Impedance maching circuit for Wireless Power Transmission system using copper coil

[Jeetkumar]

Hi All,

I am working on wireless power transmission system, i have a copper coil of 1" in diameter at transmitting side, i am looking for a way how to connect impedance matching circuit to copper coil and also how to add capacitance in between in another copper coil.

Thanks,
Jeet

 

[E Kafeman]

If receiving system cause measurable load at TX amplifier and if it is a battery charging circuit, connect everything, including rectifier and charging regulators, as it is intended to work at maximum load, before any tuning.
If tuning TX coil is tuned without actual load, will it be a less effective system when loading RX-coil later comes close and cause bad tuning of whole system.
If it is good coupling between RX and TX coil is it to prefer to do this tuning as much as possible at RX side, as you anyway want to correct for any reactive losses at that side.
Resistive impedance matching can be done by adjusting relative number of turns of the coils or by make a tap somewhere along TX coil for feed from TX amplifier.
If clever designed, do you also want to tune for the situation when there is no load. Tune for its L//C parallel self-resonance, as you then can reduce power consumption, and also get best long distance coverage. Check for high voltage reflections which can occur at self resonance and then destroy TX transistor(s).
It is possible to tune impedance for both these situations (load/unloaded) at the same time but requires then measurement tools for reactive components. A VNA is a perfect tool but a two channel oscilloscope is possible to use also.
Basic tuning can be done by measuring TX transistor DC current and DC current after rectifying at RX side. It can be done with one or two multimeters, or even simpler, with two light-bulbs.

 

[chuckey]

The first thing to do is to resonate (tune) your transmission coil. Doing this will give you the maximum RF for the minimum DC power. The DC input to the final amplifier should dip sharply as the coil is resonated. If you can measure this, do so and add capacitance across the coil until the DC power dips. If you can not measure the DC, wire a diode to the hot end of the coil and measure the voltage at the other end with a DVM to earth and tune for maximum.
Couple the receiving coil close enough to the transmission coil to get some indication of the power it is receiving then tune it by adding capacitance/ squeezing or opening out the turns until it too has hit a maximum. Thats it!
Frank

 

[Jeetkumar]

Thanks kafeman and chuckey, will try out your suggestion.
Thanks once again.

 

[kezambo]

hi Jeetkumar,

hows your project. Would u mind to share with me because I have the same problem.

 

[Jeetkumar]

Hi Kezambo,

I am waiting for my network analyzer to come, so that i can measure impedance.
so right now everything is stand still.

 

[kezambo]

hi jeet,
so how do u do with the impedance matching?

 

[Jeetkumar]

Hi Kezambo,

from tomorrow i would resume my work with new network analyser.

 

[mkn.308]

hi jeet kumar ..i am also working on wireless ...can u give ur e-mail id ..i need to ask so many questions ....my id is kishore.308@gmail.com
waiting for ur reply

---------- Post added at 15:29 ---------- Previous post was at 15:28 ----------

hi jeet kumar ..i am also working on wireless ...can u give ur e-mail id ..i need to ask so many questions ....my id is kishore.308@gmail.com
waiting for ur reply

 

[biff44]

the longest distance wireless power systems use 4 coils. Input coil, TX rexonating coil, RX resonating coil, and output coil. You resonate the two inner coils at your frequency of interest. Then you couple into those coils iwth the input and output coils. You vary the coupling by moving the coils.