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Old 01-13-2020, 07:32 PM
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How do cordless charging stations work?


I asked the sales person when I bought my new iPhone: “How do cordless charging stations work?”

Salesperson said: “Real easy! You plug in the charging station to a wall outlet, put the phone in the cradle, and it charges!”

Me: “Actually, I meant how ...”

Mrs Piper elbowed me and whispered: “Just ask your smart internet friends and don’t bother the sales person!”

So I’m Following her advice.

Please, smart internet friends, how does electricity fly through the air without a wire and charge my phone?
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Old 01-13-2020, 07:37 PM
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It uses induction: https://en.wikipedia.org/wiki/Inductive_charging
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Old 01-13-2020, 07:42 PM
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Magnets. No, really.
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Old 01-13-2020, 08:21 PM
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Moving a wire across a magnetic field causes electrical current to flow in the wire. You might remember demonstrations in school science classes. That's how generators work - by moving wires past magnets.

You can amplify the effect by having a bundle of wires. Which is why generators have coils of wires.

But it doesn't have to be physical movement. All you really need is a magnetic field that fluctuates over time. So if you have a coil of wires next to an electromagnet, and that electromagnet is fed by an electricity source that changes over time, that induces current in the coil.

It's really that simple.
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Old 01-13-2020, 08:54 PM
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Remember how in the old days you could charge your iPhone in the microwave? Well, now you can do it on your cooktop. (Known as ERCIFBERM, or Extremely Rapid Charging Immediately Followed By Extremely Rapid Melting.)
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Old 01-13-2020, 08:58 PM
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if you have a coil of wires next to an electromagnet, and that electromagnet is fed by an electricity source that changes over time, that induces current in the coil.
Is an electromagnet necessary? I was thinking just two coils of wire separated by an air (or dielectric) gap. One coil is fed AC, which induces a voltage in the other coil. Works well if there's good coupling (coils close together, etc.).
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Old 01-13-2020, 09:20 PM
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Is an electromagnet necessary? I was thinking just two coils of wire separated by an air (or dielectric) gap. One coil is fed AC, which induces a voltage in the other coil. Works well if there's good coupling (coils close together, etc.).
The coil with AC current will generate a magnetic field, so there's your electromagnet.
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Old 01-13-2020, 10:13 PM
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Transformer. B fields must be pretty strong.
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Old 01-13-2020, 10:59 PM
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Is an electromagnet necessary? I was thinking just two coils of wire separated by an air (or dielectric) gap. One coil is fed AC, which induces a voltage in the other coil. Works well if there's good coupling (coils close together, etc.).
Yeah, that's what I meant. Any coil is an electromagnet.
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Old 01-14-2020, 09:20 AM
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I’ve had this question, too. And I may need a general how a battery works refresher.
Do I understand it correctly that (new) electrons are not coming FROM the charger. The electrons are being moved/re-positioned within the battery by (the field induced by) the charger?
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Old 01-14-2020, 09:31 AM
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That's correct, shunpiker. Even a wired charger won't move very many new electrons into a device, and it moves the same amount out, and all electrons are identical anyway, so it doesn't matter.

It should also be noted, by the way, that the energy transfer in wireless charging only works at very small ranges (i.e., significantly shorter than the sizes of the two coils). So it's fine for a phone sitting in a cradle, but wouldn't work even for a phone up against your ear or in your pocket, and certainly not for a phone you're carrying around the city.
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Old 01-14-2020, 09:37 AM
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So it's fine for a phone sitting in a cradle, but wouldn't work even for a phone up against your ear or in your pocket, and certainly not for a phone you're carrying around the city.
Yeah, but when we start beaming power from our earth orbiting solar power station we might be able to keep our phones charged while carrying them around the city.

And we won't need coats because we'll all be nice and toasty.
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Old 01-14-2020, 10:01 AM
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Also of note, the NFC feature in lots of phones is the same technology, just with lower power.
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Old 01-14-2020, 10:25 AM
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Now that all this foolishness about magnets and induced electrical currents is done for... remember guys, this is GQ, not MPSIMS! The real answer is obviously MAGIC. I can't believe you all believe this hooey about induction
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Old 01-14-2020, 10:37 AM
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Is there an easy, at-home way to test if a non-phone induction charger is working? The battery in my car key fob keeps dying. It's supposed to be charged by induction from something in the steering wheel column when the car is running. I'm not sure if the induction charger isn't working or if the part in the key that charges the battery isn't working. Since a new key costs $200, I'm hoping I can figure out if the charger still works. Is there anything I can put near the steering column to know if the induction charger is working?
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Old 01-14-2020, 11:21 AM
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Yeah, that's what I meant. Any coil is an electromagnet.
Oops, my bad. Was thinking electromagnetic = iron core.
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Old 01-14-2020, 11:50 AM
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Some people are unaware that basically the power to your home goes through a number of "cordless" connections.
Every transformer is "cordless" in that a coil creates a magnetic field which is picked up by a second coil and converted to electrical current. (OK EEs, we will ignore the occasional auto-transformer).

So at the power plant the system goes current/magnetic field/current through one or more step up transformers.
Then the power travels through transmission lines.
It does another current/magnetic field/current at the distribution substation
Then the power travels through distribution lines.
It does another current/magnetic field/current at the pad-mount or pole-mount transformer near your home.

It does this because the voltage level is optimized for the situation. Lower voltage for generation, higher voltage for transmission, lower voltage for distribution and low voltage for usage.

example
Generator output voltage 22,000 volts
step-up transformer 22,000 in 161,000 out
distribution station 161,000 in 12,000 out
pad-mount or pole-mount 12,000 in and 250 out.

Last edited by BubbaDog; 01-14-2020 at 11:51 AM.
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Old 01-14-2020, 12:19 PM
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Is there an easy, at-home way to test if a non-phone induction charger is working? The battery in my car key fob keeps dying. It's supposed to be charged by induction from something in the steering wheel column when the car is running. I'm not sure if the induction charger isn't working or if the part in the key that charges the battery isn't working. Since a new key costs $200, I'm hoping I can figure out if the charger still works. Is there anything I can put near the steering column to know if the induction charger is working?
I don't know how to tell for sure, but this link (talking about BMWs, dunno if that's your vehicle) talks about ways to charge the fob, including driving while it's inserted into the ignition, and using a regular wireless charging pad.

Anyway - if you have a wireless pad, you could try putting the fob on that for a bit. Is there any kind of indicator on the fob showing that it's currently charging? If it behaves better when you try that, that might be an indicator that it's the car's charging system. That's probably more money to fix than the fob would be, but at least then you could get by with using a cheap charging pad instead.

Does your fob plug in anywhere, or just dangle near the steering column? If so, is there a chance it needs to be in juuuuust the right position for charging to work? Could you try holding your phone against whatever surface, to see if the phone thinks it's charging? (unlikely to be successful; when I tried a wireless pad for mine the thing had to be in EXACTLY the right spot or nothing happened).
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Old 01-14-2020, 12:33 PM
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I don't know how to tell for sure, but this link (talking about BMWs, dunno if that's your vehicle) talks about ways to charge the fob, including driving while it's inserted into the ignition, and using a regular wireless charging pad.
Thanks a lot for the link. My car is indeed a BMW. The key is a single unit with regular metallic part that fits into the ignition with the fob part as the head of the key. Since the key is in the ignition switch itself, it should be properly aligned. Unfortunately, there's no charging indicator light or anything on the key. Fortunately, I do have a wireless charging pad for my phone, so I'll see if that helps at all.
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Old 01-14-2020, 01:23 PM
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Thanks a lot for the link. My car is indeed a BMW. The key is a single unit with regular metallic part that fits into the ignition with the fob part as the head of the key. Since the key is in the ignition switch itself, it should be properly aligned. Unfortunately, there's no charging indicator light or anything on the key. Fortunately, I do have a wireless charging pad for my phone, so I'll see if that helps at all.
Are you saying your fob has a real, key-like stick of metal coming out of it? Or is it like the graphic in Mama Zappa's link, where the whole fob just kind of sits in the slot in the dash? Do you have Comfort Access, meaning you don't have to stick the fob into the slot to start the car? If you have Comfort Access, the battery in the fob is not rechargeable.
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Old 01-14-2020, 01:33 PM
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Are you saying your fob has a real, key-like stick of metal coming out of it? Or is it like the graphic in Mama Zappa's link, where the whole fob just kind of sits in the slot in the dash? Do you have Comfort Access, meaning you don't have to stick the fob into the slot to start the car? If you have Comfort Access, the battery in the fob is not rechargeable.
My 15-year-old car has an an old-style key with the stick of metal like this: this. I've already replaced the coin battery in the key once from a kit on ebay, but that died after a while. So now I'm not sure if they charger in the key is broken, the charger in the steering column is broken, or if the battery was not the right kind.

If I try this kind of key on a charge pad, will any charge pad work? Does the orientation of the key on the pad matter? I realized I also have one of those Sphero robot ball chargers which I think is also an induction charger. It's like a little bowl and would be the perfect shape to be a key holder.
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Old 01-14-2020, 01:35 PM
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My 15-year-old car has an an old-style key with the stick of metal like this: this. I've already replaced the coin battery in the key once from a kit on ebay, but that died after a while. So now I'm not sure if they charger in the key is broken, the charger in the steering column is broken, or if the battery was not the right kind.

If I try this kind of key on a charge pad, will any charge pad work? Does the orientation of the key on the pad matter? I realized I also have one of those Sphero robot ball chargers which I think is also an induction charger. It's like a little bowl and would be the perfect shape to be a key holder.
You are WAY over-thinking this.
Your fob takes a battery. Replace it.
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Old 01-14-2020, 02:01 PM
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If you have certain BMW models, it might charge inductively. Would need to know some specs, but as long as the battery isn't dead, it's possible an inductive phone charger would work.

That said, if you replaced the battery on your own and it's not a rechargeable one, you are totally out of luck.
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Old 01-14-2020, 02:04 PM
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So somebody please 'splain me something to fight my iggorance, because I don't think I've ever used or seen a "cordless" charger before.

Exactly what part of this whole system is "cordless"?

You plug the charger into a wall socket? That sounds cordful and conventional to me.

And you put your phone into the cradle? Isn't that how a conventional charger works?

Does this mean that the cradle has no direct metal-to-metal contact with the bottom of the phone? Is that where the "cord" isn't?

Oh wait, does this refer to phones that you charge by plugging a cord into a mini-USB port (or not)? (As I mentioned in a nearby thread, I don't keep current with the latest tech all the time. I'm still using an old un-smart cell phone, but it does get charged by plugging a wire from the charger into it. Thus, the charger has no cradle to plug the phone into.)
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Old 01-14-2020, 02:28 PM
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So somebody please 'splain me something to fight my iggorance, because I don't think I've ever used or seen a "cordless" charger before.

Exactly what part of this whole system is "cordless"?

You plug the charger into a wall socket? That sounds cordful and conventional to me.

And you put your phone into the cradle? Isn't that how a conventional charger works?

Does this mean that the cradle has no direct metal-to-metal contact with the bottom of the phone? Is that where the "cord" isn't?

Oh wait, does this refer to phones that you charge by plugging a cord into a mini-USB port (or not)? (As I mentioned in a nearby thread, I don't keep current with the latest tech all the time. I'm still using an old un-smart cell phone, but it does get charged by plugging a wire from the charger into it. Thus, the charger has no cradle to plug the phone into.)
The charger has a cord, but you just lay your phone or watch on a pad to charge it.
No need to place it in a cradle.
It’s really a solution in search of a problem...
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Old 01-14-2020, 03:04 PM
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The inductive charging is nice for smartwatches, especially the ones you might get wet. No exposed bits to worry about.
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Old 01-14-2020, 03:36 PM
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The charger has a cord, but you just lay your phone or watch on a pad to charge it.
No need to place it in a cradle.
It’s really a solution in search of a problem...
I can pick up my phone in the middle of the night, look at it and put it back on the charging pad, instead of having to keep it tethered to a charging cable or disconnect it from the charging cable and then have to reconnect it in the dark. Yes, it's an unnecessary convenience but I like it.
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Old 01-14-2020, 03:50 PM
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So somebody please 'splain me something to fight my iggorance, because I don't think I've ever used or seen a "cordless" charger before.

Exactly what part of this whole system is "cordless"?

You plug the charger into a wall socket? That sounds cordful and conventional to me.

And you put your phone into the cradle? Isn't that how a conventional charger works?

Does this mean that the cradle has no direct metal-to-metal contact with the bottom of the phone? Is that where the "cord" isn't?

Oh wait, does this refer to phones that you charge by plugging a cord into a mini-USB port (or not)? (As I mentioned in a nearby thread, I don't keep current with the latest tech all the time. I'm still using an old un-smart cell phone, but it does get charged by plugging a wire from the charger into it. Thus, the charger has no cradle to plug the phone into.)
No cradle, just a flat pad you lay your phone on.

The charging pad is connected to the electrical outlet with a cord, but you do that once and it's all set. When it's time to charge your phone, you never have to fish around for a cord and then connect/disconnect that cord to your phone. The convenience lies in quick, one handed operation: just set your phone down approximately in the center of the charger pad, and it starts charging. here's a video review of one; the disembodied hand sets a phone down on the charger at 1:12, and it starts charging right away. Done charging? Pick up the phone and walk away.

Not all smartphones have this feature. But it's popular enough so that Apple started incorporating it into their iPhones starting with the iPhone 8.
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Old 01-14-2020, 03:54 PM
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...“How do cordless charging stations work?”

Salesperson said: “Real easy! You plug in the charging station to a wall outlet, put the phone in the cradle, and it charges!”...
I'm reminded of the story about Michael Okuda (who co-wrote the Star Trek: The Next Generation Technical Manual) being asked "How do the Heisenberg compensators work?"

To which he reportedly responded, "They work just fine, thank you."
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Old 01-14-2020, 03:55 PM
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Not all smartphones have this feature. But it's popular enough so that Apple started incorporating it into their iPhones starting with the iPhone 8.
Weirdly, though, I don't think Apple sells a charging pad under its own brand. (I was at an Apple Store a few months ago and they had charging pads, I think Belkin brand, but none of their own.) It seemed odd for them to abandon the market.

Last edited by Dewey Finn; 01-14-2020 at 03:58 PM.
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Old 01-14-2020, 04:30 PM
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Is it possible to charge your Tesla with some average brand-less home cordless phone charger? How much time would it take? Or how many would you need to charge it in some reasonable time? I'd guess some compatibility problems could also occur.
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Old 01-14-2020, 04:36 PM
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Does this mean that the cradle has no direct metal-to-metal contact with the bottom of the phone? Is that where the "cord" isn't?
Look at a few examples.
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Old 01-14-2020, 06:05 PM
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Is it possible to charge your Tesla with some average brand-less home cordless phone charger? How much time would it take? Or how many would you need to charge it in some reasonable time? I'd guess some compatibility problems could also occur.
Ignoring the fact that the Tesla doesn't have an inductive coil to receive the charge:

The comes-with-the-car Tesla mobile charging adapter can do 32 amps at 220 volts. A phone inductive fast charger does 1 amp at 9 volts. That's a difference of something like 7000 watts. The inductive phone charger would provide about 0.03 miles of charging per hour. On the other hand, I think the Tesla mobile charger can charge a phone in 0.8 seconds.
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Old 01-14-2020, 06:58 PM
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It’s really a solution in search of a problem...

In my experience, the USB jack is the first part of a phone that breaks or wears out. If you mostly use a wireless charger, you won't wear out the USB jack.
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Old 01-14-2020, 07:22 PM
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There's a rumor that the next iPhone model will not even have a charging port but instead will require wireless charging.
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Old 01-14-2020, 07:47 PM
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The charger has a cord, but you just lay your phone or watch on a pad to charge it.
No need to place it in a cradle.
It’s really a solution in search of a problem...
That’s not how mine is oriented. It’s not a flat pad. It’s a circular base, with a flat piece about the size of my iPhone attached to the base and standing up at a bit of an angle. That’s what I mean by the cradle.

But it is wireless in that there is no wire connection between the phone and the charging unit. I just set it in the charger, standing up against the flat piece, and it charges.
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Old 01-15-2020, 11:36 AM
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[Monty Burns voice]”Magnets eh? That must be what powers the autogyro!”[/Monty Burns voice]

Thanks for the replies, everyone. Very interesting and informative. One less thing to befuddle the techno-peasant.
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Old 01-15-2020, 02:17 PM
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And thanks to those who answered my newbie questions with your explanations, including that link with the pics.

Interesting that multiple charging platforms by multiple manufacturers, and multiple kinds of devices from phones to watches to Teslas, can all be used compatibly, and that a single charger can charge several devices at once. Whoda imagined it? Next thing you know, we'll all start agreeing on which way to hang the toilet paper.

Still, surprising that Apple doesn't offer (and require) their own charging device for their own mobile devices.

I suppose one of these days I'll need to get with the program and update myself to at least mid-to-late 20th century, for starters. I'll get right on it as soon as I finish my current project of installing indoor plumbing.

Last edited by Senegoid; 01-15-2020 at 02:19 PM.
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Old 01-15-2020, 04:17 PM
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No cradle, just a flat pad you lay your phone on.

They come in different shapes. I like the phone stand style. The phone is more stable on it than on a pad, and it's easier to see notifications on it.

I also have this one in my car. It's great when I want to use a phone for navigation on a long drive.

Wireless chargers are definitely not a necessity, but it's a great convenience.
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Old 01-15-2020, 05:15 PM
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My '16 Avalon has a built in charging pad in front of the gear selector on the console. Very handy, until I bought a galaxy S10+ which does not fit in the allotted space.
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Old 01-15-2020, 05:32 PM
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There is all kinds of cool stuff out there. Last year I was looking at power bricks with wireless charging--some of them combine that plus solar panels and a flashlight. (Of course the solar panels would take forever to charge, but if they are "free energy" while the brick is sitting around, why not?)
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Old 01-15-2020, 05:50 PM
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My wireless charger is a little finicky - if I have the phone misaligned, it sometimes doesn't charge. But it is convenient not to have to unplug it if the phone rings (or to wear out the USB port)
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Old 01-16-2020, 12:39 AM
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Still, surprising that Apple doesn't offer (and require) their own charging device for their own mobile devices.
iPhones and the AirPods charging case use the Qi charging standard, which is pretty much the de facto standard for wireless charging.

In September 2017 Apple announced it was working on its own wireless charging mat called AirPower which it expected to come to market in 2018. It could do a bunch of things no other charging mat could do at the time, but by March 2019 Apple announced it had canceled the project, ostensibly because they weren't able to overcome overheating and interference issues.
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Old 01-16-2020, 06:16 AM
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Interesting that multiple charging platforms by multiple manufacturers, and multiple kinds of devices from phones to watches to Teslas, can all be used compatibly...
Such is the blessing of industry standards. There are thousands (millions?) of industry standards out there, including the one that lays out specs for wireless charging technology. No manufacturer has to use it - anyone is free to develop and use their own standard - but instead of their standard being widely adopted, they may find that they're the only one that uses it.

From that Wikipedia page I found a link to a competing wireless charging standard called WiPower, which sounds vaguely racist; they probably could have chosen a better name.

Obligatory XKCD reference.
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Old 01-16-2020, 07:52 AM
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Originally Posted by Dewey Finn View Post
I can pick up my phone in the middle of the night, look at it and put it back on the charging pad, instead of having to keep it tethered to a charging cable or disconnect it from the charging cable and then have to reconnect it in the dark. Yes, it's an unnecessary convenience but I like it.
The station next to my office in London was recently renovated, and they put in smart new wooden benches with little round tables on the armrests. I noticed recently that the tables have a little charging symbol engraved in the wood, and sure enough, if I put my phone on the table, it charges. So now I can sit there, drink my coffee, and add a few % to my phone battery while inviting passing pickpockets to snatch it off the table
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Old 01-16-2020, 11:06 AM
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I'm pretty sure my new electric toothbrush I got for Christmas uses this, too, as there was no metal contact that I could find. I suspect that it prevents any risk of shock from the water.
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Old 01-16-2020, 11:08 AM
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If your electric toothbrush is an OralB model, then yes, it uses inductive charging. I don't know about other brands.

Last edited by Dewey Finn; 01-16-2020 at 11:08 AM.
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Old 01-16-2020, 11:11 AM
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How does the efficiency of induction charging compare to corded charging? Does it take more electricity to charge a phone through induction rather than plugging it directly to a charger?
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Old 01-16-2020, 12:29 PM
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Quote:
Originally Posted by filmore View Post
How does the efficiency of induction charging compare to corded charging? Does it take more electricity to charge a phone through induction rather than plugging it directly to a charger?
It's 10%-15% less efficient than a cord (early versions were worse). For such low-power devices the extra electricity cost doesn't tend to bother folks, but you wouldn't want to use this technology to charge an electric vehicle.

Electroboom has a great video on this.
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Old 01-16-2020, 01:03 PM
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You really, really don't have to worry about how much electricity it takes to charge a cell phone.
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