k provided the community - some excellent information in that.

 

[John in CR]

I may go with bolts too, but Luke's posts about crimping lead me that direction. Bolts would just be insurance and give me the ability to fold another piece of AL sheet over the joined tabs and give me that additional conductor touching both faces.

I just saw the ES member produced spot welder that uses mosfets and runs on low voltage batteries in the for sale section, so I'm considering that route. Keeping flat tabs with a bunch of spot welds laid out so I could still be able to snip a bad cell out leaving enough tab to weld a replacement is an attractive proposition.

Controllers will be either 2 or 4 controllers depending on whether I want to go with dual HubMonsters. I'm working toward setting the top speed bar with a very public run, but the nearby race track has a longest straight of only 600m. The curve going into it will probably keep me under 60kph coming out of the curve, and at the end is a very sharp curve, so we have to leave plenty of room for braking. My lightweight buddy is starting to chicken out, and getting me to top speed and slowed back down will require more torque than I've been running, so that's leading me toward dual motor. That would put me in Luke's neighborhood, and I can get timed in the 1/4 mile at the same facility.

 

[Doctorbass]

A good crimp work too!

I agree with Luke about that. I was convinced that bolt was the best solution.. but i was convinced when i saw also the crimp mothod on some Zero 2013+ batery pictures on various forums :wink:

Some company already offer crimp for cell tab. I have found them. these are called thermifoil.

When i have built my 162p A123 pouch pack i have cleaned all tabs one by one with acetone and isopropylic then paid attention to not put any fingerprint on them.

I remember i saw a russian video showing soldering /brazing directly to the tabs to solder the aluminum to the copper of the A123.

Doc

 

[whatever]

low temperature aluminium solder flux should allow soldering of aluminium tabs
https://www.youtube.com/watch?v=9iwawTk9gXI

 

[whatever]

seems to be quite alot of suppliers of aluminium solder flux on ebay also

 

[wb9k]

There's no surface treatment on the cathode tabs. The anode tabs are nickel plated. I imagine any of these techniques could work, but crimping sounds the most difficult to successfully pull off...how will you crimp them?

AlSolder 500 does render aluminum easily solderable. Dissipating the required heat before it can get to the pouch is the biggest challenge there, but isn't really that hard to do.

 

[arkmundi]

I like to be able to easily deconstruct my packs, so as to service them when required. As in replacing cells or in rotating them. I and others have observed that differential cell voltage in some cases may be positionally related. Bolts provide an easy way to both construct and deconstruct that other methods are less suited to. Agnisium's kit allowed that, but there were 3 bolts perforating the tabs. The OSNPower kit has two bolts on either side of the tab. There are other methods of home brewing a bolted connection. Just another perspective. Whatever method is used, it needs to carry the current. And in highly amped applications, the connection if less than adequate can be the point of highest impedance. If a bad enough connection, its enough to melt. So the precautions you're suggesting are well worth taking.

For references above, please post links. Thanks.

I just saw the ES member produced spot welder that uses mosfets and runs on low voltage batteries in the for sale section

Some company already offer crimp for cell tab. I have found them. these are called thermifoil

 

[John in CR]

JP spot welder by Riba2233 http://endless-sphere.com/forums/viewtopic.php?f=31&t=68865