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Good News for Electric Vehicles

This has nothing to do with Prius, Leaf, or Tesla.   This is about on-the-ground EV enthusiasts’ work.

SEVA

Up until a few years ago, electric motors were lucky to get 40% efficiency.   That is, of 100% of the charge in the battery pack, the motor was only able to use 40% of that energy, the rest being lost to heat, mechanical friction, and the “cogging” effect of newer neodymium-magnet motors.   So for a given range, you needed to include 60% more batteries than you would if efficiency were 100%.

Enthusiast-built electric cars are always packed to the gills with batteries, as people want the car to go as far as possible on a charge, or as fast as possible, and the limitation is the volume inside the car that can accommodate batteries.   No revelations have come from any of the Big Three auto makers, as advancement is not generally in their best interests.

So we have one insolent upstart (Tesla Motors), developed by a billionaire (Elon Musk), which has actually created a production electric car that can be bought today.   Their first Roadster and second Model S are excellent cars which deliver what was promised, (although there were early production delays)   They use one of the best electromotive drivetrains, the very good AC Propulsion drivetrain.

However something that has always bothered me about Teslas is that the battery pack is made up of thousands of small 18650 cells, rather than larger lithium-ion batteries designed for electric vehicles.   For those who don’t know, cylindrical battery cells are designated by a number, being DDLL.L, IOW diameter and length.   So an 18650 cell is 18mm in diameter by 65.0mm long, or .71″x2.56″.   AA are 14500 and C are 25500.   The Tesla Roadster uses 6,831 of these 18650’s!   This is just not the proper application for these batteries.   There are a number of companies which make electric vehicle batteries, including Japan’s GS Battery, China’s ThunderSky, and others.   These were available when the Roadster was designed, and although some had a higher Ri (internal resistance) than today’s batteries, the GS Yuasas were quite good.

For motors, my preference up to now for cars has been the Siemens line of electric train motors.   I was an early proponent of AC (as opposed to DC) electric traction motors, many years ago before anyone at SEVA had heard of AC motors or Metric Mind (a Russian EV enthusiast in Oregon).   So I was pretty much alone.   AC motors are more efficient, and they can recapture energy while braking through regeneration, which DC motors can not.

But there’s a new type of electric motor which was actually invented by a 28 year-old dude in Alaska.   He was dissatisfied with the way the fully-charged battery in his phone would show Lo, after only a few minutes in an Alaskan Winter.   And he wanted to build an electric vehicle that would get him the 800 miles from his home to Bearflanks, er Fairbanks and back with one charge.   So he studied — Flynn Parallel Path, Bedini battery rejuvenation, back EMF harvesting, and other innovations, and built the first “axial-flux motor”.

In conventional motors the flux flows radially through the air gap between the rotor and the stator.   However in this motor the flux flows parallel to the axle of the motor.   One current design has 21 coils and 4 neodymium magnets, each with a 50-pound pull force.   The Flynn Parallel Path related setup of the magnets essentially nullifies the magnetic force except when it is called, thus removing essentially all the “cogging” effect of the motor as it spins.   The motor thus doesn’t have to overcome cogging anymore, inherent to normal neodymium motors, increasing efficiency.   Notice in the below simulation, the red areas of highest current density at the bends;   these are where the copper bars are most likely to burn out when the motor is overloaded.   Also notice the low current density at the commutator/loop interface?   This is a very good place to have low current density, as connections are always making/breaking and with high current there could be huge arcs!

Coils in an axial-flux motor are run by simple square wave AC with a 50% duty cycle, in contrast with a typical AC 3-phase traction motor which requires a complex waveform that changes by load, and thus a custom matched inverter.   This new type of motor is so efficient that it can be a fraction of the size of older motors with the same torque and power.   And it is amenable to supercooling/superconducting, so someday it could be 1/3 the size, or 3x the power!

The below simulation shows how the copper loops are commutated as the armature turns.   The two commutators are fixed toward the center in cyan.   As the armature turns the (dark blue) loops are activated sequentially to pull the armature around successively.   The fixed blue objects are the neodymium magnets.   So optimal timing is determined by placement of the commutators.

Axial Flux MotorBeing a true scientist, this inventor didn’t patent his designs, but shared and collaborated freely on the internet.   As a result, several companies have since picked up and are manufacturing his design (with no compensation to him), and one will invariably patent it.   YASA Motors’ products claim an astounding efficiency of greater than 95%! (at what point in the load curve, etc, etc?)   If this is true, I never thought this could be possible.   Further, owing to the way an axial-flux motor is designed, they can be stamped out in high volume which eventually will vastly reduce their cost as more are made.

Electric motors by their nature have very high torque at low RPM, in fact they can bring their max rated torque to bear at almost 0 RPM, in contrast with a typical car engine which offers its max torque in the band of 3,000-5000 RPM. (a ‘motor’ is electric, an ‘engine’ is fueled)   As a result most enthusiast-built EVs do not have a transmission, as it’s a transmission’s function to make things easy for the engine at low RPM and keep it in its torque-band.   YASA’s 750 axial-flux motor claims continuous power of 75kW (102 horsepower) and peak power of 100kW (136 hp). (Peak power can be exercised for short periods without burning out the motor, depending on cooling)   A typical economy car has horsepower in this range, yet the 750 is only 2.6″ thick and 14″ diameter!   It only weighs 73 pounds whereas a typical engine weighs hundreds and is filthy. (whups, no one uses that word anymore)   Why the size disparity?   Because engines are ~20% efficient, at best.   So the 750 could fit in a typical transmission’s bell housing and the rest of the under-hood space is for batteries.

And my guess is that soon someone will figure out that you can make the coils fixed and magnets the armature, eliminating the need for commutation, and allowing total control of the waveform thus performance of the motor. (shh, don’t tell anyone…)

EV geeks will be aware of NEDRA and the records set by White Zombie, KillaCycle, and others.   John Wayland (plasma boy) pioneered tandem electric motors –two DC motors bunged together– in his White Zombie, to double horsepower and torque.   Needless to say this doubles current draw as well and halves range.   Whether to tandem two 750’s, two 400’s or one of anything depends on your vehicle and goals.

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