If I honeycomb arrange my cells I can get more to fit. The stock plates I have
seen won't work as they are for square arrangements of cells, like this:
http://www.manzanitamicro.com/components/com_virtuemart/shop_image/product/4_Cell_Bus_Bar_f_4e77a3a355a78.jpg
Also, it isn't much effort and but is much knowledge gained to test Al vs. Cu.
Since the cell is Al inside, it seems like Al might be better for that reason,
but possibly worse for other reasons.
Al wire is about 1/6 the price of Cu wire, but it would be a lot of work to
hammer or crimp Al wire into a good shape for Headways. I called about
electrically conductive Aluminum sheet -- it is not commonly used or stocked,
and is very expensive (unlike the wire). So Al is either a lot of work or high
cost, two more negatives I just learned about.
Lee brings up a good point about the plates stressing the cell terminals. Here
are some more data points on that front:
o The cases on Headways are steel, so the cells are very strong.
o The Headway plastic holders are surprisingly strong and rigid.
http://www.manzanitamicro.com/components/com_virtuemart/shop_image/product/3_Cell_Plastic_H_4e77a2af4fd3f.jpg
You have to push the cells in with a fair amount of force, the stress goes to
the metal case. I made a 6x8 array with the plastic holders. That many cells
weighs about 30 lbs (14 kg). To my surprise, I could lift opposite corners but
couldn't detect the little 6x8 pack flexed or that the cells shifted at all. So
maybe you can get away with plates on Headways better than for the large block
prismatics.
o To get the equivalent of 0000 cable cross section I need Cu plate about
0.022 in thick (the current with go through about 10 inches wide). That can
bend a bit if flexed, but will still be pretty rigid between the posts... Hmmm,
do I trust the Headway rings to be tough enough for plates or do something
fancier with intercell connectors?
Thanks all for the good ideas and discussion.
Sent: Tuesday, September 23, 2014 at 11:50 AM
From: "Lee Hart via EV" <ev@lists.evdl.org>
To: g...@tylernz.com, "Electric Vehicle Discussion List" <ev@lists.evdl.org>
Subject: Re: [EVDL] Dissimilar metals on Headyways?
George Tyler via EV wrote:
> Why not just buy the link plates that headway sell, made for the purpose.
> Get the cell mounts at the same time?
Are these just a flat bar that bolts directly between cells. If so,
that's not a good way to do it.
The cells will move slightly due to road bumps and vibration, The cell
cases are plastic, which will expand and contract from temperature
changes. The cases will also swell over time as the cells age.
With rigid inter-cell jumpers, all this movement causes leaks and bad
connections to develop over time.
Your inter-cell cell jumpers should therefore have a bend or kink or
other method to provide a little bit of flexibility or "give" to avoid
straining the connections. This is true for *all* types of batteries;
not just lithium.
--
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
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