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. 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
_____ From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of Scott Kuzma Sent: Tuesday, January 15, 2008 1:33 PM To: [email protected] Subject: Re: [FLEAA] Volts and Amps...the saga continues. Shawn, Thank you for the clarification. I was uncertain of that equation. However, it is my understanding that the follow arrangement would be identical as far as power output...and capacity, since : 120 volts @ 100 A/H vs. 240 volts @ 50 A/H With my mechanical background, I relate this as being similar to having an engine produce half the torque as the other engine, but at double the engine speed, making the HP figure identical. From the little education that I have in electrical, at one point I learned that having more voltage allows you to run with a lower amperage requirement. I.E. an EV with a 60volt system would require much more (double-ish) amp load than a 120volt system in order to accomplish the same work. Am I correct to calculate that if I ran more voltage (a 240 volt system with 54 amp/hours) versus a system with less voltage (120volts with 108 amp/hours), which will actually require the same number of batteries...exactly twice as many as previously theorized. The question is: Am I confusing Amp/hours with amps in general as a load. I do not think that I am, but am looking for clarification. Also, what is the answer to the method of wiring up the diodes to maintain a proper charge/discharge setup so that they don't fight each other? ~Best, Scott Kuzma ---------- Forwarded message ---------- From: "Shawn Waggoner \(FLEAA\)" <[EMAIL PROTECTED]> To: "'FLEAA Mailing List'" < [email protected]> Date: Tue, 15 Jan 2008 08:46:48 -0500 Subject: Re: [FLEAA] listserv Digest, Vol 6, Issue 17 Scott and all, On batteries and capacity, voltage is additive in a series configuration, but capacity is constant. Voltage is constant in parallel, but the capacity is additive. Here are a couple of quick diagrams I worked up to show the difference: The first is a series circuit and you can see that the voltage is additive but the pack is still only 50Ah. The second one has the batteries in parallel so you only have a 12V pack, but the capacity is increased. If combine the 2 concepts into a series-parallel configuration, like below, you get a higher voltage and increased capacity. I also found a good battery primer on Intersil's site: http://www.intersil.com/data/an/an126.pdf Hope this was helpful, Shawn
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