Posted by Mitch Randall on Apr 19th 2015
If you are not a tech blogger, you may not know the difference between inductive versus conductive wireless power technologies. Actually, even if you ARE a tech blogger you may not know! You also may not know why this is important, but, believe me, it is...
To explain these terms, I'm going to talk about something that everyone is familiar with - light switches.
Light switches have been around for more than a century and they work well. They are nearly 100% efficient (they don't get hot), they are reliable, they are easy to manufacture, and they are inexpensive.
A light switch is so simple that no one probably ever bothered to explain it, but I will: When you flip the switch, two pieces of metal come into contact so that an electrical connection is formed to close a circuit. The light comes on.
That is what you call "conductive" technology. ...because the electrical power goes through the switch by direct conduction.
Now suppose some smart whippersnapper comes along with a breakthrough improvement to the old-fashioned light switch. In this new light switch there are two coils of wire. When you flip the switch, the coils move together and the light comes one. But there is a little more to it...
One coil of wire is connected to a microprocessor circuit that sends a test signal out periodically to detect the second coil. If it doesn't detect the second coil is close, it tries again a little while later. If it detects that the second coil is close, then it sends an alternating current at 350,000 cycles per second into the coil. The coil's inherent inductance is resonated with an external capacitor to amplify the amount of circulating current by a factor of 10 or so to increase the electromagnetic field around the coil. At the same time, a microchip connected to the second coil detects the field generated by the first coil and synchronizes itself to the alternating current. The synchronization signal is used to alternatively power electrical switches so that they charge a capacitor to a DC voltage. Depending on whether the DC voltage is too high or two low, a digital command is encoded and sent back to the first coil. This is accomplished by a variation in the loading of the second coil in an on-off fashion to send the serially-encoded command. At the same time a feedback loop is monitored by the microprocessor to adjust the frequency of the alternating current slightly above or below the nominal 350,000 cycle per second rate in order to optimize the transfer efficiency. Thus a regulated DC voltage is produced that energizes the light.
I just described the standard for inductive wireless power. This is inductive technology.
You may be asking yourself a lot of questions - like, "Why am I still reading this article?" - but besides that, it also raises a lot of questions for me as well.
Because ultimately I just want to walk over to my light switch, flick it, and have the light come on. I don't really care what is happening inside my light switch. Do you?
But I do care if it breaks. I care if it is expensive. I care if there is something in there that could affect my health. I care if it is wasting electricity.
As you may have guessed, there are good reasons why there are no inductive light switches on the market. It would provide exactly the same functionality, only more expensive, less reliable, and less efficient. And there would be a question about health safety.
So let's talk about wireless charging. Open Dots is a conductive technology, like a light switch. Open Dots products have the distinctive pattern of dots on the back.
These are electrical contacts that close a circuit just like a light switch does. All the other products on the market use coils and are called inductive. All these products, inductive or conductive, have one thing in common: To charge, you set your device on a pad.
So you may ask yourself why go through all the trouble of induction if you could just make direct conductive contact?
But there is more - here is the kicker - inductive has many more limitations than conductive. Inductive requires one coil per device. That means that if you have 5 things to charge, you need a pad with 5 coils. Unfortunately they don't have such a thing on the market. Further, inductive only handles 10 Watts - about enough for one phone. Some inductive products have coils for higher powers, but your phone won't charge on those coils.
Inductive can be hidden invisibly in a table, but the odd thing is, there has to be a mark on the table to tell you exactly where to set the device. So that is a wash.
In contrast, Open Dots does not have these limitations. You can set your device anywhere on the pad. You can charge as many devices on a pad as will fit. The technology can handle 160 Watts. That's enough to charge a LOT of phones. Or it could charge hundreds of Bluetooth headsets if you had a big enough pad. You can also charge a laptop (65 Watts) on the same pad you are charging your phone (and at the same time, of course).
I think I can summarize this for you pretty concisely: When you are looking for a wireless charger, look for the dots.