Wireless power transfer of EV's circuit design project on RC car

Thread Starter

psoutzis

Joined Nov 15, 2018
8
Hi all,

Just joined the forum.
I am currently trying to design a simple circuit and demonstrate the wireless power transfer of electric vehicles on an RC car. I am a mechanical engineering student and my electrical knowledge is limited, so any tips will be appreciated.
So, the idea is to demonstrate the wireless charging technology using primary and secondary coils to charge the Li-ion battery which is connected to the RC car.
Parts i need? : AC Power supply (230V-Wall plug) =>Transformer => Primary coil => Secondary Coil => Rectifier (AC to DC) => Battery (Li-ion-RC car)
Questions: 1) what extra parts will i need ? i was thinking to take the charger from the RC car, open it and see whats inside and then connect them up.
2) Do i have to use a rectifier after the AC supply to convert to DC and then again to AC before the primary coil ? or leave it AC and convert it to DC before the battery ?
I dont know if i am completely wrong but anyone who have done this please leave me a comment :)

Thank you
 

Reloadron

Joined Jan 15, 2015
5,600
BUILD YOUR OWN INDUCTION CHARGER
is a pretty good older article from nuts and volts magazine. A Google of Electric Toothbrush Charging Circuits should also yield several more designs. One of the earliest devices I know of using induction charging was the electric toothbrush.

The idea is we take an AC signal and run it through an induction coil but unlike a metal core transformer the transformer core is air. While air has a less than stellar coupling coefficient it does work, especially when we get our transformer secondary real close to our transformer primary. My last electric toothbrush has been going strong for about 7 or 8 years which says a lot for the charging system and battery.

There are several circuit designs but for what you are after I would focus on the electric toothbrush circuit designs. They are compact and really pretty efficient which is what you want when you plan to insert it in a little RC car model. The concept of wireless power transfer has been around a long time, Nikola Tesla was experimenting with it a long time ago. :)

You drive a coil primary with an AC oscillator and rectify the coil secondary so you start with AC then make DC then make AC which is coupled as AC and rectified to DC to charge your battery.

Ron
 

Thread Starter

psoutzis

Joined Nov 15, 2018
8
BUILD YOUR OWN INDUCTION CHARGER
is a pretty good older article from nuts and volts magazine. A Google of Electric Toothbrush Charging Circuits should also yield several more designs. One of the earliest devices I know of using induction charging was the electric toothbrush.

The idea is we take an AC signal and run it through an induction coil but unlike a metal core transformer the transformer core is air. While air has a less than stellar coupling coefficient it does work, especially when we get our transformer secondary real close to our transformer primary. My last electric toothbrush has been going strong for about 7 or 8 years which says a lot for the charging system and battery.

There are several circuit designs but for what you are after I would focus on the electric toothbrush circuit designs. They are compact and really pretty efficient which is what you want when you plan to insert it in a little RC car model. The concept of wireless power transfer has been around a long time, Nikola Tesla was experimenting with it a long time ago. :)

You drive a coil primary with an AC oscillator and rectify the coil secondary so you start with AC then make DC then make AC which is coupled as AC and rectified to DC to charge your battery.

Ron
Hi Ron !
Thank you for your answer ! It is for my final year project. I will not use a small RC car , but a big one so I can fit the secondary coil and the circuit underneath it !
Do you think the electric toothbrush design would suit me ? Isn’t it just better build my own ? If yes, do you know any simple circuits to use ? I will also be adding a display on the breadboard to show charging.
 

Reloadron

Joined Jan 15, 2015
5,600
The first circuit I linked to from Nuts & Volts magazine is a circuit I like. While I never built it it has impressive numbers. Figure it this way, as I mentioned air is lousy for coupling. You want to charge a battery and it is nice to charge a battery quickly end efficiently so you don't want to place your RC car down to inductively charge and return a week later when it's done. :)

Since this is a final year project looks count. The linked to project has a nice visually appealing look to it, it simply looks interesting and cool. Also interesting from an electrical engineering point of view is the use of a small micro controller as the heart of the oscillator circuit. The RC car will carry your ME skills but the concept of using induction charging is a nice electrical touch. Looking at the numbers:

CHARACTERIZING POWER OUTPUT & EFFICIENCY
FDH055N15A — N-Channel Power Trench MOSFET 150V, 167A, 5.9 mW
COIL DIAMETER = 2.5 | APERATURE = 1” | SEPARATION = 0.25”
FREQUENCY = 12.9 kHz DUTY CYCLE = 50%
Input Voltage = 12V Output Voltage 5.06V (31V unregulated)
Voltage Drop across 10 ohm load shorted = 0.710V ( I = E / R ) 710 mA
Input = 900 mA Output = 710 mA Efficiency = 710 mA / 900 mA * 100 = 78%

The 78% efficiency really isn't that bad and the circuit uses a simple PICAXE micro-controller which cost a few bucks and is easy to program and the article even has the few lines of code which can be adapted to a wide range of frequencies as needed. If made as described your coils should be about the same resonant frequency. Thus, I would likely run with the article design. I really think this will make for a nice project.

Ron
 

MisterBill2

Joined Jan 23, 2018
6,659
Several things come to mind with this project, the first is the operating frequency. The majority that I have read about use a higher frequency still, not 12 KHZ, but several hundred KHZ. So some research will be needed there. But the higher frequency allows smaller coils somehow.
The 785 efficiency seems quite remarkable, even amazing. Mostly nine of the articles even mention efficiency, instead they tout convenience and lower charging times. So if your demonstration system can actually display power in and power recovered out then it will be a real public service item.
 

Sensacell

Joined Jun 19, 2012
2,582
Wireless charging is not environmentally friendly.
It's like being too lazy to bring a shopping bag from home when going to the supermarket.

What's so difficult about plugging in a wire?
For this minuscule convenience, I am willing to waste 30% of the energy?
 

Reloadron

Joined Jan 15, 2015
5,600
Wireless charging is not environmentally friendly.
It's like being too lazy to bring a shopping bag from home when going to the supermarket.

What's so difficult about plugging in a wire?
For this minuscule convenience, I am willing to waste 30% of the energy?
That's a real good point. When I got my first electric toothbrush I kept looking for pins in the cradle. Never having had an electric toothbrush it took me a little while to figure out, how do it do that? No pins which mate like the cordless house phones, just that little plastic nub the base of the toothbrush slipped over in the holding cradle. I just went on with my life chalking it up to magic.

Then one day, while eating a PB&J sandwich with strawberry jam it dawned on me that since most toothbrushes, including electric toothbrushes are in close proximity generally to bathroom sinks and anything and everything in a bathroom should be GFCI the reality is everything isn't. I began to look closely at my electric toothbrush and its associated little charging cradle. This things takes the term intrinsically safe to a new level. The thing is totally sealed and potted. You could likely put this sucker on the bottom of a 5000 meter deep pool (500 atmospheres) and it would not leak and likely charge the battery assuming a long extension cord. That damn pressure increase is hell on submarines ruling out the use of screen doors.

So when they say a time and a place for everything I figure in the morning brushing your teeth at a sink with running water a well insulated intrinsically safe toothbrush and charger is a nice to have. While I have never found it or even looked I would guess there is a rule helping protect ourselves from ourselves that covers all of this.

I agree that to charge an electric battery powered RC car all of this is not needed but it does demonstrate wireless charging along with whatever mechanical feats of wonder this mechanical engineering project does.

While looking for a design I felt was safe and would make forum muster I omitted several designs where AC mains was rectified to high voltage DC and no transformer used to isolate or drop mains voltage. When I suggested cooking a hot dog by connecting each end to AC mains using nails that thread was cut really short for obvious forum rules but it made a really good hot dog.

Seriously though, while wireless charging is not at all necessary for this project and as I pointed out early on is very inefficient but it demonstrates wireless charging and the designer could point out where wireless charging is used in some intrinsically safe applications. In addition to whatever it proves it will have a proof of magnetic induction charging proof of concept.

Had supper and about time I go brush my teeth using my electric toothbrush charged by magnetic induction. :)

Ron
 

Sensacell

Joined Jun 19, 2012
2,582
I do think the toothbrush example is "appropriate use of technology"
It's a very low power device, the intrinsic safety trumps the minute energy loss.

There is a trendy, cultish obsession with ridiculous uses of technology these days, reminds me of the beginning of the dotcom boom.
A lot of great stuff came out of it, but there were some really dumb ideas floated and funded along the way.

Have you seen the Amazon Alexa Microwave?

https://www.amazon.com/AmazonBasics-Microwave-Compact-Works-Alexa/dp/B07894S727

I wish this was a joke.
 

MisterBill2

Joined Jan 23, 2018
6,659
OK, a voice controlled microwave oven, but then it seems that one must also have that alexa device and the associated service to generate the digital instructions. How is it possible to use a microwave oven without being right there to put things into it? So how can there be any actual benefit from this gimmick device? The funny part is that any device that is wifi accessable is also hackable. Just picture the neighborhood hacker adding 15 minutes to the 30 second heating cycle, just for fun. Or knowing just exactly when and how many batches of popcorn you eat. The wireless communications links are only a bit more private than CB channel 19.
One more consideration is that there are only so many link frequencies available, and when they are all full there are no more, until somebody stops talking.
 

Thread Starter

psoutzis

Joined Nov 15, 2018
8
The first circuit I linked to from Nuts & Volts magazine is a circuit I like. While I never built it it has impressive numbers. Figure it this way, as I mentioned air is lousy for coupling. You want to charge a battery and it is nice to charge a battery quickly end efficiently so you don't want to place your RC car down to inductively charge and return a week later when it's done. :)

Since this is a final year project looks count. The linked to project has a nice visually appealing look to it, it simply looks interesting and cool. Also interesting from an electrical engineering point of view is the use of a small micro controller as the heart of the oscillator circuit. The RC car will carry your ME skills but the concept of using induction charging is a nice electrical touch. Looking at the numbers:

CHARACTERIZING POWER OUTPUT & EFFICIENCY
FDH055N15A — N-Channel Power Trench MOSFET 150V, 167A, 5.9 mW
COIL DIAMETER = 2.5 | APERATURE = 1” | SEPARATION = 0.25”
FREQUENCY = 12.9 kHz DUTY CYCLE = 50%
Input Voltage = 12V Output Voltage 5.06V (31V unregulated)
Voltage Drop across 10 ohm load shorted = 0.710V ( I = E / R ) 710 mA
Input = 900 mA Output = 710 mA Efficiency = 710 mA / 900 mA * 100 = 78%

The 78% efficiency really isn't that bad and the circuit uses a simple PICAXE micro-controller which cost a few bucks and is easy to program and the article even has the few lines of code which can be adapted to a wide range of frequencies as needed. If made as described your coils should be about the same resonant frequency. Thus, I would likely run with the article design. I really think this will make for a nice project.

Ron
Hi Ron, as this circuit is very interesting, i might do it later on but for now i will do a simple model to demonstrate the Wireless charging for EV's as my aims for the dissertation are different.
I need to charge a 7.4V 1500mAh Li-ion battery. To design a simple circuit what would i need apart from:
A wall charger=> transformer => rectifier =>primary coil and secondary coil=> rectifier (AC to DC) and the battery ? i suppose 4x diode bridge connection, heat sink, transistor, resistors and a voltage regulator ? and 2 breadboards to connect them all up.

Panagiotis
 

Reloadron

Joined Jan 15, 2015
5,600
That's about it.
  • Any type of oscillator capable of producing the resonant frequency.
  • A power transistor to serve as an amplifier for driving the primary coil.
  • A set of coils that serve as a primary transmitter and secondary for the receiver.
  • A full wave rectifier to convert the incoming AC to a DC value.
  • A voltage regulator to create a useable voltage for charging depleted batteries.
  • A circuit to manage the charging process for Li-Ion or NiMH battery chemistries.
Just keep things within your aims and goals for the project. There are other simpler circuits out there for you to consider.

Ron
 

Reloadron

Joined Jan 15, 2015
5,600
I do think the toothbrush example is "appropriate use of technology"
It's a very low power device, the intrinsic safety trumps the minute energy loss.

There is a trendy, cultish obsession with ridiculous uses of technology these days, reminds me of the beginning of the dotcom boom.
A lot of great stuff came out of it, but there were some really dumb ideas floated and funded along the way.

Have you seen the Amazon Alexa Microwave?

https://www.amazon.com/AmazonBasics-Microwave-Compact-Works-Alexa/dp/B07894S727

I wish this was a joke.

Oh heck yes, I agree. I have no desire to get into conversations with my home appliances. I do not need a cam in my fridge so I can check the contents while I grocery shop either. :)

Some of the stuff I just see as unnecessary and some borderline foolish.

Ron
 

Thread Starter

psoutzis

Joined Nov 15, 2018
8
That's about it.
  • Any type of oscillator capable of producing the resonant frequency.
  • A power transistor to serve as an amplifier for driving the primary coil.
  • A set of coils that serve as a primary transmitter and secondary for the receiver.
  • A full wave rectifier to convert the incoming AC to a DC value.
  • A voltage regulator to create a useable voltage for charging depleted batteries.
  • A circuit to manage the charging process for Li-Ion or NiMH battery chemistries.
Just keep things within your aims and goals for the project. There are other simpler circuits out there for you to consider.

Ron
Ok great ! thank you for your information :)
By the way, i have a question, do i have to convert the current from AC to DC and from DC to AC again and again ? obviously to charge the battery i need DC. I was thinking as i start form the wall charger (AC) just transfer the energy from 2 coils with AC and just use a rectifier to convert it to DC before charging the battery. Will this work?
 

MisterBill2

Joined Jan 23, 2018
6,659
Ok great ! thank you for your information :)
By the way, i have a question, do i have to convert the current from AC to DC and from DC to AC again and again ? obviously to charge the battery i need DC. I was thinking as i start form the wall charger (AC) just transfer the energy from 2 coils with AC and just use a rectifier to convert it to DC before charging the battery. Will this work?
The oscillator to produce an adequate magnetic field from the sending coil to reach the receiving coil is not a trivial matter for a few reasons. The main challenge is using a frequency that will not interfere with other equipment that is using the same frequency for communications. Interference with licensed users of a frequency can be a very big deal. The second concern is similar, which is making sure that none of the harmonics of that frequency will be causing interference. Unfortunately the most efficient drive is a square wave, but that has harmonics extending far above the primary frequency. As an example, harmonics from the horizontal deflection frequency of older tube-type television sets were known to interfere with AM broadcasts for hundreds of feet in years past. So harmonic radiation is another consideration that may not be initially obvious. So at the very least a bit of research should be done before choosing a frequency.
 

Reloadron

Joined Jan 15, 2015
5,600
Ok great ! thank you for your information :)
By the way, i have a question, do i have to convert the current from AC to DC and from DC to AC again and again ? obviously to charge the battery i need DC. I was thinking as i start form the wall charger (AC) just transfer the energy from 2 coils with AC and just use a rectifier to convert it to DC before charging the battery. Will this work?
That is pretty much it. You start with mains current which is AC and convert it to a lower voltage DC which powers your oscillator circuit making AC which drives your transformer primary. The secondary of the transformer provides AC which is converted to DC and adapted to your battery charging circuit.

Ron
 

Thread Starter

psoutzis

Joined Nov 15, 2018
8
That is pretty much it. You start with mains current which is AC and convert it to a lower voltage DC which powers your oscillator circuit making AC which drives your transformer primary. The secondary of the transformer provides AC which is converted to DC and adapted to your battery charging circuit.

Ron
Ron

Thank you very much for your information ! I will try to do it, if i have any other questions, i will post them here !

Panagiotis
 
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