I have written several postings on Qi wireless power. To get a good idea how Qi really works, I bought cheap bare Qi charger board Qi Wireless Charger PCBA Circuit Board + Coil Charging (costs only slightly over two Euros / USD).Qi Wireless Charger PCBA Circuit Board + Coil Charging kit consists ofQi Wireless Charger PCBA Circuit Board + Charging Coil without any case.  The charging coil has 10 turns in it and there is a ferrite below the coil.

Features:

1.Qi wireless charger PCBA circuit board,allows to charge for any Qi-enabled device.

2.Better for DIY, you can give it a case (not too thick) or fix it on your furniture or other devices, but please note the transfer efficient distance is only 5mm.

3.High power, quick-acting charging.

4.Over 75% high-efficient energy conversion.

5.Ultrathin,lightweight,safe and reliable.

Specifications:

1.Input voltage: DC5V

2.Input current: 2A

3.Charging voltage: 5V

4.Charging current: 500-1000mA

5.Charging power: 10W

6.Charging distance: 5mm

7.Conversion: ≥75%

8.Size: 32 x 31mm

Closeup of the circuit board electronics reveals the main ICs: 8s003f3p6 microcontroller as charge controller, LM324 quad op amp and driver transistors (two C009T and two 3401).

When nothing to charge the charger sends short pulses of low power signals few times a second, measured with scope from charger coil ends with channel CH1.

When something to charge continuous signal

When receiver somewhat off optimal location the transmitter increases power to compensate more losses

Magnetic field measurement with 6 turns test coil

I have previously tested Qi wireless charging receiver model Universal Qi Wireless Charging Receiver Kit For Micro USB Cellphone.This Universal Qi Wireless Charging Receiver Kit For Micro USB Cellphone a about a size of a credit card and ultra-thin in design. It is designed so that it could be installed inside cell phone – or it can be put between your smart phone and it’s protective case.The charger promises to give out 1000mA 5V to the micro-USB connector that plugs to the smart phone like normal charger.

I had used the charger for some months nicely with several Qi chargers. The biggest downside on this charge receiver was that when it is plugged to your smart phone, you can’t use normal USB charger to charge phone unless you remove this charge receiver. There has been several cases where I have had need to use normal UBS charger, so I have had needed to remove the Qi receiver from phone. At one occasion I removed the Qi receiver and put it to pocket, I happened to bet the Qi charge receiver so much that it did not work anymore. So now it is a good time to look what is inside it, because when it is already broken, there is no danger of making situation worse by opening it (and in best case the problem could be found and it could be repaired).

The device was packed inside two thin stickers made of plastic sheet. The sticker glue kept the both sides together. It was pretty easy to separate the sides with suitable tool (small thin screwdriver).

Here is what is inside the Qi receiver. On the left side the black square looks like some kind of ferrite material but it but it is flexible. I quess it is some king of plastic with lots of ferrite material in it. Magnet sticks to it well.

On the right side you see the electronics that do the charging. There are two ICs and lots of discretes. The bigger one (with 10 pins) does not have any markings in it. The smaller 6 pin chip has some markings, but they were unreadable.

Here is close-up picture of the circuit where you can see that one end of the coil does not make contact with the circuit board anymore.

When I connected the charger bad to smart phone USB power supply, I got it working well. The phone charged well, although the pad seems to be pretty sensitive to where in it you put your phone (put it to slightly off the center and it does to charge).

Specification:
Color: Black, White, Blue, Red, Green, Yellow, Orange
Input: DC5V, 1500mA
Output: 5V, 1A max
Size: Approx. 6.9×6.9x1cm/ 2.72×2.72×0.39″
Wireless charger for smartphones under the QI-standard.
Easy to charge your phone without cables, just put your phone on the charging plate.

Operation: Indication LED is red when there is nothing to charge

It turns blue when you have the receiver placed on top pf the charger (does not matter if it is connected to smart phone or not)

This Qi-charger worked well. The build quality seems to be OK. It doesn’t get very hot. Charging was somewhat sensitive to location (I think somewhat more sensitive than Qi charger in IKEA lamp). The charger worked when the phone is placed on the pad or is few millimeters up from it.

It charger my smart phone well (approximately at the same speed as the original USB charger that came with the phone. My smart phone too around 600 mA charging current like it took from the original charger. So the charging speed should be pretty much the same as with original charger.

Notes on testing:  In the first tests I had some problems that charger for some reason starts to charge, then stops after some time and continues again. After some investigation I found out that the the charger pad needs 1500 mA at 5V, but the USB chargers I tried with it supplied less power (one had maximum 700 mA and other 1000 mA).  When I replaced the USB charger with a model that promises to give put 2.1A 5V, the charger worked well all the time when the smart phone was nicely placed on the correct location. Not phone gets constantly charged.

Other minor issues that I found out is that after some days of used I noticed that the charger starts to make some faint noise when it charging the phone. In the office or normal daytime at home that is not an issue, but when it is next to the bed I could hear some noise on quiet room (compared to Qi charger in IKEA lamp it makes considerably more noise).

I was wondering what is the efficiency of the wireless Qi charger system. So I had to test it. I did test with two USB charge meters: one connected to power input of that Qi charger pad and other placed between the Qi receiver and smart phone. I found that the USB charger and and receiver combination had around 65-70% efficiency. This means that around one third of the power is lost in the wireless charging process. The efficiency is around the same range as with other Qi chargers, for details on that check Qi wireless power efficiency presentation.

Even with some of those minor issues, I would say this is very good value for money. The other Qi chargers I have seen cost several times more. This is the cheapest Qi charger pad I know and it does what it promises to do well.

The smart phones I had did not have built-in Qui charger electronics, so I has to find a way to add a Qi charge receiver to them. For the particular smart phone models there was no readily available model specific chargers that you install inside phone, back-cover with Qi charger receiver or protective cover with Qi receiver. So I decided to buy Universal Qi Wireless Charging Receiver Kit For Micro USB Cellphone.

This Universal Qi Wireless Charging Receiver Kit For Micro USB Cellphone a about a size of a credit card and ultra-thin in design. It is designed so that it could be installed inside cell phone in three steps: Take off the back cover ~ plug in the micro usb head ~ put on the cover. The charger promises to give out 1000mA 5V to the micro-USB connector that plugs to the smart phone like normal charger.Universal Qi Wireless Charging Receiver Kit For Micro USB Cellphone with plug wired in different directions – you need to select the right model depending the direction in which the micro-USB  connector is on your phone. The charger pad needs to be in right direction (it charges only when right side of it is towards the Qi charger transmitter).

This side the the side that must face the charger

I made the charger to fit inside the smart phone case (Samsung S4 mini). The cable was a little bit longer than needed to I needed to figure out how to fit the extra cable nicely inside cell phone case. On the other phone the Qi receiver fit nicely between the smart phone and it’s protective cover.

The Universal Qi Wireless Charging Receiver Kit For Micro USB Cellphone seems to work as promised. It provides the power to the smart phone as promised (my cell phone takes around 5V 600 mA when it is charging and it supplied it as promised). The charger pad generates some heat when you charge the phone, so phone hears somewhat more than normally, but this did not seem to be a problem and the temperatures were very reasonable.

This charger worked well with my IKEA lamp with Qi charger and several other Qi charger power transmitters (more on them on some later postings). The charging worked well at least up to the promised 5 mm charging distance (some in some cases up to several millimeters more).

I was wondering how does wireless charging affect the charging efficiency. To test that I used USB charge meter and another USB charge meter to compare how much power the Qi charge transmitter takes and how much of it gets to the phone through micro-USB connector. I found that the USB charger and and receiver combination had around 65-70% efficiency. It was in the range I expected it to be.

There is LED bulb with button on top for on/off. There is also USB power connector in the front of the base.

Here is Qi charger. Small white LED lights up when charger on. It works as promised.

Power supply is quite powerful because same PSU is used by many products.

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At the time the stuation was that Wireless charging for Qi technology is becoming the industry standard on smartphones. Now some years later Qi has became so widely used mainsstream technolgy that I started to adopt it.

The Qi standard has been developed by the Wireless Power Consortium and is applicable for electrical power transfer over distances of up to 40 millimetres. The Qi wireless charging standard uses a power transmission pad that is akin to the charger that would be used in a normal wired system, and a compatible wireless power receiver that is located in the device to be charged. The power transfer then takes place using magnetic induction.  The low power category covers chargers that can deliver power in the range 0 – 5 watts (upcoming Qi revision will push that to 15W and higher power versios that are very rarely used). This will cover most of the domestic portable devices like mobile phones, music players. This is what I am adopting.

The frequency used for Qi chargers is located between about 110 and 205 kHz for the low power Qi chargers up to 5 watts. All Qi receivers (phones, sleeves, backdoors, and charging cards) that have shipped in the last 3 years and continue to ship, can be charged in inductive mode as well as resonant mode. It is the transmitter (wireless charger) that defines the operation mode.

The components I started my experimeents with were desk lamp with Qi charger from IKEA.

Cheap Qi charger that plugs to normal micro-USB smrt phone charger (takes in 5V 1A).

My smart phone did nor support qi but this accessory made it compatible and fit inside case.

In ititial testing the charger and mobile phone receiver worked together.

At initial testings I got things working and receiver fitted inside my smart phone. I have tested the system for few days. It seems to work. I think I need more Qi chargers so I can change smart phone at different locations (home, work etc..) – you know how quickly smart phone battery goes dry when you use it a lot.