> So I gather the take-home message is that this is very much a
> battery-specific exercise.
Not only that, but application specific.
The specifications, irrespective of the manufacturer, are determined
in a lab environment under "ideal" conditions. Put them in a vehicle
and all bets are off. In most cases the batteries are not temperature
controlled, peak currents are many times the tested load rating,
and DOD's are all over the place. Add a few discharges down to "dead"
and a few overcharges and the reality becomes you will likely never
see anywhere near "rated maximum" cycle life in a conversion EV.
> staying under 50% DoD for most battery types is the safe way to
> maximize energy return,
But it's not very practical. You're taking a vehicle that might have
a 40-50 mile 80% DOD range and only drive it 20-25 miles max. And
that still doesn't factor in temperature and peak currents.
> I should take lifetime mileage estimates with a grain of salt,
About the best you can do is take care of them the best you can,
never run them dead and be careful with the equalize charging. The
best I've gotten out of a set of floodeds has been 18,000 miles
at 3 years old. Some might argue I "murdered" them by using most
or all their capacity, but if I concentrated solely on pack longevity
I would never be able to drive the EV for a useful distance, or during
the heat of summer, or the cold of winter.
Another issue is that as the pack gets older, the individual batteries
diverge further and further apart, and there's nothing you can do
about it. You equalize as much as you dare, keep water in 'em and
that's about all you can do. In time the weakest battery becomes
your range limit, with 2 or 3 others not far behind. By that time
the pack is too old to swap the weak ones out for new batteries, so
you may end up replacing a pack with half or more of the batteries
with still useful capacity.
To summarize my point, published cycle life is useful for comparing
one battery to another, but to extrapolate that into pack life in
a conversion EV would be nearly impossible, short of setting your
controllers' current limit at 75A, and thermally manage them at a
constant 77F. Driving habits, care in charging, DOD levels,
and temperature will all play a part and will each contribute to
the demise of the pack to varying degrees depending on the EV, the
driver and the environment. Drive it careful, maintain them well,
get what you can out of them, and when they crap out just get
another pack and move on. After the first pack you'll get a good
idea what your EV, charging and driving habits will give you for
pack life.
Mark Brueggemann
Albuquerque, NM
[EMAIL PROTECTED]
S-10 EV
