Hey all,
Thanks in advance for any help on this.
I'm making a small kit to demonstrate wireless power transfer in my classroom (I teach HS Physics and Astronomy).
The device works, but I'm at the optimization point and I feel I've exhausted all of my options in my brain and I am in need of some other brains to look over what I've got and offer any kind advice - your help goes directly to kids in my classroom btw.
The device is what is regularly found now when you look up wireless power circuits... It's a 555 timer driving a power mosfet, which allows 12V to flow into an LCR primary circuit (the primary coil). It is nothing special or new, I've just put it into a box essentially so the kids can experiment with it and build their own coils and swap out caps and stuff.
The way that I'm transferring power might seem a bit strange but please understand this is for the classroom and students winding their own coils is not a precise activity - so, the primary coil (whose resonant frequency is around 210 khz) is actually set to around 160 khz so the kids can build a 100 uH LC pickup coil with a 103 cap. So, just letting you know my problem could be from this. So, the coils are not in resonance, what's going on is that the primary is oscillating at the secondary's res. freq. This is most likely why the oscope waveform has this weird "shelf" at around 160khz. this works, transmits power, but....
The weird thing(s) is:
- the signal as measured on an oscope across the primary coil is not +12 / -12 VAC, it is way way way higher, around +80 / -80 VAC. Is this from some type of back emf?
- the protection diodes I have in the schematic, are they necessary or are they the cause of this sloshing around / stepping up of voltage
- is there a way to focus the energy into the coil as opposed to generating so much heat in the LCR resistor and the mosfet? (the device has an on board cooling fan and heat sinks all around)
anyhow, sorry for the novel, any advice on how to clean this up and make it better would be great!
dave
Thanks in advance for any help on this.
I'm making a small kit to demonstrate wireless power transfer in my classroom (I teach HS Physics and Astronomy).
The device works, but I'm at the optimization point and I feel I've exhausted all of my options in my brain and I am in need of some other brains to look over what I've got and offer any kind advice - your help goes directly to kids in my classroom btw.
The device is what is regularly found now when you look up wireless power circuits... It's a 555 timer driving a power mosfet, which allows 12V to flow into an LCR primary circuit (the primary coil). It is nothing special or new, I've just put it into a box essentially so the kids can experiment with it and build their own coils and swap out caps and stuff.
The way that I'm transferring power might seem a bit strange but please understand this is for the classroom and students winding their own coils is not a precise activity - so, the primary coil (whose resonant frequency is around 210 khz) is actually set to around 160 khz so the kids can build a 100 uH LC pickup coil with a 103 cap. So, just letting you know my problem could be from this. So, the coils are not in resonance, what's going on is that the primary is oscillating at the secondary's res. freq. This is most likely why the oscope waveform has this weird "shelf" at around 160khz. this works, transmits power, but....
The weird thing(s) is:
- the signal as measured on an oscope across the primary coil is not +12 / -12 VAC, it is way way way higher, around +80 / -80 VAC. Is this from some type of back emf?
- the protection diodes I have in the schematic, are they necessary or are they the cause of this sloshing around / stepping up of voltage
- is there a way to focus the energy into the coil as opposed to generating so much heat in the LCR resistor and the mosfet? (the device has an on board cooling fan and heat sinks all around)
anyhow, sorry for the novel, any advice on how to clean this up and make it better would be great!
dave
Attachments
-
93.6 KB Views: 155
-
292.9 KB Views: 100
-
45.3 KB Views: 67