Charger advice sought


I read several discussions about the proper charger for the FP2. Most of them lacked some aspect that interests me, and were blocked for new comments.

This is why I start yet another charger thread…

I know, officially FP2 doesn’t support fast charging. But that doesn’t mean that it doesn’t charge fast… It does. And the phone even knows that it has more than one mode of charging!

My FP2 with FP Open OS tells me, when I hook it up to my old 700 mA charger from Samsung (for the Wave II Bada phone), “slow charging”. And it takes several hours. Although this is very good for the battery (extends its life due to less heat strain) and it increases the capacity charged, but sometimes things have to be quick.

When the FP2 does not charge slow, it must violate the USB spec, which limits the current to 500 mA @USB2 (Btw this COULD be an issue if hooked up to a PC with just USB 2, it might have chip fuses to protect the motherboard, these would blow…)

From all I know the FP2 does not make use of the Quick Charge that the Qualcomm SoC would provide, and I don’t know about VOOC from Oppo (the competing industry standard). Certainly USB 3 power management is not used.

But all this only focuses on the phone side! Current limitations may also come from the USB adapter, if it’s ciruitry does not detect a “standards compliant” quick charge…!

So what would be the best strategy when one has to purchase a new mains (or car) adapter? Go for Qualcomm Quick Charge or VOOC support, or ignore USB specs altogether and go for a dumb adapter that simply delivers up to 2 A without checking anything?


I simply bought an Anker charger which is also available for your car. The charging speed is faster than on certain other chargers or on the PC.

I have some 2 A chargers which indeed let the battery charge rather fast. Life expectancy may be measurably reduced but I don’t think I’ve noticed it yet after 2.5 years of nearly daily charging. (Power consumption improvements from newer Android versions come to mind.)

Charging current is always the outcome of negotiation between phone and charger nowadays, therefore I do not worry about it very much. There are other means to improve battery life, like holding charge between 20 % and 80 % or caring about battery temperature.

1 Like

The Samsung ETA-U90EWE (2A) is cheap and works fine here. I measured its current and it can deliver a bit more than 1A while charging during use. But it’s true that it tends to heat up the battery more than low-current chargers.

1 Like

I’m not sure about the USB2 spec violation, but I’m pretty sure this fusing part is not a real issue. USB charging from a computer is slower than from the charger —that’s meaningful for the matter. I’ve seen in the forum discussions about how wall-charging works that fast (IIRC, bridging data pins informs the phone to change mode and accept more current, or something alike)

I use a white label 1 A dual port car charger, mimicking the 1 A official wall charger specs (Edit: I forgot to specify the official charger was originally designed for the FP1). When charging with ~1.5 A or higher, my FP2 has “ghost touches” and overall digitizer malfunction. I tried a 1.2 A wall charger sometime and it worked just fine, though, plus I guess my brother’s FP2 charges fine with a 1.5 A charger.

1 Like

The USB spec is indeed violated but this happens on a large scale with USB cables that are supplied with power banks and I don’t remember any complaints about broken USB ports or blown fuses.

1 Like


I know Playstation 2 has some smd chip fuses, but I could not make out any in the conventional computers I saw from the inside up to now.
It´s quite common to let the USB host and the attached device negotiate which power level/current will be used. Overload protection is covered by the USB controller not needing any further fusing. (would be too slow in its reaction time anyway).
It´s not the attached device simply taking what it needs, but having to accept what the USB host controller provides. If this is too less e.g. for an external HD/SSD it won´t operate. Phones will adjust their charging current corresponding.

As there is nothing that can break any USB charger would do.
You couldn´t even fry your phone with a charger able to deliver 10A output at 5V DC.
Its Voltage on load should not drop too much below 5V DC, otherwise in correspondence with the charging current over time there could rise troubles. The internal charging controller of the phone expects 5V DC to assure a proper regulation, not 4.x DC. There are tolerance limits as defined in the USB charging specifications.
As there isn´t much checked anyway go for a charger with at least 2A output. If it´s compatible with Qualcomms QC mode or VOOC, why not spent more bucks, who knows what´s coming next. Maybe some day you´ll have a device that utilizes this feature not again needing to purchase a new charger.
Charging usually only works with the two power lines + & - on USB pin 1+4. If both devices are more sophisticated like a computer or QC feature then also the data lines are involved in this negotiation process.


Yep, as described in the USB charging specifications.


Luckily this works for standard USB. Serious troubles started with USB-C and Non-compliant cables coming up on the market. USB is much more forgiving and easy to handle, I don´t miss USB-C just for the quicker charging.


As confirmed in the topic I just linked, the FP2 charges with at most 1.5A, so getting a high power charger makes not much sense beyond that.

The two modes are slow charging (500mA) when connected to a computer and normal charging (up to 1.5A). Apparently there are some edge cases like your old Samsung charger which also trigger slow charging; FWIW, my 800mA camera charger from Panasonic does not trigger that mode. It doesn’t make any use of any quick charging methods like Qualcomm Quick Charge or VOOC.

Yes, generally not if it was solely for the FP2.
My thought when I do such a purchase is rather more general and multi-purpose also considering longevity. I think when going with FP this should always be taken into account.

BTW, minutes ago I tested with a 400 mA charger I have around home and it doesn’t trigger that mode on Lineage OS 14.1, :man_shrugging:

No, it isn’t. Fairphone has stated in one of the other charger threads that they did not make use of Qualcomms Quick Charge, although the SoC could do it. I have no official word on VOOC.

But even these are no “negotiation”. To my knowledge, “negotiation” only happens with USB 3 protocol. Without USB 3, the FP2 can’t do that.

So I have to asssume that the fact that FP2 will charge faster with certain adapters is only possible because of a spec violation. So it depends whether your adapter “thinks” you have a fast charging capable phone and therefore permits faster charging. Phones can signal this to the adapter by abusing the data wires, placing special voltages on them. But the FP2 won’t do that…

It is. Or rather, it was. Before the advent of USB 3, USB power got abused for lots of strange things. I have a USB coffee cup warmer here, as a gimmick.

At some point, PC manufacturers wanted to protect their motherboards with fuses. and chip fuses are the cheapest (because they can be placed on the PCB alongside all chips, resistors and capacitors. But chip fuses are hard to replace (actually needs lots of soldering skill…)

But when power to USB connectors became more sturdy and was no longer supplied by the communications chip directly (and possibly because of many repairs - we had some here where I work) they dropped the habit.

Ok, so I read deeper into the matter:

Unfortunately the article is rather confusing and does not clearly state what is actually in the USB spec (and in WHICH spec).

The most powerful mode PD (power delivery) to my knowledge is only on USB 3, and what Wikipedia calls BC (battery charge), signalled by 200 Ohms across both data lines to my knowledge is just “industry standard”, meaning it is not actually in the spec by the USB implementers’ forum.

Fairphone somewhere stated that they do not have the resistors across the data wires, so we would be stuck to 500 mA. If it takes more, than this is a spec Violation (only on USB 3 you are allowed to draw more).

Btw, maybe all of this will change, because the european commission is discussing the introduction of mandatory C type connectors (UBS 3.1) as common charging standard…

Maybe this term is not 100% correct in the way as simple devices interact with each other as between FP and any USB counterpart.
How would you call the mechanism when the charging current changes from ~500mA from a computer USB output up to ~1.4A with a wall-charger?
Maybe it is an USB2 spec violation, but if it´s not to be called “negotiation” what else is it called then? As USB2 spec violation is only the result of the process going on.

Hence it always charges with up to approx. ~1.4A on a simple charger if this can provide that much (even on my Yolk solar charger not having any power buffer) and the cable needs to have a proper wire gauge of course. The current is easy to be metered, e.g. the “Ampere” app does a good job as well.
Things change once there is a more sophisticated counterpart e.g. computer (charger with intelligence). Then the data lines come into account which are simply ignored (maybe not even connected) by simple chargers.
Depending on the voltage levels on the data lines defined by device specific resistor arrays the current is set (limited to ~500mA for FP2).

Unfortunately I´ve lost the link to someone at the xda-developer site who had a DIY all USB device charger. With it any phone (also apple) could be charged slow or fast as he was fed up with each device expecting its own type of charger to charge properly.
There was also a quite clear schematic available which showed the model specific resistor array that sets the current level as they are not all the same.

The battery charging spec you may find precisely here, a few PDF file with up to 72 pages.

Just as @AlbertJP has stated above.

I also was confused about these high currents as µUSB connector datasheets always show current limits for the connection pins which are much lower than what I could measure.

So as with µUSB which took several years to be commonly used, it again may take another ten years until it´s commonly used as the new standard.

Until then it would be nice to have regulations taking care of non-compliant USB-C cables respecting the specifications not frying any attached hardware as has happened to several customers out there in the past already.

1 Like

The USB device as being the power sink signals its demand. One method is the resistor across the data lines (+D und -D). The power source may adjust its power delivery, but it is not mandatory to do so.

Effectively it’s a mode switch. But negotiation would have to be two-way. Signalling to request a mode switch is unidirectional.


Yep, sounds feasible.
So I have one right here…

although it is manual :smile:

Called µconnect. For people who just want to charge (on the way) not needing/trusting a data connection.
It simply de-/connects the data lines to change the mode.

EDIT: µUSB magnetic add-on to any µUSB plug (white/black/purple iirc). Yes, works symmetrical with the magnet. Uses a somehow standard magnet also fitting with Goobays magnetic cable.
Yes, there can clearly be measured a current difference between the modes. But to be honest, I also have “standard” cables of not any special type which also gets the phone to charge with about ~1.4A (not on the computer). So it should not require this add-on to get FP2 to charge with its maximum current.

As I built my OTG adapter I also tried different resistors for this charging current issue but did not experience any difference here. Only with the data lines generally connected or not. The resistors I used did enable the OTG mode which in addition also uses pin 5 only available on the µUSB side.

Thank you. So this could be used to introduce the resistor that our FP2 lacks so that power supplies will mode sense a request for fast charge? What connector is that? Looks symmetrical, is this type C?

1 Like

I think it simply switches between the slow charge + data (500mA) mode and normal charge (max 1.5A) as the latter mode is activated when the charger (or out-of-spec cable) shorts the data lines, which prohibits data transfer.

My ThinkPad laptop activates 1.5A charging on one of its USB ports when it is in sleep mode - probably the same idea, shorting the data lines when no data transfer is required.

Thanks for this document. But:
“Notice: This agreement is not effective until a fully executed original has been received by the secretary at the USB Implementers Forum”. So we can take data from it , but it will have to be considered draft.

1 Like