Wikipedia:Reference desk/Archives/Computing/2019 August 22

= August 22 =

What does it mean when a cell phone charges extremely slowly ?
My Samsung Galaxy J7 "Crown" is charging at around 1% per hour. It used to charge at more like 10% per hour. It's only a few months old. I am charging it from USB connection to PC. So, what could be the cause ? Low voltage coming from the PC power supply ? Any other thoughts ? SinisterLefty (talk) 17:57, 22 August 2019 (UTC)


 * Try an external charger maybe. USB ports are voltage regulated but they are supposed to negotiate the charge rate with the device, and if that isn't happening it's supposed to limit to 100 mA which would mean a 24+ hour charge.  Are you sure it charged faster before from the exact same PC port?  If the phone came with a charger, try using that.  Or try this which is quite powerful.  67.164.113.165 (talk) 19:02, 22 August 2019 (UTC)


 * Thanks for the info. I'm not at all sure if this is the same port I used before, no. Would this slow charging be in any way bad for the cell phone ? Might it even be better for it, by not causing it to heat the battery as much ? (It's a backup phone, so I can easily leave it to charge for days at a time.) SinisterLefty (talk) 19:29, 22 August 2019 (UTC)


 * It should not be bothered by slow charging, but it's best for the battery to stop charging when it's about 80% full, and don't let it get below around 20%. If it's a backup phone I'd just remove it from the charger when it's full, and check the charge level 1x a month or so.  Phones tend to use a little bit of battery power even when they're turned off, so you could take out the battery to prevent that.  Iirc the J7 has a removable battery, which makes that convenient.  Added: if your PC has both USB2 and USB3 ports, try making sure the phone is charging from a USB3 port since they can supply more power.  The plastic insert of a USB3 port should be blue instead of yellow or whatever. 67.164.113.165 (talk) 19:39, 22 August 2019 (UTC)


 * The J7's battery is generally removable, but not in the "Crown" variant. So I really want it to last as long as possible (before it dies and makes my phone into a brick). I do try to do the 20%-80% charging cycle, and it charging more slowly gives me more chances to catch it around 80%. I also have a timer that will cut power when I specify, but predicting when it will be at 80% charge is not so easy (especially now that the charge rate seems to vary widely). I believe my PC does have USB 2 and 3 ports, but they are all black. They have different symbols below them, and I understand that those with "SS" (Super Speed) under them are the USB3 ports. SinisterLefty (talk) 20:03, 22 August 2019 (UTC)


 * This came up three times for me in the past month, all in very different circumstances. My wife's phone wasn't charging in her car. A coworker's phone wasn't charging off her laptop. My son's external drive wasn't working on his PS4. In all three cases, the cause was the same. Not all USB ports are powered. Yes, they have a little power, but not enough to power things. The car's USB port is a data port. If you attempt to pull too much power out of it, the radio actually goes out. There is a separate USB charger port below the radio. My coworker's laptop has four USB ports. Two are data-only. Two are powered. She was using a data port, so it wasn't supplying enough to trigger her phone to charge unless she had the laptop plugged into a wall outlet. The PS4 has two USB ports on the front. One is a data port. One is a powered port. I moved his external drive to the powered port and it worked fine. I feel that there are many issues causing this problem. Foremost, it is expected that all USB ports may be used to charge a phone. If the USB fits, it must work. That is not the case. USB ports do not have to supply enough power to trigger a phone to charge. Further, a USB port can supply too much power. I have a USB-rechargable razor that has a warning: "Do not use a fast or quick charger. This device is not designed for fast or quick chargers. Possible fire or explosion." Beyond that problem is the ignorance of the "experts." If you ask 10 random people about this. At least 7 will say they are computer experts and they know for a fact that all USB ports work the exact same way. So, they should all work as chargers. Finally, there is the marketing issue. Would a device sell well if the USB port was clearly marked as "underpowered"? So, marketing doesn't clearly mark the data-only ports. After learning about this, I checked seven of my AC-to-USB plugs to see how much power they put out. All of the devices put out between 4.5 and 6 volts. The standard is 5 volts, so that is within tolerance. The amperage, which is the real power, varied a lot. Some put out 0.5 amps. Some put out 1 amp. Two put out 2 amps. I checked the PS4. The left port is almost 0.2 amps. The right port is 1 amp. In my wife's car, the radio port puts out 0.4 amps and the charger port puts out 1.5 amps. So, tht is where the real difference is. Apart from all of this, I have a lamp that uses a USB connector. You can't power it with a phone charger or a computer. It has what looks like a phone charger. But, it puts out 12 volts at 4 amps. There is a warning on it telling you that it is NOT a phone charger. No kidding. 97.82.165.112 (talk) 22:59, 22 August 2019 (UTC)


 * Wow, that is an alarming lack of standardization. That last case could start a fire if you plugged in anything else. They should use a circular plug instead of USB form.


 * So how do you measure voltage and amperage on a USB ? Using a standard meter and touching the test leads to the proper pin-outs ? SinisterLefty (talk) 12:15, 23 August 2019 (UTC)
 * You get a USB current and voltage meter. £2 on eBay. Hugely useful little gadgets.  Some even measure integrated energy (i.e. battery charge capacity). Andy Dingley (talk) 15:51, 23 August 2019 (UTC)
 * Good summary. I'll note that many powered USB ports have a small symbol on them (a little lightning bolt) to indicate that they are capable of charging, but they are not universal, often difficult to see, and apparently not widely understood. Matt Deres (talk) 15:36, 23 August 2019 (UTC)


 * USB is pretty well standardized. It's just that a lot of cheap USB powered crap more or less ignores the standards.  Adafruit has some USB current metering gizmos but (per Andy) you can probably find them cheaper on ebay (dealextreme, aliexpress, etc). 67.164.113.165 (talk) 01:41, 24 August 2019 (UTC)


 * Just ordered one for $3, through ebay, from Hong Kong. No shipping charge but they don't promise delivery until October 29th, so they must have sealed it in a bottle and plunked it in the ocean with a note for whoever finds it to mail it to me. :-) SinisterLefty (talk) 01:50, 24 August 2019 (UTC)