Willie2 via EV wrote:
Thanks! Bottom line, take away: 50-90 ah on a fresh lead pack.
It's not quite that bad. The Peukert effect does not change the ACTUAL
capacity; it only describes the APPARENT capacity due to high currents.
If you have a 200ah battery and discharge it at 100 amps so it appears
"dead" after removing 100ah, it is in fact at the 50% discharged point.
That's a "safe" discharge level -- you can do that every day for 600+
cycles.
The other 100ah is still there -- you just can't use it with a 100 amp
draw. If you draw a lower current, then it will be there. :-)
That pretty well matches my gut feel that my 40ah of ebike batteries is
around half of a good lead pack. I believe, in general, 80% or more of a
lithium pack can be used.
The same 50% capacity limit applies to lithiums, too. If you discharge
them to 80-100% on every cycle, you won't get as long a life. (How long
the life will be depends drastically on the type and quality of the cells).
I recall that using lead, you got very little time with good performance
since the voltage declines ~linearly. With lithium, you can't guess the
SOC from performance; the carts are sprightly most of the time.
It is indeed tricky to compare the two. Lead-acids have an internal
resistance that is often lower when fully charged; but it goes up as
they discharge. In a high-amp application, you can't use more than maybe
half their rated amphour capacity.
Lithium internal resistance doesn't change until they are almost dead.
This is good for high-amp loads -- you can get more of the rated
capacity. *But*, nothing is free -- you also get less than rated life
due to the high currents and deeper discharges.
--
Pollution is nothing but the resources we are not harvesting. We
allow them to disperse because we've been ignorant of their value.
-- R. Buckminster Fuller
--
Lee Hart, 814 8th Ave N, Sartell MN 56377, www.sunrise-ev.com
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