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Home » Electrical Systems » Electrical Documentation for the Third Degree Burner |
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PARENT CATEGORY Electrical Systems |
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LINKED PROFILES Third Degree Burner |
ARTICLE
Electrical Documentation for the Third Degree Burner OCID cn00000256 |
LINKED CATEGORIES Batteries Electrical Systems Vehicle Wiring Design |
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Electrical Documentation for the Third Degree Burner by Alex Tung created 12/10/1999 submitted 2/12/2003 10:44:02 AM Includes System Overview and details/thoughts on Array, Power Point Trackers, Batteries, Shunts, Wiring, Connectors, Fuses and Switches for the Third Degree Burner, as raced in Sunrayce 99. Quick reference parts list System Overview Although you might think that the electrical power system for a solar car would be pretty complicated, there's actually not much to it at all. Boiled, down, the electrical system simply connects the two sources of power - the solar array and the batteries - to the electric motor. Depending on how much energy the sun generates (and how much of that energy the solar array harnesses), the motor will take power from the solar array or the batteries. Any excess energy from the array goes into the batteries. The main power system of the car consists of wires that route this energy wherever it needs to go. Of course, there are many details that make the electrical system more complex than that, but knowledge of the basics of electricity will allow you to understand them all. Main Power System - Batteries - GP Batteries, 9 12 Volt NiMH modules The batteries are the main power source of a solar car (especially when solar energy is lacking, like in Sunrayce '99!). The size, weight, and capacity of a car's battery pack will greatly influence its design and performance. Most solar cars require more power than a single battery can provide, and so teams must use multiple batteries in some combination of series and/or parallel configurations to get the capacity and voltage that they want. Our team this year purchased two battery packs - one lead-acid pack, and one nickel metal hydride (NiMH) pack. Each consisted of nine 12-volt batteries connected in series to form a 108 V pack. The lead-acid batteries were used for testing purposes as we waited for the NiMHs to arrive. The NiMHs are rated at 45 Ah (Ampere-hour, unit of charge used to describe battery capacity) (See battery section for more information). - Array - American Solar Energy, 14.5% efficient cells, ~ 1 kW - Power Trackers - 7 Brusa/Solectria Model ?? The peak power trackers (PPTs), when used correctly, ensure that peak power is harnessed from the sun's energy. On the Third Degree Burner, seven PPTs were used for the seven different sections of solar cells. Each power tracker takes two inputs from a section of solar cells and optimizes the amount of current it outputs according to a complex arrangement of circuit elements to achieve peak power at all times. The outputs of the seven power trackers are placed in parallel with each other, the battery pack terminals, and the motor controller power inputs. This allows the motor controller to draw power from the array and batteries. Each power tracker also has a number of cutoff settings. The peak output voltage of a tracker can be set by changing two resistors on the underside of the tracker. - Shunts We use precision e-meter shunts to measure the battery, motor, and array current in the car. These shunts are basically very small resistors machined to the thousandth of an ohm in resistance. Using a small resistance in the path of the current you want to measure allows you to measure that current as a number proportional to the voltage across the shunt. If you have a .001 ohm resistor and 10 amps running through it, the voltage will read 10 mV. They are called e-meter or ammeter shunts, because this is exactly how those types of meters measure current in a circuit. Shunt ratings come in a mV to A ratio, which tells you the general operating parameters for that shunt. A 50 mV/100 A shunt, for example, will read 50 mV across its terminals at 100 A. For array current, a 50 mV/50 A shunt sufficed, but for measurements of battery current and motor current, 50 mV/100 A shunts were used. - Wiring, heat shrink Wiring should be kept as short as possible to reduce power loss (after all, every wire has a finite resistance!), but should be long enough as to not be a hassle when switching components in and out. The Third Degree Burner had the misfortune to be designed without a physical electrical system in mind, and so the electrical box was made as modular and flexible as possible. The car ended up having a mass of wires, which fed up and over the electrical box into the car (not the ideal situation). The ease of disassembly and shifting about was useful, but having an immobile but well planned electrical system would be preferable. In selecting a wire gauge, you must take into account the peak current that the wire will see, as well as the weight of the wire, flexibility, and volume. We used 4 gauge stranded welding cable for most of our heavy wiring (motor, array, and batteries), but 18 gauge or smaller wiring for smaller components (brakelights, horn, fluke). Always use stranded wire, as solid wire is hard to work with and tends to brake more easily. Whenever you wire up the system, be sure to have some heat shrink tubing available as insulation for the various connections. Colored tubing is not necessary but can add an artistic flair to your design (or a clever color coding scheme, though electrical tape wound around the cables works well, too). - Connectors, ring terminals Two main kinds of connectors were used for the main electrical wiring of the car (the big thick wires) – Anderson SB Connectors and PowerPole Connectors. We used them mainly because they were free and had proven worthy in the past. The SB connectors have two terminals , which is useful for battery, array, and motor cable routing. The PowerPole connectors are single terminal but can be linked together to form a, say, triple pole terminal (very useful for motor phase wiring and switch wiring). Be sure to choose your wire gauges before requesting these connectors, because they come with specific terminal lugs, and although using a 1/0 lug on 4 gauge wire is possible (be sure to crimp the hell out of it!), it’s not ideal. For smaller wiring schemes, ring terminals were the product of choice. Ring terminals are easily purchased at Fry’s (when they’re in stock), as are the terminal blocks they connect to. You may be tempted to use spade terminals instead, but beware that you have to be sure that the terminal block screws won’t come loose. You must account for a whole lot of vibration in a solar car. Also, be sure to crimp AND solder the terminals or they could come off very easily. - Fuses A fuse is an electrical system’s last line of defense. It’s basically a special kind of wire that opens a circuit if too much current passes through it. This protects the devices on either end of the fuse from taking too much current. The fuse is generally placed on the high end of the circuit, so that the positive terminal of the device is not at high voltage when the fuse blows. Fuses come in two types – slow and fast blow. Slow blow fuses can handle their peak rating of current for a few seconds before they open the circuit. Fast blow fuses open immediately when they reach their peak current. Fuses usually have a voltage rating as well, which should be chosen at or above the maximum voltage of the system. Fuses are needed in any electrical circuit with current-sensitive components (and that’s pretty much everything!). In the case of the Third Degree Burner, there are fuses for the array and motor (the motor fuse is the first component out of the battery pack). Switches 12 Volt System - Blinkers - Horn - Fluke power 1242 words | tungsten
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