fifteen volts?

Thursday, April 2nd, 2015 09:46 pm[personal profile] darkoshi
darkoshi: (Default)
Qiao's no-name Chinese tablet that he bought off Amazon (however long ago) is no longer turning on or taking a charge. After prying the back cover off with the help of some plastic toothpicks, I can see the battery model number. The only place the battery is for sale is on aliexpress.com.

To make sure it isn't an issue with the charger, I checked the charger's output voltage with a multi-meter. Seems good. It's a variable voltage charger (don't remember what happened to the original charger), and is set to the correct voltage. The tablet indicates 5V, but not what polarity. Regardless, switching the charger's polarity doesn't make a difference. Tablet still doesn't respond.

But maybe there's something else wrong with the charger; maybe it's not putting out enough power. So I was going to try another variable voltage charger which I had hooked up to my old but treasured clock-radio; it wasn't even plugged in for the longest time. But first I checked the voltage on this charger. It displays as 15V regardless of what setting the selector is switched to. Does that mean that *this* charger is bad?? Now I don't dare plug it back into my clock-radio.

Addendum
I hooked the tablet back up to the charger which shows the correct voltage, then pressed and held the power button, and the tablet started up fine. ::rolls eyes:: It even shows a full battery charge. All's well that ends well, except for my other charger.

Date: 2015-04-03 02:36 am (UTC)From: [identity profile] randomdreams.livejournal.com
You may already know this, but some chargers don't produce the right voltage unless they're running into a somewhat significant load, so measuring them with a multimeter will give a false indication that the charger doesn't work.

Date: 2015-04-03 04:31 am (UTC)From: [identity profile] randomdreams.livejournal.com
Possibly but without access to some tech data it's hard to decide what resistor will provide enough load. Maybe something in the 1k range? That shouldn't pass enough power to melt, but should provide enough load to at least make the power supply think it's doing something.

Date: 2015-04-03 04:50 pm (UTC)From: [identity profile] randomdreams.livejournal.com
It isn't. Wall voltage varies so they tend to make the supplies produce slightly higher voltage than they really need, and deal with it downstream, and unregulated or poorly regulated supplies, or switchers that rely on feedback from a loaded system, look just terrible when measured with a multimeter.

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