A question was recently posted on Quora asking why there are no viable wireless chargers available on the market. Of course, viable is a relative term depending upon what one expects from a charger. Certainly, there are chargers available that work. So why would someone ask this question? No doubt it is because of their expectations or lack of success using the technology. I think I can help here.
I’ve been researching wireless charging for the past few years and have concluded that there are three distinct groups of users:
- Those frustrated because it doesn’t work for them reliably, if at all.
- Those disappointed with the speed of charging.
- Those who are happy with their charger because they don’t have to deal with aligning small connectors or dangling cables whenever they pick up or place down their phone.
Despite the shortcomings experienced by Groups (1) and (2), it is clear to me that wireless charging is only going to grow in usage. Nevertheless, everyone needs to be happy with a solution before it becomes universally acceptable. This is not yet the case with wireless charging.
While there are several blogs online that teach the basics of how to use a wireless charger, no one provides objective insight, nor do they explain how specifications distort the true capability of not only the charger, but the phone it is designed to charge. As it turns out, the phone plays a huge role in wireless charging and not in the way manufacturers lead one to believe. Regardless of which group you fall into, my goal in sharing my research is to empower others to save money, time, and frustration.
This first blog is one of a series of four blogs [ 1 , 2 , 3 , 4 ] that covers all of the issues to consider when deciding on a particular charger, or if wireless charging is even a reasonable option for you.
First Group Experiences
The experiences of those in Group (1) hail from one or more of four possible sources: misalignment, foreign object detection, phone cases, and low power chargers.
Misalignment
The first hurdle to climb is phone alignment. Here the center back of any wireless charging smartphone should be aligned with the center of a charger’s coil, which is buried immediately below the surface of the charger.
Contrary to what is often written though, misalignment does not directly affect the rate of charging. For example, the coils in charger docks are not circular, but rather oval, as shown in the picture below. This is done to accommodate all of the various popular smartphones, which don’t have their coils in the same relative location anyway.
Oval charger coils to accommodate various phones
On the other hand, flat chargers do have circular coils; but that turns out to be a curse for alignment, and the reason why wireless docks provide the best experience.
Whereas a flat charger requires two visual alignment steps looking from above, a dock requires only one alignment step which can be accomplished by feel. This is great for visually impaired users, especially given the capabilities of smartphone voice assistants such as Siri, Alexa, Bixby, and others.
Docks simplify alignment through two features.
First, docks have a bottom pedestal that inherently aligns the vertical center of a phone’s back with the coils inside the charger. As mentioned above, this is possible because docks use oval coils, not circular ones.
Secondly, docks have a back rest that is slightly narrower than the phone. This enables one to reliably and horizontally align by holding their phone just as they do when answering a phone call, and then using their thumb and fingers as guides while sliding the phone down on to the charger pedestal. The fingers and thumb can feel the charger edges as the phone is slid down the backrest. This method always provides accurate horizontal alignment.
While flat pad chargers certainly work, I wouldn’t recommend buying one. This is not only because of alignment issues, but also because I can’t use the phone with it lying down. I can’t watch a video playing or read streaming text with the phone laying flat. And the camera can’t see my face for facial recognition or video calling.
Foreign Object Detection (FOD)
All chargers should, and most do, have the capability to detect foreign objects. A foreign object is any metal object near (or covering) the backside of the phone. The most obvious reason for metal to be present is when there is a metal object inside or on the phone’s case (i.e. zipper, metallic business or credit card, house key, etc.).
Phone case example that can create FOD failures
While metal doesn’t block the process of charging, it does absorb power transmitted by the charger. If charging is permitted to continue, the metal will continue heating up. This is similar to what happens with a pot sitting on top of an inductive cooktop in your kitchen. Neither situation is safe. Hence quality chargers will not attempt to charge a phone if a foreign object is detected.
Interestingly, I have tested some wireless chargers out of China that don’t have FOD capability, or if they do it doesn’t work. I conducted my tests with a piece of aluminum foil laid on the surface of a charger. After some time, the foil became too hot to touch. I wonder what would have happened overnight had I left a phone on top of the charger with metal in its case.
Another interesting observation was that even for those chargers that had FOD detection, I could hear clicking noises inside the charger that no doubt was a consequence of the coils switching on and off during the perpetual FOD monitoring tests. This is not so much a safety issue, but rather a quality issue. A charger built with higher quality components doesn’t suffer from this issue. I hesitate to recommend anyone do this test on their charger, so I won’t and don’t. But should anyone try this despite my cautions, don’t leave the metal in place or unattended for a long time. You might get burned, you might start a fire, or worse.
Phone Case
For safety as well as radio interference reasons, there are government regulatory requirements that set the amount of power that can leak out of a charger into the surrounding environment. This is similar to limits placed on microwave ovens, and for similar reasons.
To stay within those limits, the coils inside a phone and charger are sandwiched between two ceramic sheets with magnetic properties. This arrangement creates a containment region around the coils so that charger power couples almost exclusively to the phone.
This sandwiched region is extremely thin when a case-less phone is laid against a charger’s surface. But for certain rugged cases, such as the Defender case sold by OtterBox, the sandwiched region is no longer relatively thin. The distance between the charger and phone coil is substantially increased. There are potential consequences that can result.
An interesting aspect of wireless charging is that the phone and charger are constantly speaking back and forth while the phone is resting on the charger. It is through this communication that a charger can detect the increased distance when using a rugged case.
Beyond a certain defined distance, the charger will refuse to charge the phone. It will appear as if the charger is not working. While this can be frustrating, it is in the best interests of public safety that there are limits when the distance is too far. While a bit of an extreme comparison, no one wants a microwave oven running with the door open either.
During my research I have found that quality chargers work with a maximum distance of about 4 mm to 8 mm. A rugged case is typically over 4mm thick. Therefore, users with rugged cases can experience situations where their phones won’t charge with certain chargers. The best chargers seem to be those that support a separation distance of up to 6mm. The OtterBox Defender series falls well within this range.
If your phone has a rugged case, I recommend checking whether your cased phone charges while separated from the charger by a stack of 4 or 5 paper business cards; or something similar to business cards. I designed a set of spacers for my testing, which are shown in the picture below. But whatever you choose, just don’t test with something metallic.
Spacers to test that a phone will reliably charge through its case
Such a test will verify that there is enough performance margin should your charger-case-phone combination be right on the edge of not working. When it comes to electronics, even small changes in temperature make all the performance numbers move around. What charged one day, might not charge another day. Just verify the margin, and you’ll most likely not see any problems provided you always lay your phone flat against the charger; emphasis on the word flat. Should you lay it at an angle, that is the same thing as adding distance between the coils. The same consequence may result; no charging.
I had another interesting experience in regard to rugged case charging with a certain charger purchased off Amazon; the wild west for shopping. Over the course of several months of research, I had purchased eight of these certain chargers; not all at the same time. I tore most of them down.
Early on, I had been able to charge an iPhone Xs through a Defender case with this particular charger. Later in my research I had reason to buy three more. On Amazon, buying more of the same item is an easy, search free, transaction.
One day I noticed that charging had stopped at 65% using one of the more recently purchased chargers. Initially I thought that perhaps the charger was bad, so I tried another. That one also didn’t work. Clearly, these were not the same as the original version chargers I purchased. I eventually discovered that the earlier chargers had only the text “FCC” on the charger label, whereas the newer chargers had a complete FCC ID number which I was able to verify online. Why is that important?
FCC is an acronym for the Federal Communications Commission of the United States (U.S.). The FCC is an agency of the U.S. federal government whose job it is to oversee things such as charger leakage; although they call it more formally radiation emission limits.
Based upon the above observations, I concluded that at first the charger manufacturer either never submitted their charger for FCC certification or they failed certification testing and chose to sell their product anyway. At any rate, no number. Apparently, when it became necessary to meet the requirements, they had to make design changes that included lowering the maximum charging power to a point where the Defender case was now too thick. Hence charging was no longer possible.
On that same charger, I also measured an extremely hot point on the surface nowhere near the coil. The temperature was much higher than I ever measured over the coil. I believe this is also what caused a discoloration of one of my test charger cases.
The moral of the above story is that for safety reasons, it is best to ensure that any charger you purchase has a legitimate FCC ID number, not just the text FCC. Every charger I bought directly from China had only the FCC text. Several that I bought from the wild west shopping mall in America also only had text.
The FCC ID number can be found on the label of a charger and can be verified by checking the number on line at the FCC ID verification site. But spending time checking a number only makes sense for those trying to save every last dollar, euro, or yuan. For the rest of the population, buy a charger manufactured by a respected brand name company and be done with it. Personally, I don’t think it is worth debating over a $30 price difference to reliably and safely charge a $800+ phone.
Low Power Chargers
Many wireless charging adopters opt for the least expensive chargers that are 5W rated. A typical recommendation from low power charger manufacturers is that users power their 5W wireless chargers with USB charging adapters that are capable of at least 10W or more. Most 5W chargers won’t even start with a 5W USB adapter.
Unfortunately, the dominant wattage of USB adapters lying around a home or office are the 5W variety. And naturally they use the same cables as higher wattage USB adapters. So, it seems perfectly reasonable that someone would plug a 5W USB adapter into a 5W charger and expect everything to function. Of course, it generally won’t work. So, make sure that, even for the lowest power chargers, you use a 10W or higher USB adapter.
Second Group Experiences
The next blogs in the series will cover the topics:
- More watts do not equal more watts.
- Why is there no relationship between charging speed and Watts?
- Qi, the wireless standard, is not so standard after all.
- Wireless charging is all about heat and the thickness of your phone.
- Do you really want a cooling fan in your charger?