On 25/02/2012 00:45, John Rumm wrote:
On 24/02/2012 21:26, Bob Eager wrote:
http://theunderstatement.com/post/18...-tesla-motors-
devastating-design

Its a common problem with lots of modern battery technologies - they
must never be left to go flat, and have high auto discharge rates.

I think it is the batteries own self discharge rate in the pack that is
the problem here and not the permanently on power subsystems. They just
deliver the coup de grace at the end taking it into unrechargable brick
state. In other words the no self destruct protection is activated.

Some of my camera batteries have about the same lifetime ~11 weeks on
the shelf if left unused too. It is faintly annoying but they are
cheaper to replace if they get wrecked. Most of my portable PCs
batteries die a horrible death in 3-5 years of near continuous use.

What might be an issue is that most sensible standby electronics
switches off when the battery gets too close to its death zone.

In the case of the Tesla it should probably sound an alarm or send a
"Charge Me" text to the owner or something when the battery is close to
becoming a brick. The only sensor needed is a low battery alarm!

I cannot see how the addition of 100ft extension cable that was not
running hot could decrease the charge rate to a point where the car
could die whilst being on charge. The pack is nominally 375v and 50kWh
so delivering 3A for an hour would put 1kWh into it and 1A would be more
than enough to hold it. I suppose it is possible that the charger is too
clever by half and sees even a small resistive load in the cable as
nearly charged battery. You do have to be very careful with Li-ion cells
as their tendency to self immolate if overcharged is notorious.

Here is Telsas own more flattering description of their battery:
http://webarchive.teslamotors.com/di...terySystem.pdf

I reckon it is far more likely that the idiot user unplugged it!

--
Regards,
Martin Brown