h a l f b a k e r yBaker Street Irregulars
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Install, somewhere in the engine compartment, a high efficiency 120 Volt 60 Hz inverter, probably producing three phase output.
Convert as many of the vehicle's electrical loads as reasonable to run on this AC power.
Since using higher voltage results in requiring fewer amps, we should be able
to use thinner gauge wire throughout the car, and smaller, lighter, electric motors.
The reduction in weight of copper wiring and electric motors sizes should offset the added weight of the inverter.
Note that, unlike "42 volt" car concepts, which also supposedly allow lighter wiring systems, this idea doesn't suffer from electrical arcing in various user controlled switches (like window switches, power locks, etc).
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Whoa there. Why three-phase? |
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Also, if "42 volt car concepts" suffer from arcing, why won't
a 120V system? Also, surely it'd be better to go for the
more normal 220/240V? |
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Also also, if you've got 220V (or even 120V) running around
a car, you're going to need the same safety measures as
are used in domestic electrics. |
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Also, according to one link on 42V cars: "The programs may
be pushed out
due to current economics" - some people really can talk and
think independently. |
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What, has the Sterling-Amp exchange rate plummeted or something? |
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There's a historical analogy going on here, somehow. Consider the power distribution system alongside vehicles: |
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* Started as individual low voltage dc generators: vehicles 6V
* Voltage increased: vehicles 12V, 24V, 42V
* Changed to alternating current: goldbb
* Individual generators joined together
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The final step, then, is to join all the cars together using 3 phase power lines. |
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Like a herd of electric elephants. |
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Herd of electric elephants? Yes, of course I have. |
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3 reasons I blasted this idea: |
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1: The reason you see the DC typically stop at 42V battery (48V live) is because that is the maximum that is considered "touch safe". Anything higher than that wil have much higher safety measures, a new area for cars and mechanics used to 12V. Past that, there is really no reason not to keep going to 300+V for the main setup, and keep using lower voltages for the misc lights and things around the car. Even at 12V most wire is already small and dainty. Converters are not. |
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2: The main appeal of AC is the ease of power transmission via generators straight thru transformers. Your electronics rectify this to DC before using it. In a car, the batteries provide a DC system. No point in converting to AC then back to DC again. It wouldn't even help the motor driver, which produces a frequency that varies with speed. |
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3: Electrical arcing becomes worse with higher current, but much much worse with higher voltage. I assume you are thinking about zero-voltage switching where the power is switched at the low V area of the sine wave. This is sophisticated for a switch. If you are going to do this, the best way to control arc damage is to use low voltage and low current (signal only, milliamps) in the mechanical switches, and solid state to switch the actual power to the device.
It is also the only option safety wise, unless you want high voltage going through those window buttons that routinely get coffee spilled on them. |
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There's a lotta development going on in this field. High voltage motors, some AC, some DC, are used for propulsion. 42v was an industry-standard proposal to reduce power losses on DC motors and cables for high-load accessories like the AC compressor, and to allow stop-start systems and electric power assist of the brakes and steering. The logic was that it would be more efficient to power these items electrically than with a mechanical connection to the engine.... engine speed varies widely, accessory needs don't.
In practice, power loads have been refined down so that most things can be powered by 12v (steering and brakes), and variable-ratio transmissions added to accessory drives to cut power losses.
12v lives on because it's established, therefore reliable and cheap. On something like an electric window motor, the added costs and weight of 42v components would outweigh any advantages - more effective to add gauge width to the cable. |
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At a cetain point, you need a large series of cells to step up the voltage to 300+, so there's a practical limit beyond where you're inviting a long series of battery resistances. |
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