How to test USB charging for yourself

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In our recent article – USB charging – check the adapter AND the cable  we tested some USB cables to see how much power they supplied from the same AC adapter.  The results showed that a poor quality cable would only transmit a fraction of the available power and that means a much slower charge time for a device.

You can do the same tests with your own cables to see which ones are good.

Firstly, find an app which shows the milliamps/mA currently being received by the charging device. For these tests we’re not interested in what the USB socket is supposed to output or has labelled.  We want to know how much power the device is actually receiving.

There are plenty of battery info apps out there but few which give this vital detail.  For Samsung Galaxy devices there’s Galaxy Charging Current Lite, a free app that works for many Galaxy devices. At this stage we’ve not seen an equivalent iPad/iPhone app – please let us know if you find one.

Viewing the actual milliamps/mA actually coming into the device is very useful.  With the app you can see the maximum possible charge and what the device is currently receiving.

The above screen shot is about as good as we got in the tests.  A USB socket rated for 2100mA (2.1A)  shows a maximum of just 1,800mA.  Combined with the cable, the device is receiving 1,200mA which is good for a smartphone or small tablet.

Now you can start testing your cables.  Keep the same USB socket and device, just switch the USB cable between them.  Note the reference value for each socket/cable combo.

Our Tests

We have four microUSB cables for charging.  All are generic, unbranded cables bought off ebay retailers (often the cheapest and easiest way to buy small accessories).

There’s a standard blue 1m USB cable and another 1m black cable, both look the same to an untrained eye.   A handy ‘three in one’ cable which charges old and new style Apple devices plus microUSB.  Finally an orange curly cord which is convenient to use on the road but, as well see, now sits unloved in the bottom of the case.

Here are the test results using the same device on different USB sockets and the three cables shown above.  The last column shows the labelled power output for the charging sockets or the official power output for the two laptop sockets.

See notes at the end of this article for more details.

As you can see, none of the cables pass through anything like the full possible power.  There’s understandably some power loss, though probably more than you might expect.

Charging at 1,200mA is enough to fast charge most devices while avoiding the (low) risk of overheating or ‘burning’ the device.   Newer iPads are rated for 2,100mA power input but even 1,200mA will do the job, just slower.

The orange curly cable only passes through a fraction of the available power on the high output sockets.  No wonder charging with that cable was so slow.  That could be caused by the curly nature of the cord (a longer cable) or poor quality of the cable itself.  Either way, that cable is now in the ‘use if desperate’ box.

Update: After our tests were done, we found a generic 2m cable that output some more power than the 1m cables, showing that a shorter cable isn’t always better.

Both the ‘three in one’ and black generic cables worked very well indeed off the special charging socket, but could not pass through the higher amps from the USB 3 socket.  That’s probably because the cables have USB 2 plugs that work but aren’t fully compatible with USB 3.

Notes:

  • All cables have USB 2 plugs at one end and microUSB at the other.
  •  All cables were unbranded, purchased from ebay vendors over time.
  • You’d hope that the ‘official’ cables from the device manufacturer are better quality and therefore better power throughput than generic cables.  Sadly there’s no guarantee that’s the case.
  • So called ‘premium’ cables may be better, or it might just be the labeling.  There’s no way to be sure until you test the cable yourself.
  • Tests were done on a Samsung Galaxy Note 3 with the Galaxy Charging Current Lite app.
  • AC adapter tested with only one socket in use.  Results were lower when other devices used the same adapter simultaneously
  • The USB 2 laptop socket is outputting more than the usual 450mA given the results via two of the cables.
  • The low USB 3 socket results are probably because the cables have USB 2 plugs which aren’t fully compatible with the USB power specification.

If you seriously wanted to test power output, there are USB testing devices available cheaply via ebay.

Though we prefer getting the reading from an app on the device so we know what the device is really receiving.


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