Resonant Wireless Charging (through surface transmitters)

Thread Starter

variable

Joined Mar 4, 2008
9
I've been watching resonant charging for years, and every now and again you'll see a news article drop and nothing come of it... seemingly vapourware. But I know it does exist, just maybe not in a commercial saleable form (yet). I'm hoping that I'm missing something and there is a solution or some kit out there that has been released either for Rezence or what have you. It's just a hobby project of mine for a single through surface (desktop) application, so inductive is out of the question. Any ways, here's hoping someone else has encountered and solved this! Thanks!
-Eric
 

joeyd999

Joined Jun 6, 2011
4,477
I've been watching resonant charging for years, and every now and again you'll see a news article drop and nothing come of it... seemingly vapourware. But I know it does exist, just maybe not in a commercial saleable form (yet). I'm hoping that I'm missing something and there is a solution or some kit out there that has been released either for Rezence or what have you. It's just a hobby project of mine for a single through surface (desktop) application, so inductive is out of the question. Any ways, here's hoping someone else has encountered and solved this! Thanks!
-Eric
I found this. Helpful?
 

MrAl

Joined Jun 17, 2014
8,136
Hi,

The transfer of energy from one coil to the other depends on the mutual inductance and there is a certain coil shape that has the best transfer ratio. I cant remember the name of this coil but maybe someone can look it up. You can calculate the transfer efficiency once you calculate the mutual inductance.

The most important thing though and this is true of most magnetic circuits, is the distance between the two coils. The distance affects the mutual inductance a lot so the closer the better.

I guess the main concern here was is it really possible to do this, and the answer is yes but the design of the two coils and their relative position to each other decides just how good the system works.
 

Thread Starter

variable

Joined Mar 4, 2008
9
Hi,

The transfer of energy from one coil to the other depends on the mutual inductance and there is a certain coil shape that has the best transfer ratio. I cant remember the name of this coil but maybe someone can look it up. You can calculate the transfer efficiency once you calculate the mutual inductance.

The most important thing though and this is true of most magnetic circuits, is the distance between the two coils. The distance affects the mutual inductance a lot so the closer the better.

I guess the main concern here was is it really possible to do this, and the answer is yes but the design of the two coils and their relative position to each other decides just how good the system works.
Entirely agreed. I've seen Rezence numbers of 40mm transfer, which is inline with my desired ~1 3/8", and I only need about 250mA at 5V.
 

Thread Starter

variable

Joined Mar 4, 2008
9
I found this. Helpful?
Thanks Joey - I had come across that article prior, but it is a good read to be sure. Essentially states what I've found so far that the market is still developing. I'd just hoped there'd been progress since that article was written in 2016.
 

MrAl

Joined Jun 17, 2014
8,136
Thanks Joey - I had come across that article prior, but it is a good read to be sure. Essentially states what I've found so far that the market is still developing. I'd just hoped there'd been progress since that article was written in 2016.

Hi again,

I dont think there is as much to this as it may sound like at first. It might sound like some sort of black magic because of the things we see about Tesla's experiments, but it's not very complicated in theory so as far as development i think it will just be a matter of cosmetics more than anything else.

The main points are the mutual inductance and the amplitude. If you increase the mutual inductance and increase the amplitude in any way possible then you get more power transfer. It's as simple as that. This is the way any transformer works and that's all this is.

Since distance is so important, the closer the coils are to each other the better, but what else could help is the introduction of a core material, and since there would be one section for each coil, if the two cores could touch during transfer the energy transfer would be just as good as a single transformer that had a very small air gap.
I believe this is the key to maximum power transfer. If the two core 'halves' touch, it will act just like a wall wart (wall warts often have small gaps to limit current during fault conditions).

I am sort of assuming you want to build a system yourself, but if not that's ok you might find this interesting anyway :)
 

Sensacell

Joined Jun 19, 2012
2,774
Much is hyped about this subject- but the basic physics doesn't change, you need two coils with mutual inductance.
I have also seen articles written like they have some breakthrough technology that changes the game, but it's all marketing BS.
 
Resonant wireless charging is very much available in commercial form right now.

Witricity recently partnered with Dell to make a wirelessly chargeable laptop.

Samsung phones use the Qi standard, which is basically resonant inductive charging operating at close to the resonant frequency.

The Apple watch also charges with a standard very similar to Qi.

You can also buy off the shelf Qi transmitter and receiver hardware from places like Adafruit and Digikey.

FYI I recently published a course about this stuff where I show how to build such circuits from scratch and/or use off the shelf Qi parts.
 

BR-549

Joined Sep 22, 2013
4,938
Not to be contrary, but what is the advantage? I could see the convenience of not plugging in......if I could recharge in 3-4 minutes. Sorta a setup time to charge time ratio. But if the charge takes 2 hrs......plugging in and out doesn't seem like much. Now if you can set up one charger in the house......and charge all household devices........that's different. But if the device has to be within close proximity to charger......what's the advantage over plugging in?

It's the battery that requires the charge time, not the method of delivery right?
 

nsaspook

Joined Aug 27, 2009
8,253
Much is hyped about this subject- but the basic physics doesn't change, you need two coils with mutual inductance.
I have also seen articles written like they have some breakthrough technology that changes the game, but it's all marketing BS.
It's a great way to heat a room when 50% to 60% of power (at normal wired power cord distances from the wireless transmitter) is lost heating coils instead of powering devices or charging batteries. EM energy is always directly transmitted 'in the air', it's the energy guides (electrical wire or a cord) that concentrate energy and maintain that energy concentration over distance that govern the efficiency of that transmission. It's trivial to get 99% efficiency connections with high power wired connections at 6 feet while the inherently less efficient Witricity only gives you 45% under optimized conditions. No Thanks to that.

We also have this wireless classic.
 
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ubeam will definitely never be viable for home use. With regards to the heating you mentioned, I think the bulk of wirelessly powered devices in the home will just continue to be low/medium powered. If a phone normally charges with 5W, if things are 50% efficient then 5W of heat being dumped in your room is no big deal in the grand scheme of things. But companies making claims of wirelessly powered televisions are total BS.
 

nsaspook

Joined Aug 27, 2009
8,253
ubeam will definitely never be viable for home use. With regards to the heating you mentioned, I think the bulk of wirelessly powered devices in the home will just continue to be low/medium powered. If a phone normally charges with 5W, if things are 50% efficient then 5W of heat being dumped in your room is no big deal in the grand scheme of things. But companies making claims of wirelessly powered televisions are total BS.
That's just 5W for a single phone. The world-vision for wireless enthusiasts is wireless everything, that could add up to hundreds of lost Watts in a typical room and you will be paying that bill * millions of households nationwide. It seems a incredible waste of energy for very little convenience. High speed/high density/high efficiency wired (or very close contact) charging systems seem much more logical.
 

MrAl

Joined Jun 17, 2014
8,136
Hi,

Some good posts by all you guys :)

I'd like to add that if the design is such that the two coils have core material (as i was talking about before) then the efficiency would be just about as high as with a wall wart, but the drawback is that the thing to be charged has to be positioned so that most of the core of the receiver lines up with the core of the transmitter, which may again make it a little less convenient.

However, if we see too much of a loss whatever way it is done (such as the previous post was talking about) then i think we are going backwards as far as green goes (eg greenhouse gases) and that is because in the last several years we've seen a decrease in quiescent power consumption of wall warts and i'd hate to see that change. This means a method to detect if the device is being used at all would be nice so that it can power down all by itself, then power up when needed.

A few weeks ago i was looking into some topics that required calculating inductances and energy transfer and i'll see if i can find them. I remember the running efficiency wasnt that great but cant remember the quiescent power dissipation now.
 

Alec_t

Joined Sep 17, 2013
11,997
The only advantage of wireless charging solutions like Qi is the convenience factor.
There are some circumstances in which wireless charging is (almost) essential. Examples are charging of medical implants and any equipment which is in a waterproof housing (e.g. toothbrushes).
 

nsaspook

Joined Aug 27, 2009
8,253
A few weeks ago i was looking into some topics that required calculating inductances and energy transfer and i'll see if i can find them. I remember the running efficiency wasnt that great but cant remember the quiescent power dissipation now.
Qi has some transfer efficiency data on their site.

https://www.wirelesspowerconsortium.com/technology/transfer-efficiency.html


https://www.wirelesspowerconsortium...s-power-standards-force-efficiency-trade-offs

https://www.wirelesspowerconsortium.com/blog/246/dreaming-of-power-through-the-air
Misleading claims are common, and the presenters of this NASA video were sensitive about efficiency’s significant challenges. The NASA video takes some liberties, but at least they explained how they measured the 82%. The actual numbers are 500 kW transmitted and 34 kW received. That is 7% efficient -- and it doesn’t take losses inside the transmitter into account. It’s understandable why the NASA prefers to use the number 82.

A product that charges mobile devices at a mere 7% efficiency is not viable by today’s standards. Responsible suppliers should think twice about using this type of technology in their products, and regulators wouldn’t look favorably at these inefficient products.
 

MrAl

Joined Jun 17, 2014
8,136
Hi,

Looks like some good data there.

After i did my own calculations i came to the conclusion that greenwise we would be going backwards, and that looks like the same conclusions they are coming too also. What a shame.
 

nsaspook

Joined Aug 27, 2009
8,253
Hi,

Looks like some good data there.

After i did my own calculations i came to the conclusion that greenwise we would be going backwards, and that looks like the same conclusions they are coming too also. What a shame.
I agree.

It's a shame that you can't change basic electromagnetics or physics by spending other peoples money. Many have tried from Tesla to modern VC money burners but they all have failed.

A detailed view of wireless power transfer that explains the efficiency issues in most of the long range devices.
 
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