Can I use pc charger?

Some correction is in order here.

USB power supplies actually don’t controll the charging of the battery at all.

All they do, is provide a negotiated voltage up to a given current. By default, that’s 5V at 900mA (=0.9A) for USB 3, or 5V at 500mA for USB 2.

USB PD (which stands for Power Delivery, not Power Direct) can be used to negotiate up to 20V at 5A. This only happens, when a USB PD negotiation is successful, so this cannot harm devices that don’t support USB PD. In that case, it falls back to 5V.

The voltage is supplied by the power supply, but how much current (ampere) is actually used is determined by the device. The ampere ratings of the power supply don’t determine how much current flows, but what’s the maximum amount of current, that can be drawn safely.

Overcharge protection, same as the charge process in general is completely managed by the phone and has nothing at all to do with the charger.

Otherwise, phones would blow up each time you connect them on a dumb charcher which just supplies 5V and leave them there over night.

To prove the point, I’ve got a non-USB power supply here, that supplys 5V with 11A at maximum. That’s about 12 times as much maximum current as USB 3 normally supplys. I cut up a USB cable and connected it only to the 5V output. So here we got a supply, that can supply crazy amounts of current at regular USB voltage, but with no USB PD negotiation.

When I connected it to my phone, it totally worked, and charged my phone. At 0.9A. The reason is, that, since there was no USB PD negotiation, the phone didn’t know the capabilities of the power supply and thus fell back to only using as much current as it knew would be safe: USB 3 standard 5V@0.9A.


  • A power supply cannot overcharge a phone battery
  • A higher power USB certified power supply is always safe, even when plugged into devices that don’t support USB PD (except if the power supply is defective or something)
  • A power supply supplys power. It does not even know that there is a battery charged by it, and it certainly has nothing to do with the charging process.

The explanation might sound impressive, sadly almost everything of it is wrong…


Maybe you could correct me and I could edit or delete my comment. Thanks

I did, here: Can I use pc charger? - #20 by Dakkaron

OK I don’t see a problem but you may not like one part

“The only concern is that if there no control the phone may take a bit too much when it is already nearly fully charged, you can only tell by looking at the rate of charge which isn’t easy.”

There is such a concern and this is why Fairphone note not to fully charge a battery if not essential as ‘fully’ charging can lead to quicker battery degradation. Even if a phone is plugged into 5V for an extended period the phone can ‘keep’ charging the battery even though it is ‘full’

Full is just a setting the battery can be pushed to that limit and being held there is not the healthiest thing for it.

That is just not true.

First of all, the USB port always supplies 5V, no matter what the phone does with it.

Maybe, I’ll first have to explain how charging of a Li-Ion or Li-Po battery works.

With those batteries (contrary to e.g. a lead acid battery) the charge level directly correlates to the voltage the battery outputs. A Li-Ion battery cannot discharged below 3.0V without causing permanent damage (deep discharge). So usually, a Li-Ion battery is only discharged to 3.3V or 3.5V (this is then 0% or an empty battery).

3.7-3.85V (80% charge) is the optimum level for the battery to be stored at.

4.2-4.4V is the full level of the battery. This is the highest voltage to which it is acceptable to charge a battery to. But this charge level is stressing the battery, so it should not be kept at that stage for extended periods.

The battery should NEVER be charged higher than that, since it can quickly cause bloating and fire from that point on.

No charge circuit will ever charge beyond that point, ever, unless they are trying to start a fire.

So, how then is a battery charged?

First, we start of with an empty battery, say at 3.3V. The charger will pull up the voltage from those 3.3V, which will cause current to flow into the battery, charging it. The higher the voltage difference between what the charger supplies and what the cell currently has, the more current flows into the battery.

This phase of the charge is called “fast charge” and the voltage is raised to the point, where a specific current flows, e.g. 3A. This current is limited by the cell’s maximum charge speed and the power the PSU supplys, what ever is lower.

Once the battery reaches around 3.7 to 3.85V (depending on the specific battery), the charging circuit switches to “trickle charge”. Here it will not pull the voltage higher than the cell’s maximum charge level (4.2-4.4V). This meansn charging slows down a lot.

Once the battery reaches its maximum charge level, it will stop charging. Your phone still displays the charging symbol (since it means “USB power is plugged in” and not “phone is actively charging”) but it is not charging, until the cell’s voltage discharges below a certain threshhold, then it will start charging again until it reaches maximum voltage.

So, no, a full battery will not be charged even a tiny bit.

But your bigger mistake is actually thinking, that the USB power supply is somehow responsible for limiting charge current. Thats utter nonsense. That’s the responsibility of the phone’s internal charging circuit.

You can take a USB chord, cut it open and remove all wires except VCC and GND ( the power wires), so that there is no communication between the PSU and the phone, and it will still charge and not overcharge (though USB PD will not be available).

Next issue: without USB PD negotiation, the fallback profile is 5V@0.9A for USB 3, not 5V@3A.

You didn’t even get the name of USB PD (which means Power Delivery, not Power Direct) right.

Honestly, there wasn’t much at all correct in your post.

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I think the point people were trying to make, is that this none of this depends on the type of charger connected, and is thus off-topic here. You can’t create any more damage by connecting the wrong charger, unless that charger is doing something really off-spec.

Thanks for your detailed reply and

  • first yes PD is Power Delivery not Power Direct
  • The 5V 3A
    If you are referring to “If the Fairphone gets no response from the charger it will just use the lowest voltage and but as that, according to your ‘specs’ still provides 3A it should charge fairly rapidly.”

I’m not saying that 3A will be forced into the phone, just that the charger the person is using is capable of providing 3A. This is dependent upon the battery ~ a large battery may well take all the 3A. This was not a reference to a USB standard.

I’m sure I didn’t say that ???

  • The full battery charging refers to the overworking battery being charged each time it drops 'below a certain threshold" as you put it. Not that it will just keep charging without a break. As you say, and you note the battery has safety features to stop at a set point.

This what I was referring to when saying not to leave it plugged in without paying attention as when the battery is ‘full’ it is still subject to intermittent charging to keep it so. And as you point out that isn’t a great idea.

So whereas I agree with your understanding I think you have somehow not seen my text in the same light.

There are parts of your tidy explanation that I would argue with, but it’s fine and more detailed than my effort.

So I will leave the issue to you to ponder. If there is any error in my post please specify so I can correct, otherwise I will end this discussion as it is getting very off topic.

Simple question, simple answer
Yes you can

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Ok, let’s go through it. I see, you removed the “overcharge” part of your answer, which was the most dangerously wrong part, but let’s go through the rest:

Hi and hello :slight_smile:
The voltage range and current are common for PD chargers and the Fairphone uses QC
[Power Dilivery or Quick Charge]


They are different protocols which communicate the charging rate required by the device, depending upon it’s state of charge, but most modern chargers handle both protocols.

Nope, devices don’t communicate the required charging rate, and that communication doesn’t depend on the state of charge.
They communicate power requirements, and the value is usually negotiated at the beginning of the communication and not changed afterwards. This is important, because USB PD can also power devices that don’t actually have a battery. (E.g. a laptop with disconnected battery.)

I the Fairphone gets no response from the charger it will just use the lowest voltage and but as, according to your ‘specs’ still provides 3A it should charge fairly rapidly. (rapidly may not happen)

Nope, it’s not 3A, but 0.5A on USB 2 and 0.9A on USB 3. That’s the maximum a device is allowed to draw, if no negotiation determined another voltage/current.

The only concern is that if there no control the phone may take a bit too much when it is already nearly fully charged, you can only tell by looking at the rate of charge which isn’t easy. (This refers to the fact that a fully charged battery left plugged in will be topped up keeping the battery at an increased stressful level)

Not true. USB PD communication will change nothing at that fact. Any USB power supply (PD or not) will keep delivering power, because it knows nothing of the charge state. And no matter what kind of power supply you use, the phone’s battery charging circuit will keep the battery topped up. And that circuit also reduces the current needed, if necessary.

Ensure you keep an eye on the phone as it reaches 90% 95% and see if it says it is charging slowly, that means it is communicating and there should be no concern that it overcharges.

Not true. Again, the charging speed during topup charge is controlled completely and only by the battery charging circuit built into the phone. There is no communication happening with the power supply that would limit anything here.

Saying that, there are many recommendations, including by Fairphone that battery ‘life’ can be extended by not fully charging the battery. Some people use 80% as a max so they either root the phone to install a control app or, as I do, keep my eye on the phone.

This is true, but again, has nothing to do with the USB power supply. In these control apps, the phone shuts down it’s charging circuit. It does not communicate with the USB power supply to turn of the power.

On the note of battery ‘longevity’ it is also touted not to let the battery go too low, especially in cold climes. Although I have no routine I rarely let the battery drop below 10% nor charge it above 90%, with commonly an even smaller range.

This is actually correct.

But the main point where you went wrong is that you think, a USB power supply can actually reduce it’s power output below 5V.

To get back to the basics: The PSU can only determine the voltage. And it has a certain “power” to hold that voltage, depending on how much current is drawn.

When a PSU says, it does 5V@3A, that doesn’t mean it can somehow limit how much current is flowing. That means, it promises to be able to safely deliver a voltage close to 5V if no more current is drawn than 3A. If you draw more, the PSU will likely get hot and the voltage will drop below the rated 5V.

A PSU usually has no way of limiting the current.

So when PD negotiation failed, the phone will only draw 5V@0.5A/5V@0.9A, not because the PSU did anything, but because that’s the highest current, that the phone knows is safe to draw. There is nothing stopping the phone from drawing more, but the phone doesn’t know if that might damage the PSU. So it sticks to the safe limit it knows.


Why would you think warning someone about overcharging would be dangerous ?

You seem to have read me wrong.

  • I didn’t say a USB power supply can reduce it’s power below 5V
  • If you want to be picky and accurate, which seems to be where you are heading
    • Power is a product of Amperage and Voltage and the power drawn from any source, including a USB can drop to almost zero once the battery is ‘charged’ or the laptop in hibernation.

Again you seem to have misunderstood.

There is no mention in my post that the 3A is being supplied via a USB A comming from a computer using USB 2 or USB 3
In fact my

  • USB A can supply 2.4A and has a voltage range down to 3.4V
  • USB C provides 3.3A

And you aknowledge the battery will keep charging ??

Though I could agrue your comments more, and no doubt you may have some ‘good’ intenttions, this is off topic and maybe a good idea to stop here :slight_smile:

Why would you think warning someone about overcharging would be dangerous ?

Cause it will make them afraid of something that isn’t happening. You could also warn people from their TVs blowing up. Or air turning into butter.

I didn’t say a USB power supply can reduce it’s power below 5V

Ok, if the PSU does not reduce it’s power below 5V, how exactly do you suppose that it can then limit the charging rate in any way?

Go back to Ohm’s law. Current is a function of voltage and resistance. Resistance is controlled by the consumer, voltage is regulated by the power supply. The PSU cannot change the resistance (since that’s the domain of the consumer), only the voltage.

So if the PSU doesn’t change the voltage, it cannot control the current.

Power is a product of Amperage and Voltage and the power drawn from any source, including a USB can drop to almost zero once the battery is ‘charged’ or the laptop in hibernation.

Correct, and that is purely the consumer’s domain to control, unless the PSU reduces the voltage, which (with USB) it doesn’t.

There is no mention in my post that the 3A is being supplied via a USB A comming from a computer using USB 2 or USB 3

You do know, that USB 2 and 3 are standards, that are not tied to a computer?

USB A can supply 2.4A and has a voltage range down to 3.4V
USB C provides 3.3A

Dude, basics. USB A and USB C are standards for plugs, they have nothing at all to do with what’s happening on them. Yes, they are rated for that current, but that doesn’t mean that they actually supply that current. It just means, that’s the maximum a basic USB A/USB C plug need to be able to supply without damage to the connector/cable (unless it’s a USB PD certified connector/cable, in which case they need to be able to supply more).

Just grab a random older, cheap USB Power Supply. They often have ratings as low as 1A or even 0.5A on them. They don’t supply 2.4A or even 3.3A.

And you aknowledge the battery will keep charging ??

No. A fully charged battery will not keep charging. Charging will be switched off, until the battery is not full any more, then it will start charging again. Google the word hysteresis for that concept.

Though I could agrue your comments more, and no doubt you may have some ‘good’ intenttions, this is off topic and maybe a good idea to stop here :slight_smile:

Nothing to do with good intentions. You are posting quite a bit of nonsense, with most of what you post being misunderstandings. I am here to clear that up.


-) Don’t know what’s the difference between USB A/C (which are standards for connectors), USB 2/3 (which are standards for protocols and minimum capabilities) and USB PD (which is a separate power supply standard)
-) Don’t know the difference between a power supply (which supplies power and doesn’t care what happens with it afterwards) and a charger (which knows about battery state and supplies the correct voltage/current fitting to a charging curve)
-) Don’t know Ohm’s law and it’s application (mainly, voltage is controlled by the power source, resistance is determined by the load)
-) Don’t know about charging control
-) Don’t know about the charging cycle of Li-Ion/Li-Po batteries

But still you defend your misunderstandings and keep adding others to the pile.

As I indicated you seem to be misunderstanding and repeatingly so. My comments were to the OP not to you, so sure you can be picky and have taken things out of context.

I have created a Guide to clarify, which you may have issues with, but as I have said this is way of topic here. See you there :slight_smile:

By the way I was an electronics engineer some 60 years ago so have some understanding of Ohms law :slight_smile: but I do have dyslexia and so spelling and word disassociation are common as you were so keen to note, :blush: in Power Direct and the spelling of delivery.

Hi @amoun, I am “misunderstanding” your posts in the same way. I understand that you don’t want to charge a phone to 100%, but there is no point going into that discussion in a topic about chargers and negotiation, because it is not related to the type of charger.

This quote is the one that bothered me:

You keep talking around this point by telling us why keeping a battery at 100% is bad.


Thanks for the input.

I can see how this may seem problematic.

Charging a phone to 100% isn’t argueably the best for the battery, though it may suit the user. Secondly as charging a phone to 100% requires accurate calibration of various pieced of equipment, especially communication between the battery and the phone there is an increased risk of damage to the battery by excessive charging that would occur if it is not charged according to the phone.

None of this relates to the actual battery state of charge just the perceived charge via the phone.

I’m not saying charging to 100% is bad, far from it, but I’m not saying it’s good. It’s a matter of choice for the user.

My intial response, which has been thorougly questioned was to say to a non tech user that if they use an unknown charger then if they have any worries about damaging the battery was a) not to charge fully, which in some case could amount to excessive and ‘overchrged’ and to keep an eye on it’s state. Unlike the FP3 there is no LED indicating when the battery is deemed 90% charged.


No specifc type of charger was mentioned only some specs, so my answer was a bit generalised to allow for caution with any type of charger.

Input 100-240VAC 50/60Hz 1.7A Max
Output 5.0V/9.0V/12.0/15.0V=3.0A, 20.0V=3.25A
Total 65.0W Max

I won’t argue this point but you will find many that would argue it is not a good idea to keep a battery fully charged. Anyway unless you are plugged in continuously this won’t happen.

not sure why you keep on going this road of discussion and you are quoting out of context.

so AlbertJPs comment was not really about the general advise on how to prolong a batteries lifetime in general, you are linking to above, but to your comment that a battery will overcharge when you do not unplug latest at 100% which is

Maybe we can again agree that some disagree and hope everyone can take out the important parts for themselves and stop this discussion here as the initial question was answered already.

On the contrary I think that once a sub topic of an issue related to the specs of a charger it can be useful to clarify the arguments that arise.

However this post of mine last was more a reference point to an earlier argument.

Thanks for your addition and link, although that seems to further extend not just the sub topic but at first glance to says. “It is not true that charging a battery to 100% will damage a battery”

It definitely will but that’s a user choice not a matter of opinion. Any use of a battery will wear it out and damage it. The higher and lower it is pushed the faster the wear occurs. So damage refers to wear that can be avoided by some people if they choose to be careful.

The issue is about monitoring the wear when using a specific charger though it can be applied to any form of charging.

The whole issue of monitoring became a sub topic and then of course the concept of overcharging in that arena.

You did the same thing again. The issue with this line is this:

The charger (meaning the USB power supply) cannot in any possible way overcharge a battery, since it doesn’t charge a battery.

It provides power, and the charging circuit in the phone charges the battery. No communication is necessary here and no communication happens.

A Lipo charged beyond 4.4V will rapidly start to burn. This can only ever happen if the charging circuit in the phone is severely broken. In the real world, this does not happen. If it were to happen, there would be major lawsuits regarding that.

No, no, no, no, trickle charge can physically not overcharge a battery. Trickle charge works this way: The charging voltage is set exactly to the maximum voltage that the battery is supposed to be charged to.

If the charging circuit supplies 4.35V (for example), the battery can physically not charge higher than 4.35V. It is literally not possible.

Yes they are failsafe. Their failure rates are incredibly small and they fail open (meaning, when they fail they stop charging).

Again, not true. Just have a look at any battery voltage readout app. If your phone is fully charged (100%), the app will read out the rated maximum safe voltage for the battery, which is equal to fully charged. If your battery charge goes much beyond that, your phone will quickly turn into a ball of fire.

90% of what you are typing is just plain wrong.

If you’ve been an electrician 60 years ago, that puts you at the age of 80. Also, being out of the loop for 60 years means, almost all of your knowledge is really outdated.


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