Lawrence Winiarski via EV wrote:
Suppose you run a single wire out to 150 different batteries and you
have a good system. Suppose ONE of those 300 different connections
goes bad... Wouldn't it be nice to be able to have an alternate method of
communication... that didn't cost anything extra except a little
software to twiddlethe balancing shunt...that could be used in a
quiescent system to troubleshoot those 300 different
connections?....so you at least knew where to start taking stuff
apart?
Lawrence, I understand where you're coming from; I really do. 150 cells
means 300 connections between them; and that's just for the propulsion
wiring. They *have* to be reliable, or you don't have a practical car.
Reliability analysis works by figuring out the failure rate of each
part, and then multiplying it by the number of parts. If a part has a
failure rate of once every 10 years (gee, that sounds pretty good), then
300 of them have about 300 failures in 10 years, or 30 every year --
almost one a week! Such an EV would be un-drivable.
*Doubling* the number of connections -- for example, by adding a BMS
that needs two more wires per cell -- makes the problem is TWICE as bad!
The only way to make such a system work is for each connection to be
*extremely* reliable. You need failure rates 100 times better. That
won't happen with basement engineering or sweatshop manufacturing.
When Tesla announced they were using thousands of cells, and hundreds of
thousands of connections in their battery packs, I was skeptical that
they could ever make that work. But they did! Though it took an
*enormous* amount of money, engineering, and manufacturing effort to
pull it off.
With that kind of effort, I'm sure they could also make a
mains-communication system work. But again, I'm skeptical that any of us
will ever have the amount of skill, time, and money to perfect it.
I *do* think we could make a wired system reliable enough. I know,
because there are real-world examples to learn from. But... they don't
use cheap connectors, ad-hoc engineering, and extreme complexity to do
it. You have to look at ultra-reliable dirt-simple setups like telephone
systems and alarm systems to find your examples.
I also think there is promise in wireless or optical technologies. They
too have working examples with very high reliability. But again, you've
got to be sure you know what you're doing. Use parts and methods with a
*proven* reliability record; not whatever is cheap and handy.
Lee
--
If happiness is on your mind, here's a daily list to find:
- something to do
- something to look forward to
- someone to love
- someone to take good care of
- and misbehave, just a little
--
Lee Hart, 814 8th Ave N, Sartell MN 56377, www.sunrise-ev.com
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