Introduction: Elveet. Kinetic Charger Powerbank

Once I was on a trip and I had a problem with recharging my gadgets. I traveled for a long time on the bus, did not have the opportunity to charge my phone and knew that I would soon be without communication.

So came the idea to create a kinetic charger, which will not depend on the power outlet.

If you need to recharge your gadget on a trip, hike, on the beach or in transport, then Elveet will help you. You can just shake Elveet or put it in your bag (backpack) and go to work (go hiking, to the beach, to the mountains, etc.). The device is charging when you are moving.

Elveet is a kinetic charger.
The principle of operation Elveet is based on the phenomenon of electromagnetic induction


Step 1: Component Parts of the Elveet

1. The Inductor consists of a 9-magnetic Halbach array and three coils.


2. PCB contains an inductor 200mA step-up-converter, a battery charger, and a battery step-up converter 5V 2A output.

3. The lithium-polymer battery 2800 mAh.

4. The case consists 4 parts and is made with 3D Printer.

The whole project is created in Fusion 360.

Step 2: Elveet Inductor

The inductor converts the kinetic energy of your movement into an electric current. The efficiency of the inductor is the most important parameter. The amount of accumulated energy in the internal battery depends on the efficiency of the inductor.

The inductor consists of three coils, a Halbach magnetic array, and three diode bridges.
The working field of the coil is the part above which the poles of the magnets pass, that is, the longer this part is, the more energy we can get.

Further, the outputs of each coil are connected to the diode bridge, that is, the coils are independent in voltage. And the current of all three coils is summed up after the diode bridges.
Diode bridges use Schottky diodes with very low forward voltage PMEG4010 produced by Nexperia. These are the best diodes for such applications and I do not recommend changing them to others.

The magnetic Halbach array concentrates the magnetic field on one side. On the other side, the magnetic field is very weak.

Halbach array requires almost double the number of permanent magnets but the efficiency of the Halbach assembly is very high.

The magnetic array passes over two parts of each coil and always the poles pass over different parts. Since the coils are electrically independent due to diode bridges, their influence on each other is excluded.

The inductor uses an assembly of 9 neodymium magnets 5X5X30mm N42. Two more magnets 2X4X30 N42 are used as springs.

The efficiency of the inductor depends on the rate of change of the magnetic field. For this, the path of the magnetic assembly is increased. Thus, the rate of change of the magnetic field is increased substantially due to the large acceleration of the magnetic assembly during motion.

This inductor is much more efficient than an inductor with a cylindrical magnet in the center of the coil. The cylindrical inductor has only the upper and lower working part of the magnet. The middle part of the cylindrical magnet almost does not work in the current generation. Therefore, its efficiency is low.


The Elveet inductor has a 4-pole magnetic system which is directed strictly perpendicular to the wires of the coils.

After the diode bridges, the current of the coils is summed up and fed to the converter and charger board.

Step 3: Elveet PCB

The circuit and all components of the boards.
It contains three main parts:

1. Step-up 200mA converter inductor current. The chip NCP1402 is used.

It is a boost converter that operates from 0.8 volts and gives a fixed voltage of 5 volts and a current of up to 200 mA. The task of this chip is to provide a comfortable voltage for charging the battery.

2. Charge device chip STC4054

This chip receives 5 volts from the inductor or from an external source (via micro-USB) and charges a Lithium-polymer battery with a capacity of 2800 mA. The inductor current and the current from the external source are decoupled via Schottky diodes.

Also, the second pair of Schottky diodes allow Elveet to operate as an uninterrupted power supply, that is, you can charge Elveet and receive current from it for your devices at the same time.

3. Step-up output converter. It boosts the battery voltage to 5 Volts and provides a current of up to 2 Amperes to power the gadgets. In this case, the LM2623 chip is working.

A good feature of the LM2623 is an internal high-power transistor and an output current of up to 2 Amperes with low output voltage ripple. The output voltage is fed to a standard USB connector.

In addition to these parts, the board has a touch-sensitive load switch (for example a powerful traveling lamp or other constant loads). There are also output pins for connecting the wireless charger instead of the USB cable, but this option is designed for the future.

Step 4: Elveet Case

All parts of the case and the magnet holder are printed on a 3D printer.

All STL files are here.

Case dimensions:

18 - 54 - 133 мм (5, 24 - 2,13 - 0,728 in)

Step 5: Coils

On a rectangular base 5x35 mm high 8 mm, we reel coil with a wire of 32 AWG (0.2 mm).

The coils are made with a wire of 32 AWG (0.2mm) on a rectangular base. The number of turns is approximately 1200.The width of the entire coil should not be more than 20 mm. You can apply a thicker wire, but for a boost converter, this will be a heavier mode of operation. A thinner wire will give more voltage but the current will drop and ohmic losses will increase.

After winding all coils should be wrapped with PTFE tape.

Step 6: Board Diode Bridges

This is a narrow board for 12 diodes.

It is located next to the coils.

The outputs of each coil are connected to the bridges after the board is placed in the groove.

Step 7: Checking Connections

To do this, you need a thin board, which is mounted 10-15 white LEDs and one capacitor of approximately 2200 microfarads.

LEDs are connected in parallel and soldered to the board of diode bridges.

When moving the magnetic assembly over the coils, all the diodes should shine brightly.

Further, the test board is removed and the bridge board pins are connected to the converter board.

Step 8: Final Assembly

We connect the battery and inductor wires to the board.

After that, we collect the upper and lower covers of the device using two screws.

The device is ready to work.


Now you are completely energetically independent!

Good travel and good charge to your gadgets!

Comments

author
lm386 (author)2017-08-03

Hi Tetiana / Tanya

Very good article

How critical are the size of the magnets, 5x5x30 seem difficult to find?

You show a pattern in the 9 magnets and look like they are placed in a certain way, can you tell me how they are lined up.

author
TanyaAkinora (author)lm3862017-08-03

Thanks for the comment.
You can see the location of the magnets in step 7. The poles of the magnets are marked with a red marker.
The size of the magnets affects the power. The longer the magnet, the more power.
You can use magnets from https://www.indigo.com/magnets/rare_earth/blocks/neodymium-slab-magnet-25x5x2.5mm.html
But this will require a double amount and the power will drop a little.
I used magnets from a local manufacturer. I can send them to you if you want.
Best
Tanya

author
lm386 (author)TanyaAkinora2017-08-03

Hi Tanya
Thank you for the offer of the magents but should be able to find similar ones on ebay...
I have now learnt that rare earth magnets differ from ordinary ferrous bar magnets and can have poles along their length not just at the ends.
Best Regards Richard

author
warhawk8080 (author)2017-07-31

Got an idea...would using a very low voltage energy harvester chip instead of the NCP1402 chip be better...then put a button cell .47F supercapacitor on the output side of the coils (where the 10uf tantal is located)...the below chip can charge down to .08vdc (startup voltage of .33vdc)
Coils dump voltage/current into the supercap...the BQ25504 trickles into the 4.2vdc Li Ion...much more efficient use of the low power pulses from the motion of the magnet and coils?

http://www.ti.com/product/BQ25504?keyMatch=energy%...

author
TanyaAkinora (author)warhawk80802017-07-31

Thanks for the comment.

Elveet inductor gives a current of more than 300 mA, so this chip is not suitable for this device.

author
the_3d6 (author)TanyaAkinora2017-08-01

I believe you have not measured this properly. If there really was present 300mA current, it would have destroyed NCP1402 which you used: your coils have copper resistance of more than 50 Ohms, so if you would get there 300mA, it would mean that at the very least 15 Volts of EMF were produced (that completely ignores all other parts of circuit and inductances, so more likely you'll need 25V to get 300mA through coils). NCP1402 absolute maximum input voltage is 6V.
Since it survives your device operation, it can be safely assumed that your peak current doesn't normally get above 50mA.

And even if it was going higher than 300mA for a few milliseconds, any decent capacitor would have reduced it greatly. Average current in this device will be in a few milliamps range. 10uF might be not sufficient for that purpose, but 0.47F supercap would be more than enough.

BQ25504 is much more efficient in converting power, so this is a good option.

author
TanyaAkinora (author)the_3d62017-08-01

No problems. You can apply BQ25504. This is your choice.

author
the_3d6 (author)2017-07-31

The main problem with kinetic chargers is a tiny amount of energy. For this setup, you'll need to shake it about 6000 times to theoretically put in enough energy to charge 100mAh battery (so in practice, with friction and all conversion losses, you'll need at least twice more).


Although it can make a nice emergency light

author
TanyaAkinora (author)the_3d62017-07-31

I think that you confuse Elveet with a shaking flashlight.

author
jenov (author)2017-07-31

Hi TanyaAkinora, do you have the drawing for the diode bridge board? Thanks

author
TanyaAkinora (author)jenov2017-07-31

Hi,
See Elveet PCB

author
warhawk8080 (author)2017-07-31

What program did you use to make the .pcb..do you have it designed in eagle?

author
TanyaAkinora made it! (author)warhawk80802017-07-31

I added Gerber

Gerber_ELVEET(1).ZIP
author
warhawk8080 (author)TanyaAkinora2017-07-31

Nice...do you have it with single board..the gerbers you gave are panelized..there are 8 of em on one design :)

author
Sepherim (author)2017-07-31

I love your idea... i had an idea about it myself:

Why not add same pole perm. Magnet strips to the end of the moving magnet and the encasement of the magnet like:

|+ +|movingmagnet|+ +|

This may you can stop harder impacts from happening inside the Charger AND you can even use these harder impacts to make it bounce back and forth a few times.

author
TanyaAkinora (author)Sepherim2017-07-31

There are two magnets as springs. They are inserted into the nests on the right and left. The parameters of these magnets are in the text.

author
Sepherim (author)TanyaAkinora2017-07-31

Ah i see. They are just on none of the pictures so i somehow overread that part. I saw the spaces so i had thought you might have had that plan ;)

author
jenov (author)2017-07-31

Thanks for sharing this wonderful battery charger. :P

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Bio: Hello! My name is Tetiana. One of my hobbies is 3D printing. My work covers various areas of engineering to the decorative. You can see ... More »
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