Safe unattended wireless charging

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jcloftis
 
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Joined: Fri Nov 18, 2022 10:01 am

Safe unattended wireless charging

Post by jcloftis »

I am trying to create a UV Lantern for our escape room. I want to base it on the LED module in a flashlight with 51 UV leds. The draw is 12.3 watts and currently runs on three AA batteries. I would like to create a wireless charging system that can be left on the charger unattended. The lantern needs to run at full brightness for about 10 minutes every hour and re-charge in between uses and overnight. All of this needs to be rather compact and safe.
Any help would be appreciated.
Thanks
J

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adafruit_support_mike
 
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Re: Safe unattended wireless charging

Post by adafruit_support_mike »

That raises a few design challenges:

First, rechargeables operate at a lower voltage than alkaline cells.. typically 1.2V at full charge. That would drop your maximum supply voltage from 4.5V to 3.6V.

There's good reason to think the LEDs will still work at that voltage, but it's something to check. You don't need to go out and buy a set of rechargeables for that, just leave a set of alkalines in the lamp until they discharge to about 1.2V each.

Second, assuming 3.6V does work, AA-sized rechargeables tend to use the Nickel/Metal-Hydride (NiMH) chemistry. That chemistry is a bit touchy, so like all rechargeables you need a charger designed to work with the cells. I don't know of any board-level NiMH chargers you could adapt for wireless use.

Third, your lantern needs the cells to be in series to get 4.5V for the LEDs, but a charger will want the cells to be in parallel. It's possible to build a relay system that swaps from one set of connections to the other, but that would be bulky.


Honestly, if your lantern can operate at 3.6V, it will be much easier to switch over to a 3.7V LiPo. They come in several sizes:

https://www.adafruit.com/category/574

And we have chargers that will fit inside an existing device easily:

https://www.adafruit.com/product/1904

That board can charge the LiPo at 500mA if you close a jumper on the back, so it would be able to accept power from a simple inductive charger:

https://www.adafruit.com/product/1407

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