Frank (and others),
On the subject of how many Ah needed, I got lost. My anticipated use
would be light cruising at very low throttle loads. Vehicle weight around
2500 pounds. Minimum distance required per charge would be 25 miles in the
city (about 45 - 60 minutes run time), with 50 miles (60 - 90 minutes) being
optimal on the highside. While this would not have an impressively long
range with a small battery size, it would be practical for +90% of it's
use.
I also would imagine that the smaller battery size would enable it to
re-charge (on a 110v outlet) considerably quicker than a much larger pack,
such as Andrew Roddy's eBOX for example. I like the idea of not having to
search for a 220v 50+ amp outlet, and be able plug into nearly any 110v
outlet
~Best,
Scott Kuzma
---------- Forwarded message ----------
From: "Frank Leslie" <[EMAIL PROTECTED]>
To: "'FLEAA Mailing List'" <[email protected]>
Date: Tue, 15 Jan 2008 14:05:00 -0500
Subject: Re: [FLEAA] Volts and Amps...the saga continues.
Scott,
FIrst the easy part, the diodes are placed at the positive end of a series
string with the banded cathode on the plus side. The battery box in "Toot"
the electric boat, 3 strings of two 12V deep cycle, batteries is at
http://my.fit.edu/~fleslie/Toot_Boat/tootboat.htm<http://my.fit.edu/%7Efleslie/Toot_Boat/tootboat.htm>.
Not shown are three large diodes at the near side that sum the power flow to
the main switch (the red handle). The highest voltage battery supplies all
the power until the voltage drops to the next highest string level. (This
boat was a donation to the university.)
With ampere hours, use Ah or even A-h as the symbol, not A/h, which implies
division.
An electric source consists of the electric potential or electromagnetic
force in series with the internal resistance. You can measure a stopped
generator resistance. Maximum power transfer occurs when the source
resistance (really impedance) matches the load resistance. You can measure
the motor resistance with an ohmmeter, but not the source resistance
(usually). Instead, compare the open battery voltage with the loaded voltage
using a low resistance, high power resistor. Suppose the internal resistance
is 3 ohms and you place a 3 ohm resistor across the battery. The voltage
falls to (roughly) 1/2 or half inside and half outside. If a 120V battery,
the 60V with 3 ohms means that the internal resistance is the same, and
maximum power is transferred to the load.
Since the battery is to be matched, very roughly, the motor resistance of 3
ohms and a nameplate rating of 120V indicates the current is 120V/3 ohms =
40A. If you want a drag racer, maybe six minutes is adequate, or 40A times
0.1 hours = 4 Ah. For a long drive road vehicle running 2 hours, the battery
would need 40A times 2 hours = 80 Ah. (Of course, the motor draws different
currents at various voltages dependent upon acceleration.)
The mechanical analogy is the continuously variable transmission, where
torque forces slide the pulley sheaves to let the V-belt move higher or
lower and change the ratio. For electricity, the device is the Maximum Power
Point Tracker (MPPT, but not Microsoft!). Solar controllers use these.
System design must begin with the load and then work back to get a nominal
system.
Hope this helps, or HTH, as I saw somewhere today.
Frank
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