Issues with Qi wireless charging receivers/transmitters - Page 1
Forum section: electronics / projects

author: electr_peter
author_rank: Unknown
timestamp: April 01, 2015, 10:41:20 am
content: I am testing few Qi receivers and transmitters as a power transmission system for a project. I know it is inefficient by design and very limited in range, but potential benefits offset disadvantages.I have a transmitter and receivers (like thishttp://www.ebay.com/itm/271754375854and thishttp://www.ebay.com/itm//281497846751). Data sheets are not provided.Transmitter seems to power up and shows blue/red LED (pulling up to 4A in bursts), but receiver does not show any signs of life - no voltage is generated at contacts. Contacts on receiver have diode connected across them, so connection should be OK. Transmitter coil has low resistance, coil is definitely being switched on/off.Receiver and transmitter are both supposed to be Qi compliant. Maybe one of them are not compliant or have different frequency, but at this point I guess that receiver is faulty. Another possibility is that receiver has to be in some special condition before starting up, I am not sure.Maybe experts on Qi charging could provide some hints before I try to disassemble receiver?

author: Marco
author_rank: Super Contributor
timestamp: April 01, 2015, 01:23:53 pm
content: Try plugging into your phone first to see if it works, it probably detects the USB connection (which you should be able to fake with a couple resistors) before it initiates power transfer.PS. short circuiting it with a diode wasn't really a great idea BTW. It probably has protection, but still ... not a great idea.

author: electr_peter
author_rank: Unknown
timestamp: April 01, 2015, 01:43:47 pm
content: Connector on receiver has USB micro connector with power and ground only, all other pins are missing. I tried plugging phone, small USB powered load, 5/10 Ohm load, no load - receiver does not start power delivery.I am opening receiver bit by bit. RX coil is ~0.2-0.3 Ohm (maybe it is too low?), there is ~2V AC voltage directly on coil. However, output caps charge to only ~140mV and stop.List of suspects: component failure on receiver side; soldering failure; TX/RX frequencies are mismatched; handshaking is not properly implemented.

author: Neverther
author_rank: Regular Contributor
timestamp: April 01, 2015, 07:35:06 pm
content: I tested mine loose before fitting inside phone (motorola droid 4, ready copper contacts for wireless backcover).My transmitter has two leds, yellow when power, blue when transmitting. Other one has red on power and blue for transmit.Worked fine even with no load, 5v output.Sure your micro-usb supply for transmitter is not a "smart" one (probing/shutting down in case nothing is connected to data pins)?

author: electr_peter
author_rank: Unknown
timestamp: April 02, 2015, 09:49:09 am
content: Both RX and TX have only GND and VCC contacts/cables used (see eBay listings to get an idea). TX was powered by PC USB cable and by lab PSU - behaviour is the same: RX powers up, blue LED lights up after start, then goes to red. It changes to blue at random times when RX is nearby (and then goes back to red), so some activity is occurring.Quote from: Neverther on April 01, 2015, 07:35:06 pmProbably not, but not 100% sure. One micro USB port has all 5 contacts soldered, but they do not seem to go anywhere (except for VCC/GND).Checked RX PCB soldering, all looks good. Some passives are not placed, maybe they went missing during assembly or it is for different versions. I have capabilities to generate low power AC, I have to try that next.RX/TX behaviour is as follows: TX is powered, red LED lights up. RX is put on TX coil, TX lights up blue LED brightly/dimly (seems to have two brightness levels, strange). However, RX shows no power at output. If RX is removed and placed back, TX just shows red LED and does nothing.RX component list:S8, 2 pin - 200mV Schottky diode431 - adjustable precision zener shunt regulatorBQJV, 5 pin - unknown (gap in PCB and soldered from below (!) to save height)7AL 19, 3 pin - unknown4NL, 6 pin - unknownHOVC 47, 6 pin - unknownSome pictures of setup:

author: nctnico
author_rank: Super Contributor
timestamp: April 03, 2015, 10:37:54 pm
content: Quote from: electr_peter on April 01, 2015, 10:41:20 amI recently designed such a system for a customer. Forget all the datasheets and appnotes. You really need to develop such a system from scratch if you need to push the envelope. I got to around 70% efficiency over a distance of 25mm while transferring 30W using resonant mode.

author: electr_peter
author_rank: Unknown
timestamp: April 04, 2015, 07:24:11 am
content: Quote from: nctnico on April 03, 2015, 10:37:54 pm70% and 30W are serious numbers. I am certainly considering rolling my own solution in the future to get specs I need.Do RX/TX have to be placed in special fixture to get excellent coupling, or is it free to move?

author: nctnico
author_rank: Super Contributor
timestamp: April 04, 2015, 11:47:29 am
content: You have to align the rx/tx coils but it doesn't need mm accuracy to work.