I am interested to learn about and experiment with low power (<1W) wireless power transmission over short distances (mm range), initially just to
power LEDs. A cursory search led me to the website of the wireless power consortium where one can download the 'Qi' low power specification standard.
I am considering following the specification for the power transmitter design A11 on p54 of that standard which looks simple enough for someone with a
basic understanding of electronics to follow... maybe... well I'm assuming that the requisite Litz wire can be purchased from somewhere?
Am I kidding myself that this is doable/playable for a novice?
One question is how to drive this coil. Some additional digging online led me to the IDTP9030 made by Integrated Device Technology, but this is for
the 'sophisticated' A1 design standard and has a whole bunch of features I really don't need, after all, I want to power some LED's only and not
recharge an iPhone or tablet.
Could someone point me in the right direction as for 'simple' circuitry? I believe I need a low power full bridge inverter circuit operating at
175kHz? Is there and IC that can do this for me?
Appologies for the newbishness, electronics is not my forte, chemistry is... perhaps I should just stick to that Metacelsus - 15-9-2014 at 04:51
At my summer internship, I designed a ten watt wireless power system, using a circuit very similar to a ZVS induction heater. I can U2U you the
circuit diagram if you want.deltaH - 15-9-2014 at 05:14
Thanks Cheddite, that would be very useful, please do!Metacelsus - 15-9-2014 at 13:33
Since I don't think I can put an image in a u2u, here it is for all to see:
The coils are modeled as a weakly coupled transformer.
Operating frequency is around 35 kHz but varies with load and distance between the coils.
[Edited on 15-9-2014 by Cheddite Cheese]aga - 15-9-2014 at 14:48
Why ? But then, Why not !
@ 175 Khz the good old NE555 will be your best friend ever.
Replace the 1k resistor with a coil and EM energy will float around.
Optimum power transfer happens when the Frequency of the Oscillator exactly matches the Resonant Frequency of both the transmitting coil and the
receiving coil.
'Coil' being a coil of copper wire.
'Resonant' being the right number of Turns of wire of the same diameter, wound on the same material, also of the same diameter.
Adding a capacitor in parallel with the coil creates what is called a 'Tuned' or 'Resonant' circuit where the Inductance of the Coil and the Capacitor
combine to determine the Frequency at which it works best.
Opera singers can break wine glasses if they can sing High enough to match the Resonant frequency of the glass structure, because at Resonance, max
energy is transferred to the glass, and it has to go somewhere, so it shakes apart.
[Edited on 15-9-2014 by aga]deltaH - 15-9-2014 at 21:47
Thank you so much both Chedite and aga!!! This is very helpful indeed!
@aga
Thanks for the explanations, I had just recently read those links you posted to Wiki. The reason that I am following the Qi standard is because they
have specifics on exactly how to design the coils and the cap to use for a certain resonance and to match them to the receiver, so that way there is
less chance that I #@%#^ it up
So even 'just' a triple-five can drive this thing? I did not think to do that, I suppose my power requirements are low enough for just lighting up
LEDs. I can work with Chedite's circuit if I need more power at a later stage, but I will need to make the changes necessary for
175kHz.
As for the 'why': I love inventing and there are a few ideas of mine that would benefit greatly from a small wireless recharge, actually, it opens up
a wealth of possibilities, hence I thought it's high time I learn to make them
As for the Qi standard, while there are many others, it seems to be a major one, well for now anyhow lol
@chedite
About your circuit, time for my stupid questions...
I assume the C1 cap is then one I would need to change for my specific coil? According to the Qi A11 design standard, it uses a series 0.4 micro farad
cap while the coil assembly has a self inductance of 6.3 micro henries. Is it fine to use this in series as I've described?
Also what is the purpose of your L1 inductor and centre tap on the primary coil?
Thanks again for your tutorage!
[Edited on 16-9-2014 by deltaH]deltaH - 15-9-2014 at 23:58
Thanks Little_Ghost for the advice. I'm not too hung up on maximising efficiency, so I hear you Yes I noticed my toothbrush one, in fact, that's what got me interested
Okay, I am sourcing the Litz wire at the moment, then I think I will be set. I'm probably going to start by driving the coil with a 555 and then go
onto the transitor driven circuits like chedite's after that.
Thanks all again for your support!deltaH - 16-9-2014 at 02:10
Thanks little ghost. I'll try to stick the with the 555 then as it's for electronic dummies lie me I hear you on the variable resistor, this is a good idea!
Okay, I feel more confident now, I think I can put together a 555 circuit and wind/glue those Qi standard coils.
Don't worry, I have little interest in high power stuff, as one gets older, you see the beauty in little things more and more... that or I'm just
getting dumber, either way Metacelsus - 16-9-2014 at 04:52
The transistor type oscillator circuits (I havnt actually seen the one you been given, but assume its pretty much standard), are a step backwards from
the 555 timer type circuits. Its easier to control the frequency etc of a 555 timer than to adjust one using transistors (sort of).
Yes, but the transistor one I posted adjusts its frequency to resonance automatically. With a 555 circuit, changes in the load or coil distance will
change the resonant frequency, but the 555 will not compensate, resulting in power losses. However, if you're not worried about efficiency then by all
means feel free to use a 555.deltaH - 17-9-2014 at 02:04
Cheddite, what coil did you use for your circuit, I was thinking to toss the Qi standard as I'm battling to find the fine Litz wire
they specify and so would prefer a far lower resonant coil that I can wind with simple fine gauge enameled wire, hence copying your circuit 'as is'.Metacelsus - 17-9-2014 at 06:49
I wound my own out of regular magnet wire (18 gauge). The transmitting coil gets slightly warm when operating for extended periods, but it is
otherwise fine.
[Edited on 17-9-2014 by Cheddite Cheese]franklyn - 17-9-2014 at 21:53
" wireless " what a concept. Initially pioneered by Mr. Tesla using capacitive coupling using even the earth as
the coupling capacitor at huge voltage. It works providing the operating frequency is high and requires one point of contact common such as ground.
Outputting in the electromagnetic spectrum at radio frequency to transmit power requires large equipment and coupling is nearly nonexistent which
necessitates making the sending apparatus directional and the one receiving , highly resonant. You could just substitute a laser or even employ a
microwave oven magnetron and achieve better results. Which leaves just the first concept investigated , magnetic coupling. Effectiveness varies with
proximity of the driving solenoid to the one receiving , the Q you speak of , is also affected by metal objects nearby that develop power sapping eddy
currents. Other oddball means employed use ultrasound at usable but poor transmission efficiency.
.deltaH - 18-9-2014 at 01:51
In fact, franklyn, I had considered ultrasound, briefly, as I thought it might work for some of my inventions, but ultimately the
coil ones, I think, are the way to go. I have read about sonically coupled transformers that work with piezoelectric element stacks as primary and
secondary around a solid core to transfer sound, which I thought was very cool
***
Just discovered an amazing and amazingly simple step by step description with videos of an LED lighting wireless power transfer mini project.
Where does lightning come from ? There is a continuous transportation of charge
upward by rising air convection. This produces a voltage gradient which discharges
when the breakdown ionization of the intervening air occurs. This voltage gradient
can be tapped anywhere to do minor work.
