Wireless charging circuit design using 7~10V input

[SujithZis]

I needed help designing a wireless charging circuit for a mobile phone using about 7~10V input .....


I'm using stored energy from 2*5.4V super capacitors connected in series


I also need a step down switching regulator circuit to convert the output from super caps in series. to 7~10V range so that it can be used as input for wireless charger

 

[audioguru]

A wireless charging system uses inductive coupling from a coil in the transmitter to a coil in the receiver. The inductive coil in the transmitter is driven with the fairly high voltage and current of a high frequency AC signal. The receiver rectifies and filters the AC received by its coil then regulates it to feed the charger circuit.

I do not know why you are using super-caps.

 

[JimB]

I think that the super-caps are from some energy harvesting device using a piezo thing.
The charging and self discharge of the caps is discussed in another recent thread.

As I am sure AG will agree with me, a wireless charging system will be a lot less efficient than one which is wired.

JimB

 

[NorthGuy]

I think by "wireless charger", OP means a charger for wireless phones

 

[Reloadron]

Some good examples of inductive charging systems can be found in electric toothbrush circuits. The downside of these circuits, as has been pointed out is they are not very efficient. Not very practical yet for devices like smart phones or cell phones.

Ron

 

[SujithZis]

I'm plannign on making a peizo harvesting system on the shoe which wirelessly charges mobile phones kept in you pocket


So yes I'm talking about
Low range transmitting
Wireless mobile charger
10v is the max I can do

 

[SujithZis]

I think that the super-caps are from some energy harvesting device using a piezo thing.
The charging and self discharge of the caps is discussed in another recent thread.

As I am sure AG will agree with me, a wireless charging system will be a lot less efficient than one which is wired.

JimB

But who would these days actually plug their mobile phones

And where s the fun in that


BTW 10V input and I just need charge a mobile phone 2cm awaya from it .

 

[Reloadron]

I'm plannign on making a peizo harvesting system on the shoe which wirelessly charges mobile phones kept in you pocket


So yes I'm talking about
Low range transmitting
Wireless mobile charger
10v is the max I can do

With the shoe on the foot and the phone in a pocket it will not work. The Inductive coupling needs to be in very, very close proximity. Do a Google as I mentioned of electric toothbrush charger circuits. That should give you an idea of the proximity needed for inductive coupled charging circuits.

Ron

 

[SujithZis]

With the shoe on the foot and the phone in a pocket it will not work. The Inductive coupling needs to be in very, very close proximity. Do a Google as I mentioned of electric toothbrush charger circuits. That should give you an idea of the proximity needed for inductive coupled charging circuits.

Ron

Yes I can rearrange my project


I can feed the input to to a belt where the circuitry goes in and attach the wireless charger and place its coil inside the pocket so the phone charges when it comes in contact with the pocket

 

[alec_t]

Piezos are good for generating voltage, but how much current are you expecting? Have you calculated how long it will take (i.e. distance walked) to charge the caps, even if your energy capture were 100% efficient?

 

[audioguru]

I'm plannign on making a peizo harvesting system on the shoe which wirelessly charges mobile phones kept in you pocket

Last year a student put a piezo in his shoe and used it to charge his cell phone. He walked and ran and walked and ran and walked and ran and walked and ran and walked and ran and walked and ran ALL DAY AND ALL NIGHT then made one short phone call then the battery in the phone was dead again.

Energy harvesting with a piezo in a shoe is used to power an LCD watch that uses extremely low power, not a high power cell phone.

 

[SujithZis]

Butdioguru, post: 1165471, member: 16360"]Last year a student put a piezo in his shoe and used it to charge his cell phone. He walked and ran and walked and ran and walked and ran and walked and ran and walked and ran and walked and ran ALL DAY AND ALL NIGHT then made one short phone call then the battery in the phone was dead again.

Energy harvesting with a piezo in a shoe is used to power an LCD watch that uses extremely low power, not a high power cell phone.[/quote


First of all I'm using PVDF FILMS much better
I'm connecting 23 pvdf films in one sole ..series connection ...

I ll find out how much it generates per footstep
How much long it takes to charge the super caps

And let you know the results

If the results are convincing would you like to help

 

[audioguru]

Have you calculated how many times the super caps must be charged to charge a phone? Maybe one thousand?
If the piezo films need one thousand footsteps to charge the super caps then you will be walking and running all day and all night like the other guy, just to make one short phone call. And you will not be able to use your phone all day and all night.

 

[alec_t]

Let's do some sums.
A quick google showed:-
7g is the typical acceleration at the ankle when running in conventional running shoes,
A PVDF transducer generates ~ maximum 16uW at 0.92g acceleration.

So, with 23 PVDFs at 7g you could get a max 23 x 16uW x 7/0.92 = ~2800uW = ~2.8mW.
That's the peak output during the impact of shoe on ground. Let's assume the average is half the peak = 1.4mW.
Let's assume, too, that when running or walking each shoe is on the ground for half the time. If each shoe is fitted with 23 PDFs then the total energy harvested is 1.4 x 2 / 2 = 1.4mW.
So, for a 3 Volt 2000mAHr battery, you would have to walk/run for 3 x 2000/1.4 hours = 4285 hours = 178 days to charge it !!

 

[audioguru]

Let's do some sums.
So, for a 3 Volt 2000mAHr battery, you would have to walk/run for 3 x 2000/1.4 hours = 4285 hours = 178 days to charge it !!

That is half a year of running (not walking) without eating or sleeping or fooling around.
I wonder what the super caps are for? Their charge won't last long enough for some fooling around unless it is just a quickie.

 

[SujithZis]

Let's do some sums.
A quick google showed:-
7g is the typical acceleration at the ankle when running in conventional running shoes,
A PVDF transducer generates ~ maximum 16uW at 0.92g acceleration.

So, with 23 PVDFs at 7g you could get a max 23 x 16uW x 7/0.92 = ~2800uW = ~2.8mW.
That's the peak output during the impact of shoe on ground. Let's assume the average is half the peak = 1.4mW.
Let's assume, too, that when running or walking each shoe is on the ground for half the time. If each shoe is fitted with 23 PDFs then the total energy harvested is 1.4 x 2 / 2 = 1.4mW.
So, for a 3 Volt 2000mAHr battery, you would have to walk/run for 3 x 2000/1.4 hours = 4285 hours = 178 days to charge it !!

Jeez thanks mman. (That type of calculation could have taken me years)

Could you please do those calculations backwards
Like how much is the required output from peizo (so that i could change my element)

Aalso ,
In the peizo film that im using im getting 2.5V 0.02 mA per step ON ......... ONE PEIZO........
Is that any good ?

 

[alec_t]

how much is the required output from peizo

Depends how many days you plan on running non-stop to charge the battery!

In the peizo film that im using im getting 2.5V 0.02 mA per step ON ......... ONE PEIZO.

I assume that's the peak voltage/current. That's 50 uW, i.e. it's about 3 times better than the PVDFs quoted above. So it would only take 1/3 of the time estimated above to charge the battery, i.e. about 178/3 = 59 days of running! That figure doesn't account for self-discharge of the battery, or use of the phone.

 

[ronsimpson]

I know this is not on topic but, I am playing with this part and its brother. This part stores up energy until there is enough to run a device. Then it signals "I have power".
Energy harvesting is a big topic at linear.com

 

[audioguru]

The article about Energy Harvesting talks about it providing bursts of a small amount of power after storing up the power for hours or days.
It also talks about vibration on the transducers that is continuous, not the occasional clump, clump clump of a shoe.
Somebody somewhere made a long and wide sidewalk of piezo transducers and got hundreds of people to walk on them. There was a small amount of power produced.

 

[Misterbenn]

You'd have more luck with a mass - spring type system. Where the mass is a strong magnet the spring made from a cantilever beam this can then be tuned for a slow jog. Energy can be harvested by the magnet moving through a coil.

The more powerful / successful energy harvesting devices all use this method. My old professor created a spinoff company from the university **broken link removed** and I did a peer review of the different technologies during my time with him, this is where my knowledge arises.