USB Ports seem to fade in power output over time

Thread Starter

Lumenosity

Joined Mar 1, 2017
521
It seems that almost all the USB ports that I use for charging devices eventually get very slow to charge.
When I put a device in them to check output voltage it is often around 4.8v - 4.9v instead of 5.1v so devices charge too slowly after a while.
I've tried many different USB cables and none help so it does seem to be the port.

What I'm wondering is what causes this?

Is there a capacitor, resistor or transistor that could be replaced to restore their full charging capability?

This seems to happen regardless of where the port is whether it's in a PC, an inverter, a wall dongle etc.

Thanks
 

Delta Prime

Joined Nov 15, 2019
1,030
Hello there! :)
What I'm wondering is what causes this?
What is the battery chemistry?In other words what type of battery are you charging ,make,model, serial number of charger?
Independent of what type of battery or battery chemistry is used ,energy in the battery diminishes over time.
Rechargeable batteries and the way they are charged can be very confusing if you don't have the information, that's okay. Can you perhaps take a photo of the items in question.We could go from there.
 
Last edited:

Alec_t

Joined Sep 17, 2013
12,091
When I put a device in them to check output voltage it is often around 4.8v - 4.9v instead of 5.1v
Those voltages are all within the normal range and well above the terminal voltage of any common battery that is charging. The problem therefore is much more likely to be due to the battery rather than the charger. As DP mentioned, batteries lose capacity as they age.
 

Thread Starter

Lumenosity

Joined Mar 1, 2017
521
Hello,

I'm not sure what you mean.
The ports in question are inside a PC (personal computer desktop) and in an inverter.
With the inverter it makes no difference what battery it is connected to or it's SOC.
So I have ruled out any battery issue.

Is there nothing in a USB circuit that could cause this?

Thanks
 

Tonyr1084

Joined Sep 24, 2015
6,000
As batteries charge their charge current drops. When the charge voltage equals the battery voltage all current stops flowing. Same as a capacitor when it reaches 5T.

I have two older DeWalt 18 volt battery for my tools. One battery reaches full charge within 30 minutes while the other takes a couple hours to charge - all on the same charger. The faster charging battery also gets hot when charging and when in use, and loses its power quickly. One or more of the 1.2V NiCad batteries have gone bad internally. This battery will just sit and wait until the other battery starts showing signs of trouble. I will then disassemble both batteries and select the strongest cells and combine them into a single unit so that I'll have one 18V battery. Replacements are hugely expensive, mostly because NiCad's are getting to be hard to come by.

I wouldn't be surprised if it turns out that all the batteries you've tested have grown weak. But without actually observing your testing technique none of us can be sure you're doing it right - - - or wrong. All we have is your word you've eliminated certain possibilities. However, it would seem like all the charging sources you're using appear to be working properly. Again, without observing - - - . Logic seems to suggest the issue is with the batteries and not the many chargers you've tried. I would especially trust the PC USB port. Wall warts ? ? ? Now that's a different subject.
 

Thread Starter

Lumenosity

Joined Mar 1, 2017
521
Do they get ”slow” during a charging session or do you mean they become slower to charge from the start?
Hello,
You make a good point.
I think some of the previous comments assumed I was using the ports to charge a battery, such as a cell phone
That is not the case here.

I am referring to the raw output voltage and current of the voltage and amps measured with a test device.

It is true that the USB ports in question are slow in charging batteries also.
 

Delta Prime

Joined Nov 15, 2019
1,030
Hello,
You make a good point.
I think some of the previous comments assumed I was using the ports to charge a battery, such as a cell phone
That is not the case here.

I am referring to the raw output voltage and current of the voltage and amps measured with a test device.

It is true that the USB ports in question are slow in charging batteries also.
Hello there again! :)
We try our best with the information provided, we were gently nudging you!
Unfortunately many times we must make assumptions which is counterintuitive to our train of thought!
In no way are we trying to beat you up! I mean that in the best possible way.;)
 

Thread Starter

Lumenosity

Joined Mar 1, 2017
521
Hello there again! :)
We try our best with the information provided, we were gently nudging you!
Unfortunately many times we must make assumptions which is counterintuitive to our train of thought!
In no way are we trying to beat you up! I mean that in the best possible way.;)
Understood.
Sometimes the description posted does not include the complete information.

Thanks for your patience.:)
 

Thread Starter

Lumenosity

Joined Mar 1, 2017
521
As an experiment, I took a particular cell phone and a particular USB cable and plugged them into various USB ports on various devices. All of the ones I have used for a while say either "Your device is SLOW CHARGING" or do not charge at all.

putting that exact same phone and exact same cable into a new device with USB ports and there is no "Slow Charging" warning and the phone begins to charge MUCH faster. The only variable is the device with the USB port and the age of the device and how much the USB port has been used.

It "seems" clear at least to me that something is happening to the USB ports over time and use that is dropping their voltage and or current.

I'm going to tryo to probe the protector IC as suggested and look for 0 ohm resistors
 

anniel747

Joined Oct 18, 2020
825
As an experiment, I took a particular cell phone and a particular USB cable and plugged them into various USB ports on various devices. All of the ones I have used for a while say either "Your device is SLOW CHARGING" or do not charge at all.

putting that exact same phone and exact same cable into a new device with USB ports and there is no "Slow Charging" warning and the phone begins to charge MUCH faster. The only variable is the device with the USB port and the age of the device and how much the USB port has been used.

It "seems" clear at least to me that something is happening to the USB ports over time and use that is dropping their voltage and or current.

I'm going to tryo to probe the protector IC as suggested and look for 0 ohm resistors
That tells a whole other story. You are looking at USB evolution. https://en.wikipedia.org/wiki/USB_3.0#Power_and_charging
 

andrewmm

Joined Feb 25, 2011
1,497
EDIT ***
from what I hear you saying, It seems its unlikely to be this
EDIT ***

BUT

Some USB ports use a simple PTC resistor, to limit the current at the 500mA of the original USB1 spec,

If you try to take more current, then the voltage is dropped,
the interesting thing is there "cold" resistance gets higher as they are repeatably over currented.
So if your load is more than 500 mA, and the ports have simple PTC limits, this could be the cause.

To be honest, its amazing how many devices have no current limit,
and can provide amps,,,

Decent laptops and computers have always used good circuits,
and the proper protection circuits are now as cheap as the "cheap" PTC version,
so most computers I would say now use proper protection circuits.

There is also the range of negotiated powers,
that depend upon what version of USB the two ends support.
 
Last edited:

Thread Starter

Lumenosity

Joined Mar 1, 2017
521
from what I hear you saying, It seems unlikely
BUT

Some USB ports use a simple PTC resistor, to limit the current at the 500mA of the original USB1 spec,

If you try to take more current, then the voltage is dropped,
the interesting thing is there "cold" resistance gets higher as they are repeatably over currented.
So if your load is more than 500 mA, and the ports have simple PTC limits, this could be the cause.

To be honest, its amazing how many devices have no current limit,
and can provide amps,,,

Decent laptops and computers have always used good circuits,
and the proper protection circuits are now as cheap as the "cheap" PTC version,
so most computers I would say now use proper protection circuits.

There is also the range of negotiated powers,
that depend upon what version of USB the two ends support.
Very good information. Thank you.

Whenever I connect a device to USB that draws a current, let's just say a cell phone for example, I have no control over the current draw. it seems that whatever device with a battery that is connected will draw as much current as it can and often that exceeds 500mA.;....or used to.

A resistor that has increased in resistance will limit current but leave voltage alone right?
This sounds precisely like what is happening.
 

anniel747

Joined Oct 18, 2020
825
Some USB ports use a simple PTC resistor, to limit the current at the 500mA of the original USB1 spec,

If you try to take more current, then the voltage is dropped,
the interesting thing is there "cold" resistance gets higher as they are repeatably over currented.
So if your load is more than 500 mA, and the ports have simple PTC limits, this could be the cause.
True, I have seen that a few times but not lately.
 
Top