Why do USB cables lose the ability to charge quickly over time?

I've noticed this over the years. I'll get a brand new USB cable and measure it as charging my Galaxy S5 at a rate of 1500 mA. Over a year or so the same cable, on the same phone, on the same charger, on the same operating system, will only be able to put out 500 mA or so.

Doesn't repeated bending of the thin-gauge power transfer wires in a USB cable eventually increase the internal resistance of the cable, preventing them from attaining the same current speeds as before?

I've often wondered if it would be worth it to take apart the housing of a USB cable and solder on thicker or higher-quality wires to ensure that charge rate can be maintained even with all the physical handling.

Without controlled testing and evidence.... it's hard to conclude on something like that for now. First need to document everything..... including what power source is being used etc. You mentioned operating system.... which suggests computer. And usb was once rated for 500 mA.... not 1500 mA. Etc.

The micro usb connector can be stressed as the phone is used with the cord plugged in, eventually leading to the metal part being loose in the housing so it can wiggle around, leading to fatigue of the connections, resulting in them having higher resistance than they otherwis3 would, reducing current handling ability. Usb cables should be replaced once the metal part of the small end is loose.

Above issue, or sharply bending/kinking the cable can break the connections entirely - if a data line goes, fast charging is lost since the charger cannot tell the device to pull more than 500mA, nor negotiate quick charging.

There is a huge variation in quality between brands, and it's not always clear which will be better - but all usb cables should be considered consumables

And does new cable charge faster? From my experience with phone batteries (but I use low end phones) they are quite used after a year - I would suspect the battery is unable to charge at faster rate.

IME dying phone batteries appear to charge faster (judging by percent or app) all else being equal - because the overall capacity is lower. But it sounds like OP is actually.measuringnit with one of those usb charge speed meters

Hi, If you look at the construction of the plugs, the contacts are sliding surfaces, the thickness of which is very very thin.

I have a similar cable and I believe from the way it plugs in so easily, compared to a new cable that charges well, that the contact surface has worn down to be very, very, very,very thin.

They have to wear out sometime and with smarty phones needing to be charged every couple of hours, the plug will wear out.

Sorry I have a proper mobile phone not a smarty-distraction people killing phone, 2 to 3 days on its battery. cable is 5years old.

http://www.abc.net.au/news/2017-09-21/doco-captures-young-drivers-using-phones-behind-the-wheel/8965066

Tom.. :)

Potentially the battery management chip on the phone may be throttling back the charge rate as the battery ages to improve battery life, or perhaps more simply the battery's internal resistance increases with age. By comparison changes in the cable resistance will be tiny effects (until it fails completely).

(Of course if you have a cheap CCA cable, all bets are off, evil stuff that copper-clad aluminium...

It would be super-rare for a cable to "develop resistance". Even if three's only one wire-strand remaining connected, it will have fairly low resistance. And with sufficient voltage-drop (and current) that last remaining strand would probably burn-up and go completely open, or the same mechanical stress that broke the other strands will soon break the last remaining one.

If you've seen this happen once, I'm surprised but I'll believe you. If you seen it happen twice, something else is going on. (I've never seen that happen with any kind of cable, and I'm an old guy with many years of electronics experience.)

Sometimes the wires can break and make intermittent contact or a connector can get flakey (intermittent contact). But in those cases where the cable isn't completely broken, wiggling the cable/connections usually makes it pass/fail.

Lightning cables seem very susceptible to corrosion on their contacts which makes me wonder if that might lead to voltage drop

I once had a cheap powerbank which damaged all of my micro usb cables. It took me a while to figure out why all of my devices were charging at an unusually slow rate. It even destroyed a bunch of new cables that I bought within a week itself. Finally I got rid of that powerbank and and the problem never happened ever again. I was lucky my devices were not damaged.

So it could sometimes be the charging device that damages your cables.

Noobian: I once had a cheap powerbank which damaged all of my micro usb cables.

That's interesting. Exactly what damage did it cause to the cables that made them charge slower?

I can imagine a bad powerbank damaging batteries but I can't work out how it's possible to damage a cable so that it still works but not as fast.

Steve

slipstick: That's interesting. Exactly what damage did it cause to the cables that made them charge slower?

I don't know exactly what damage but whatever it was it did not show anything in external appearance. I sacrificed quite a few cables (including an oem lightning cable) to figure out what actually caused this problem with my cables since I also used the same cables to plug into the wall charger. Eventually I noticed only those cables that were also used with that powerbank ended up faulty. At that time I never bothered to check whether the cables got hot. I bought the powerbank from a small cellphone shop in Dubai.

fuzzybabybunny: I've noticed this over the years. I'll get a brand new USB cable and measure it as charging my Galaxy S5 at a rate of 1500 mA. Over a year or so the same cable, on the same phone, on the same charger, on the same operating system, will only be able to put out 500 mA or so.

Doesn't repeated bending of the thin-gauge power transfer wires in a USB cable eventually increase the internal resistance of the cable, preventing them from attaining the same current speeds as before?

I've often wondered if it would be worth it to take apart the housing of a USB cable and solder on thicker or higher-quality wires to ensure that charge rate can be maintained even with all the physical handling.

Phone chargers generally do not communicate with the phone to negotiate what current is needed. This would be too expensive to include into the charger's circuit. Until recently (some years ago) there was no standardized way to tell the phone what current is available from the charger. So different manufacturers developed different methods to do a simple signaling through the USB data lines which are otherwise unused when charging. Apple e.g. used two resistor voltage dividers to raise the data lines to some defined voltages. This was to tell the phone "this adapter can provide 100mA / 500mA / 1000mA". I don't know what Samsung's method is, I think it will be similar. The reason for charging problems does not lie with the power lines, but with the data lines. The signaling voltages are easily distorted by corrosion, loose contact springs etc. then the signaling is broken and the phone adjusts the current to some false value.

olf2012: The reason for charging problems does not lie with the power lines, but with the data lines. The signaling voltages are easily distorted by corrosion, loose contact springs etc. then the signaling is broken and the phone adjusts the current to some false value.

Ah, yes, that's more likely.

As the data lines carry only very tiny currents their contacts will not be self-cleaning like the high current contacts. Thus oxidation/corrosion can build up.

In case people were wondering about resistance of a cable changing as it wears out, think about the fact that the cable is many strands in parallel that are all in contact along their length - so any weak or broken strand will be worked-around with only a very short section of higher resistance, making little difference to the overall cable until the last strand breaks and arcing happens.

I recently had a notebook charger cable fray and fail, and the symptoms were a sudden lose of charging. Some arcing visible through the black pvc cable sleeve when wiggled... (The cause was a completely rigid strain-relief sleeve, ie a sleeve that looked like a strain-relief sleeve, but molded from the same rigid plastic as the connector body - thank you Toshiba!)