Issues with wireless charger

Had been struggling with my wireless charger.

Turns out that with the EV3 ON it never charges. It starts, gets a few decimals of Volt and then it starts discharging.

The EV3 battery LEDs are both ON (RED and GREEN, meaning it is charging). Battery level, according to

cat /sys/class/power_supply/lego-ev3-battery/voltage_now

is 6912400 so 6.9 Volt

The Qi emitter is using a 2A USB charger. The LED shows it is coupled with the Qi receiver. For the first 15 minutes or so it charges a bit but no more that 0.1V… then it starts discharging. After 3 hours, the ev3dev turns itself OFF.

Tried a different Qi emitter. Also a few different USB chargers. The Qi emitter gets hot. Sometimes one of them blinks, I thought it was a coupling problem but now I think it is an overcurrent or thermal protection…

Not sure about the efficiency of this Qi couple and also not sure about the efficiency of the boost circuit… I suspect that I need more than 2A through the emitter to get a full charge and they can’t handle it more than a few minutes and then they “throttle” current.

I trimmed the boost circuit to give 9.02 V instead of 10.02 V. Less voltage should mean more current available but didn’t notice any effect.

Last night I left the battery charging  with EV3 off (it had not enough charge for ev3dev to keep running) . This morning the GREEN light was ON and the RED was off so it charged. Turning EV3 ON it reported


So the battery is not quite full charged but much better than what I get with EV3 ON.

With a small 4-port USB hub, an Edimax wi-fi dongle and a CSR 4.0 BT/BLE dongle the ev3dev reports 208 mA

cat /sys/class/power_supply/lego-ev3-battery/current-now

I plan to get a current meter and watch consumption with several dummy loads. Perhaps I can tune my gadget a bit but I think I’ll have to find a better Qi receiver (and probably also a better Qi emitter).

So, for now, Juan’s idea of using this for charging an autonomous Ev3 robot is paused. The better we can do is bringing the robot to the charging point and turn it OFF to let it charge. But someone has to go there to turn it ON again after charging is complete.

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