USB charge time.

I'm sure the Wife's Samsung S8 charges at 9v with it's factory lead and charger.

All Lithium batteries will have a protection/ charge circuit to prevent damage or potentially fire..
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My conclusion is that the Computer power supply is so well regulated (at 5 V) as to really not be suitable for "charging" purposes.
The reason is that USB ports on computers are designed to meet the original USB 2 specifications, which allow a maximum of 500mA for any device and have no provision for charging or high power.

Devices and chargers which provide higher power have various ways of signalling that higher current is available or wanted.
There are now standards for such things - but before that manufacturers used their own methods with the result that for optimum charging you needed to use a charger from the same manufacturer as the device - otherwise the default 500mA would be used.

Junk cables with ultra thin wires and no data lines connected just add to the mess.
The only way in which one can "charge" a battery (of cells) is to provide a voltage higher than the output of the cells and a relatively low resistance charging path to the cells concerned, which will then force current to produce a chemical change within the cells concerned.
Considering the very small current involved in this process when charging any "5 volt" Smart Phone battery of cells, the prime consideration must be the voltage of the charging supply.
(The resistance of any conceivable "Wire" concerned must be negligible.)
Once upon a time that was true, however today we have inverters, so I can plug a battery into a USB outlet and the battery will charge from it, I then take it out with me and when my phone goes flat plug the phone into the battery which recharges my phone. Clearly to work some where along the line an inverter raises the voltage.

The same applies with cars and caravans, the inverter draws for example 10A from car battery and charges the caravan battery with a stage charge starting at 14.8 volt even when the car battery is only at 12 volt. Today with alternators which only charge on over run to save energy the old split charging relay or diodes are no longer any use.

However with the car battery clipping on an ammeter is easy, with a USB lead getting access to some thing which you can measure is a problem. So last night my phone was connected with a Pound World lead to a 2.1A USB outlet, it was less than 25% charged the warning had come up, this morning it is 85% charged, move it to PC with Samsung lead to transfer some pictures and 1 hour latter 86% charged, move it back to a 2.1A USB socket in a 13A plug and another hour and fully charged.

OK today no hurry, but when there is, you take a bunch of leads in your hand and you know at least one is a genuine lead, and will charge fast, but you have no idea which is which.

And I charge my camera battery from a USB outlet, camera battery is 7.2 volt and USB is 5 volt. So clearly all down to inverters some where.
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Well the little meter has arrived. Test one cheap Pound World cable into mobile phone, charge rate approx 0.5 amp just over 5 volt, then swapped lead, more expensive type but same thickness and around 0.9 amps at same just over 5 volt.

5.22 volt no load, drops 5.08 volt when charging, clearly my tablet and phone are now fully charged, the charge rate quickly falls to zero for phone and seems to step down for tablet 0.9, 0.5, 0.2 and touch it and it springs into life and the current jumps to 0.7 amp.

It does confirm some cables will not allow the full charge. In the PC and the current and voltage are steadier, 4.99 ~ 5 volt and 0.41 to 0.43 amps into tablet, there is however no real change in charge rate between 4.99 volt and 5.22 volt, clearly some internal switch mode device in the tablet controls charging rate. Powering off the tablet left it at 5.02 volt and 0.35 amp then 5.18 volt zero amps as one would expect. Switch on and back to 5.02V 0.35A until screen turned off then between 5.09 and 5.18 volt current zero most of the time flicks to 0.02 to 0.08 every so often.

Really I need something nearly flat to test fully, specially as to which leads are fast and which are slow.
I've just bought a pair of Samsung wireless charging pads for me and my wifes S8's.

The are a godsend!, just pop the phone on the pad when you go to bed and fully charged by morning, no faffing about.
I seem to remember reading on how Nikola Tesla built a power station that he tried to power a town this way.
However it is a rather wasteful system. The advantage with small items is you can make them fully water proof, if you don't need to plug anything in to charge it there is also no place for water to enter. Great idea for a tooth brush.

However it is so easy to forget to put your phone on charge, my early phones it was easy, simple get a spare battery, but today many phones will not allow you to swap battery, so people want to cram as much energy into their phone as quick as they can, so I would look at a host of charging leads with no idea which would charge quickly and which would just give a trickle charge. So at last I have a method to test lead and output and compare.

What will be interesting is to compare the PC to a USB wall socket. But need a discharged phone or tablet to test with.
The are a godsend!, just pop the phone on the pad when you go to bed and fully charged by morning, no faffing about.
Well I just pop the cable in at night when I go to bed and also find it fully charged in the morning - no faffing about ;) Not to mention, "standard" chargers and cables are so cheap that it's easy to have a few around the house.
The pads were only £10 each and use "standard" chargers ;).
The computer has around 0.35 amp output even with a good lead, and with a cheap lead the output is still 0.35 amp so with the computer may as well used cheap leads, but with 13A sockets with USB outputs 80% charged phone between 0.65 and 0.94 amp, some with 4 USB outputs some with 2, the odd thing same socket tested twice two different readings. Maybe the phone went just over the threshold to draw less.

All outputs rated 2.1A per pair. However clearly some outlets and cable combinations can deliver twice what others can.

I continued to test, using my tablet as a load, it became apparent % charge is important, same outlet and cable at 74% charge showed 0.94 amp and at 44% charge 1.24 amp.

In the main be it TV or computer, cheap or expensive cable outlets really designed for coms not charging seem to charge at around 0.42 amp, if you want fast charging then the USB outlet needs to be on something only designed to charge, be it a well sockets or a cig lighter socket, and since output seems to be linked to battery state one can't really make a list of good and bad.

But the tablet display is clearly wrong. Plugged in showing 1.22 amp from a 3.1 amp USB built into 13A socket, tablet 44% charged, it reported charge time 36 hours, 3 hours latter charge rate was zero and tablet fully charged, so much for 36 hours. I can now identify slow leads and slow chargers, but as to if it helps not sure.

The tester does have one extra good point. It shows when charging is complete without having to look at phone.

Wife has ipad around 4 years old, with an outlet rated 3.1A per pair, it was drawing around 1.48 amp to charge, this is well over what my table draws, most seen mine draw is 1.28 amp.
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