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Ipad/phone/pod wireless charger and acrylic question

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large_ghostman

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You all seen those cheap copies of the I whatevers wireless chargers? Now supposing I have an acrylic square 5 inches square, with a low voltage pic in and a few smd Leds.

Anyone got an idea of the size of pick up coil I would need to power the pic and leds from the wireless charger? Total current from leds and pic is roughly 40mA. The idea is simply to power a colourless acrylic square while its sat on one of those chargers, apart from converters etc and maybe a JT, i was wondering what size coil to use near the base of the cube?
The coil will be roughly 5mm from the top of the charger.

I tried working it out and got brain fade! I would just try a few, except i am still in shock at the price of that clear acrylic!!! Nearly fell off my perch when i saw what it costs!

I have been asked to make 32 of them, they are a trophy for a primary school class competition. Obviously every kid gets one because being a competition, everyone wins...:rolleyes:.

Apparently kids feel bad if they dont do well, so they encourage them to be non competitive! Kinda counter productive, i did ask why they wouldnt let them loose, my reasoning being the more it hurts the less they are going to want to loose and the more effort in.

The look i got i thought she had misunderstood me and had asked if i could do inappropriate things to her with a pineapple.
 
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large_ghostman

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Thanks Mike, it never occurred to me to look up a chip app note, TBH last time i looked at this kind of thing they didnt have dedicated chips like that. Its not what I was expecting! Not sure what I expected inside the charger unit but not so many coils like that.

Seems more than doable for what I want, infact i dont think i have to add much circuitry. Makes sense seeing as most mobiles dont have huge coils inside, thanks again mate thats helped alot.
 

gophert

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Based on a tear down I've seen, it looks like an inverted top-hat shaped inductor core. The winding is around the narrow section of the top hat. THe brim was about 3/4" (19mm) and cylinder was about 1/2"(12mm). You will have to adjust for size of charger's coil. Very short top hat but that is the shape.

The shape was used to facilitate (optimize) the completion of the magnetic circuit. It was made of insulated iron powder or ferrite. Based in the frequency and current, I assume it was insulated iron powder based on frequency and current but ferrite should be fine for your application.

Using a cutoff 19mm bolt may not work well because of eddie current heating. A stack of thin washers with wax paper or Saran Wrap between each washer will also cut down on eddie current losses.
 

large_ghostman

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Based on a tear down I've seen, it looks like an inverted top-hat shaped inductor core. The winding is around the narrow section of the top hat. THe brim was about 3/4" (19mm) and cylinder was about 1/2"(12mm). You will have to adjust for size of charger's coil. Very short top hat but that is the shape.

The shape was used to facilitate (optimize) the completion of the magnetic circuit. It was made of insulated iron powder or ferrite. Based in the frequency and current, I assume it was insulated iron powder based on frequency and current but ferrite should be fine for your application.

Using a cutoff 19mm bolt may not work well because of eddie current heating. A stack of thin washers with wax paper or Saran Wrap between each washer will also cut down on eddie current losses.
You mean use washers as the pick up coil inside the acrylic? i am just checking i have it right...

Sounds like an excellent idea! I got to be honest, i dont own one of these chargers and havnt until now seen inside. Actually washers with a separation layer Would look cool, Also i have a box of super caps i was given, i think they are something mad like 6F and 3V. they are tiny!! So thats got me wondering...... Going to be a cheapo for now and use wax for testing!! £33 for 250ml of acrylic!!
 

gophert

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You mean use washers as the pick up coil inside the acrylic? i am just checking i have it right...

Sounds like an excellent idea! I got to be honest, i dont own one of these chargers and havnt until now seen inside. Actually washers with a separation layer Would look cool, Also i have a box of super caps i was given, i think they are something mad like 6F and 3V. they are tiny!! So thats got me wondering...... Going to be a cheapo for now and use wax for testing!! £33 for 250ml of acrylic!!
My idea is to make the pickup coil in the acrylic from a stack of washers (ideally washers made of ferrosilicon (silicon steel) like a transformer plate material to minimize eddie currents but do what you can - even if carbon steel it should work if washers are thin. Obviously, don't use brass or aluminum washers.

The idea is to prevent current from flowing any distance with an air gap. The magnetic core will be much more efficient than an air core for a given volume (space is limited in the phone).

You can also use something like a ferroxicube or the TDK, Vishay or MicroMetals equivalent if you find one easily for an experiment before ordering a set of them.
 

gophert

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Also note that the multiple coils on the Freescale example charger is a patented design idea that allows a phone to be placed on the charging pad at any orientation or off-centered position and the perfect coil or set of coils will start switching based on maximum coupling. You will have a very simple design because you can force alignment.

Other early patents had ideas to use extra coils to physically move the phone (magnetically) on a low-friction charging surface but that idea was foiled when most users put a TPU or silicone case on the phone. Any case decreases coupling but the tacky materials for cases prevent the phone from moving on the pad (I had to rewrite that last sentence because v1.0 sounded pornographic).
 

gophert

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Any guesses what company invested millions in wireless charging/wireless power way before hand-held devices were a target for the technology? They are now licensing their patent portfolio because they have nothing to do with mobile devices.

Bonus points if you can name the parent company and targeted use for this mystery company's wireless power (it was not used to light trophies - but not far off, it was used for a lighting application).
 

JimB

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Hey LG...

How about making one which will light up when it is near a fidget spinner.....

:banghead::banghead::banghead::banghead:

JimB
 

gophert

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Hey LG...

How about making one which will light up when it is near a fidget spinner.....

:banghead::banghead::banghead::banghead:

JimB
Light up near a fidget spinner? Are you talking about wireless power or a 7-year-old child's face?
 

dr pepper

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I used a bit of plastic 20 x 40mm I think as the coil former and 60 turns for the coil, the circuit is just a Jt:
The base is clear plexi, but thats only cause I have a big sheet of the stuff.

 

JonSea

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I was surprised that my Samsung Note7 would inductively charge while in a thin aluminum case. It didn't seem to matter at all or make any difference in charge rate.

Making the acrylic as thin as possible probably helps the charge rate. Maybe a 1.5mm top cover surrounded by a thicker frame?

Regarding acrylic prices - fabricators often have a bin for cutoffs which they sell cheap. That's where I get the stuff I use for laser projects.

Not every phone has inductive charging. Extra sad if you know you got one of these for coming in last, and it won't work with your phone!

I have several inductive chargers. One from Ikea, which seems to be picky about positioning the phone just right, and uses a 15 volt wall wart. Two different ones from China don't care too much about exact position and use 5 volt supplies. I secured one in a compartment in the car. I just put my phone there when I'm driving and it gets charged.
 

large_ghostman

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Hey LG...

How about making one which will light up when it is near a fidget spinner.....

:banghead::banghead::banghead::banghead:

JimB
Jim I am a pro, obviously i have designed in multiple protection measures should it get within 20 meters of a fidget spinner!! Cant have kids with acrylic cubes exploding!! Just because some numpty spins up a fidget spinner near them!! Actually now you mention it...I will put a warning label on the bottom, DO NOT PLACE NEAR FIDGET SPINNERS! this device is designed for a maximum of 600,000kVA. :D
 

large_ghostman

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Thanks Gophert, note i am using the prebuilt charger units, i am only doing the cubes to sit on them. But I will put two lips on the bottom of the cube to position the it inline.

John your right, its mind bending how far they have come with this tech!! Wasnt long ago we discussed this in terms of large copper pipes bent and a few hundred Volts to get 6 inches of distance with the power!!

No idea which company, but if its microsoft i am not going near it!!
 
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