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... 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