Bill Dube wrote:
I used a setting of 1.00 on my pack of 100 Ah ThunderSky cells. Seemed
to work just fine.
Willie2 wrote:
Yep, "1". You are likely to find the meter counts back to nearly exactly
zero on charging. That's a good indication you are getting almost all
the charge energy back on discharge.
No; that is "charge efficiency"; what the E-meter/Link-10 calls CEF.
Lithium cell charge efficiency is indeed very good -- the CEF is
0.98-0.99 which is very close to 1. But you don't want to set your CEF
to exactly 1; if you do, it assumes that there is no loss at all in the
charging process. A BMS shunting current to balance, or any leakage
current at all will cause a cumulative error.
Peukert is often misunderstood. It is *not* charge efficiency. Nor does
it say that amphours are "lost" at high discharge currents. A battery's
amphour capacity is essentially the *same* at high or low currents. It's
just that you can't get all the amphours out at high currents.
Consider a sponge: You put the dry sponge in water, and it holds 1 cup.
So we'll say its amphour capacity is 1 cup.
The Peukert exponent tells us how fast we can get the water out of that
sponge. Suppose to squeeze it for 1 second; you only get 0.9 cup. The
other 0.1 cup is still in there; you just can't get it out quickly. If
you put it back in water, it will absorb 0.9 cup -- exactly the amount
you took out. No capacity was "lost".
If you squeeze and twist and wring out that sponge for a minute, you get
0.99 cup. If you put it in the sun for an hour, you might get 0.999 cup.
But you have to leave it out in the sun all day to extract the entire
1.0 cup.
That's how Peukert works. It's only telling you that the faster you
discharge a battery (i.e. the higher the current), the fewer the
amphours you can get out before it reaches its "cutoff" voltage. The
amphours aren't gone -- they are still in the battery. You can continue
discharging to get them all out -- just at a lower current. You also
don't need to replace the "missing" amphours on charge.
--
Ring the bells that still can ring
Forget your perfect offering
There is a crack in everything
That's how the light gets in.
-- Leonard Cohen, from "Anthem"
--
Lee Hart's EV projects are at http://www.sunrise-ev.com/LeesEVs.htm
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