RoadTest: Wireless Power Design Kit - Medium Power
Evaluation Type: Development Boards & Tools
Did you receive all parts the manufacturer stated would be included in the package?: True
What other parts do you consider comparable to this product?: null
What were the biggest problems encountered?: My general comment is: This kit from my perspective was designed more to address marketing needs rather than engineering. Yes you can find some data about kit ( http://www.rohm.com/web/eu/wireless_power ) however you cannot find i.e software or some guidelines how to connect with Microcontroler using UART and read for example efficiency etc... I need to admit that I didn't tried to obtain this data via query form. Maybe in this way I could get more data.
Firstly I want to thank Element14 for allowing me the chance to review this product. Also I need to apologize in advance if my description will contain some mistakes but it is a first time when I am writing a review of the product like this.
Wurth Electronik ( WE ) always deliver the dev kits in the great packages. It is a pleasure to receive the kit from them. Great quality, clean and professional solution. The Design kit compose of
- Transmitter board
- Receiver Board
- LED module Board
- power supply with exchangeable plugs ( US/EU etc )
Final setup for testing:
I wanted to check how the wireless system could be useful in the situation where we wanted to mix the fluids which are stored in the plastic or glass containers and we don't want to make opening in the canisters or use the magnetic field to rotate the blade inside the container ( laboratories using this method right now ).My thought is the following if you we can place in the canister the DC motor with blades which allow to push the fluids and we can wireless supply it we could potentially have a nice alternative for existing methods. In order to verified it I wanted to check few points:
- Check how much power the wireless system can deliver
- Transient response of the wireless system depends of the load
- Possibility to supply DC motor what is needed
- What will happen if between TX coil and RX coil water layer exist
In order be able to verified it I build the Test setup see below:
Fig.1 Test Setup ( on top 3 load resistors )
Fig.2 Lead connected get Vout and GND
Fig.3 How I get out the output for testing.
Fig.4 Oscilloscope with current probe which I have used for testing
Fig.5 Mode which I was using for testing ( Transmitter board )
Fig.6 Switches setup on the LED Module
Fig.7 CH1 output voltage , CH2 output current
If we calculate Current mean value x Voltage mean value = 11.12W Poutput
Fig8. Transient response to switch full load ( rise )
As we can see system response within 1us and drop in voltage is around ~1V
Fig9. Transient response offload ( fall )
As we see response withing 1us and overshoot in voltage occurred around ~15V
After this tests I know that
a) system is able to deliver around 10W
b) load need to be able to withstand 15V over voltage conditions at least for 1us
First application of the DC motor shows that the system was shout down. I was not sure why until I measured the current demands. Due to the in-rush current demands system simply shout down. In order to restart I have to remove the receiver coil from transmitter and restart everything.
Fig.10 CH1 output voltage , CH2 inrush current on the DC motor.
I resolve this problem by adding low resistance in series with DC motor (for the final application the best could the PTC resistor ) , after this modification I was able to supply the DC motor from system
Fig.11 CH1 output voltage , CH2 current consumption by DC motor
Last point was to check how the system will behave if between TX coil and RX coil liquid is present.
Fig.12 Plastic container with water
Fig.13 Receiver coil protected by scotch tape
Results shows that liquid between RX and TX coils affect the communication and the power transfer is not occurring. Even if the water is very shallow
Additional tests with some drops on the TX coils show that whenever the coil is not completely covered by water then the power transfer is possible:
Fig.14 This condition power transfer is possible
Fig.15 This condition power transfer is possible
Fig.16 This condition power transfer is not possible
Above quick testing confirm that the power output is stable and reliable to supply the loads. Transient response also allow us to understand how quickly system adopt to new conditions which is great in terms of defining the how to use the charger in the proper way. The liquid between TX and RX coils shows the limitation of the application in the original thought ( it is an air transformer ). However it also help to understand how to mount the RX module in the canister in order to have the right and correct power transfer. If the design of the canister allow to keep the air gap between RX and TX the solution will work ideally.
What is also important is that pushing the power to the device inside the liquid which we are steering , open a huge use cases like i.e transfer information about temperature,, density, viscosity etc via communication link between RX and TX. This kind of solution also open a possibilities to mix the substances which are flammable , since the motor will be sealed and no "sparking" parts are exposed.
Generally: Great modern technology, I am very greatful Wurth Elektronik and Rohm Semicoductors to allow me test this dev kit
Yes the fluids are stored in the plastic cylinders. I am thinking to add one magnet on the outer side of the cylinder and second on the device inside the canister. Since I can use the wireless power the device inside the cylinder could be completely sealed. I will blog for sure about it. So far the test with the motors was very promising. I can deliver enough power to it.
With Best Regards,
Thank you very much for your comments and I am super happy to also read your very professional review. Impressive work and clear guide how I should do it next reviews . I agree with your observation that 10W is setup but 15W is possible. I was missing a bit the software description that is the reason why I rate it a bit lower because I would like to at least see what parameters are changing and how they affect the performance.From my stand point I was looking to see if I can use this wireless charger to supply electronics which I would like to place in the containers with fluids ( potentially nice way to charge the submarine models etcc.. ) It looks like it will work very good but I need to make sure that between receiving and transmitting coil there is not to big ( I was thinking to use the neodymium magnets to keep both together tight ). In general very good chance to learn a bit more.
Thank you very much once again and we are in touch....
Awesome review! And very useful and interesting results. I am glad by coincidence we got to try different things with it, with your power-receiver-side measurements and my power-transmitter-side measurements.
Based on the combination, I can possibly try to piece together and explain some of the behaviour, the microcontroller is configured for 10W, but 15W is possible (needs a code change, or swap out with a different microcontroller like Arduino), I think you noticed this too. However, the reason for the drop when the load is switched on/off is quite likely partially due to the the slower closed loop, because the wireless receiver has to notify the wireless transmitter what the error between desired power and received power is (it wouldn't have been noticeable if the load change was small, because the LDO input would have had some head-room). This is totally fine for battery charging, and for many other use-cases, but not all scenarios without such consideration, i.e. retrofitting Qi to a previously non-Qi scenario needs consideration of the load, and what range it will change and at what rate. This is a characteristic of Qi method as far as I can tell, since this is the way it controls the power delivery.
The overshoot during the load transients is very likely due to how you measure the voltage. Using the scope probe with the standard ground pigtail connector creates an inductance which shows this behavior. You need to make this connection as short as possible. See this blog post by TI for some more details.
Nice basic road test report.
Not bad for your first test.