Hi Scott,
The difference on Amps versus Amp-Hours is amps are a point in time measured amount of current and amp-hours is a measurement of amps over time. So what does that mean? You can measure the amount amps that a load is drawing, in the case EV's, the load would primarily be the motor. At any given point in time the motor will be drawing a certain amount of amps. An amp is a measurement of current. On batteries, you can measure how amps a battery is putting out at any given time. However, amp-hours are a measurement of capacity. A battery might have a rating of 60 amp-hours (Ah). This means this battery should be able to deliver 60A for one hour or 10A for 6 hours. The Amp Hour rating tells you how much amperage is available when discharged evenly over a 20 hour period (C/20 rate). The amp hour rating is cumulative, so in order to know how many constant amps the battery will output for 20 hours, you have to divide the amp hour rating by 20. Example: If a battery has an amp hour rating of 75, dividing by 20 = 3.75. Such a battery can carry a 3.75 amp load for 20 hours before dropping to 10.5 volts. (10.5 volts is the fully discharged level, at which point the battery needs to be recharged.) A battery with an amp hour rating of 55 will carry a 2.75 amp load for 20 hours before dropping to 10.5 volts. As far calculating various factors in an EV, one or two people have put together some great sites with EV calculators on them. Here is one of the better ones: <http://www.geocities.com/CapeCanaveral/lab/8679/evcalc.html> http://www.geocities.com/CapeCanaveral/lab/8679/evcalc.html Shawn _____ From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of Scott Kuzma Sent: Thursday, January 17, 2008 9:46 AM To: [email protected] Subject: [FLEAA] Clarification of Ah needed..... 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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