I was on this topic a few weeks ago for my own use and also sent a query to the support about the highest current FP2 could actually draw from a charger, but with no answer. A bit surprising, as they generally don´t deliver FP2 with any appropriate charger and are probably not mainly interested in also making money with such accessories.
So I read from different sources on the net and also crossed some very nice, interesting but easy solutions to meet any challenge out there related to usb charging. I´m glad not keeping up with A***e. Well I don´t have many usb powered devices, but also wanted to have a (simple) option for charging anything by only one (strong) supply. I had to learn how long it takes to charge FP2 by my computers usb 2.0 output. The initial OS was not very tolerant accepting all available usb chargers out there, so I had to be patient until my solution was ready (and meanwhile FP2 should accept every generic usb charger). I also tested those different circuits with different resistors (actually a simple setup when using a few potentiometers of 1kOhm).
No matter what setup I´ve tried with the data lines, I could not get FP2 to draw more than about 1,4 amps, which is a common current level when not quick-charging. I do believe it cannot take more or does not support “quick-charge”. Actually therefore I did not need any additional circuitry. So to have enough power to charge any device out there up to some time in the future I bought a simple notebook psu with 5V/6A power rating. Therefore I made a converter cable from barrel plug to µUSB (only power lines). Due to the issue concerning capacitive displays and the grounding while charging to keep them operational I disconnected the ground wire from the main power line. Most usb chargers in EU only have a dual-wire euro plug without protected earth pin, also many PSUs for notebooks. Anyway the psu is completely isolated in plastic and internally a proper design expects a galvanic separation between ac and dc circuit. Also do not only put your focus on the charger, but test different usb cables as well. If the wires are not capable of delivering the higher current a powerful charger won´t help. That´s why I did not alter any finished usb cable, but used my own type and attached each connector separately.
Now with this solution I can generally charge any µUSB device. My FP2 needs from 0%-100% about 60 mins while switched on. This is absolutely acceptable for me. By the way I was thinking of making a multi-outlet board to meet every option needed. Data syncing is secondary for me. It may be of use reading here: “http://www.usb.org/developers/” "
This quick-charging issue (also or maybe mainly) depends on the used Qualcomm cpu. Our Snapdragon™ 801 in FP2 as I could read in the specs DOES at least support Quick Charge 2.0. But FP decided not make use of this feature which seems to become more and more attention. I assume engineering the pcb layout with quick charge support would had been a lot more expensive.
Actually I kept it as simple as possible. So there are no resistors used at all and the phone charges with up to 1,4amps. The data lines are not connected in any way. I only connected the wires for the power. But as I wrote the cable must have wires with a slightly bigger cable cross-section. That is often a limit when already having a strong charger at hand. Manufacturers don´t necessarily deliver cables of high quality with their chargers. I shortly used a solar charger with a slim-line µUSB cable for laying under the balcony door or window. It couldn´t deliver more than 0,6 amps. So I tried another conventional cable and with it I got up to 1,4 amps. The solar charger can deliver up to 3 amps. With decent cables it finally could charge my FP2 and a LG G4 both switched on with about 1,3 amps each, simultaneously.
Made my own test-equipment for measuring the charging current via USB. If I connect my FP2 with my AC-charger with floating data-lines then my phone does not charge! That should be the reason why cheap cables without data-lines (for charging only) do not work with the FP2 …
I highly disadvise from disconnecting the ground wire (“Protective Earth”) from any device!
If a device has a grounding wire, it’s there for a reason! I know, that most devices work very well without grounding, but as said above, it’s the Protective Earth, it protects your life in case of failures!
You are correct, most PSUs don’t need a PE Wire, but when a PSU has a PE, it mustn’t be removed!
There are rare cases (e.g. my laptop charger), where the cable of the PSU has a PE wire, but it’s not connected on the charger-side. But in this case, disconnecting it wouldn’t change anything…
I tested my test-board and noticed a small resistor which was hidden from earlier experiments. It took the D±pin to 3 Volt. Now the data-pins of the phone-side are really floating and the FP2 charges at the max what the charger is able to deliver.
The result of this exploration is:
The FP2 does not need any data-pins, nor the data-pins connected in any way for charging.
I will test further if any resistor or voltage on data-pins changes the charging behavior …
Yes, at some point I agree with you. Anyway in electronic engineering you whether have a fully isolated plastic casing not needing the third wire “pe” as there is very often now spot to actually connect it OR a design (metal casing like any tower pc psu) requiring a connection to protective earth.
Just as you say, your notebook psu does not have the pe connected internally, Since it most probably does not keep a touch sensitive display, disconnecting the pe wire wouldn´t change a thing…but charging a smartphone at the end keeping a touch sensitive display surely does change a thing as I realized. Doing this keeps my phone operational while being charged.
Other FP users faced this phenomenon earlier and asked for help in this forum at last. So I also could read about others having this trouble with their unmodified standard chargers they owned and some one explained the reasons why. It was feasible and I could solve my problem this way. Still my psu casing is fully isolated and regulations for design requires a galvanic separation internally between ac and dc to prevent accidentally contact with ac in case of a fault.
This is not true. Some devices have a mains filter which needs the PE to conform to the rules of the European Economic Area. If you didn’t design the charger (or saw the schematics at least), you don’t know for what the PE is for!
Is just nonsense. It’s not connected internally! So it doesn’t change anything and with or without touchscreen doesn’t matter. Please re-read what you wrote, it’s absurd.
And as I said, if disconnecting the PE changes something, it’s connected anywhere, so it’s needed and mustn’t be removed.
I personally don’t care what you do at home, but do not advise/tempt anybody disconnecting the PE wire. It’s just dangerous/weary of life.
And there are news about the touch-issue, it might be related to the voltage (and not to potentials, which is pretty surprising for me):