There was a time in the early years of wireless charging when Qi* was only a 5W standard, officially referred to as the baseline power profile (BPP). All phone chargers could charge all Qi 5W capable phones without issue. But the user experience at 5W was generally poor. So, it became important to move the power capability up to what is known as the extended power profile (EPP), which permits up to 15W of charging power. But what does 15W even mean?
As I’ve shared in previous blogs of this series, I’ve seen no correlation between a claimed wattage benefit and a realized benefit. Whereas 5W heating was manageable, at 15 W heating is a big challenge. Perhaps the only challenge. This is why manufacturers invariably build modern chargers with various methods using fans, vents, and larger coils. What was once standard, is no longer standard.
So, now the market has evolved such that proprietary chargers are becoming the new norm. I predict that eventually all phones won’t charge with standardized EPP wattages. We already see the early signs of this. Google’s Pixel 3 phone is one example. Xiaomi’s 20W phone and chargers are another example.
Consequently, users should expect that public wireless charging pads and stands will most likely only charge at 5W. This means that wireless charging in public places will be useful only for a partial battery charge, and even then, only if you are not using the phone. It is a good idea to plan accordingly.
On the other hand, wireless charging will become the accepted method of charging once it has reached the point of being good enough; just as with wireless internet. But this will only be true if there is no new battery technology that eliminates recharging all together (i.e. nuclear batteries?). While there are new battery technologies on the verge of being introduced, they are oriented towards faster charging rather than longer times between recharges. I suppose this is where advanced technologies like Gallium Nitride electronics become valuable, albeit a very expensive technology.
Cases, Coils, and Fans
The charging current in a phone is generally independent of a phone case provided the case is not too thick. I write "generally" because I have seen situations where the opposite is true. While I didn't fully research this phenomenon, it does seem that this is related to whether the dominant heat flows from the charger surface or occurs internal to the phone. Both have coils that heat.
For those chargers that don’t support long distance charging, typically beyond 4mm, they might not charge a phone at all. Perhaps worse, charging can be hit or miss depending upon something as simple as room temperature or having your phone set on the charger at a slight angle. The phone might start charging for a while, then all of a sudden, and without warning, stop charging.
For those chargers that do charge across the thickness of a case, the charger coil will heat up substantially more than for a thin case or a phone without a case. This is because the charger seeks to overcome the distance power loss by simply increasing the charger’s coil current. Hence, there is an increase in coil temperature at the surface of the charger; the surface that touches the back side of your phone. This can have an effect on charging time, but more importantly, some chargers may shut down due to getting too hot.
You have no way of knowing if a charger shuts down due to overheating except that your charging time may be longer; a lot longer. This situation can happen if charging stops while the charger cools down, and then tries to restart charging again some time later. This process will continue to cycle until the phone is charged.
The chart below is an example of a charger overheating and then cycling while the charger cools down. As the chart shows, it took over four (4) hours to charge a Galaxy S9 while sleeping.
Fanless charger overheat cycling throughout the charge cycle
I find the above situation a bit disturbing since high temperatures are not a good thing for the phone’s battery; not to mention your phone case might suffer from discoloration. Mine did. This brings up the topic of fans.
I have learned that a charger with a fan will definitively charge faster than a charger without a fan. But just having a fan is not sufficient.
I’ve reviewed perhaps 16 wireless chargers over the course of my work. The majority with fans. Not all chargers with fans were able to provide sufficient cooling to allow continuous charging while using the phone. For those fan-enabled chargers that didn’t, the fan only accelerated the recovery time from overheating. If using the phone while charging is an important consideration, you will need to compare fanned chargers to find the best for your situation.
There is a downside with a fan. Noise.
All fanned chargers produce noise that is detectable. I must say, though, that the latest Samsung Charger 2.0 dock is by far the quietest I’ve found. They have a fan designed into the housing rather than a separate fan mounted onto the housing.
Samsung Charger 2.0 Dock with Internal Fan Cooling
Despite fan noise, it is less objectionable if the fan runs only while charging. Surprisingly, I uncovered premium chargers where the fan never went off. This is very annoying. Imagine having such a charger by the bedside if you are a light sleeper. Unfortunately, this feature of a charger doesn’t show up on packaging. So, this is another buyer beware issue.
What is One to Do
This blog is the fourth in a five blog series on wireless charging smartphones. It has been a long road, with lots of turns, to get to this point in the blog series. Perhaps even a little overwhelming at times. That certainly was the situation for me as I waded through nearly one-year of testing, ripping apart numerous chargers while studying a multitude of phones and cases, and all under various operating conditions. I have certainly tried to be thorough and fair, but I suppose being overwhelmed is one consequence.
By now it should be very clear that just buying any wireless charger, and setting your phone on to that charger, will not lead to the best results and minimum frustration. So let me cull everything down to a few simple observations and actions so that you may derive the best experience from wireless charging.
First, ignore claimed wattages. Until a new generally accepted method for classifying wireless charging speeds is available, it will remain on the shoulders of consumers and unbiased research to provide true metrics.
If high speed wireless charging is important to you, it is best to use a charger with a fan. If you purchase a fanned-charger, verify that the loudness of the fan is acceptable and that the fan shuts down once charging has completed.
Second, it is important when buying a charger to carefully read the phone compatibility list. There are chargers that state Qi standard compliance with a capability of 10W to 15W charging power. Those chargers also claim to support iPhones. But supporting an iPhone can mean Qi compliance at 5W rather than the iPhone’s limit of 7.5W. This is an example where one would buy a charger and have a terrible experience. How would one know that the charger they purchased was only 5W capable? Without some basic electronic tools, they wouldn’t.
Likewise, be sure that your phone will support charging from all non-proprietary higher wattage chargers, if that is important to you. As I wrote previously, Google’s Pixel 3 is one example where this is not true. To charge at the fastest rates requires their proprietary charger.
Third, I would verify that a charger for use in the United States has an FCC ID number, not just the letters FCC or the FCC logo. This is from a safety perspective as much as a radio interference perspective. I don’t mind telling everyone that I would be a little concerned about regularly using anyone’s 30W or 40W wireless charger that didn’t have an FCC ID number.
I just read the other day about recent FCC approvals for long range wireless chargers. These are chargers for low power devices where charging can happen over large distances. Here, large means feet or meters. Not millimeters. Most of this work is being done by startup companies.
One of the specifications I read claimed that for a 30W long range charger, the distance to a human must be over 20cm. From my perspective, I wouldn’t care if it were 1 mm. The very fact that a number is assigned already concerns me.
If like many consumers, you purchase electronics from stores in Amazon’s wild west shopping mall, my fourth recommendation is to keep in mind that product description pages on some online stores can be downright misleading. For a product where you have virtually no ability to validate the performance other than if it charges your phone or not, I highly recommend buying a charger from a brand-name company with a reputation to protect; not to mention at least a website with a contact address and phone number.
While I hesitate to make such a suggestion, Amazon does have a liberal return policy, so, one could purchase 3 chargers and test them out, returning all but the best charger. I would certainly verify first if that is an option. Perhaps it might also be best to visit a block and mortar store.
A fifth consideration that I haven’t discussed at all are the LED notification lights. Lights on chargers is not an option. For one, they are required on chargers purporting to be Qi compliant. But even if a charger is not Qi compliant, the LEDs serve to notice that a phone has been detected and the phone is charging. Without such a notification, you might not know if charging had commenced for several minutes. For example, iPhones don’t provide a notice of charging until the battery is at 2%. At 5W, that can be a long time of hanging around waiting for a beep.
For a charger placed in a bedroom, it is perhaps important to also check the brightness of these LEDs. Some start bright, then dim. Some stay bright. If this is important, be sure to check what the LEDs do with no room light.
My sixth and final suggestion--and this is perhaps the easiest piece of advice I can offer—if your only requirements are that your phone is charged overnight, on the nightstand next to your bed, then just buy a brand name charger dock without a fan and be done with it. You will be happy not to deal with cables when picking up or looking at the phone in the middle of the night, and the phone will be certainly charged overnight because the phone slept also.
My only concern would be for those nights when you might need to leave the house in the middle of the night for an emergency. The phone might not have a sufficient charge, which will be very irritating.
Going Forward
My company has publicly released the previously mentioned iPhone app that has proved very valuable to us while conducting our research. Likewise, the app enables consumers to run their own charging tests under their particular configuration of phone, charger, case, and usage. We have developed an Android version that was used to produce results in this blog series. With sufficient interest, that app can be released on Google Play.
I’m also willing to manage the collection of user metrics, compiling those metrics, and then openly sharing the results. The objective would be to help establish industry standards for comparison metrics, which is what is truly required given the complexities involved in charging wirelessly. Until simple metrics are established--which was supposed to be the purpose behind Qi--it will be hit or miss for wireless charging adopters.
For those readers who think any of the above suggestions would be a valuable service, please leave comments in the comment section for this blog. Also, please subscribe to our Newsletter so that we may keep you informed as future blogs and vlogs on wireless smartphone charging become available.