[chbot] Homebrew powerwall

[Charles Manning]

On Wed, Oct 5, 2016 at 9:44 PM, Henri Shustak <henri.shustak at gmail.com>
wrote:

>
> > The amount of time and money he spent building up those modules! Once in
> those big packs the time spent in maintenance is huge as well, when one
> cell goes south. The only thing going for them is compactness (but that
> might cause heat problems?) and good looks. I'm still not convinced
> directly soldering onto the battery is a good idea either.
>
>
> How about opting for a lead based battery chemistry. Lead carbon although
> far heavier (not great for power to weight ratio in a car) offers some
> interesting benefits such as cycle life over deep cycle gel and even AGM
> depending upon your usage.
>

Indeed. This is one of the big reasons why the "smartgrid" ideas whereby
the grid gets topped up from EV batteries is a bad idea.

Engineering is the art of compromise, including with batteries. Making a
battery small, light and energy dense (eg. for a car) means compromises
need to be made in terms of lifetime and other factors. Stationary battery
banks with no weight/size restrictions are probably still better served by
lead acid.


> However, in terms of the awesome factor of lots and lots of 18650's + a
> more modular approach just purchasing some Tesla Model S battery modules
> could be a simple (if not more expensive) approach than constructing your
> own modules.
>

I use 18650s for LED torches for hunting etc. They are highly variable in
the lifetime they produce and their ability to hold charge. Some have
lasted reasonably well, others have been thrown out after a few uses. Not a
great approach for a long term solution unless you just want something that
looks cool and you like swearing a lot.

Remember too that Tesla doesn't have to come up with an awfully good
solution to stay in business - they get US federal funding to the tune of
about $35K per car they produce.


>
> I agree that soldering is probably the best approach, ideally some sort of
> spot welding approach would be better. Although it is not going to offer
> the easily replaceable option. You will not have a 18650's falling out
> during an earthquake.
>

If you do spot weld, you'd still want it modular so you can easily identify
and replace cells (eg. maybe screw lugs or something like fuse holders).

>
> Critical feed back would be welcomed :)
>
>
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