Homopolar Generator Power built on Mars

SpaceNut · 2017-05-13 17:09:07

After a couple of time meantioning this type of power generator I think that a topic should be created. Reference post follow:

kbd512 wrote:

If there's a way to construct a stirling engine and a simple electric generator, like a homopolar generator, on Mars using a solar array and a tank of molten salt, then the means to produce electrical power should rate high on the list of "nice to have" items.

kbd512 wrote:

I think Dook has the right idea, as far as vehicle power is concerned.
Electric motors don't require the support infrastructure that internal combustion engines require. There are no lubricants or fuels to manufacture, store, or transport. Current Lithium-ion battery technology is rapidly being eclipsed by graphene-based super capacitor technology. Super capacitors recharge in seconds, can operate at temperatures far outside the acceptable range for Lithium-ion batteries, and have cycle lives measured in the low millions of cycles before capacity is substantially reduced. The fact that the energy density is not as great as it is in Lithium-ion batteries is not that a major problem if the vehicle also has an onboard RTG and solar panels to recharge the capacitors.
If you look at the expected operating lives of RTG's and super capacitors, they're more closely matched than they are when paired with current Lithium-ion batteries which have cycle lives measured in the low thousands of cycles.
It only takes about 62We of power to drive a homopolar generator that produces 1.5v * 1000a. Ordinarily, we can't do anything with that kind of electrical power. The voltage needs to go way up and the amperage needs to go way down. However, super capacitors can recharge quite rapidly with that kind of amperage input with very minor creativity in the charging circuitry (parallel vs series recharging). A 300We RTG can easily produce enough electrical output to drive a small electric motor to turn two or three homopolar generators.
Let's say we have a 339kg (let's just call it 350kg after we add the electrical connectors and charge controllers) super capacitor bank that stores 2.5kWh worth of electricity. This is current commercially available super capacitor technology from Maxwell, model BCAP3400. If the super capacitor is divided into two banks of 120v or 240v modules, then while one bank recharges the other can provide motive power. The generator can recharge the other bank in seconds. It only takes very little power, perhaps 5hp to 10hp, to continue rolling on a road using wheels at a speed of 20kph to 30kph, more like double that using tracks in an off-road environment that's relatively flat and level, so let's say 20hp or 15kW.
Every 60 seconds of continuous power with a 15kW draw from the super capacitor bank is .25kWh worth of electricity, so each capacitor bank stores approximately 5 minutes worth of run time (obviously it will be somewhat less than that if higher output is required and unless we increase the number of super capacitors to contend with current leakage and whatnot). Presuming an improbable 24/7 use and consuming all of rated capacity, that's 288 cycles per day from a device rated for 1,000,000 cycles or 3,472 days (9.5 years, pretty close to the RTG's rated life time of 10 years).
After 10 years, we swap 450kg (RTG / super capacitors / electric motors) or so worth of parts and the vehicle's power train is as good as new. At 20kph to 30kph, we're unlikely to throw any tracks but extra track segments are required, so let's say 1500kg worth of replacement parts every 10 years. The track pads and road wheels can use the tough, very low Tg, and radiation resistant metallic rubber compound NASA's contractors developed for cryogen tank seals, called Thoraeus (sp?) rubber.
I seriously doubt any sizable LOX / LCH4 plant would weigh less than 1500kg, never mind all the storage and transport equipment required for the fuels and lubricants, never mind replacement engine blocks for piston engines or hot sections for gas turbines, never mind the tools and test equipment required to ensure the ICE's are functioning as intended. I can swap electric motors, super capacitor banks, and a RTG with a torque wrench and CarbonX clothing to handle the hot RTG. No individual component of this system would require a crane or winch, either.
Well, there it is. No requirement for liquid hydrocarbon fuels or the massive logistics tail that follows them. Small tracked vehicles, in the Japanese Type 60 class (a small armored personnel carrier; obviously we'd not need the additional armor of an APC) using RTG and super capacitor power, would require about 1500kg worth of replacement parts every decade or so. That seems doable. I could be off by a factor of 2 and we're still talking about far less total tonnage for initial or ongoing operations.

kbd512 wrote:

The graphene-based super capacitors in Maxwell's labs are substantially lighter and have substantially higher capacitance, but you still need a nuclear power source and a homopolar generator to provide 24/7 power.

SpaceNut wrote:

Just taking a peek at the quoted supercapacitor BCAP3400 specifications ratings of 2.85V, 3,400 Farad.
The series resistance of this capacitor is 0.28mΩ for power loss as heat when charging or discharging to provide power to the circuit of choice. It has to be in a temperature controlled enviroment as the operation temperatures are Minimum -40 C, Maximum 65 C... with Maximum Continuous Current (ΔT = 15°C)9 131 A RMS, Maximum Continuous Current (ΔT = 40°C)9 211 A RMS bad news is that much like lithium batteries temperature heat degrades not only the working farads but also causes the series resitivance to also increase with both of these making the available charge to output for use less over time quickly the hotter you get it.
The farads to load account for the discharge time before its empty. Series test current was 100 amp's but if you want this device to last you will need to drop that to 50 amps and make pararell circuits to be able to have the power that we would need from them. The next problem with series charging is cell voltages will not be equal which is the same problem for lithium batteries.

kbd512 wrote:

SpaceNut,
My last post was very off-the-cuff since I was busy with other things. My math was wrong as a result. The total mass isn't that far off, though. In retrospect, the new K2 cells, not the BCAP3400 cells are what we'd want for this application. Maxwell's K2 cell model number is "BCAP3000 P300 K04". The K2 cell's nominal voltage is 3.0v, capacitance is 3000F, maximum stored energy is 7.2Wh/kg, nominal mass is still 520g (same as BCAP3400), and nominal cell dimensions are still 60.7mmD x 138mmL (same as BCAP3400).
To generate 120vdc, a minimum of 40 K2 cells per module must be connected in series. We'd probably use 48 cells per module, 8 modules per bank, and 2 banks per vehicle installation. Each installation contains 399.36kg of K2 cells and stores 2,875.392kWh of electrical power. To deliver 15kW of output to a 120V or 240V electric motor, the amperage draw would be 125A [EDIT: draw is 125A for all modules in one bank or 15.625A per module, at 120V or 240V].
P = I * V
so...
15,000W = 125A * 120V (requires 8 modules with 48 cells per module)
or
15,000W = 62.5A * 240V (requires 4 modules with 96 cells per module; more realistic input voltage for an actual EV motor)
[Edit:
or even more realistic for the latest EV's...
15,000W = 31.25A * 480V (requires 2 modules with 192 cells per module; falls in line with actual EV motor operating voltages)
The reason EV motors use high voltages is to diminish resistive losses (electricity converted to waste heat) during power transmission and to reduce the diameter and thus mass of the copper conductors. The electric motors found in Chevrolet and Tesla electric vehicles are all in the 300V+ range and higher voltages are quite common in EV racing motors. Google "YASA Motors" for examples of high voltage EV motors. Although YASA's motors are intended to run at high RPM, motors can also be designed to make nearly all of their torque at much lower RPM ranges. DARPA has funded development of motors for electric aircraft that are excellent examples of motors designed for lower RPM ranges.
Power loss is defined in the following equation:
P = I^2 * R
I used 120V as the voltage in my examples because most people are familiar with the 120V that comes from their wall outlets. This is unrealistic for a power train with minimal cooling requirements.
I should also define what I mean by a module. The bus that carries the current to the electric motors is separate from the physical super capacitor modules. To ensure that each super capacitor module in a bank is easily handled without mechanical assistance in the form of winches or cranes, an actual unit would use tool-less slide-in removable modules containing no more than 48 cells. That equates to 24.96kg on Earth or 9.4848kg (a little less than 21lbs) on Mars. There will also be an associated thermal management system mass, in the form of heat pipes and aluminum plates, added to the mass of the super caps.
The charge / discharge controllers would be built into the wiring bus as separate removable modules. To use a 480V motor, at least 4 of the 8 modules (192 cells) have to be connected to the bus. The 192 cells at nominal charge are charged to 576V, so voltage regulation electronics are also required. An input/output or charge/discharge voltage regulation system is common to all EV's.]
Either way, current output is well below the maximum current limitation for individual cells. Your comments about individual cell charge level apply equally to battery or super capacitor modules and both types of power packs include circuitry that adequately resolve such issues.
Our best electric motors are only about 95% efficient, so these figures are obviously not representative of the actual output requirement to deliver 15kW to the tracks of a tracked vehicle to maintain 20kph in an off-road environment. To figure out what the actual power requirement is, there are a series of relatively accurate but complicated calculations to determine our losses and thus the actual power output requirements to maintain a given speed in a given terrain.
Edit: 95% efficiency means 5% is dissipated as heat and not converted into mechanical work. At a 15kW draw, this correlates to 750W, therefore the actual output requirement to convert 15kWe into mechanical work is about 15.8kW.
If someone is interested in doing that, knock yourself out:
Google "Theory of Ground Vehicles by J. Y. Wong" or...
A Mobility Model for Tracked Vehicles by Karl H. Gleason
US Army TARDEC - Analytical Model for the Turning of Tracked Vehicles in Soft Soils
Australian Army Engineeering Development Establishment - Skid Steering of Wheeled and Tracked Vehicles - Analysis with Coulomb Friction Assumptions
Now, about super capacitor technology...
It's true that the operating temperature requires some thermal control, but no Lithium-ion battery I know of can operate at 150C nor -40C (yes, I'm aware of the fact that some very specialized Li-ion batteries can operate at -40C, but only at substantially reduced discharge rates). Watch the video on this page and tell me what would happen if you did the same things to any Lithium-ion battery:
FastCAP Systems
The FastCAP super capacitors manufactured by the company from the link above currently has NASA contracts for use aboard satellites.
The graphene-based super capacitors still in the labs are the least temperature sensitive of all the current generation super capacitor technologies. In about 5 years, this will become COTS technology because there are so many applications for the technology here on Earth.
Activated graphene breaks record for low temperature storage of electrical energy
Here's a tidbit of what NASA is working on, with respect to low temperature super capacitors:
Low-Temperature Supercapacitors
And then we have Murata's super capacitor technology for different applications:
Murata Super Capacitors
The point is, there are different types of caps available for different storage capacities, discharge rates, and operating temperature ranges. To this day, we basically have a handful of different Lithium-ion cell chemistries to choose from since all other cell chemistries are distant seconds in a variety of ways unless mass, volume, or charge/discharge rates are irrelevant.

kbd512 wrote:

Apart from the ball bearings and shaft, our homopolar generator prototypes are 3D printed because it costs too much to have a machine shop mill the parts. The bearings are ceramic and expensive. The shaft is carbon steel, but could be plastic at the low speeds we're turning it at. The permanent magnets would be nearly impossible to make on Mars.

kbd512 wrote:

Dook wrote:
The main component of a generator is the copper wiring. Where are you going to get the copper from on Mars? Are you going to wrap the copper wiring by hand?
There are no windings in homopolar generators, not even the kind we're building. The quantity of copper required is as minimal as the ampacity of the material allows since our conductors are not solid copper discs. Most homopolar generators generate massive amperages at low voltages, but our voltage problem has been solved by using counter-rotating segmented discs. The prototype produces 24 times as much voltage as a solid copper disc of the same diameter using the radially segmented conductors printed onto plastic. If the rotors had greater diameters, we could further multiply the voltage by using more segments.

kbd512 wrote:

SpaceNut,
The super capacitor / RTG power source requires a homopolar generator (HPG) connected to the RTG. The RTG makes electricity from the Seebeck effect to spin the HPG, the HPG produces otherwise unusable output to charge the super caps, and the super caps either provide bursts of power or regulated output to drive an electric motor or charge a battery.

SpaceNut · 2017-05-13 17:11:52

I believe that it was stated that the generators are low DC voltage but with hugh level output current to which I thin that is where we start using motor contact theory for brushes versus other methods to pass the generated power to the connection points for use.

SpaceNut · 2017-05-13 17:36:55

http://www.gocs1.com/gocs1/Psionics/Hom … erator.htm

http://www.overunity.com/8934/bruces-di … ReUoTVIosY

https://plus.google.com/+IgorKolodrub/posts/MtVgUutjz9c

High-voltage%2BHomopolar%2BGenerator.png

http://www.writeopinions.com/homopolar-generator

The way that the magnet is arranged to the pickup coil it sort of reminds me of capacitor plate theory in someways for how this works...

The top image is simular to how axial flux generator is designed as the coil stays fixed while the magnets move.

SpaceNut · 2017-05-13 21:32:56

http://jnaudin.free.fr/html/farhom.htm

This particular image reminded me of the vcr capstan motor assembly which has multiple poles of coils inside arranged in a 3 phase manner to step the pulse of power into which in turn makes the capstan move. The same capstan assembly once you remove the drivers and rectify is a generator when the shaft is spun creating DC energy.

Critique of the N-Machine Zero Point

SpaceNut · 2017-05-14 21:11:12

Capacitor
cap19.gif?x98918

cap18b.gif?x98918

elderflower · 2017-05-17 04:52:27

I think the power per unit mass of Homopole generators and motors is not very good, compared to a large conventional electrical machine or to a small permanent magnet machine. This is because of magnetic saturation effects as the available iron area decreases towards the centre of the device.

kbd512 · 2017-05-17 10:22:45

Elderflower,

With respect to homopolar generators, it depends greatly on how the generator is designed. If it's not well-designed, then what you say is probably true. That's also true of any other type of poorly designed motor or generator, so it's a lot like saying "a bad design is a bad design". My contention is that most conventional generators are poorly designed, if power input required when the generator is under resistive load is the measure of efficiency. This is the typical method for analyzing generator efficiency.

Let's use an electric motor prime mover as the reference mechanical power input source for our electric generator. At a given voltage input into the prime mover, how does the amount of current drawn from the prime mover's electric power input source vary to produce the mechanical input power needed to overcome the resistance to current flow produced by a resistive load if the objective is to keep the generator spinning to produce a given level of electrical output while it is subjected to the resistive load?

The answer to that question is what electrical engineers determine by model (Maxwell's equations) and experiment (prototyping) to ensure that an electric generator is suitable for an application requiring a given level of output. Ultimately, after losses from known sources are minimized, then it is almost entirely dependent upon the physical geometry of the conductive components moving in the presence of the magnetic field to produce the electrical output. Geometry and direction of movement through the B field either greatly increases or reduces counter-electromotive force, or CEMF, produced as the generator spins. No engineer who wants the biggest bang for their buck (watts in to watts out) will voluntarily subject their generator design to an equal CEMF as it turns, but that's exactly how 99.99% of generators are designed.

Lenz forces aren't entirely absent, but the effect of the Lenz forces exerted on the generator's rotor can either be dramatically reduced or increased as a function of geometry. The greater the Lenz forces exerted, the worse the design is for overcoming a resistive load. It takes very little thought to understand why this is so. Conventional generator design, which involves moving a conductor perpendicular to a magnetic field through the field, is terrible for minimizing CEMF.

You'll never get more output than input if you move the conductor thus because whenever the conductor moves through the B field in that way, there is always an equal force resisting the movement conductor in the opposite direction as it moves past the B field. Heinrich Friedrich Emil Lenz was not wrong, that is exactly what will happen if you do that, and the concept is so well proven experimentally that there is no point in arguing that that happens. For the love of Maxwell, why on Earth would you ever do it that way if the goal is to maximize the output to input ratio? Have we "learned" so much that our scientists and engineers have some sort of mental block when it comes to recognizing what is so obviously true that it's printed in virtually all physics and electrical engineering textbooks on the subject?

Then there's the homopolar generator. Physicists explain what happens, or doesn't happen, like it's some sort of brain fart that Faraday had. There's scarcely a word on the subject apart from the obvious effects, even though what doesn't occur during parallel movement of a conductor through a B field (no equal CEMF in the direction opposite to the direction of movement) is every bit as obvious as Lenz's Law is. You can spin the damn thing with a permanent magnet permanently affixed to the spinning rotor (i.e stationary) and it still produces electrical output. Yet for some reason, almost nobody in electrical engineering is working on this design and none of them can explain why. That's ridiculous.

It doesn't much matter if an electric motor requires at least 746We of input to produce 1hp output. It still works really well, far better than any internal combustion engine in existence. The problem is created when that same attitude is applied to electric generator design. If the requirement is for the input to at least equal the output, then that's a major problem that only worsens if a resistive load is applied.

This is stuff that can be both mathematically and experimentally proven. It does not require any deeper understanding of physics or electricity than we already possess, and no overly-exotic design is required to achieve what I stated. If a couple of guys can do this in their garage in their spare time, then just imagine what people with formal training, years of experience, and access to millions of dollars worth of test equipment and fabrication hardware could accomplish. There are no excuses that pass muster that explain why we're not doing it.

KevinSalyer · 2018-11-27 02:27:27

There is no commutator in this generator

kbd512 · 2018-11-27 08:34:24

KevinSalyer,

First, Welcome to the forums.

Second, is there some point of discussion you wanted to make regarding the design of homopolar generators that produce AC power?

SpaceNut · 2018-11-27 19:16:25

If the coil is stationary then there is not commutator or brushes in the design but that is not what most designs are doing.

Both DC or AC is fine so long as there is plenty of current for the application to draw from....

Mars_B4_Moon · 2022-09-15 16:12:39

'What Is an Electric Generator?'

https://finallygreen.net/main-article-o … generator/

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#1 2017-05-13 17:09:07

Homopolar Generator Power built on Mars

#2 2017-05-13 17:11:52

Re: Homopolar Generator Power built on Mars

#3 2017-05-13 17:36:55

Re: Homopolar Generator Power built on Mars

#4 2017-05-13 21:32:56

Re: Homopolar Generator Power built on Mars

#5 2017-05-14 21:11:12

Re: Homopolar Generator Power built on Mars

#6 2017-05-17 04:52:27

Re: Homopolar Generator Power built on Mars

#7 2017-05-17 10:22:45

Re: Homopolar Generator Power built on Mars

#8 2018-11-27 02:27:27

Re: Homopolar Generator Power built on Mars

#9 2018-11-27 08:34:24

Re: Homopolar Generator Power built on Mars

#10 2018-11-27 19:16:25

Re: Homopolar Generator Power built on Mars

#11 2022-09-15 16:12:39

Re: Homopolar Generator Power built on Mars

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