Xenon - charging LED flashing, no LiPo connected


I set up 3new Xenons last evening, 2 of them started flashing the yellow charging LED after the setup. I have no LiPo connected, they are powered via USB.

Can someone explain this behaviour? Is it an indicator for something?


I have a single Xenon (shipment was wrong :roll_eyes:) and my charge light is also flashing 3-4 times per second. If D7 is high the flashing stops.

Mine are flashing 3-4 times per sec as well but I can not reproduce the D7 behaviour. Setting it to LOW or HIGH has does not change the flashing.

It may be just a indication from the charging chip that indicates no battery is present. The Electron does the same thing when plugged into USB power and no battery is connected.


@RWB can be but I think this is not a feature :wink:
My 2 electrons don’t show that behaviour and also only 2 Xenons are flashing yellow, not all.

None of my 3 flash yellow.

Both my Xenons flash yellow (3-4 times per second) except when D7 is high

None of my Xenons (3), my Argon or Boron have this issue. In fact, if anything, the light does NOT come on all the time when a battery is plugged in.

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I tested mine again with LiPo disconnected/connected:

Xenon 1 / Argon

USB power & no LiPo = yellow LED off
USB power & LiPo connected & charging = yellow LED on
USB power & LiPo connected & full charged = yellow LED off
LiPo power only = yellow LED off

I think that is the normal behaviour, according to documentation (which says nothing about yellow LED flashing)

**Xenon 2 / 3 **

USB power & no LiPo = yellow LED flashing 3-4x / sec
USB power & LiPo connected & charging = yellow LED on
USB power & LiPo connected & full charged = yellow LED still on 
LiPo power only = yellow LED off

I can see no correlation to D7 LED, switching D7 LOW/HIGH has no impact for me.

After further research: they only keep flashing when they are still in the black foam (from delivery). They behave normally in a breadboard. In the foam they sometimes don’t flash, but after wiggling a little, it is possible to get them starting to flash. Pressing the foam on the sides close to LiPo connector will always do the trick in my case.
Also, in the black foam, the D7 led is dimly on (except when forced to HIGH or LOW). So maybe there is a connection…?

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You should not keep the device in the foam as it is slightly conductive in order to “dissipate” static electricity. Hence keeping the device on it will create unwanted effects e.g. bridging supply voltage to GND directly.


Thx @koenn that indeed seems to be the root cause. Removing the foam stopped the LED behaviour.


Public service announcement: The black foam is conductive foam! You should NOT power up any device while inserted in the black conductive foam. You are effectively shorting all the pins together if you leave it in the foam (granted… it’s not as bad as setting the device on top of a piece of metal foil or something else with very low resistance.)

I just put my multi-meter leads in some of the foam and read as low as 500k Ohms.

More discussion/information here:


Funny enough now I’ve removed them from the black foam they’ve stopped flashing :smiley: Mystery solved!

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oops, I’ve been keeping some of my devices in the foam. I thought it was high enough resistivity to not cause a problem.

BTW the yellow LED should only come on (solidly) when a battery is connected and it’s not close to being fully charged.

I’ve got an odd one…my xenon had a flashing yellow led by the usb connector, same as many people above. It was in a breadboard and when I moved it to a different location, using a different usb charger and cable, it no longer flashed.

Turns out the usb charger in the original location was plugged in to a triggered outlet which wasn’t on at that moment. Guess the Xenon uses so little power and the USB charger has large enough capacitors that it could stay powered long after that outlet had lost power. The voltage on the usb was ~4.54v when off, vs 4.94v when that outlet was powered.

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