current sensing --> voltage adjusting USB charger

MikeA

Joined Jan 20, 2013
192
I noticed that when using my cell phone as a navigator in the car, even when it is plugged in, the battery is draining about 20% per hour. And it doesn't stop, it goes down all the way until the phone shuts off.

I'm suspecting that it's the wire gauge of the USB cable. I'm using a 4ft cable which I assume is 30 gauge based on cutting up some other similar USB cables. If it is 30 gauge, then at 1A and 5V at the USB socket, would result in only 4.17V at the phone input. Factor in that the battery charging circuit needs say 0.5V above to what it can charge, and suddenly with the navigation suit running, it can't keep up.

Am I on the right track here?

MikeA

Joined Jan 20, 2013
192
I have an older Samsung that doesn't do any charger sensing. I have also plugged in a USB power meter that shows 0.24A, while an app on the phone shows 0.4A charging rate. Major voltage drop?

Alec_t

Joined Sep 17, 2013
10,592
I have also plugged in a USB power meter that shows 0.24A, while an app on the phone shows 0.4A charging rate.
I don't see how the charging current can be greater than the current the USB port is providing. Are you sure your power meter is correct?

Joined Feb 20, 2016
3,154
The current at both ends of the wire will be the same. Try your current meter on a resistor that you can measure the current with another meter, or calculate it, to see which one is not reading correctly.

MikeA

Joined Jan 20, 2013
192
The whole thing is confusing. I think the phone app shows charging rate for the battery. The phone could be using more current through the wire, for GPS and screen and everything else while plugged in. But the app is showing only what is going to the battery. So it might be showing 0.4A charge rate, while the phone is pulling say 0.8A to keep itself running.

I need to cannibalize another USB cable and measure at both ends with a multimeter.

Too bad USB doesn't have an extra wire so it could measure voltage at device, and boost voltage at the charger to compensate.

MisterBill2

Joined Jan 23, 2018
4,490
A phone is an expensive thing to be experimenting with voltage boosting on. And why believe either one of those current reading devices if they are not calibrated to some good standard. Also, the USB line current will not be the same as the battery charging current, because the internal charger is not 100% efficient, and some of those little apps keep drawing power no matter what you do.