Just got a Zapino, and am a bit confused about the battery "gauge". It seems to fluctuate depending on power being consumed. On a fresh charge, if I head up a hill, it will drop into the red. Once I'm back on level ground, it returns into the green. The manual is even not much help.
Is this normal behavior? Is it a measure of energy being used at a given time, or one of remaining power?
Thanks in advance.
its a measure of pack voltage.
as a fuel guage, it is useless (unless you are at the end of charge, in which case it is plain)
it is the same for all electric scooters.
for an accurate gauge, i suggest the cycle analyst (formerly known as the drain brain)
its an AH counter, and is very reliable instrument for working out battery state of charge.
Matt
Daily Ride:
2007 Vectrix, modified with 42 x Thundersky 60Ah in July 2010. Done 194'000km
Thanks, Matt. I just wanted to be sure....
Think of a battery cell (or a pack of cells) as a voltage source (that gradually falls as the cell is discharged) in series with a low-ohm resistor, perhaps 0.01 ohms per cell.
Then, when draws 100 amps from the 3.0 volt cell, there would be I x R (100 x 0.01 = 1 volt) drop across the resistor, so the 3.0 volt "ideal" cell would look like it is only 3 - 1 = 2.0 volts.
Drawing 50 amps, a 3.3 volt cell would "look like" 2.8 volts.
Drawing only 10 amps, the "drop" is only 10 x 0.01 = 0.1 volts, so a 3.6 volt cell would measure as 3.6 - 0.1 = 3.5 volts. Of course, things are actually more complex, but this "idealized" internal cell resistance is a reasonable representation for basic understanding.
So, the measured "external" cell (or pack) voltage drops (sometimes drastically) with load.
The commonly-used meter shows a range of the pack voltage, trying to represent the "average" cell's voltage. Since the "useful" range of LiFePO4 cell voltages is something like 2.9 to 3.6, and the expected under-load voltage-drop might be 1.0 volts, the meter might show 3.6 cell-volts and over as "full" and 2.3 cell-volts as "empty".
Cheers, Gary
XM-5000Li, wired for cell voltage measuring and logging.
all true, though i suspect the zapino uses lead acid batteries, 2v nominal (12v for a 6 cell block)
the voltage source value can be modeled by the nrnnst equation.
the internal resistance value can be modeled by the arrhenius equation
if you are using instantaneous voltage and current to work out state of charge, i recommend this:
www.qsl.net/k5lxp/ev/evgauge/evgauge.html
with a bit of trial and error, you can work out where the green, yellow and red zones should be.
i only recommend it for lead acid (and other chemistries with significant and repeatable variance of resistance and voltage proportional to SOC)
definately doesn't work well with LiFePO4
An AH counter can be used with any chemistry (particularly useful when you are running lead acid now and about to upgrade to lithium)
Matt
Daily Ride:
2007 Vectrix, modified with 42 x Thundersky 60Ah in July 2010. Done 194'000km