Jamison and I are starting an engineering project1Jamison’s project is based on the Instructable, “Low-Power Wireless Charging. for his school’s science and engineering fair. This is the second year his school’s fair accepts engineering projects. Instead of doing a science experiment using the scientific method, we get to engineer:
Identify a problem
Research how others have solved it
Develop our own solution
Refine our solution
We want to transfer electrical power over a short distance without a direct, hard-wired connection. Here’s where we’re starting our research:
It’s hard to beat cheap, so we’re going to attempt the Wireless Electricity (for under $20) project, though that cost estimate seems to assume already having a stocked experimenter’s lab. This is sending us down the bifilar winding rat hole and into Tesla territory. A lot of strange stuff (and denizens) there.
Sunday was a big day! Jamison and I started with another trip to Fry’s. We needed more magnet wire, a better power supply to clean up the noise we saw on the cheap one we already had, and some perfboard. On the way home, we stopped by Home Depot for 6″ pipe and Fred Meyer’s for reading glasses. Never needed those before… B-)
Upon our return home, we set up our lab and pulled out the new power supply. After deciding to use a different scope probe and calibrating it (we missed that step last time), we got a nice, clean 5V voltage. Because we wanted to see the contrast, we then connected the probe to the cheap “wall wart” power supply. Look at that — a nice, clean 5V voltage! Huh. I guess the new power supply can go back and I’ll try to be more understanding when a customer calls for tool assistance and hasn’t calibrated his scope probes.
Jamison wrapped a second coil and we hooked it up to a green LED. Connect the power, move the coils close together. First light! Yes!!
Now it was time to improve Jamison’s project.1Jamison’s project is based on the Instructable, “Low-Power Wireless Charging.” We tried a full-wave rectifier to increase the LED’s brightness, with not a large (if any) effect. We built a two-stage Cockcroft-Walton generator, with much better success.
Next, we decided to improve the coils. We cut the 6″ pipe into short lengths, an inch and a half or so. We wrapped the magnet wire around them and used the oscilloscope to tune the number of wraps to get the desired frequency. It seemed like we were having to remove too many coils, so we found a formula for the inductance of a short air-core cylindrical coil. Plotting inductance as a function of wraps showed we could get by with much fewer than the 18 wraps we thought we needed for the desired 53 Î¼H.
Emboldened with new information, we continued experimenting and found twelve wraps got us nearest to the desired 80-kHz frequency. We built a second, matching coil and we found we could transfer power much farther. The first set of coils had to be nearly touching. The second set could be more than four inches apart.
Unfortunately, we hadn’t left long enough leads on the coils, so we decided to wrap another set using all the information gained along the way. The forms were only an inch “long.” We sawed deeper grooves for the wire’s start and end so the coils wouldn’t need to spread and we spaced tape around the coil to hold them tight. I haven’t measured, but I think we can have six inches between the coils and still light the LED.
We want to try making a smaller secondary coil, maybe an inch in diameter. That will be for another day.
We thought we’d decided what project to build (I thought we were building Wireless Electricity), but Jamison changed his mind. After further research, he decided to build the Low-Power Wireless Charging he’d found on Instructables.com. I’m pleased. We’ll have more control over this project.
Buy materials for prototype
Once we knew what project to build, we thought it would be easy to buy the parts. Wrong!
Buying capacitors is a confusing process. The units are insane. The instructable specified a 100 nF capacitor. That sounds easy enough. Unfortunately, Fry’s shelf labels would list it as a 100000 pF or a .10 MFD. That’s if they actually had it. After trying to find the right caps, we decided to do our shopping online instead and headed over to digikey.com. We had all the parts we needed the next day. :-)
Prototype building went well, at least for the circuit. Once Jamison understood how the little holes in the breadboard are connected, the oscillator went together fairly quickly.
The first coil went together fast, too. The instructable said to do 18 wraps of 15 cm loops. Jamison wrapped the coil around a form, about 4.5 inches square, and then rounded the coil by hand.
Tuning the coil was a problem. The oscillator was designed for 80 kHz. We should have been able to tune the coil by connecting it to the oscillator and removing coils until the oscilloscope showed something near 80 kHz.?Famous last words. Instead of a nice sinusoidal signal, we got a noisy, stepped signal. Removing coils didn’t seem to do anything. Maybe the coils were separating, so we wrapped it in electrical tape. That made no noticeable change. Maybe the cheap power supply was causing the noise. Fry’s could rescue us with a nice benchtop power supply.
Time to call it quits and figure out our next step.
A little more than four years ago, when Jamison was in sixth grade, he did an engineering project for his school’s science fair. It was a lot of fun for both of us.
Being the proud dad that I am, I wrote a series of blog posts on Jamison’s project as he was doing it. They have been some of my more popular posts and the subject of a few comments and many emails asking for help.
The first questions came from three 8th graders who asked for help in the comments to the project’s first post. I did my best to help them and steer them away from danger.
More questions continued to come by email from college engineering students, many apparently hoping to score a quick senior project. One particularly excited individual described himself, “im really glad to see u in ur forum nd im doin btech 2nd year frm india..!!” He also asked for the information to “send me links which r accurate standard pdf ‘to make it as theory’!!!”1If only he’d gone to the Instructable Jamison used, he could have downloaded it as “accurate standard pdf,” and it includes a theory of operation section. I pointed out the information he was requesting had already been provided.
This morning, I received another email:
I saw the interesting and simply designed wireless powering project it have been done in your website.
I am a PhD student, a part of my project is wireless power transfer.
I am wondering if you can send me the schematic of the wireless project.
I send you the attachment to know which project I mean.
I appreciate your hel
Nabeel last name2Almost all personally identifiable information redacted. But the requester emailed using his university email address and has a Facebook profile describing hims education as “Doctorate at [prestigious university] and stating his opinion that The Spice Girls are the greatest British band of all times. prestigious university country
I think this is the first Ph.D. student asking for help—at least, he’s the first to admit it. Jamison should be proud that his 6th-grade science fair project is helping graduate students worldwide. My response (with all snark hopefully removed):
Thanks for your interest in my sixth-grade son’s science fair project. I’m sure he’ll be proud to learn that a doctoral student would like further information on it.
Jamison followed the instructions documented in an Instructable: Low-Power Wireless Charging.3This fact was mentioned in the fourth post of the series, Wireless Power Transmission, Part IV. I have added a footer to each post in the series to make this fact more obvious to future knowledge seekers. There’s a lot of really good information in the Instructable, including a theory of operation section and schematics of the various modules. You should be able to find everything you need to duplicate Jamison’s project. After all, it was Jamison’s primary source of information.
Best of luck with your project. I know Jamison had fun doing it!
Almost all personally identifiable information redacted. But the requester emailed using his university email address and has a Facebook profile describing hims education as “Doctorate at [prestigious university] and stating his opinion that The Spice Girls are the greatest British band of all times.
This fact was mentioned in the fourth post of the series, Wireless Power Transmission, Part IV. I have added a footer to each post in the series to make this fact more obvious to future knowledge seekers.
hey sir.!! im really glad to see u in ur forum nd im doin btech 2nd year frm india..!! frm childhood im very interested in these microcontrollers play..!!!! frm ur forum im starting dis(wireless transmission of electricity) project nd i gt all d components with me nd i wnt to make theory work as first…!!! so please kindly send me links which r accurate standard pdf…to make it as theory…!!! plz help me up sir…!!!
If this was the first such request, I’d ignore it. Unfortunately, this is only the latest of many requests I have received from college engineering students wanting me to help them duplicate Jamison’s 6th-grade science fair project.1Jamison’s project is based on the Instructable, “Low-Power Wireless Charging.” As is typical, he is requesting the information I already provided.
Every four years, I like to post the official picture of the outgoing and incoming presidents meeting in the oval office. This is a special time for our nation and nearly a religious experience for me. As I wrote more than twelve years ago:
An amazing event is taking place: the orderly, peaceful transfer of power. From President George W. Bush to President-elect Barack Obama. From the Republican party to the Democratic party. Without guns or threat of violence. The political process works.
It’s times like this that I’m proud to be an American.
And yet, this transfer is different. Like many norms, the norms of transfer have been cast aside, but the fact of transfer hasn’t. I can’t post a picture of something that didn’t happen. But, democracy is still strong. America works.
We have a lot of work ahead of us. We need more than an America that works. We need an America that works for all Americans. To get there, we’re going to have to work together, unite together. As President Biden said earlier today:
My whole soul was in it today. On this January day, my whole soul is in this: Bringing America together, uniting our people, uniting our nation. And I ask every American to join me in this cause.
Uniting to fight the foes we face: anger, resentment, hatred, extremism, lawlessness, violence, disease, joblessness and hopelessness. With unity, we can do great things, important things. We can right wrongs. We can put people to work in good jobs. We can teach our children in safe schools. We can overcome the deadly virus. We can reward, reward work and rebuild the middle class and make health care secure for all. We can deliver racial justice and we can make America once again the leading force for good in the world.