Hello,
I have been having some strange issues regarding a product under development using wireless charging, where we develop both the transmitter and the receiver. I recently procured a current probe allowing me to see what is actually going on during the charging, and I identified some strange behaviour.
We have two prototype versions of the wireless transmitter, one with an integrated magnet (A5) and one without (A11). Both are from WE. The following behaviour has been identified:
- (1) Transmitter without magnet, PMOD / FOD at standard values (~350mW): Charging works correctly, no PMOD / FOD identified (flashing green LED)
- (2) Transmitter with magnet, PMOD / FOD at standard values (~350mW): Charging does not work, PMOD / FOD identified (flashing red LED)
- (3) Transmitter with magnet, PMOD / FOD at high values (~800mW): Charging works correctly, no PMOD / FOD indentified (flashing green LED)
- (4) Transmitter with magnet, PMOD / FOD at medium values (~450mW): Charging does NOT work, no PMOD / FOD identified (flashing green LED)
Everything is as can be expected, except for case 4, that I have repeated numerous times with the same result. The charger indicates that charging is underway (as can be seen by the flashing green LED), but no current flows into the battery. When meauring the current into the battery using the current probe, I can see that ~60mA (my set charge current is ~70mA so this is to be expected) enters the battery for about 5 seconds, but then the current flow stops. The resulting current after this fluctuates. Sometimes it charges for a second, then it stops charging for a few seconds. The total energy going into the battery is negligable, except for the first few seconds. Increasing the PMOD / FOD to slightly higher values (~600mW) did not help, same behaviour. However, when PMOD / FOD is disabled, or set to ~800mW, charging works reliably.
My only conclusion based on these observation is that the PMOD / FOD functionality throttles the power without indication, but I do not understand how this can happen. It is easy to believe that the charging works when the green LED is flashing, but this is appareantly not always true?
Could anyone please help me understand what is going on?
As a side note, I am using a rather odd receive coil (WE 760308101103 , normally used as a Tx coil). It should work, based on information from WE, and it does indeed work reliably with the A11 coil, and with the my BQ500212A evaluation kit. The reason for using this particular coil instead of a "normal" RX coil is that the large coil shield provides a good magnetic holding force to the permanent magnet in the A5 coil, which is required for my product.
Our previous coil (from Mingstar) does not offer the same holding force. Additionally, when using the previous coil, PMOD / FOD flashes red even with the high values (~800mW). I assume that this is because the Mingstar shield is smaller and thus does not offer the same protection against our PCB, which contains ground planes and is placed directly behind the receiver coil.
Thank you
/ Martin
