@texases. Are you telling me that electric car motors are like CVT transmissions? I sort of remember the Citicar of the 1970s having different windings that changed as one depressed the pedal.
If this is the case, we could have wonderful debates about whether multiple speeds vs infinite speed motors are better.
No transmission, just variable speeds via the ‘gas’ pedal. Don’t ask me how…
I’ve seen an electric motorcycle that offers gearing choices that change the range of the motorcycle, but those gearing choices can’t be made during the ride. The settings are changed before the ride.
As I remember the first Tesla (the sports car) was originally supposed to have a two-speed transmission, but that turned out to be too complicated/expensive/whatever, so they went with just one gear (there’s a fixed gear reduction between the electric motor and the drive axle, it’s 9.73:1 for some versions of the S, I read). Seems to be working out fine in all the subsequent Teslas.
Could the Tesla’s power/speed be regulated by a square wave DC to AC generator? Increasing and decreasing the hertz ratio would easily control speed with little wasted current.That had been my SWAG.
Why would anything that is battery-operated convert from DC and AC? Converting from DC to AC is very inefficient. Many of our plug-in appliances convert AC to DC (hence the big square plug), but as far as I know, anything that runs on batteries has a DC power source and a DC motor.
Well…
“Tesla motors use Induction motors. Speed of the motor is controlled by frequency of supply. Since Tesla uses battery to store power ,an inverter is used to convert DC to 3 phase AC supply. Also tesla uses regenerative braking to convert the kinetic energy into electrical energy and store it in battery.”
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you can control what power goes to the wheel and its funner.
I think that is true of all vehicles .
Yes! Tesla uses an AC induction motor. If it were hooked to home electrics it would be driven by a steady 60 hz signal from the power company. To change speeds, you change the windings to change the timing and rpm.
Modern electronics can vary the DC-to-AC frequencies by a wide range. The Tesla’s power invertors can send a low frequency, 2 Hz, for example for slow rpms to 180 Hz or more for high speeds. It can reverse the same amount pretty easily. Modern electric AC forklifts are driven the same way. DC battery through a variable frequency invertor.
Not these days. Modern invertors reach 92-95% very easily.
@Whitey-- I wonder about d.c. to a.c. conversion myself. I know that solar panels produce d.c. which is stored in batteries. There are inverters that convert the d.c. to a.c. Why not have more things that operate on d.c. For example, I just converted light fixtures in the church I attend by replacing the 4 foot fluorescent tubes with 4 foot LED tubes. The LED tubes have drivers on the end of the LED tube that, as I understand, convert the 60 Hz 125 volt a.c. to about 10 volts d.c. Wouldn’t it be simpler to have LED tubes that operate directly on d.c.?
As far as motors are concerned, there have been d.c. motors for years. The downtown of my hometown had its own power plant that generated d.c. power. The plant was coal fired and the steam produced not only powered engines to drive the generators, but the excess steam was pumped through the downtown area to heat the buildings. Years after the downtown was powered by a.c. off the grid, the plant still generated the steam to heat the downtown and still generated some d.c. power. One large church had an organ blower motor that ran on d.c. and a special line was run from the power plant to the church long after the rest of the building was powered by a.c.
As I understand it, d.c. motors are series wound and can start under heavy loads. I know that there are repulsion start/induction run motors that start as a series wound and then a centrifugal switch switches the motor to an induction run.
It would seem to me that a d.c. motor that instantly produces full torque would be the best motor for a battery powered car.
@Mustangman. Your comments about varying the frequency to vary the speed of an induction motor reminded me of an article back in the early 1950s with plans on how to build a device that would control the speed of a record player motor. In those days, the motor drove an idler wheel that rotated the turntable at 78 rpm. Vinyl records were beginning to become popular that required the turntable to rotate at 33 1/3 rpm. The circuit would change the 60 Hz frequency to the motor so that the new “long playing” records could be played.
It was probably cheaper and more satisfactory just to replace the record changer with one that would play the 78 rpm records, the 33 1/3 records and the 45 rpm records. The speed changes were accomplished with a mechanical step pulley.
Not usually. On net metered solar systems the invertor is tied directly to the incoming power with no storage. Storage systems double the price of the install. Most solar doesn’t use batteries. Those that do would need DC-DC convertors at the least. Some places, like Hawaii and California are requiring batteries, though, from what I read.
I think it will be more likely to convert America to metric than to have the entire world convert to AC. AC was chosen over DC before quantum mechanics(and the semi-conductors that operates based on it) became an idea. While modern electronics can change DC voltage efficiently, AC voltage was easier to convert 100 years ago with a simple transformer.
Today, there are regions where AC is generated at power plants, converted to DC and transmitted as HVDC (high voltage dc), then step down again at local region and converted back to AC just because you cannot change the wiring in every house in the world. Supplying DC has advantages over AC. You don’t need to match frequency and phase. Power factor, where you’re trying to drive the consumer’s device that’s lagging behind the grid, is not an issue with DC. There’s no skin effect. You can safely place high voltage transmission lines close to where people live because you’re not producing electromagnetic wave.
A dc motor in an electric car would mostly likely not be series wound. Friction at the brushes eats up energy and will wear out. I’ve seen blender with covered holes that are meant for access to the brushes when they needs replacing. Modern dc motors are brushless. They use hall sensors to determine the spinning magnet’s location and electronically switch on and off appropriate coils. However, brushless motors do have their drawbacks. For one, they usually use rare earth motors.
Also, spinning magnets produces eddy current in other parts of the motor even when you’re coasting and that wastes energy. Induction motors have no spinning magnets hence it doesn’t have that issue.
As I’ve said before, using the full torque of a motor at low speed is inefficient because the motor does not produce any back emf and allow the full voltage of the source to produce a high current through the winding. High current gives you high magnetic force for the torque that you very much enjoy. But it also produces a lot of wasted heat.
You can use short gearing to allow the motor to get out of that low speed inefficient range asap. But a high speed rotor is subjected to aerodynamic drag.
Electric motors have a efficient range of operation and some electric cars uses a multi speed transmission to keep them there. Tesla toyed with a transmission before giving up. BMW i8 has a 2 speed transmission for the front motor. Some formula e cars have 5 speeds.
I agree with you about A.C. When I think about solar panels for home use, I thought the D.C. generated might go directly to LED bulbs.
I realize that the rpm of induction motors depends on the frequency of the A.C. current. This may be a better way to propel an automobile–i.e. controlling the frequency of the A.C. applied to an induction motor than using a D.C. motor.
Prior to the introduction of AC power to diesel electric railway locomotives, the engineer would start accelerating the locomotive with the 4 or 6 traction motors connected in series which served to maximize torque but limited speed. When the locomotive reached a speed of approximately 15 mph, the engineer moved the “transition lever” which changed the traction motor connections from series to parallel, which allowed greater speed but limited torque. By the end of the 1950’s, automatic transition had become the norm
@old_mopar_guy. I wonder if some of the old time locomotive engineers preferred to shift the transition lever manually rather than have the transition from series to parallel done automatically. I suppose the younger engineers would prefer the automatic transition.
As an old Mopar guy, had Chrysler corporation made the locomotives, the engineer would back off the throttle at 15 mph and the transition from series to parallel with the traction motor connection would occur. (As an old Mopar guy, you remember the “,lift and clunk” semi automatic transmissions where you released the throttle to make the shift.
You cannot just hook up LED to a DC power source. Diodes, including LEDs, has a forward voltage of around 0.7V (LED is around 1.5V). Below that, essentially no current flows through. Slightly above that and its current increases with voltage exponentially. LED is actually a very small diode wrapped in a relatively large, light diffusing lens. If you supply too much voltage, let say 0.3V above that forward voltage, the diode will be destroyed by the heat it generates.
For simple LEDs in your appliances, they are connected in series with a current limiting resistor because it is the simplest solution.
But current limiting resistors are inefficient when you need more light than indicators on your appliances. LEDs are commonly hook up to LED drivers that are similar to buck converters. LEDs are still connected in series to a resistor, albeit one with very low resistance whose purpose is to sense the current passing through rather than limiting current. When too much is detected, the electronics will cut the power from the supply until the LEDs’ current drops to an acceptable level. Hence, the driver provides energy on an as needed basis rather than continuously wasting energy through a resistor.
Edit: since most LED drivers are powered by AC, there’s a rectifying bridge converting ac to high voltage dc before the actual sensing and switching electronics. Switching electronics, which was not available during Edison’s days, is how high voltage main can drop to your cell phone’s voltage. It switches on the main power to charge up a capacitor on the output side until it gets too high, then cuts that power until
the output voltage drops too low.
I think part of your post was cut off.