Fire 10 HD wall-mounted tablet and charging issue after 11 months

I’ve had a wall-mounted Fire 10 HD tablet with some dedicated Lovelace views for about a year. I used existing alarm wiring to send power from my basement up one floor to the tablet location… a direct distance of probably 15-18 feet, so figure the conductors are something longer than that. I’m using two solid-core copper pair for positive and two for negative, right up to the wall mount where I’ve soldered a USB-C cable for charging the tablet.

For the supply, I’m using a cheap wall wart adapter that reads 5.4VDC at the terminals. That’s plugged into a Z-wave module that is set with a Node-RED flow to switch off when the tablet battery reaches 80%, and back on when it reaches 20%. That has all worked well, until around a month ago.

The charging of the tablet has become very slow, and lately it won’t even reach 80%. With the charging power on, the battery begins to deplete until the tablet shuts off completely. Yesterday, I removed the tablet from the wall and plugged it into a standard power supply and it charged up to 100% quickly. I’ve re-mounted it on the wall to see what happens.

I also have a continuously-variable power supply on the way so I can possibly increase the voltage to the tablet. The trouble is, I can’t really read what voltage the tablet is getting while charging… and I don’t really know what’s optimal. I must be losing voltage along the conductors, but I don’t know how much. I’ve thought of how to read the resistance of the circuit, but I don’t have a USB… oh, well, maybe I can find something I can scrap to plug into the USB-C cable at the wall mount just to read the voltage. Hm. That’s a thought.

Anyway, here’s a chart of what’s going on lately with my charger and battery level. I was trying to combat the battery depletion with a trend and some additional conditions in my Node-RED flow, but I think it just comes down to my power supply. Ultimately, I want my wall charging circuit to accomplish the same rate of charge as the regular charger. I’m open to any ideas!

Did you just provide bare power to the port or did you power a buck converter/USB-C charger board? That device supports usbc power delivery and Amazon even sells a 15W USBC charger for it… What that means is the device is manipulating its power draw based on communication with a compliant charger. If you’re not providing the interface, who knows what it’s trying to do.

It also means behavior could change depending on what Amazon does to firmware on the device. Mine (I have two Fire10HDs in my setup) pulled a recent os update? Who knows?

Just bare power. I have a bunch of buck converters lying around I could try. My trouble is, I don’t know how they should be set to account for conductor losses. Or maybe that’s not even my problem and I truly just need a USB-C-specific power supply. Does a USB-C-compliant power supply utilize more than two conductors? If so, I may be out of luck.

Any usbc power supply should just be able to take raw power (+/- x Volts at Y Amps) from any buck converter. You will need to make sure your wire is rated to provide the power the charger is rated for. Melting wires is no fun. It would then have all the smarts to communicate to the tablet.

Theres a number of articles out there about building a usbc power supply. I’m sure you can find one that will fit your use case. But fair warning… There’s also as many people complaining about lack of availability of the parts to do so… You’re probably going to be hunting parts.

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Thanks. I’ll have a look around. I didn’t realize I might need a USB-C-specific charger.

One of the biggest pros on USBC is its ability to use the USB power delivery spec to throttle the power on the line and drive up to 90Watts. To do so it has to communicate with the source. You ABSOLUTELY need a specific charger (or at least one that conforms to spec.) the days of just sending power over a USB cable are about gone.

Check the temperature of the tablet.

What I am finding is that if the tablet charges too fast it will over heat and stop charging until it cools off. Unfortunately being against an insulated wall it takes to long to cool off and eventually dies. I’ve tried using a smart plug to regulate temperature but haven’t found a solution yet.

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Perhaps you should look at the battery health before changing anything. I believe the Fire uses an Android OS, so this link might be useful.

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