Power toothbrushes are becoming more popular each day. Some simpler power toothbrush models operate with AA or AAA batteries so when power runs out you need to replace the batteries. The higher-end, more expensive models have a build-in rechargeable lithium battery which is recharged using wireless power technology. I happen to have one of those. Cool! That calls for a wireless charger experiment.
Experiments using wireless power transmission have been around for a while. Back in 1891 Nikola Tesla lit electric lamps wirelessly at his New York offices, providing evidence for the potential of wireless power transmission.[1] Forward to the 2000’s this technology can now be seen in bathrooms around the world.
How wireless charging works
In simple terms, the wireless charging base station creates an electric current. Per the law of electromagnetism, changes in electric current creates a magnetic field in the space around it.
That magnetic field is energy. And that energy can be picked up by placing a wire in that proximity. Picking up a magnetic field is called induction. We’re inducing a current in the wire.
In a nutshell, this is the theory of operation. However in the real world, for you to have meaningful energy transfer between the charge station and the toothbrush, they need to be very well “tuned” to work with each other. If you take a random wire and put next to the base, you’ll not get any useful amount of energy.
This tuning is extremely complicated. Parameters include:
- coil wire gauge
- number coil winding turns
- coil core material
- coil inductance
- modulation frequency, voltage
- distance from transmit and receive coils
- material between coils (air, plastic)
(Fortunately there’s a group called Qi Wireless to facilitate the progress of the technology. Products sold under that makes it easy for developers to get up and running quicker)
Wireless charger experiment
Just because it’s a complicated technology does not mean we cannot start learning more about it.
One simple experiment is to use an oscilloscope to measure the modulation frequency of the wireless charging station is using to transmit power. Another measurement is the effects of number of coil turns in the receiving station.
We can achieve way to measure that is the connect the signal and ground clips of the oscilloscope, then wrap that cable around the center protrusion of the base. As easy as that you now have a simple “wireless power analyzer” 🙂
So, let’s go ahead and watch the video where I show how the number of coil turns around the primary coil of a wireless toothbrush charger affect the output voltage in the secondary coil.
This voltage picked up by the secondary coil is ultimately proportional to the power to charge the battery.
Also, I show a quick and easy way to measure the modulation frequency of the charger unit. The modulation frequency is a number chosen by the toothbrush manufacturer after tuning the transmitter and receiver units.
Check out the video where I do those measurements:
[youtube http://youtu.be/dIoXLFuqggY]
This is the wireless charger. It’s the charger from an electric toothbrush, make is Braun Type 3709
Further reading:
- Inductive Charging in Wikipedia
- How Wireless Power Works at How Stuff Works