On 1/26/2013 6:00 AM, Jim Wilkins wrote:
"Daryl" wrote in message
...

It sounds like they are being overcharged. That is prevented by a
simple card addition that prevents it on only of overcharging but
undercharging. Easy fix.

Daryl

The Lithium medical and electric vehicle packs I worked on were
controlled by ICs that monitored and recorded individual cell voltage
and overall charge and discharge current. Those are point measurements
that are easy to do. What's harder is detecting unexpected hot spots
away from the temperature sensors. Minor differences (improvements)
between the acceptance sample and production devices can change heat
flow paths.
http://www.mpoweruk.com/lithium_failures.htm




I can see a problem that is being addressed in Electric Vehicles.
Heat and cold.

On an electric vehicle, getting the battery too cold will (not
can) result in a degrading of the performance of the cells. The
fix is adding an "Electric Blanket" to keep the battery warm (not
hot). The residual power required by the blanket is negligible.
You get back much more than you lose.

Heat. I can see problems with the Lipo batteries. The battery
they chose is one that is not on the list of Vehicle safe
batteries. It is the best, the highest output but with it comes
problems. Lithium cobalt oxide (LCO), for vehicles, is listed as
unstable compared to the rest. It's very suspeptable to heat.
And sitting on the ground running up on a hot day, the battery
compartment will sky rocket in heat. The safest to use is the
lead acid but it's very short lived in this application. To use
any Lipo battery, it requires a cooling and a heating system to
keep the battery at an optimal temperature. The LCO is just the
worst of the lot for overrunning (catching fire, generating
Oxygen when it burns) than any other Lipo battery.

The Fix? Get rid of the LCO and temperature control the battery
compartment. Even a Lead Acid doesn't like excessive cold or
heat. But it won't turn into a major oxygen fire. Sometimes,
newer isn't better. But the various other Lipo batteries are
safer than the LCO which has a proven track record of burning.

BTW, the LCO isn't the cheapest by far. The LipoMG battery is
the cheapest but it has a low service charge rate. The Lipo4 has
a decent service rate and is what is primarily used in various
vehicle applications. But, maybe, the old Lead Acids may be the
way to go on this one. They are the most stable and the most
safe if you keep them in a wide range of temperatures.

Newer isn't always better.

Daryl



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