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  • Author Author: janisalnis
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02 Wireless charging in household items - construction and wallplug efficiency

janisalnis

Previous blog entry: 01 First experiences and plans for Wireless Power Challenge

Next blog entry: 03 Searching for Electro-Magnetic Interference (EMI)

 

Wireless charging with inductive coupling has been around in our homes some time.

One application is linked to medical equipment. Electrical toothbrushes remove plaque more efficiently than conventional ones and are intended to be rinsed with water or disinfected. Electrical toothbrush tipically contains a 1.2V NiCd and is charged by putting it into a stand containing wireless charger. The chargers of the toothbrushes are also hermetically sealed. Cost is from 24 EUR and upwards.


Philips toothbrush

image

  • It is from year 2000.
  • On the transmitter indicated power consumption 3W.
  • Oscilloscope picks up quite nice sine wave with T= 19 us, frequency 52 kHz.
  • No automatic transmitter shutdown. Transmitter continues to oscillate also when toothbrush is removed.

 

Braun Oral-B toothbrush

image

  • From year 2010.
  • Wireless charging of 1.2 V NiCd. One can find youtube videos how to replace the NiCd.
  • Oscilloscope picks up quite nice sine wave with T=30 us, frequency=33 kHz.
  • No automatic transmitter shutdown. Transmitter continues to oscillate also when toothbrush is removed.

 

 

Pocket Flashlight Torch

image

Another application for wireless charging is a pocket torch. They are used in garages, basements and construction sites where moisture and dirt could be a problem and wireless charging prevents from contact oxidation and allows to hermetically seal the torch. It can be easily grabbed and put back in holder while being in the darkness.

 

  • Bought in Swedish home-repair shop for 12 EUR.
  • 9 white LEDs with lenses. One dim blue LED indicates charging.
  • Three AAA rechargeable batteries. Specified 440 min burn time at 13 lm.
  • Automatic transmitter shutdown  when flashlight is removed. Automatic charging start when torch inserted. Coil is wound by normal magnet wire, many turns, without magnetic shielding. Concentric with recever coil. Frequency 27 kHz. Can be seen on oscilloscope if the probe is near the coil.

 

 

Curiosity was driving me to examine it inside.

image

Construction is held together with screws and hermetic seals made with rubber rings. Transmitter coil is driven in transformer-less circuit from 220 V. On the board is rectifier, 10uFx250V and a few other components. Coil has only 2 wires and is driven by something looking like a single transistor. A42 B331 written on it. Searched but could not find a datasheet. Probably it is something more smart. Because circuit has an automatic shut-down when flashlight is removed.

 

 

Samsung Galaxy S 4 Qi Wireless Charging Pad

It is the most recent application up to date. One can find for reviews in the Internet. Transformation is done by replacing the original Samsung battery and cover. It is the same standard as used in Texas Instruments wireless power kit that will be used in the upcoming blog posts.

 

 

 

Examining Wireless charging wallplug efficiency

 

Let’s examine wallplug power efficiency with a Voltcraft Energy Monitor 3000.

image

We will measure active power dissipated. Device displays also reactive power that is tipically about two times higher, but we are not paying for it.

 

Philips toothbrush

  • idle without toothbrush   2W
  • while charging also   2W

 

Braun toothbrush

  • idle, toothbrush removed   0.7W
  • when charging   0.7W


ClasOhlson Torch

  • idle, torch removed   0.9W
  • when charging   1.1W

 

Texas Instruments QI wireless power kit

  • wallplug power used without receiver board    0.0W
  • with Würth Electronics LED load board    2.0W

 

Excellent! Shows that TI Qi automatic shutdown is working nicely.

In summary, only the TI Qi meets the EU regulation stating that standby consumption should be <0.5W.

 

 

Next blog entry: 03 Searching for Electro-Magnetic Interference (EMI)



Parents

  • The torch doesn't look to me as if it really shuts down at all when the load is removed. The small reduction in power drain may be simply due to the removal of the charging load increasing the impedance of the coil.

     

    If the EU regs are in force then the torch is non-compliant  - is it CE marked ?

     

    Oh, and how confident are you about the power meter accuracy at very low powers like these ?

     

    MK

  • in reply to michaelkellett

    Thanks for reading through my blog.


    I will look on Monday if the torch has CE mark on it's sticker.

     

     

    Thanks for valuable remarks about the power meter that it might not be accurate <1.5 W.

    I will redo measurements with  some bias load (for example a 60W lamp) on Monday.

     

    Below are the specs of "Voltcraft Energy Check 3000 energy costs indicator":

    Effective power range 1.5 - 3000 W

    High accuracy starting from 1.5 W through real-effective value measurement (True RMS)

    Accuracy class ± 1 %

    Parameter resolution

    Voltage measurement : 0.1V

    Current measurement : 0.001A

    Frequency : 0.01Hz

    Active and apparent power : 0.1W/0,1VA (for 1.5 to 1000)

    Own consumption 1.8W

  • in reply to michaelkellett

    There are similar power meter devices sold over here, and they are way out.

    I suggest the only real way is to expose the mains through a small resistor on the neutral side, and measure the voltage across the load, and the voltage across the resistor, apply some ohms law to get the real figure.

     

    Even a 60w lamp is nominal, so unless you use a measured resistor, (105.8k for 0.5w @ 230v ) you won't know.

     

    Mark

  • in reply to mcb1

    There is a big jump in cost if you want an accurate measurement at low powers - Tek's PA1000 doesn't look too bad on paper (and there is a road test on E14) but it cost about £2k.

    It does have  a 2mA full scale current range at it's most sensitive !

     

    MK

  • in reply to michaelkellett

    I'm thinking the resistor and a small box with terminal is a lot cheaper.

     

    Mark

  • in reply to mcb1

    But doesn't tell you as much image

     

    But for a quick garbage/not_garbage test quite good enough I would think.

     

    MK

  • in reply to michaelkellett

    But doesn't tell you as much

    Well it means you have to do some calculations, but there is no reason why you can't read peak (assuming your meter allows it).

    Thus you have average current, peak current, and if you use an oscilloscope, you could even get the current in the first cycle.

     

    We have a similar device at work to measure the instantaneous currents for various equipment.

    Some are extremely high, in the order of 40Amps or more ...hence we don't want more than one on a single breaker.

     

    That's why we know these devices are not very accurate.

     

    Mark

Comment
  • in reply to michaelkellett

    But doesn't tell you as much

    Well it means you have to do some calculations, but there is no reason why you can't read peak (assuming your meter allows it).

    Thus you have average current, peak current, and if you use an oscilloscope, you could even get the current in the first cycle.

     

    We have a similar device at work to measure the instantaneous currents for various equipment.

    Some are extremely high, in the order of 40Amps or more ...hence we don't want more than one on a single breaker.

     

    That's why we know these devices are not very accurate.

     

    Mark

Children
  • in reply to mcb1

    The proper analysers multiply current and voltage in real time and also work out phase angle and thus power factor - of course the steady state current isn't the whole story but the EUP directive (Energy Using Products) is concerned with steady state power in idle and active operation.

    The PA1000 gives you harmonics as well which is essential for CE or similar approval.

     

    Probably much safer to use a current sensor (rather than a sense resistor) for experimental work (no need to break the mains wiring).

     

    MK