# Wireless charging

I am trying to make a circuit to transfer power from one coil to another

I have tried difference frequencies here are the results

Fun Fact: When I am producing frequencies between 20Hz and 20kHz I can hear the buzzing sound, I can guess that this is our hearing range

simulate this circuit – Schematic created using CircuitLab

So basically I want to increase the voltage on the receiving coil the maximum voltage I have reached is 3.5 volts, any idea how to increase it?

• are you able to modify the coil at all? – Pop24 Apr 9 '18 at 8:51
• I recently looked into wireless charging and they seem to use resonance at the receiving side. If so your optimal frequency depends on L3 & C3 or vice versa. – Oldfart Apr 9 '18 at 9:26
• @Pop24 I can build a new one, though, it would take time but I could try if I knew how the coil should be – DrunkProgrammer Apr 9 '18 at 9:49
• The voltage you get means little, the coil is an inductor so there is bound to be some frequency dependent behavior. What if you got 100 V at L3 but the voltage collapses if you load it with only 1 uA? – Bimpelrekkie Apr 9 '18 at 10:32
• @DrunkProgrammer Can you type up the frequency to voltage table? It is difficult to read in your image. – davidmneedham Apr 9 '18 at 14:09

So basically I want to increase the voltage on the receiving coil the maximum voltage I have reached is 3.5 volts, any idea how to increase it?

• Make sure your bridge rectifier (on the receive coil) is good for high frequencies - most are not. If necessary use 1N4148 diodes but not (say) 1N400x diodes.
• Use a parallel tuning capacitor across your receive coil to maximize local reception of flux changes to a higher voltage
• Using tuning on your drive side (can be parallel or series) to optimize the driving circuit to use power more efficienctly from your 12 volts
• For your circuit I'd definitely consider parallel tuning the drive coil and use careful amplitude level control on the gate to bias the MOSFET a little but not cause an over-drive situation. A sim will help you understand this better.
• Use a simulator and develop a circuit using two inductors coupled via "k" and vary k to see the effects. Add tuning capacitors (as appropropriate to the driving frequency you want to use).
• So basically you are saying that I have to modify the receiving circuit if I want to increase the voltage of the secondary coil, should I change the receiving coil itself? – DrunkProgrammer Apr 9 '18 at 12:15
• I'm saying you need to add resonating capacitors to both coils and make sure your rectifier can run efficiently at your operating frequency. As to whether you change the coils, that is down to the operating frequency you choose to use. Higher frequencies naturally means fewer turns. – Andy aka Apr 9 '18 at 13:06
• I just found out that my diodes on the bridge are getting really really hot!I have three 1n4148 diodes(they are getting to hot) and a random one that its type has faded which is not getting that hot – DrunkProgrammer Apr 10 '18 at 10:45
• Use 4 diodes that are the same type and make sure you wire them up correctly. If using the 1N4148 then make sure that your received voltage does not peak above the maximum limit for the diode. If drawing load current, make sure that this is also not exceeded else use diodes rated for a higher power that have fast reverse recovery times (like the 1N4148). – Andy aka Apr 10 '18 at 12:01