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Re: (ET) New Member


On Thu, 3 Jul 2008, David Roden wrote:


On 3 Jul 2008 at 8:59, Michael S Briggs wrote:


High internal resistance effectively translates into a high Peukert
number, as more energy is lost over the internal resistance at high
discharge rates (and high charge rates), and thus not available for
use by the external circuit being powered.


Go out and mow your lawn.  Now put your hand on a battery.  Too hot to
touch?  No.  Warmer than ambient?  Probably not.  The ET simply does not 
use
enough current for the small loss of golf car batteries to matter.  It is
negligable.
Sorry, but that is simply untrue. If you get a voltage sag, then the internal resistance matters. Period. It is the internal resistance (and current) that *causes* the voltage sag (since you get a voltage drop over the internal resistance equal to the current coming out of the battery multiplied by the internal resistance). If you ignore all other losses (such as in the charger), the roundtrip efficiency of a battery effectively equals the ratio of the voltage during discharging divided by the voltage during charging. Because of the internal resistance, you have an overvoltage during charging and an undervoltage during discharging, and the greater those voltage swings (which equal the internal resistance multiplied by charging/discharging current), the lower the efficiency. That of course ignores some losses that do effect the efficiency, but gives a simple view of why internal resistance matters. If lead acid batteries had a negligible internal resistance, we wouldn't see a voltage sag when using the tractors. 


Some years ago I installed supplemental electric heat in a cool room of our
house.  I bought an electronic (non-programmable) thermostat to control it.
It cost about twice as much as a mechanical thermo, but it promised tighter
temperature control.

I replaced that thermostat twice in 3 years.  The first time I tried 
another
electronic thermo.  When that failed too, I put in a $12 mechanical
thermostat.  The mechanical thermo is still working fine 5 years later.  
The
comfort is just as good as it was with the fancy electronic thermostat; at
least I can't feel the difference.   Sometimes low-tech is the appropriate
solution.
Or you could install a programmable thermostat, and set it such that you don't waste energy when you don't need to be heating/cooling the home (or don't need to remember to adjust the thermostat when you leave the house, go to sleep, etc.). But yes, sometimes low-tech is appropriate. But, when high-tech can result in greatly improved efficiency, there is no reason to stick with low-tech just because it "works". 


I would also note that many ET owners feel this way about the GE control 
vs.
electronic controller upgrades.  The contactor controller may be "Apollo-
era," as one EE has called it, but it works well enough for them, and 
(maybe
more importantly) they can work on it.
True - I still have the original control system in mine, with the workability of it being a key reason (and the cost of replacing it being the other). But, it is important to realize that the simple approach of using a voltage divider to control speed isn't particularly efficient (which is why I try to avoid using the first two speed settings, in which significant energy is wasted across resistors). 


For me, an electronic controller is appropriate; for many other ETers, the
old tech contactor and resistor controller is appropriate.

To cut to the point -- please excuse me for saying so, but I think that
using lithium batteries for an ET is an inappropriate use of the 
technology.
As I've detailed before, lithium batteries offer no significant advantages
for the average ET user, Meanwhile, they run up the cost and complexity
markedly.
As I've said before, your analysis is based purely on *currently available* Li-ion batteries. I've explained why I feel new Li-ion batteries that should become available in the next few years have (IMO) advantages that will make them appealing *to me*. I've also clearly said several times that I am not telling other people they should wait around for new battery technology - I just figured people might be interested in knowing what is "around the corner". But, apparently you are not. 


Lithium battery technology is not proven, and lithium is far less plentiful
than lead.  It's not clear that there's enough to mass-produce EVs using
lithium batteries for dozens of years.
Actually, lithium is considerably more plentiful in earth's crust than lead: 
http://en.wikipedia.org/wiki/Image:Relative_abundance_of_elements.png
(note that that is a logarithmic plot)


Lithium is also geographically concentrated in strategically questionable
areas : I may have misunderstood, but from what I've read, China controls
most of the world's supply of lithium.


Nope.


I don't know about lithium's ability to be recycled, but lead is certainly
proven in that matter.  If the supply is limited, let's hope it's easy - 
and
doesn't require a lot of energy - to recycle it!
Both can be recycled. Unfortunately, contrary to popular belief, lead-acid batteries are not highly recycled anymore - at least if you look at it globally. 
http://www.things.org/~jym/greenpeace/myth-of-battery-recycling.html

Mike