# Trying to make a wireless charging circuit with an AC source

i'm making a project on wireless charging and according to my understanding if i attach a ac source with a coil and attach a voltmeter to an other coil i should get voltage on the voltmeter provided they are close to each other

Im using an AC to AC step down transformer and then i attach a coil with it does the coil behaves as a short circuit? if yes then why?

• Your question is very unclear i.e. "does the coil behaves as a shot?" - what do you mean by "shot"? – Andy aka May 31 '15 at 14:33
• @Andy Probably "short [circuit]". – Russell McMahon May 31 '15 at 14:39
• AC power can be transferred between two correctly aligned coils. However - (1) the driven coil needs to have a significant impedance (AC resistance) at the driving frequency so that power can be delivered to it. If it has a very low AC resistance it will "load down" the AC source and look like a short circuit. {2) You can drive the coil in current mode but this adds complexity (3) The coils on sender and receiver must be "resonated" at the transmit frequency with a capacitor to get good power transfer or range. – Russell McMahon May 31 '15 at 14:44
• @RussellMcMahon thanks for replying so for the circuit to work (1) My coil must have impedance.(2)It must be resonated. My problem is that the load is about 1.5 amp can a resonate and oscillator circuit withstand that load and if yes can you send me a link to a circuit like that. Thanks a lot – Ahsan Saeed May 31 '15 at 15:49

AC power can be transferred between two correctly aligned coils.
However -

(1) the driven coil needs to have a significant impedance (AC resistance) at the driving frequency so that power can be delivered to it. If it has a very low AC resistance it will "load down" the AC source and look like a short circuit.

(2) You can drive the coil in current mode but this adds complexity

(3) The coils on sender and receiver must be "resonated" at the transmit frequency with a capacitor to get good power transfer or range

Q: (1) My coil must have impedance.(2)It must be resonated. My problem is that the load is about 1.5 amp can a resonate and oscillator circuit withstand that load

"Have impedance" is essentially correct - ie the circuit which the inductor is part of must provide a finite non zero load to the transmitter. You do not mention frequency, power level, desired range, any limitations on size or cost etc. Far more detail is needed.

To achieve compactness and to use allowable frequencies this is usually done at at least 10's of kHz and ideally many Mhz range. There is a lot available on-web

Here is a you tube video of a system that looks well thought out and implemented.

Here is a related forum page This is only one example of many available, but seems better implemented than many others.

The basic principle and practice are both reasonably simple.

Images are from above site.

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