RPM Wide-speed-range DC Generators --
Description & Specifications
Main Features of our Generators
DC (direct current) generated from wind power is a good combination with photo-voltaic solar panel building-integral on-site installations. Together, solar and wind power is less variable, and thus can reduce battery storage. Installations in structures that increase and limit wind speed at turbines coupled to wide-speed-range generators enable high energy yields with high reliability and low cost, in locations where low average ambient winds are not practical for conventional wind powered generators. In structures shown in this webpage, loads are protected from over-voltage; turbines and generators are protected from severe weather, and bird kills are prevented. Our integral turbine-generator harvests power at low wind speeds, in contrast to existing high friction+cogging+loss generators coupled to turbines on towers, that harvest power at needed voltage only at high wind speeds.
Power generation efficiency exceeds 95% over a 10-to-1 speed range, with DC load current and voltage control by integral switch-mode boost-regulation power interface electronics.
Modular disk assembly affords wide power range selection, with less production parts inventory, to maximize yield from various rotary power drive sources.
Zero cogging torque and no gearing, plus boost-regulation integral DC power interface electronics, provides useful current and voltage regulated generator output DC power over a very wide speed and torque range. So energy yields from wind can be 100 times more than a conventional generator with its shaft coupled to the same size turbine mounted on a tower ! !
That's in addition to delivering far higher power quality (current and voltage control protects loads; never draws power from loads; supplies steady power during low winds and over a very broad speed range; supplies DC current with no ripple). Our higher energy yields are clearly measured and documented. Our current and voltage control, without power disruptions, provide highest quality power from our generator that protects batteries and loads from damage.
Energy yield per total system (including structure that increases and limits wind at turbines) installation cost, in any year, would be at least 10x that of commercially available wind turbines, towers and generators. Service life of our wind turbine and generator would be far greater than those on towers, in our on-site installation that protects it from severe storms and ultraviolet; and ours won't need maintenance.
No gears and hence no gear friction or cogging and far less periodic maintenance, no output disconnect switchgear, and no cooling systems for gear lubricants or generator coolants.
Our generator's DC output current regulation facilitates parallel connection of like generator power interface electronics. And it facilitates parallel electronics power interfaces, connected to stacks of stator disks of the same generator assembly, thus accommodating a wide power range with a small inventory of different parts.
Its DC output power is uniquely compatible with RPM's flywheel batteries as well as all available chemical batteries.
Our Generator Versions
Another version installed in electric vehicles (EVs) or electric power water-craft would augment onboard battery power while affording a healthy exercise option. This version could also produce electric power from health club exercise equipment.
Customized Models for specific applications
Left: Vertical axis version, mainly for coupling to vertical axis wind turbines, over a wide range of power ratings to optimize yield from a wide variety of wind turbine sizes. We have built and tested 2 prototypes that each generate 500 watts at about 1000 rpm, with useful power down to about 85 rpm, that charge a 48 vdc battery pack.
The vertical axis version has a relatively large diameter and large number of axial-field poles, to accommodate direct shaft connection by a flexible coupling to relatively low speed vertical axis wind turbines, and does not need the normal speed-up gearing of conventional generators (which would include drawbacks like friction and stiction and need for periodic maintenance, lubricants and additional bearings).
Left: Horizontal axis version, mainly for coupling to horizontal axis wind turbines, over a wide range of power ratings to optimize yield from a wide variety of wind turbine sizes.
Another version, with foot pedals attached to the shaft at each side, can be installed in an ultra-light electric vehicle, to augment onboard battery charge by generating electric power from a recumbent cyclist driver and/or passenger. This would extend the range of the EV while affording a healthy and convenient exercise option.
Both the vertical and horizontal axis versions provide regulated DC current and voltage to their loads through boost regulators in their power interface electronics. Both are self-starting, and never need to be disconnected from their loads. So they deliver far better power quality, at regulated voltage, optimized for the normally varying mechanical power driving their shaft.
Early applications for our broad-speed-range generators, with mechanical shaft input power supplied by wind turbines, will supply regulated DC current and voltage to a 48-volt DC power bus, connected to 48vdc chemical batteries.
Later version broad-speed-range generators can accommodate higher DC voltages. For example, generator versions that will supply DC power to poly-phase AC inverters, can provide relatively very high quality power synchronized to poly-phase power grids.
Test Setup to Demonstrate Controlled DC Output Current and Voltage over a Wide Speed Range
Testing the RPM Wide-speed-range Generator output current and voltage over variable selected shaft speed and torque is illustrated by the photo below.
DC electric output power and electromechanical power conversion efficiency as a function of shaft speed, for a representative RPM Wide-speed-range DC generator for use with wind turbines, is shown by Efficiency curve and Power curve in left image.
Dashed part of Efficiency curve is zero until generated power exceeds a few watts needed for its integral electronics.
With wind power above these few watts, DC output power increases with turbine speed3.
This generates maximum DC electric power, with optimum turbine torque load varying as speed2.
Our PWM (about 100 kHz switch-mode Pulse Width Modulation) boost-regulated integral electronics output DC voltage and current as a function of speed is shown at left.
Note that output voltage equals load voltage, over entire broad-speed power generation range.
Also note that DC load is protected from over-voltage.
Rectified voltage and current of a conventional self-starting (common alternator type) generator is shown at left.
Note that generated power is zero until its rectified voltage exceeds voltage of its battery load.
Also note that loads are not protected from over-voltage, unless voltage regulation electronics is included between this generator and its load.
Left image shows power to 3-phase grid from a typical wind-farm tower-mount induction generator.
No output voltage or power is generated, unless this generator is connected to the grid, and its speed is higher than needed to synchronize with the grid.
Note that, when this generator is first connected to the grid, brief negative power is drawn; also that its blade pitch and wind angle control, plus gear oil and coolant pumps, consume power even when its circuit breakers disconnect it from the grid.
Wind Power and Yield Calculations
Electric power from a wind powered generator = (.005)(windspeed)3 (swept area)
(wind capture percent / 100)
where power is watts, and wind-speed is miles per hour MPH
swept area is square feet swept by wind turbine blades
wind capture percent is for wind turbine and generator.
Since wind is so variable, average wind-speed is used to predict duration at
each speed, which follows the Rayleigh statistical distribution:
Probable time at each wind-speed V varies according to V / Vavg2 * exp(-.785 * V2 / Vavg2)
where total time is 720 hours/month
Vavg is the average wind speed at the wind turbine.
Probable time at each speed, in hours, for winds from 0 to 50 MPH is plotted below, with probable incremental power KWH (obtained by multiplying power generated in KW at each speed V by mean hours at V) as mean KWH at MPH for 10 MPH average. Probable energy yield over a period such as 1 month is the area under the curve Mean KWH at MPH.
The curve showing Mean Hours at MPH for a 10 MPH average wind speed is determined for a representative location by compiling anemometer and/or Pitot tube recordings, typically available for many locations over decades. If a specific location has a different average wind speed from the 10 MPH average shown above, its Wind Speed axis for the above graph would accordingly reflect the Average Wind Speed for that location, with the same ratios of Mean Hours at MPH to Average Wind Speed, and following the same statistical distribution except for different Wind Speed parameters.
The curve of KW at MPH shows available shaft power from a wind turbine as a function of wind speed. Shaft power varies as the third power of wind speed. Hence the RPM Wide-speed-range generator power interface electronics control output current so that power generated is also proportional to the third power of wind speed. This attribute extracts and produces maximum available power from the turbine shaft over a far wider wind speed range than other generators.
For a wind power installation where average ambient wind-speed is 10 mph that is channeled so 25 mph average wind-speed drives a 40 sq.ft. wind turbine and generator with overall wind capture efficiency of 35%, power generated at 25 mph wind would be about 1 kw, for a simplified average yield of about 720 kwh per month. Probable energy yield, by adding KWH at each wind-speed from winds covering the total statistical distribution, but with power limited at the wind turbine to 8 kw, would be about 1500 kwh per month. Very little energy yield is lost, by limiting the maximum wind-speed at the turbine to about double its average, because wind-speed above that will be so infrequent. Besides protecting the wind turbine, this speed limiting accommodates efficient broad range current and voltage control, and lower required peak power ratings. For example, by limiting wind-speed at the turbine to 50 mph (double the average wind speed at this wind turbine), the generator and power electronics maximum power rating would need to be 8 kw. All power ratings would need to be substantially higher without a speed limit: Power electronics would need to have higher voltage and current limits. Efficiency at low wind speeds would also be less if generator speed is not limited, and buck regulators would be needed to protect battery loads from over-voltage.
My US Patent 7646178 "Broad-Speed-Range Generator" and my patents pending fully describe and illustrate our generator's many details.
Custom wind turbines mounted integral with the generator rotor assembly afford substantial advantages over usual installations with turbines having separate bearings. Integral turbine-generator assembly circumvents need for turbine bearings that also need flexible shaft couplings and critical shaft alignment of generator to turbine.
Conventional Permanent-magnet Generators
Common alternator output voltages substantially vary proportional to shaft speed. Hence they cannot reach output voltage levels high enough to charge batteries or drive DC-to-AC power inverters, until wind speed is relatively high. And if connected to loads with no current regulation, internal losses may cause generator overheating and/or excessive load currents if shaft speed is not limited.
Most have iron poles that tend to align at rotor angles where magnetic
reluctance is minimum, thus causing magnetic cogging torques.
Shaft alignment common practice is laborious and expensive. Despite that high labor and expense, the coupled shafts always incur high friction and mechanical cogging torques, because the coupled turbine and generator bearings inevitably can't be aligned and maintained in adequate alignment, even by the most skilled installers.
Friction and cogging torques prevent startup at low wind speeds. No output power is delivered to DC battery loads until stator voltage plus rectifier forward voltage drops plus (when included) series voltage regulator circuit voltage drops exceed the DC battery voltage. So useful generator power at low wind speeds is forfeited. As the above Rayleigh chart shows, conventional generators that can't produce useful power at low wind speeds harvest under half the average energy over time, compared to RPM generators. They also don't produce power when it is most needed, compared to RPM generators. DC power to loads, without ripple (particularly if for flywheel batteries), generated when most needed, plus load current and voltage control, are RPM generator power quality attributes that are not available from conventional generators.
Conventional Induction Generators
Widely used induction generators can only generate power when their shaft speed exceeds the synchronous speed of the power grid connected to them, to augment grid power. At shaft speeds below synchronous, they would consume grid power, and so must be disconnected as wind speed fluctuates. At shaft speeds where induction generator losses are very high, the grid connection must also be disconnected, because power exchanged fluctuates excessively and internal generator losses can cause generator overheating. Although these shortcomings are widely recognized, induction generators are widely used in wind farms, directly connected to 3-phase power grids with no power interface electronics.
Utilities limit numbers of induction generators connected to them, because they have caused grids to fail due to inherent generator disruptions, power reversals, and uncontrolled phase. Also, wind farms where induction generators are usually installed require very windy locations.
RPM Generator Versions with Integral Wind Turbine and Enhanced/limited Wind-speed
This version circumvents existing high installation costs and shaft coupling problems, because its bearing pair serves as both generator and turbine bearings. Also, its generator speed limiting and broad wind speed range is optimized as a complete system that harvests maximum energy with highest power quality.
A custom VAWT (Vertical Axis Wind Turbine) in a structure that can increase wind-speed at the turbine to nominally 3x ambient, and can limit turbine wind-speed, is illustrated below. For example, in a location where average ambient wind speed is 10 miles/hour, average wind speed at the turbine blades can be increased to 30 miles/hour and limited to 60 miles/hour.
Its custom 4-blade Savonius turbine is integrally attached to our generator's rotor shaft. This avoids in-line shaft alignment problems incurred by the common existing practice of coupling generator shafts to standard turbines that include turbine bearings.
That common existing practice incurs inevitable high mechanical cogging torque and friction loss, high installation labor to align generator and turbine shaft, and need for flexible shaft coupling.
Common practice does not normally include turbine and (more importantly, in many cases) generator speed limiting.
The wind diverters shown increase wind-speed driving the turbine blades moving in the same direction as the ambient wind, regardless of ambient wind direction.
The wind diverters also prevent reverse torque incurred in normal practice, from wind on blades moving in a direction opposite the ambient wind, which normally causes Savonius turbines to harvest only 15% of power intercepted by their blades.
Increasing wind-speed at the turbine to 3x ambient will increase wind power 27x. And preventing reverse torque from wind on the opposite blade side can increase normal 15% harvest of wind power reaching a Savonius turbine through the opening area to over 40%.
The wind diverter structure also includes shutter vanes at its 4 openings that automatically limit wind-speed at the turbine. And the structure can protect the turbine, generator, and associated electronics from rain, snow, and sun, which otherwise cause damage to normally exposed wind powered systems.
Savonius turbines have a rectangular wind-intercept area, which facilitates a matching rectangular wind opening. Thus, most of the wind through the opening is caught by the turbine blades.
A Savonius turbine with more than 3 blades will incur considerably less torque fluctuations as it rotates, compared to those having 2 blades. Those with only 2 blades may not start rotating unless wind is at angles that produce higher torque than their 2 "dead spot angles". This problem is compounded by cogging, friction and stiction, in common wind power generators. Conversely, our integral design 4-blade turbine spin startup will be reliable and prompt, with blade speed almost equal to wind speed.
A profile view of this installation is shown below, with one of many turbine area and channeled wind to turbine and integral generator options.
An example of minimum energy harvest ratio, from our integral turbine-generator in a diverter as shown in these images, which funnels winds to 3x ambient velocity, compared to an identical size conventional Savonius turbine with shaft coupled to an alternator type generator:
RPM compared to conventional Energy Harvest Ratio = (Capture Efficiency Ratio) x (Wind Speed Ratio)3 x (2x speed range)
RPM compared to conventional Energy Harvest Ratio = (40% / 15%) x (3/1)3 x (2) = 144 ! ! !
Total land area needed for conventional small-scale wind turbine towers that can generate as much total power clearly exceeds the roof-top area of this wind diverter installation. Conventional towers are costly. Conventional turbines and generators on towers exposed to storms incur unacceptable failures. Long power cables from conventional towers are costly. Conventional wind power is poor quality and unreliable. So conventional small-scale turbines don't have wide market acceptance.
An on-site building-integral solar plus wind powered installation that can produce far more reliable, far lower cost per kwh generated, better power quality, is illustrated below.
Its dependable, zero-maintenance, low service lifetime electric power cost, and abundant on-site generated electric power, could make connection to central grid power optional.
Installations that channel wind from only 2 directions (compared to the 4 directions possible in the figures shown above) would need 2 openings with wind limiting (compared to the 4 openings shown above). A wind power installation between 2 high buildings would have wind from either of 2 opposite directions. Axial wind turbines are a good choice for buildings compatible with 2-directional wind installations, because their rotational speed can be high compared to Savonius turbines, so the generators they drive can use widely available low cost rotor magnets and so are lower cost.
A custom axial wind turbine HAWT (Horizontal Axis Wind Turbine) may be preferable to a VAWT for this environment. One HAWT can be mounted on our generator shaft extending from one end of our generator assembly, plus a second HAWT on the opposite end, as illustrated below.
This integral 2-HAWT and generator assembly can (like the above VAWT) be in an enclosure that increases wind-speed in it to about 3x ambient and limits wind-speed at the turbine to about double its average in this installation.
HAWT rotational speed is considerably higher than VAWT speed, so our HAWT driven generator can have less rotor pole magnets, and thus correspondingly lower cost.
This integral HAWT design requires less space than common axial turbines requiring a tail so their turbine axis follows wind direction.
This HAWT design does not require slip-rings because its turbine and generator assembly do not need a horizontal rotation axis to follow wind direction. Slip-rings are needed for common HAWT towers, to prevent generator output conductor damage, by excessive twisting as its angle changes to follow wind direction.
Our 2 HAWT turbines are identical to each other. Both turbines harvest power from wind, to drive the generator shaft. The turbine facing the wind can harvest about 45% of wind power passing through its spinning blade area. The turbine at the other side can harvest about 30%. So total power from the generator shaft can be about 75% of wind power passing through this installation. Wind passing the first turbine incurs a rotational speed component opposite the turbine spin, which would reduce power harvested by the second turbine. The rotational wind speed component is reduced substantially by the fin shaped generator mount at its bottom, top, and 2 sides.
Each HAWT has blades with a gradually varying optimum pitch angle vs. distance from their spin axis.
For example, pitch angle at blade tips may typically be about 15o from wind direction; whereas pitch angle where blades are attached to their hub may typically be about 45o, with a gradual pitch angle transition from tip to hub. Blade width is greater near the hub, compared to the tip. So maximum power yield is delivered to the generator, and blade stress at hubs is very low compared to common available axial wind turbines. We have not found any commercially available wind turbines with enclosures as described here. So they are subjected to wind storms. Most don't have variable blade pitch to limit blade speed and stress in high winds. High blade shaft stress at hubs is responsible for many turbine failures of common axial wind turbines.
An example of energy harvest ratio, from our integral turbine-generator in a wind funnel and limit installation as shown in these images, which increases winds to 3x ambient velocity, compared to an identical size conventional tower-mounted horizontal-axis turbine with shaft coupled to an alternator type generator:
RPM compared to conventional Energy Harvest Ratio = (Capture Efficiency Ratio) x (Wind Speed Ratio)3 x (2x speed range)
RPM compared to conventional Energy Harvest Ratio = (75% / 45%) x (3/1)3 x (2) = 90 !!
Along with far more energy harvest compared to equal cost conventional wind turbines on towers, our integral generator and turbine installation can provide far longer zero-maintenance service life, with inherent generator and turbine protection from severe weather.
Both the custom VAWT and HAWT illustrated above should preferably be installed within enclosures providing wind-speed limiting that protect the turbines, generators, and their loads. This wind-speed limiting also enables generator assemblies and their PWM boost-regulated electronics to be built with components having lower maximum power and voltage ratings. This results in lower cost, broader speed range of power delivery to (for example) 48vdc or 170vdc loads, and higher efficiency (resulting in higher energy yields).
Some wind turbine and generator brochures quote their maximum power ratings as if those ratings were the power yield. Actual power and energy yield from such devices is far lower than what they imply. Our generator's output, over a typical wind speed range, can be readily demonstrated by mounting our turbine-generator on a truck and recording power to batteries it charges vs. truck speed, when ambient wind speed is essentially zero. This demo can prove actual performance, of our turbine-generator, and of our turbine-generator in wind funneling and limiting enclosures.
Electric motors that automatically control vane closing/opening make wind-limit adjustments only when wind is high and generator power needs to be limited; so no electric power yield is lost driving the motors.
Since wind funneling and limiting, also protecting wind turbine and generator, are not common practice, educating customers about its advantages will be challenging. But customers might be easier to convince, whose traditional turbines were destroyed by strong winds, or damaged by normal weather, or caused frequent battery failures, or had turbine blades damaged by the sun, or did not harvest even a small fraction of energy levels that vendor brochures imply.
Other advantages of this integral design approach include: Far higher service life and reliability for all UPS elements, with far less maintenance. No need for turbine-generator shaft alignment and flexible coupling. Lower total cost of turbine and generator -- facilitating light-weight low-cost turbines, lower generator peak power ratings and thus lower cost generator and electronics, rain protection, preventing turbine collisions with birds, etc. And our wind power systems will deliver our specified far higher energy yields, with far better power quality, than all others.
The wind-funneling diverters and protective wind-turbine housings shown above are mainly for existing structures. New functional architecture buildings can have exterior walls that funnel wind, with average speed at wind turbines 3x to 5x ambient, as shown below:
RPM Generator and Flywheel Battery in Solar/Wind-Powered Building
Left: Building-integral solar and wind power generation with flywheel battery power storage and regeneration to provide uninterrupted electric power as needed.
Advantages of solar+wind power building-integral installations are:
The building exterior walls channel wind to the turbines driving the generators, which increases wind speed 3x to 5x at the turbines. Doubling wind speed increases generated power 8x. Tripling wind speed increases power 27x, etc.
The generators and wind turbines do not need towers to support them.
Screens around the generators and wind turbines can prevent birds from colliding with turbine blades.
Motors powered by our generators can limit wind speed at the turbines by vane angle control, to provide steady and regulated generator output power during wind storms and to prevent turbine damage. Motor vane angle control is needed only in high winds, when generator output is highest, so no generator power yield is lost to drive the motors.
The building can also protect the wind turbines and
generators from rain and sun. Achieving these exceptional goals requires a
dedicated team of engineers, physicists, and architects, plus resources to
manufacture and implement the technologies described.
Combining wind and solar power reduces energy storage requirements, compared to power from only one option. But reliable, low-loss, long-term energy storage will be essential to most building-integral installations. A brief description of our flywheel battery development is presented below:
Our flywheel battery that stores and regenerates electric power as needed, as kinetic energy of its spinning rotor, from our broad-speed-range generator and solar panel power maximizer electronics
Photo at left shows our 1st version flywheel battery prototype we built and tested, having a non-contacting rotor whose axial and radial position is stabilized by servos.
It is described in Fradella's U.S. Patent 6,794,777.
While its rotor balancing is not critical, its size is scalable, and its probable service life is long, it needss many rotor position and rate sensors and close proximity magnetic bearing servo electronics, due to ground loop problems and signal interference.
Its magnetic bearing servos are difficult to stabilize, and need over 2kw to position a 40-pound rotor.
It has challenging problems that we learned how to circumvent with 2nd and 3rd version flywheel batteries.
Photo at left illustrates prototype tests, with descriptions of main elements, for our 2nd version flywheel battery. It has repel magnet lift, radially stabilized by ceramic ball bearings.
Its integral regenerative motor is inside the rim and its top and bottom rim holders.
The motor stator is fixed to the center shaft. Its four 2-phase stator wires and four connections to two aligned Hall sensors are accessed by a center bore that can be seen at the top of the center shaft.
Main rotor axial lift is provided by the ring magnet shown and an identical ring magnet that it repels upward, in the bottom rim holder. The rotor is radially aligned by a ceramic ball bearing in the top rim holder and another in the bottom rim holder.
An axial preload spring under the top ball bearing and another under the bottom ball bearing prevent ball skipping and sliding, and provide consistent additional rotor lift force to each inner race. Main rotor axial lift is provided by the magnets.
The 4 power (from 2-phase regenerative motor stator windings) and 4 sensor (from 2 Hall-effect devices each aligned to a respective stator winding, that sense rotor spin angle) conductors of the assembly, connect to power interface electronics, which exchanges DC current with a 48vdc power bus.
Fradella's U.S. Patent 8,242,649 "Low-Cost Minimal-Loss Flywheel Battery" fully describes and illustrates its many details.
We are now developing a 3rd version flywheel battery. It has pairs of concentric ring magnets that maintain rotor centering and provide rotor lift force that is stabilized by a single axial servo. The servo startup power to axially position a 40-pound rotor is under 200 watts. It can achieve steady-state rotor position in about one second, and then needs about 2 watts to maintain axial position. It is expected to cost about the same as the 2nd version, and will not incur its size, speed, and service lifetime limitations.
Status of the our broad-speed-range generator and flywheel battery
We developed and tested the generator and flywheel battery prototypes shown above; but none are in production. Prototype tests and demonstrations have been conducted for our 2 wind powered generator versions and 3 flywheel battery versions. Our 3rd version flywheel battery prototype tests are not completed.
The technology shown and described above is described in Fradella's U.S. Patents 4085355, 4520300, 6566775, 6794777, 7646178, 8242649, plus U.S. patent pending 13/080,488 and others in preparation.
Horizontal Axis Broad-speed-range Generator Version and Motor-wheel for Ultra-light Solar-Fitness EV
Left: A "see-through" view of a personal, 4-wheel ultra-light "Fitness EV" that seats 2. PV can be applied on all top surfaces, that would collect more than 1500 watts for several hours daily. Thin-film amorphous PV in window glass can reduce glare and interior heat load from sunlight, comparable to conventional tinted glass or reflective coatings that don't provide electric power.
Intelligent power electronics can enhance this EV, by providing infinitely variable speed control, with synchronized non-conflicting proportional regenerative braking.
With power electronics, its 2 rear wheels are each driven by a brushless regenerative motor-in-wheel, a special version of the motor described in US Patent 4520300. Instead of conventional connection to tire rims, it has springs between the motor housing and rear wheel rim, and between the front wheel hubs and rims. So unsprung mass (only its tires and rims) is very low, and its motor-in-wheel is cushioned from road shock.
This EV weighs 700 pounds or so. Its ultra-efficient motor has cruise control for any speed from zero to maximum. It also controls downhill speed, and regenerates power to charge the battery whenever braking or decelerating.
Optional pedal power supplied by a driver in a recumbent position (where we output the most power without tiring) to our EV version generator (shown in red) can augment solar power. Effort level is selectable, like cardio workout gym equipment. As can be seen from the graphs below, a champion athlete can generate 370 watts almost indefinitely, a physically fit person 180 watts. So a driver, pedaling in daylight with 1500 watts from onboard PV, could travel indefinitely at about 45 mph average speed, carrying a few hundred pounds of cargo, without discharging onboard batteries. This EV would be capable of traveling at speeds up to 75 mph, on mostly battery power, recharged by plugging into a garage power outlet, by its onboard PV, and by pedal power.
Left: Block diagram of ultralight EV with onboard battery power, charged by ac or dc plug-in sources, probably in owner's garage.
Batteries are essential for regenerative braking, whenever the EV's 2 motor-in-wheel brushless regenerative motors decelerate the EV.
While driving, power can be augmented by about 1500 watts from multi-junction photovoltaics on all upper EV exterior surfaces, including its front and rear windows. Also, power can be augmented at any speed, by the pedal-powered generator. A second generator can be easily included for a passenger who might also want the exercise it affords, while extending the EV's range. Pedal effort level can be selected by the user. Depending on the user's fitness level, each generator can output up to 1.5 hp (1100 watts) for brief periods and 0.5 hp (370 watts) for over an hour, as can be seen in the graph below. Total sustained power, from 1 generator and the EV's PV, can thus average about 2000 watts. So the EV can thus be driven for extended durations at speeds averaging 45 mph, without discharging onboard batteries.
If provided in-transit power, via the 2 red extendable contacts shown, on electrified highways, it could maintain 60 mph indefinitely. We need to make the public aware of this simple, clean, very low-cost electric highway option, so politicians will come onboard, and permit the highway infrastructure for it.
Main motor and braking effort may be applied to the two rear wheels, by regenerative bi-directional motor drive and braking, plus a friction brake (as a parking brake, and backup mechanical brake). No motor clutch or gearshift or differential gear is needed. With 2 large diameter motors in the 2 rear wheels, no speed reducer is needed. If the batteries ever fail (and are disconnected), the EV may be driven powered only by PV and/or pedal power. It can be driven forward or reverse at 0-15 mph from an onboard generator driven by pedal power only.
Two red stripes are shown at the EV's rear left side. Early versions may have only an extension cord, to plug into 60 Hz outlets. Until we have electrified highways for EVs, the 2 red extendable contacts shown could be used as charging contacts, automatically extending to engage recessed electrified conductive charging strips, in a future home's garage.
PV and sustained pedaling power can sustain ~45 mph without discharging the batteries. Considerable data from cyclists is available. It's compiled in the chart at right:
Note that the time scale is logarithmic. Also note that a champion 160-pound athlete can output 1.5-hp for several seconds, while a physically fit person can output about 1-hp.
The athlete can sustain about 0.5-hp for well over an hour, while the fit person can sustain about 0.25-hp. A driver wanting to power his vehicle more from his pedaling will probably choose to have 4 onboard 600 watt-hour batteries or less.
This lightweight "fitness EV" might have only 2.5 kwh onboard battery capacity. Its aero drag coefficient could be 0.1 (large area, sloped PV windows, and narrow large-diameter tires, help achieve this). Its frontal area could be 12 square feet. Nickel-metal-hydride, lithium-ion batteries, and ultracaps may soon cost less, and high efficiency multi-junction PV with 2000 watts output may be worth the higher cost for this market segment.
With 10-kw peak motor power, this EV with full cargo load, can accelerate to 15 mph in 2 seconds, 30 mph in 7 seconds, and 45 mph in 20 seconds (mostly on battery power).
Aero drag will increase when interior ventilation is needed, during high driver pedal effort. But that's no problem at speeds up to about 35 mph (where rolling friction considerably exceeds aero drag).
The images below are from 3D CAD models. Analysis shows RPM's generator, with electronics that includes selectable effort level; plus a motor-wheel version of RPM's regenerative motor having a tubular non-rotating shaft that supports its motor-wheel ball bearings and is a conduit for its 8 electrical connections to its power interface electronics, can enable a very low cost no-gas "solar-fitness EV". Spring connections between the motor and wheel rim enable very low unsprung mass; and with its large diameter/width ratio tires, incur low rolling friction (inverse to tire diameter) and smooth ride.
While applications for the "cleantech" electric power products we hope to manufacture and distribute shown above may seem diverse, their technologies are related. And the generator, flywheel battery, plus the ultra-light EV shown above are very compatible with each other and with solar power.
RPM's other 11 webpages also cover sustainable technology we are developing; to improve our environment; increase building and vehicle safety; lessen global dependence on fossil fuels and nuclear energy (and their serious negative consequences); and provide far more convenient and reliable UPS (Uninterruptible Power Supplies). To view them, please click on any of the links below.
Dual-mode Electric Highway Vehicles -- a great way to travel, if relatively low cost infrastructure is permitted
RPM's Minimal-loss Flywheel Battery -- an enabler for reliable UPS, solar/wind powered buildings, electric highways
Building-integral Solar and Wind Powered Buildings -- a serendipity of great converging sustainable technologies
Flywheel Basics Tutorial -- a review of rotational dynamics and some new flywheel battery perspectives
Comparison of RPM's flywheel battery with others -- a somewhat detailed study
Brief Summary of RPM's Business Plan -- what we've done and plan to do for the future
RPM's Resources -- our people, tangible properties, office and lab facilities, etc.
Flywheel Facts and Fallacies
Technology: Public and Business Policy
RPM's UPS can enable future distributed on-site solar/wind power, and more
RPM's brushless regenerative
motor and generator in ultralight EVs
RPM greatly values your interest in this exciting venture, and welcomes your participation.
If you have comments or suggestions, email Dick Fradella at email@example.com
Edited March 2014