Using the wireless charger PCB component

Discussion in 'General Electronics Chat' started by dtekumse, Dec 18, 2015.

  1. dtekumse

    Thread Starter New Member

    Dec 15, 2015
    Dear all,

    I am currently working towards a device which we are deciding whether it should or shouldn't include a wireless charger of Qi supported devices, such as Android smartphones.

    The device is supposed to be an independent system and, therefore, a PCB will be developed. Now, I am pondering on how to implement a wireless charger on that PCB. I've read through the threads concerning this subject (such as Building a wireless power charger and Design wireless charger), but found no specific information to answer my questions - as I don't want to design one, but only to incorporate a standard module (a component) in my device.

    Before asking the questions, here are the actual components I found and I may consider using:

    The pricing is similar enough for all of these, thus I am concerned about the way to connect (the simplicity of it) and the power.

    Are this finished products in the sense that I plug it to 5 or 12 V power and that's it - it's charging any Qi-enabled smartphone within 4 cm range?

    What is the power consumption? I found only "output current" for 1 and 3, being 400 and 700 mA, respectively. I guess this is the current provided on the receiver side, as these two components are actually a pair each: a transmitter and a receiver. But what is the consumption of the transmitter?

    For component 2, I see "input current" of 1A. I mean, I know what that means, but is this really true - one whole Ampere? Based on this, the wireless charger could never (with our current technology) be portable - right? Because, if this thing really sucks in 1 A, it means that it dries out a 2000 mAh battery within just two hours...

    Also, having 1A current on a PCB requires additional measures - during design, but also concerning safety.

    Did I get something wrong, or this is how things actually are?

    Thank you for your time.
  2. sailorjoe


    Jun 4, 2013
    dtekumse, I'll try to provide some answers here, but without knowing more about exactly what you're building, it's unwise to provide design advice.
    In your list of links, items 1 and 3 appear to be very similar, except for the coil construction. Item 1 has more distance because of the increased number of coil windings. Something to consider in your design choices.
    Item 2 says "No longer available." But on the same page are a lot of products that look to be plug and play, so maybe your design just needs to have USB connectors to be able to attach to the available devices. My very quick scan of the products made it look like they're all designed for QI charging, but I may have missed some others.
    Item 1 says that input voltage is 12 VDC, and not more than 13.5 V. It doesn't list the input current. You can estimate it by noting that the output voltage is 5 VDC at 600 ma. That's 3000 mWatts. That energy is coming from the coils, which are essentially like an air core transformer. So 3000 mWatts divided by 12 VDC is 250 ma. Assuming some losses in the transformer and other circuitry, let's make it 500 ma max. That will get you in the ballpark, but eventually you need to measure it to be sure.
    You can use similar logic with the other devices to help you choose. And yes, the transmitter could be pulling 1 amp, which would imply that it's expected to be fed by a power supply that's plugged into a wall outlet for primary power. Similar to an iPhone charger that has a little power supply on the wall plug and feeds to the phone through a USB connector.
    In general, for a fixed amount of power required, increasing the input voltage will reduce the current requirements.
    So item 1 uses 12 VDC input to reduce the current down to a half amp or so. Item 3 can't tell you the input current because they don't know what input voltage you plan to use, and they allow a range from 5 to 12 VDC.
    1 Amp sounds like a lot if you're not used to it, but it's not that bad in terms of safety. It can get ugly if you're switching it on and off, because that creates a lot of magnetic flux causing noise on the rest of the circuit, so shielding may be called for in sensitive areas, or with careful layout. In this case, I doubt the input and output currents are being switched, although I'd want to look into the input current further to be sure. Buy one and see. You'll get a lot smarter about these things once you have one on the bench and you're looking at signals on a meter or o'scope.
    Let us know how it goes, so other can learn from your experience.
  3. dtekumse

    Thread Starter New Member

    Dec 15, 2015
    Thank you, sir, very much for your response.

    Before I respond, I would like to apologize for the really late reply - as it was the end of semester and then all the holidays... I hope you understand.

    Anyway, to get back on track, from what I could read in your past it seems to me that I was on the right track - our conclusions agree. Now, my question is how do I actually design the PCB so that it is "charger-ready"?

    Say that I choose to go for number 1. From what I can see in the image, there is some circuitry already there - but to it only two leads are: supply voltage and GND, I assume. So, my conclusion here is that the best idea is probably to just make two connectors on my PCB and than to simply solder those two leads of charger (the circuitry shown in the image and the coil). What is your opinion on this, do you agree with me?

    Best regards, thank you for your time and, once again, I apologize for the long delay.