Since they have a stamped and formed end that is threaded, then steel makes sense to allow good clamping force with little thread engagement. Extruding a hole like that and then tapping it is a good practice, economical and effective. The extrusion work hardens the steel - even better.
Reviewing the image again, the thing is probably nickel plated. It doesn't look bad on the outside. But electroplating down in a depression is dicey,and it is probably thin there, hence the corrosion underneath there. I wouldn't call these spot welds as spot welding is usually done by trapping the two pieces between two electrodes across the thickness of the material, these are probably little TIG zaps around the perimeter. I have never seen anything quite like that before. I don't see anything alarming about that from an electrical conduction POV, probably not a very strong joint physically, but it might not be a problem. I don't see that the rust is a problem either, just don't submerge or spray them with salt water. At any rate I don't find this as alarming as some folks. It may be better than machined, drilled and tapped aluminum pods for bolting. The fellow who took the pictures mentioned glue between the aluminum and steel - I am thinking sealant not adhesive. If the welds fail the glue would be pointless - sealant however... I really like reverse engineering stuff. I have a small Headway pack. Now I can't wait for it to give out someday so I can check it out. A note on galvanic corrosion - it is not a concern with fused joints or if there is no mositure. On Fri, Sep 19, 2014 at 7:05 PM, via EV <[email protected]> wrote: > A magnet sticks to the end, and there are people that have had the ends > rust, so it looks like the cell ends are steel. Folks on endless-sphere > think that is for strength for the screws. > > I have run 100 A for 90 seconds through the cells, and the ends were cool > afterwards (using Cu intercell connectors). I'm measuring 6 milliOhms > internal resistance, not bad for an 8 Ahr cell. Just for fun I'll try it > with Al to see if it runs hotter. > > I just ran across this, this page shows a galvanic corrosion chart: > http://www.corrosionist.com/galvanic_corrosion_chart.htm > > It looks like steel to Al is about the same as steel to Cu, but Cu to Al > is about twice as bad. Is it as simple as the chart or are there more > things to worry about? > > Just thinking out loud, is a pressure contact more likely to have > problems? Maybe that us why welding on tabs is so common (thanks for the Cu > and steel clad comments for inspiring that line of thought). > > Many thanks for all the the good inputs. > > -----Original message----- > Sent: Friday, 19 September 2014 at 18:51:18 > From: "Michael Ross via EV" <[email protected]> > To: "Lee Hart" <[email protected]>,"Electric Vehicle Discussion > List" <[email protected]> > Subject: Re: [EVDL] Dissimilar metals on Headyways? > Why do we think the cap is steel? Nickel is a better choice if you don't > look at cost. Or a bonded bimetal. > > There are probably ways to do a good job of this. I have cooking pots that > are aluminum bonded to stainless steel. Like wise copper to stainless. I > have used silver bonded to brass (admittedly not a bad combination as we > might assume aluminum to be). Anyway, if you get a good fusion bond then > you can stop worrying about the dissimilar metals bit because no moisture > can be involved. > > Earlier this year someone mentioned that the conductivity of stainless is > far less than that of nickel, however the conductivity of wire is expressed > as cross section and length. That means you can have a connection with a > enough cross section and very short length and the resistance does not sum > up to anything worth worrying about. > > One thing I have not sorted out yet - the choices of electrode materials in > Li ion batteries. I have heard that it doesn't matter that one is copper > and the other aluminum - could be two of copper, or presumable two of > aluminum, or two of nickel. Given what can go awry with stacks of thin > aluminum electrodes clamped together with a terminal - what makes that a > common choice? > > On Fri, Sep 19, 2014 at 12:39 PM, Lee Hart via EV <[email protected]> > wrote: > > > via EV wrote: > > > >> So my basic question is if the cell is already Al to Steel > >> internally, might it be better to go Al to Steel to Al (that last Al > >> being my intercell connectors) than to do Al to Steel to Cu (which > >> would be copper intercell connectors)? > >> > > > > What little I know about metallurgy tells me that attaching steel to > > aluminum is a bad idea. Maybe it can be done right by experts with > special > > techniques. Others who are knowledgeable about such things may have more > > data with references. > > > > But it's something that would normally be avoided. Just because the > > Chinese did it does not make it good practice (they favor cheap, not > good). > > Certainly, for connections outside the cell in the "real world" of water, > > oxygen, dirt, corrosion, etc. I would definitely avoid it. > > > > If you insist on doing this anyway, then you should plan to measure the > > actual resistance of each and every connection. > > -- > > If you would not be forgotten > > When your body's dead and rotten > > Then write of great deeds worth the reading > > Or do these great deeds, worth repeating. > > -- Ben Franklin, from Poor Richard's Almanac > > -- > > Lee Hart's EV projects are at http://www.sunrise-ev.com/LeesEVs.htm > > _______________________________________________ > > UNSUBSCRIBE: http://www.evdl.org/help/index.html#usub > > http://lists.evdl.org/listinfo.cgi/ev-evdl.org > > For EV drag racing discussion, please use NEDRA ( > http://groups.yahoo.com/ > > group/NEDRA) > > > > > > > -- > Put this question to yourself: should I use everyone else to attain > happiness, or should I help others gain happiness? > *Dalai Lama * > > Tell me what it is you plan to do > With your one wild and precious life? > Mary Oliver, "The summer day." > > To invent, you need a good imagination and a pile of junk. > Thomas A. Edison > <http://www.brainyquote.com/quotes/quotes/t/thomasaed125362.html> > > A public-opinion poll is no substitute for thought. > *Warren Buffet* > > Michael E. Ross > (919) 550-2430 Land > (919) 576-0824 <https://www.google.com/voice/b/0?pli=1#phones> Google > Phone > (919) 631-1451 Cell > (919) 513-0418 Desk > > [email protected] > <[email protected]> > -------------- next part -------------- > An HTML attachment was scrubbed... > URL: < > http://lists.evdl.org/private.cgi/ev-evdl.org/attachments/20140919/87c00b90/attachment.htm > > > _______________________________________________ > UNSUBSCRIBE: http://www.evdl.org/help/index.html#usub > http://lists.evdl.org/listinfo.cgi/ev-evdl.org > For EV drag racing discussion, please use NEDRA ( > http://groups.yahoo.com/group/NEDRA) > _______________________________________________ > UNSUBSCRIBE: http://www.evdl.org/help/index.html#usub > http://lists.evdl.org/listinfo.cgi/ev-evdl.org > For EV drag racing discussion, please use NEDRA ( > http://groups.yahoo.com/group/NEDRA) > > -- Put this question to yourself: should I use everyone else to attain happiness, or should I help others gain happiness? *Dalai Lama * Tell me what it is you plan to do With your one wild and precious life? Mary Oliver, "The summer day." To invent, you need a good imagination and a pile of junk. Thomas A. Edison <http://www.brainyquote.com/quotes/quotes/t/thomasaed125362.html> A public-opinion poll is no substitute for thought. *Warren Buffet* Michael E. Ross (919) 550-2430 Land (919) 576-0824 <https://www.google.com/voice/b/0?pli=1#phones> Google Phone (919) 631-1451 Cell (919) 513-0418 Desk [email protected] <[email protected]> -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://lists.evdl.org/private.cgi/ev-evdl.org/attachments/20140919/9d8e7914/attachment.htm> _______________________________________________ UNSUBSCRIBE: http://www.evdl.org/help/index.html#usub http://lists.evdl.org/listinfo.cgi/ev-evdl.org For EV drag racing discussion, please use NEDRA (http://groups.yahoo.com/group/NEDRA)
