Linear alternator discussion

[theropod2]

Linear alternators are at the heart of those "battery-less" flashlights that you shake back and forth to light the LED. Their problem, as I see it, has little to do with the alternator design, rather the energy losses when reversing the mass of the moving magnet (or coil assembly) at the ends of each cycle. Add to that frictional losses on the moving magnet (or coil assembly) which are likely to be much greater than losses on a well made bearing for a rotating mass. Those two factors I think make an inexpensive efficient linear alternator impractical.

Though it's technical problem little bit critical.But i think Linear alternators have greater efficiency. also more compact because of it's higher output for a minimum amount of power required to turn it.

Sorry, but linear alternators are NOT more efficient than a dual disc axial flux alternator. Just not possible. Also, a linear alternator cannot operate as smoothly, because of reciprocity of mass, as a spinning axial mass, and thus must have a shorter mechanical life than an axial flux alternator.

RS

[Ian S C]

The linear alternator is the ideal way of generating power with a free piston engine, there is only two moving parts, the displacer, and the power piston, magnet, makes quite a compact unit, the important bit to get is a high enough frequency, preferably somewhere about 50 or 60 Hz, but 20 Hz is OK, the lower the frequency the more iron required in any transformer connected to the alternator, and the more difficult it is to smooth the current if converting to DC. Ian S C

[theropod2]

Sorry Ian, but that's not right. The linear alternator must stop its motion at both ends of the stroke. That time spent at BTC and TDC is wasted. The reciprocating motion also requires acceleration from a dead stop to full speed and again return to a dead stop. Only at the mid point of the motion would the magnet(s) be at top speed. Also it would be very difficult to arrange the linear alternator magnet(s) flux lines to cross both sides of the field coil(s). The axial flux dual disc alternator will offer little extra resistance to turning until a load "cut-in" speed is reached. This optimal operational RPM can be tuned with the discs diameter, air gap, magnet strength, coil wire gauge, number of turns in the coils and arrangement of multiple phases to closely match the output of any prime mover. I say watt for watt of engine input a properly matched, multi phase, dual disc axial flux alternator will produce more watts out than the best linear alternator possible. The physics of electromagnetism, because of the axial flux from two magnetic field lines cutting across the coils, must produce more power than any arrangement of a single field line. Increasing magnet strength in the linear alternator will cause inductive heating and the coils will suffer if pushed to produce power. There's just no way a linear alternator, with the same magnetic mass, coils and engine input can match a properly matched axial flux machine.

R

[GREEAD]

Hi there, I can confirm the engine shown in the picture is used by Viessmann inside a Mchp boiler, this is one of our customers and just one of the applications. The engine is a 1kW electrical output engine with linear alternator, its made by Microgen Engine Corporation ltd; I am the group technology and program director for them. We have made more than 10,000 engines and have many million run hours on engines.

[theropod2]

Hi there, I can confirm the engine shown in the picture is used by Viessmann inside a Mchp boiler, this is one of our customers and just one of the applications. The engine is a 1kW electrical output engine with linear alternator, its made by Microgen Engine Corporation ltd; I am the group technology and program director for them. We have made more than 10,000 engines and have many million run hours on engines.

So why can't I buy one in the USA, if this is possible what are the details?

R

[Ian S C]

The main advantage of the linear alternator on the Stirling Engine is that it has no mechanical linkageas in a crank shaft, making it very compact, some allowance can be allowed for the stop start, the magnetic armature can move past a number of pole pieces per stroke. They can't be too bad if Microgen have built 10,000 of them.
Ian S C

[Wolfhart Willimczik]

Just released:
“Breakthrough in linear alternator design”
http://www.wolfhartindustries.com/linearg1.htm
For all – and specially for the ones involved in the development of linear alternators for licensing and cooperation.
Wolfhart Willimczik
Physicist & owner of Wolfhart Industries

[Sameman]

Does anybody use HDD Voice Coil Motor like linear alternator? How easy to connect working cylinder and VCM? Please help - where can I get example?

[Tom Booth]

I just discovered that there is an abundance of information about these linear alternators to be found in downloadable PDF form by searching for the acronym:

NASA/LA or just NASALA (caps, probably unnecessary)

I'll post links to anything I find of importance as I sort through it all, which, by the looks of the search results, could take days or weeks.

What I'm mainly interested in is what kind of intellectual property / patent restriction might exist.

It looks, so far, like "STAR™" may just be a trademark not a parent on the technology or alternator configuration, which seems to go back quite a ways.

Government / NASA projects typically avoid proprietary technologies. So far I have been unable to locate any actual parents covering these "STAR" alternators, and flexure bearings are nothing new.

[Tom Booth]

The planar spring or flexure bearings is an essential part of a linear alternator type Stirling engine generator.

I thought it might be nice to see one in action. I came across this video recently while looking for videos of Ringbom Stirling engines.

About half way into the video Blade Attila attaches a planar spring to a thermal lag Stirling.

Skip to middle of video:

https://youtu.be/zV8edaVOUlg?t=160

This could be adapted to many other types of Stirling engines, I think, possibly reducing friction to near zero in some instances, this unusual "single cylinder" Ringbom for example, possibly.

https://youtu.be/MIS11qIoM8I

[Tom Booth]

In that last video it can be seen that the displacer is held in place with a similar internal planar type rubber "spring" of sorts.

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In the NASA free piston Stirling two such planar bearings are used, which is necessary to support the piston and/or displacer for frictionless operation.

I have some plans for using the sheet silicon rubber oven mats in a similar way as planar bearings. I think they may be sufficiently rigid, if stretched just tight enough, are very heat resistant, strong, tough and economical.

IMG_20211205_213107458.jpg (152.51 KiB) Viewed 4221 times

[Tom Booth]

In looking for information and sources for linear generators, I received a response from John Corey, co-inventor of the STAR linear generator, who has been very helpful and informative.

It seems the INFINIA linear alternator, though similar, is not a STAR alternator.

He wrote:

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And also provided some sources that show the construction of the Infinia alternator in greater detail, I'll show and/or link to in another post.

[Tom Booth]

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https://www.researchgate.net/publicatio ... plications

[Tom Booth]

Aside from the crank, this is a variety of linear generator.

https://youtu.be/jAJld70e6XU


Though, I'm not especially impressed with the output of this demonstration engine, I'm wondering about the possible advantages. Just a good solid steel rod being the only moving part, could be driven by a free piston Stirling, possibly of the thermal lag variety, so the rod and piston still constitute just one moving part, aside from planar springs for frictionless operation.

To ramp up the power, maybe have a ring of such generators wired in series attached to the same shaft, something like this, maybe ?

Resize_20220922_061342_2469.jpg (300.49 KiB) Viewed 4187 times

The weight of all the steel rods could add up, but if oriented in an upright position, the rod(s) could be suspended and/or counterbalanced in some way perhaps? At least the bulk of weight of all the magnets and coils is eliminated .

Sorry about the crude and inaccurate drawing. The coils should actually be inside the ring magnets and stationary, so only the rods need to move.

A generating ring could, I think, be on both sides, (or above and below) so as the rods are withdrawn from one set of magnets/coils, the other set is activated.