GB2558516A

GB2558516A - Electrical generator

Info

Publication number: GB2558516A
Application number: GB1608198.6A
Authority: GB
Inventors: Webster Craig
Original assignee: Pavegen Systems Ltd
Current assignee: Pavegen Systems Ltd
Priority date: 2016-05-10
Filing date: 2016-05-10
Publication date: 2018-07-18
Also published as: GB201608198D0; WO2017194937A1

Abstract

An electrical generator (10) configured to convert axial kinetic energy into electrical energy comprises a housing (100), an actuator (200) movable axially relative to the housing and a rotatable member (300) being rotatable relative to the housing and cooperating with the actuator such that axial movement (220) of the actuator causes rotation of the rotatable member. The electrical generator further comprises a stator fixedly attached to the housing (130) and a rotor (120) configured to receive rotational kinetic energy from the rotatable member configured to interact such that rotation of the rotor relative to the stator results in production of a three-phase alternating current. The actuator is transfers kinetic motion to the rotatable member comprise a ball screw (301) and a ball nut (201). A plurality of balls (400) is located in a helical channel (430) formed from a first groove (330) and a second groove (230) reducing the friction in operation. A ball return channel is also provided between the first end of the helical channel and the second end of the channel opposite the first end.

Description

(54) Title of the Invention: Electrical generator

Abstract Title: Electrical generator using a ball screw to transfer kinetic motion to the rotor.

(57) An electrical generator (10) configured to convert axial kinetic energy into electrical energy comprises a housing (100), an actuator (200) movable axially relative to the housing and a rotatable member (300) being rotatable relative to the housing and cooperating with the actuator such that axial movement (220) of the actuator causes rotation of the rotatable member. The electrical generator further comprises a stator fixedly attached to the housing (130) and a rotor (120) configured to receive rotational kinetic energy from the rotatable member configured to interact such that rotation of the rotor relative to the stator results in production of a three-phase alternating current. The actuator is transfers kinetic motion to the rotatable member comprise a ball screw (301) and a ball nut (201). A plurality of balls (400) is located in a helical channel (430) formed from a first groove (330) and a second groove (230) reducing the friction in operation. A ball return channel is also provided between the first end of the helical channel and the second end of the channel opposite the first end.

FIG. 1

At least one drawing originally filed was informal and the print reproduced here is taken from a later filed formal copy.

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FIG. 2

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Relationship of lead screw ratio (pitch) to rotor inertia

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Lead screw pitch mm

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Electrical generator

Background

The disclosure relates to a generator for generating electricity from impulse forces that may be harnessed from pedestrians or other traffic moving on a surface.

WO 2011/138585 discloses a motion converter which converts linear displacements caused by traffic-related impulse forces, to be converted to rotational motion for driving the rotor of an electricity generator.

UK patent application GB 1516234.0 discloses a flooring system that employs linear displacement electrical generators for converting impulse forces that land on the flooring system into electrical energy.

Since linear displacements derivable from traffic-related impulses may be intermittent and each may be of the order of 5 to 10 mm, there is a desire to improve efficiency of conversion of each linear displacement to electricity generated.

Summary of disclosure

According to the invention, there is provided an electrical generator configured to convert axial kinetic energy into electrical energy, the electrical generator comprising:

a housing, a rotor and a stator, wherein the stator is fixedly attached to the housing; an actuator movable axially relative to the housing and biased in a first axial direction;

a rotatable member being rotatable relative to the housing on a rotation axis parallel to the first axial direction, the rotatable member configured to cooperate with the actuator such that axial movement of the actuator in a second axial direction opposite the first axial direction causes the rotatable member to rotate about the rotation axis;

wherein the rotatable member is configuration to transfer rotational kinetic energy to the rotor;

wherein a first one of a set comprising the actuator and the rotatable member comprises a ball screw and a second one of the set comprises a ball nut; and wherein the electrical generator comprises a plurality of balls between the actuator and the rotatable member.

Brief description of the drawings

For a better understanding of the invention, and to show how the same may be put into effect, reference is now made, by way of example only, to the accompanying drawings in which:

Figure 1 shows a cross-sectional representation of an electrical generator in accordance with the invention;

Figure 2 shows a perspective view of part of a flooring system including a plurality of electrical generators and a plurality of triangular tiles;

Figure 3 shows a graph showing relationships between properties of a ball screw and generator rotor moment of inertia; and

Figure 4 shows an exploded view of the electrical generator of Figure 1.

Detailed description of an Electrical Generator in accordance with the disclosure

Figure 1 shows a first embodiment of an electrical generator 10 in accordance with the invention.

As can be seen in Figure 1, the electrical generator 10 comprises a housing 100, an actuator 200 and a rotatable member 300. Each generator 10 further comprises a rotor 120 and a stator 130.

The housing 100 comprises an annular surround 160 that surrounds a substantially circular aperture 170 through which part of the actuator 200 projects. The annular surround 160 has an upper surface that lies in a first plane of the electrical generator 10 and the actuator

-3200 projects in an axial direction having an axis that is substantially orthogonal to the first plane.

The actuator 200 is operatively engaged to the rotatable member 300 such that axial movement of the actuator 200 in the axial direction results in rotational movement of the rotatable member 300 about the axis, as explained in more detail below.

The actuator 200 is biased in a first axial direction 210 (which is upward in the orientation of Figure 1) and electricity is generated as a result of movement of the actuator 200 in a second axial direction 220 which is opposite the first axial direction 210 (and is downward in the orientation of Figure 1). In Figure 1, the actuator 200 is positioned in its lowermost (actuated) position relative to the housing 100. Accordingly, the actuator 200 is at the end of its travel in the second axial direction 220 and acting against the biasing in the first axial direction 210.

The actuator 200 comprises an actuation surface 260 configured to receive a force (directly or indirectly) by which the actuator 200 is caused to move axially in the second axial direction 220.

The annular surround 160 covers an annular cavity 180 in which the stator 120 and the rotor 130 are located. The stator 120 is fixedly attached within the annular cavity 180 so as to prevent movement of the stator 120 relative to the housing 100, whether axial or rotational. The rotor 130 is located radially within the stator 120 such that the rotor 130 is rotatable but its axial position is fixed. The rotor 130 is located at a periphery of a flywheel 350.

As the skilled person would readily appreciate, it may be appropriate in alternative embodiments to reverse the positions of the stator 120 and the rotor 130 such that the rotor 130 is radially outside the stator 120.

The rotatable member 300 is engagable with the flywheel 350 via a clutch arrangement 340 such that rotational movement of the rotatable member 300 is transferrable to rotational movement of the flywheel 350 which means that the rotor 130 rotates relative to the stator 120. Suitable arrangements of magnets and coils may be provided (not shown) on the stator 120 and the rotor 130 to generate electricity from the rotation of the rotor.

-4In the illustrated embodiment of Figure 1, the rotatable member 300 comprises a ball screw 301 and the actuator 200 comprises a ball nut 201.

A plurality of balls 400 (e.g. ball bearings) is located in a helical channel 430 between the ball screw 301 and the ball nut 201. In this way, the plurality of balls 400 reduces an amount of friction that would result from using a conventional screw and nut combination in the same context. Furthermore, a shallower thread angle is possible than with a conventional screw and nut combination.

The helical channel 430 is formed from a combination of a first helical groove 330 in the ball screw 301 and a second helical groove 230 in the ball nut 201. The first helical groove 330 complements the second helical groove 230 such that together they form a helical the channel 430 having a circular cross section for accommodating the plurality of balls 400.

As the skilled person would readily appreciate, in alternative embodiments (not shown), it may be that the rotatable member 300 comprises a ball nut and that the actuator 200 comprises a ball screw.

The actuator 200 further comprises a plurality of pins 240 each pin extending in a direction parallel to the first and second axial directions 210, 220. The housing 100 comprises a plurality of apertures 140, each of the apertures 140 being configured to receive one of the plurality of pins 240. Each pin 240 and its respective aperture 140 is located radially outward relative to the rotatable member 300. The pins 240 are distributed evenly around the actuator 200.

The pins 240 and apertures 140 may act to retain the relative positions of the actuator 200 relative to the housing 100. Furthermore, the pins 240 and apertures 140 may prevent or at least reduce the likelihood of the actuator 200 moving other than in a direction that is in the axial direction. For each pin 240 and its corresponding aperture 140, a biasing member 140, in particular a spring 140, is located between the pin 240 and the aperture 140 such that the actuator 200 returns to an upper position once a force is removed from the actuator 200.

-5The biasing members 250 may each be a helical spring that may for example be torsional or compressional.

As the skilled person would readily appreciate, in alternative embodiments (not shown), it may be that the pins are located in the housing 100 and that the apertures are located in the actuator 200.

As mentioned above, the electrical generator comprises a clutch arrangement 340 between the rotatable member 300 and the rotor 120.

In the illustrated embodiment, the clutch arrangement 340 comprises an overrunning sprag clutch that enables continued rotation of the rotor 120 by inertia after rotation of the rotatable member 300 concludes. The length of axial movement of the actuator 200 combined with the screw pitch of the ball screw and ball nut are such that full axial travel of the actuator 200 from an uppermost position to a lowermost position is 10 mm and converts to approximately 720 ° of rotation of the rotatable member 300. By using an overrunning sprag clutch 340 that drives a flywheel 350 on which the rotor 120 is mounted, rotation of the flywheel 350 (and hence the rotor 120 may continue after the actuator 200 changes direction in response to biasing forces applied by the helical springs 140 to move the actuator 200 upwardly once a force on the actuator surface 260 is removed. Accordingly, the flywheel 350 may rotate for considerably more than 720 ° of rotation and thereby for a longer period of time.

Without a clutch, the rotor 120 would switch direction of rotation when switching between the downward and the upward strokes of the actuator 200. Furthermore, the presence of the flywheel 350 is such as to increase a period of time for which the rotor 120 passes the stator 130.

The electrical generator 10 of the illustrated embodiment further comprises a deep-groove bearing 360 that is located in a recess 191 in a bottom surface 190 of the housing 100 furthest from the actuator surface 260. The deep-grove bearing 360 is configured to facilitate rotation of the rotatable member 300 relative to the housing 100 whilst preventing axial movement of the rotatable member 300. The term deep-grove bearing 360 is known to the skilled person as referring to a type of bearing that resists axial movement of a rotatable member that rotates relative to the bearing. In short, given that inner and outer

-6portions of the bearing comprise deep grooves to hold balls of the bearing in place, axial movement of the rotating member is substantially prevented.

The housing 100 further comprises apertures 101 for fixing means (not shown) by which the electrical generator 10 may be attached to a surface such as an existing floor.

A flexible gasket 150 is provided between a radially exterior perimeter of the actuation surface 260 and a radially interior perimeter of the annular surround 160 of the housing 100. In this way, a gap between the radially exterior perimeter of the actuation surface 260 and the radially interior perimeter of the annular surround 160 is filled by the flexible gasket 150 at all axial positions of the actuator 200.

The flexible gasket 150 may be fastened to the annular surround 160 by a first gasket ring 161 that is fixedly attached to a perimeter of the annular surround 160 by a plurality of fastenings 162 such that the flexible gasket 150 is held between the annular surround 160 and the first gasket ring 161.

Similarly, the flexible gasket 150 may be fastened to the actuator surface 260 by a second gasket ring 261 that is fixedly attached to a perimeter of the actuation surface 260 by a plurality of fastenings 262 such that the flexible gasket 150 is held between the actuator surface 260 and the second gasket ring 261.

The flexible gasket 150 may comprise or be formed of: rubber; neoprene; TPV; TPE; and/or a polymeric material.

The housing 100 may comprise an upper housing 102 and a lower housing 103 such that the annular cavity 180 is formed between the upper and lower housings 102, 103. The upper and lower housings 102, 103 are fastened together by conventional fixings 104 such as threaded bolts and correspondingly threaded holes.

In a variation on the first embodiment, that is not illustrated, the electrical generator may further comprise a ball return channel that connects a first end of the helical channel with a second end of the helical channel opposite the first end. In this way, balls may constantly circulate around a closed loop formed by the helical channel and the ball return channel.

-7 In still further variations on the first embodiment, the electrical generator may comprise a plurality of helical channels distributed lengthwise along the ball screw. Each of the plurality of helical channels may comprise its own ball return channel that connects a first end of its helical channel with a second end of its helical channel opposite the first end.

The electrical generator 10 may further comprise two or more adjustable feet (not shown) extending from the housing 105 to enable its height and orientation to be adjusted.

The actuation surface 260 may comprise a plurality of pivots (not shown) via which one of a plurality of tiles 20 may be supported as explained further below. Each pivot may allow one tile 20 to tilt relative to the actuation surface 260, and preferably also to slide relative to the actuation surface 260.

The actuation surface 260 may comprise a support gasket (not shown) which may preferably be made of resilient material to muffle the sound of footsteps. Preferably, the gasket comprises or is formed of: rubber; neoprene; TPV; TPE; and/or a polymeric material. Tiles 20 may be supported on the support gasket.

In some embodiments, the support gasket comprises a plurality of rollers. The rollers may be seated in complementarily-shaped indents in the actuation surface 260. Rollers may be any suitable shape, e.g. cylindrical, but are preferably spherical or generally spherical. The rollers are complementary to the indents in the tiles 20. The rollers and indents can allow rotation of the tile 20 in multiple degrees of freedom.

Screw pitch is defined as distance from the crest of one thread to the next is an axial direction. In the context of a ball screw, therefore, screw pitch is a distance at one radial position at an exterior of the screw between one position in the helical channel and an adjacent position in the helical channel.

In the event that the screw pitch is too small, friction may prevent rotation of the screw in response to axial movement of the actuator 200 altogether. In the event that screw pitch is large, the amount of rotational movement that is generated by axial movement of the actuator 200 is too small only a small rotation of the rotor 120 will be produced which limits the amount of electricity generated.

-8Figure 3 shows the relationship of rotor inertia (which scales with cost) to screw pitch in order to accelerate the rotor to a constant kinetic energy from a pulse of constant force input. The constant kinetic energy may be 3.7 J. A screw pitch of 10 mm is shown to result in 0.0014 Nm of torque per N of axial force. A screw pitch of 5 mm is shown to result in 0.0007 Nm of torque per N of axial force.

In one embodiment, the screw diameter is 16 mm, the screw pitch is 5 mm, the maximum length of travel of the actuator 200 is 10 mm and the length of time over which energy is obtained from an impulse force on the generator is 200 ms. The resulting torque is 0.0007 Nm per N of axial force.

As is well known, electromagnetic induction results when coils pass through a magnetic field. The movement of rotor coils relative to stator coils thereby results in electromagnetic induction.

The electrical generator may be configured such that alternating current is produced. For example, three-phase alternating current may be produced. The alternating current may be rectified to produce a direct current output.

As a consequence of the relatively short travel of the actuator 300 and the nature of the actuation force being that of an impulse and the eddy currents flowing in the windings, the properties of the electromagnetic induction may be highly variable.

The applicant has determined that efficiency can be significantly improved by using the generator to produce a fixed constant current. In doing so, the voltage induced in the coils and the speed of rotation of the rotor may be allowed to vary considerably in order to achieve the fixed constant current. For example, for a fixed constant current of 350 mA, voltage may be allowed to vary between 3 V and 100 V.

Using the generator to produce a fixed constant current in this way has been found to minimise l²R losses in the windings of the stator and/or rotor and, furthermore, to minimise frictional losses.

Implementation of the fixed constant current output may be achieved by use of a flyback converter.

-9The fixed constant current may be between 150 mA and 500 mA, preferably between 350 mA and 400 mA.

Description of a flooring system comprising the electrical generator

Figure 2 shows a flooring system that makes use of a plurality of electrical generators 10 and a plurality of tiles 20. In this embodiment, the floor tiles 20 are triangular and are arranged in a tessellated pattern. The plurality of tiles collectively defines a floor surface on which people may walk or vehicles may pass.

Each generator 10 comprises a housing 100 and an actuator 200 that is movable with respect to the housing 100. Each generator 10 is arranged to generate electricity from linear motion of its actuator 200 relative to the housing 100 in a downward direction in an orientation of use. Each actuator 200 is biased in an upward direction in an orientation of use to provide a restoring force following displacement.

As can be seen from Figure 2, each generator 10 supports a plurality of tiles 20. As a user walks across the tiles 20, the support 10 will be displaced from an equilibrium position. This will generate electricity using the generator 10, as explained in more detail below. The support 10 will then be returned to the equilibrium position by the biasing means (described in detail later in relation to Figure 2). The support 10 will move only over small distance so as to avoid an unpleasant sensation for the user. However, the cumulative effect of many steps from many users over a large area can generate a significant amount of electricity.

The tiles 20 are pivotably supported by each generator 10. It will be noted that this can prevent trip hazards from arising, since neighbouring tiles will move together.

In the arrangement of Figure 2, when a user steps on the flooring system, each footstep will move the actuator 200 of one (e.g., if the footstep lands on a generator 10), two (e.g., if the footstep lands on the boundary between two neighbouring tiles 20), or three generators 10 (e.g., if the footstep lands in the middle of a tile 20).

- 10Similarly, each tile 20 is supported by a plurality of actuators 200. Thus, a user stepping on a tile 20 can provide motion to each of the corresponding actuators 200, and thereby generate electricity via the corresponding plurality of generators 10. In doing so, each tile 20 will displace vertically and/or tilt by a small degree.

Each tile 20 is generally planar with a first major surface 21 and a second major surface 22. The first major surface 21 forms an upper surface in use. The second major surface 22 forms a lower surface in use.

The tiles 20 substantially tessellate to form collectively a substantially continuous floor surface. By “substantially” is meant that the tiles 20 do not meet exactly along each edge, but that a small gap is provided therebetween (to allow for relative rotation of neighbouring tiles 20). Furthermore each tile 20 meets at a generator 10, where a gap is provided between the multiple tiles 20 supported by that generator 10. The gaps along each edge and at each generator 10 are only small in comparison to the surface area of the floor surface taken up by the tiles 20, and so they can be said to substantially tessellate.

Preferably, the major surface of each tile is generally shaped as a triangle (most preferably, an equilateral triangle). By “generally shaped” is meant that the tile need not have perfectly sharp corners. Since the corners are only truncated by a small amount, they can be said to be generally triangular.

Preferably, each tile 20 is supported by exactly three generator actuators 200. That is, an actuator 200 may support each corner of a tile 20. The tiles 20 are biased by the biasing means acting on the actuators 200 to be flat and level when a user is not standing on the floor surface.

By using this arrangement of tiles 20, the possible degree of tilting of the tiles 20 may be larger than if other arrangements were used. For example, if a user steps on the corner of a square tile 20, the opposite corner could protrude by a corresponding displacement. However, with triangular tiles, the movement of one corner represents the rotation of the tile about one edge, and so undesirable deformations of the floor, such as producing trip hazards, can be avoided for equivalent displacements.

- 11 The longest dimension of each tile 20 is no more than 100 cm. Preferably, the longest dimension of each tile is in the range 300 mm to 700 mm.

For a square tile 20, the longest dimension would correspond to the distance between to opposite corners.

In the context of a generally triangular tile 20, the longest dimension is the length of one edge. This substantially corresponds to the distance between actuators 200.

For the flooring system 1 to allow sufficient motion, it is preferable that each tile 20 has a thickness T that is as small as possible. This also reduces the need to excavate a large space for installation. However, the tiles must carry the weight of a user and so they must be rigid and strong.

Further detail regarding the types of flooring system 1 in which the generator might be used is provided in the Applicant’s co-pending UK patent application, GB 1516234.0.

Claims

CLAIMS:

1. An electrical generator configured to convert axial kinetic energy into electrical energy, the electrical generator comprising:

a housing, a rotor and a stator, wherein the stator is fixedly attached to the housing; an actuator movable axially relative to the housing and biased in a first axial direction;

a rotatable member being rotatable relative to the housing on a rotation axis parallel to the first axial direction, the rotatable member configured to cooperate with the actuator such that axial movement of the actuator in a second axial direction opposite the first axial direction causes the rotatable member to rotate about the rotation axis;

wherein the rotatable member is configuration to transfer rotational kinetic energy to the rotor;

wherein a first one of a set comprising the actuator and the rotatable member comprises a ball screw and a second one of the set comprises a ball nut; and wherein the electrical generator comprises a plurality of balls between the actuator and the rotatable member.
2. The electrical generator of claim 1 wherein the rotatable member comprises a first helical groove and the actuator comprises a second helical groove that complements the first helical groove such that the first and second helical grooves together form a helical channel having a circular cross section for accommodating the plurality of balls.
3. The electrical generator of claim 2 wherein each of the plurality of balls has a diameter that corresponds to a diameter of the circular cross section of the helical channel.
4. The electrical generator of claim 2 or claim 3 wherein the diameter of each of the plurality of balls is selected to minimise friction and to maximise conversion of axial to rotational movement.
5. The electrical generator of any of claims 2 to 4 further comprising a ball return channel that connects a first end of the helical channel with a second end of the helical channel opposite the first end.

- 136. The electrical generator of any preceding claim further comprising a clutch arrangement between the rotatable member and the rotor.
7. The electrical generator of claim 6 wherein the clutch arrangement comprises an overrunning clutch that enables continued rotation of the rotor by inertia after rotation of the rotatable member concludes.
8. The electrical generator of claim 6 wherein the clutch arrangement comprises a sprag clutch:

that enables transmission of torque from the rotatable member to the rotor when the rotatable member rotates in a first direction of rotation; and that prevents transmission of torque from the rotatable member to the rotor when the rotatable member rotates in a second direction of rotation opposite the first direction of rotation.
9. The electrical generator of claim 8 wherein the first direction of rotation results from movement of the actuator in the second axial direction and the second direction of rotation results from movement of the actuator in the first axial direction.
10. The electrical generator of claim 6 wherein the clutch arrangement comprises both an overrunning clutch and a sprag clutch either separately or as a single clutch.
11. The electrical generator of any preceding claim further comprising a flywheel between the rotatable member and the rotor.
12. The electrical generator of claim 11 when dependent upon claim 6 or any claim dependent upon claim 6, wherein the flywheel is between the clutch and the rotor.
13. The electrical generator of claim 2 or any claim dependent upon claim 2 wherein the helical channel is one of a plurality of helical channels each accommodating a plurality of balls.
14. The electrical generator of claim 13 further comprising a plurality of ball return channels, one for each of the plurality of helical channels, wherein each ball return channel connects first and second ends of its respective helical channel.

- 1415. The electrical generator of any preceding claim further comprising a deep-groove bearing configured to facilitate rotation of the rotatable member relative to the housing whilst preventing axial movement of the rotatable member.

16. The electrical generator of any preceding claim wherein a first one of a group comprising the actuator and the housing comprises N pins each extending in a direction parallel to the first and second axial direction, where N > 1; and wherein a second one of the group comprises N apertures, each of the N apertures being configured to receive one of the N pins.

17. The electrical generator of claim 16 wherein the N pins are distributed evenly around the actuator or housing.

18. The electrical generator of claim 16 or claim 17 wherein each of the one or more pins and its respective aperture is located radially outward relative to the rotatable member.

19. The electrical generator of any preceding claim wherein the actuator is biased in the first axial direction by one or more biasing members.

20. The electrical generator of any of claims 16 to 19 wherein the actuator is biased in the first actual direction by N biasing members, each of the N biasing members being located between one of the N pins and its respective one of the N apertures.

21. The electrical generator of claim 19 or claim 20 wherein each of the one or more biasing members or the N biasing members comprises a helical spring.

22. The electrical generator of claim 21 wherein the helical spring comprises a torsional helical spring.

23. The electrical generator of claim 21 wherein the helical spring comprises a compressional helical spring.

- 1524. The electrical generator of any preceding claim wherein maximum axial movement of the actuator in the second axial direction causes the rotatable member to rotate about the rotation axis approximately two revolutions.

5 25. The electrical generator of any preceding claim wherein the rotor and stator are configured to interact such that rotation of the rotor relative to the stator results in electromagnetic induction in the rotor and/or the stator which produces three-phase alternating current wherein the electrical generator further comprises:

an electronic circuit comprising a rectifier configured to convert the three-phase

10 alternating current to direct current; and a current controller configured to regulate the direct current to be a fixed constant current.

26. The electrical generator of claim 25 wherein the electronic circuit comprises a
15 flyback converter.

27. The electrical generator of claim 25 or claim 26 wherein the electronic circuit comprises a battery and a diode.
20 28. The electrical generator of any of claims 25 to 27 wherein the fixed constant current is between 150 mA and 500 mA, preferably between 350 mA and 400 mA, more preferably is 350 mA.

Intellectual

Property

Office

Application No: GB1608198.6