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(@asjolund)
Contributor
Joined: 5 months ago
Posts: 1
February 19, 2019 4:16 pm  

I'm not sure if I should post this here or on Reddit.  I wish there was more clarity on that.  But here goes:

I just received my table and I love it!  I saw a reddit user mention that there are some unused USB ports under the table and I had this awesome plan to install a Qi charger under the "ring" so I was testing this out by plugging a generic Qi USB thingy into one of the free USB ports under the table and the results were not good.

When I plug the Qi unit into the USB there are no issues.  When I place my iphone x on the Qi charger it charges fine.  I figured I was home free. But when I take the Iphone X off of the Qi base the table freezes and needs to power-cycle before it can be used again.

I only tried it with one if the USB ports.  It seems there is some kind of power surge or something when I take the phone off the charger.  Or maybe I just cheaped-out and should have bought a higher quality Qi base.

Can someone shed some light on what is going on here?  Anyway to resolve it?

Also, you really should have an option for a Qi charger on the table.  That would be awesome!

TIA for reply - I'd really love to get this working!  The ring seems made for a hidden Qi charger underneath with no additional cable management to speak of!

This topic was modified 1 month ago by asjolund

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(@bruce)
Admin
Joined: 11 months ago
Posts: 140
February 19, 2019 7:27 pm  

@asjolund - This is the right place to post! Thanks for relay this info - we learn far faster from our growing user experience. I'm not familiar with the Qi charger specs, but will pass this along to our embedded systems engineer to see whether this is a limitation of the Raspberry Pi, our control board (which powers the Pi), or Qi chargers in general.

Bruce


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(@bruce)
Admin
Joined: 11 months ago
Posts: 140
February 19, 2019 7:42 pm  

A quick search reveals that the RPi's default setting is 500 or 600ma max/ USB port, and Qi chargers provide 7.5 - 10 W - so with the USB 5V standard, that's 1500 - 2000 ma needed. It appears there is a software setting on the Pi that can bump it up to 1200ma / port, but that sounds inadequate as well. Let's see what our engineer has to say...


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(@bruce)
Admin
Joined: 11 months ago
Posts: 140
February 19, 2019 7:46 pm  

... Brian wrote back:

What's probably happening is that the Qi charger is pulling too much power from the 5V USB rail when the iPhone is removed. That's browning out the Pi, and requiring a reboot to get things synchronized again. 
 
The primary problem is that the little 5V switcher we're using doesn't have enough oomph (current) to power the Pi and the Qi charger. It's amazing that it works at all when the Qi is drawing power - I'm really surprised by that. But the big kick appears to be at the end of the charge when the phone is removed - it's possible that the Qi does not regulate its current draw very well, so it generates a spike or something? Not sure, not having worked with a Qi before - I'm just guessing.
Simplest way to solve the problem is for him to use a powered USB hub under the table (i.e. keep the Qi completely separated from the Pi) to power the charger.
 
The Pi itself takes most of the current capacity of our 5V regulator, so you really can't guarantee there's any left over current for anything a user plugs into those USB ports.
 
Of course, we can upgrade to a larger 5V supply if you want to officially sanction the Pi as a USB hub/charging station. But that would raise the cost on all tables, just to satisfy the few who want this.

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(@heropup)
Contributor
Joined: 11 months ago
Posts: 14
February 20, 2019 1:34 pm  

Some time ago, I plugged in an Anker 5W wireless charger into one of the USB ports under the table, and I have not had any issues with it interfering with the function of the table.  That said, the charging is extremely slow; not surprising given the low wattage of the charger.  But my somewhat unscientific observations (I've not done any timed testing comparisons) is that it seems even slower than when the charger is plugged into a dedicated adapter.   Based on this latest news, I think I'm going to unplug the charger from the table.  I wasn't even really using it given the slow charge rate.


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