If I cut the cable in half, and isolate the wires, how would you
recommend I set it up so that it could become a test jig
(to see how much charging current a device actually draws)?
Have you done this before and have advice for how to make that jig?
Specifically, how would you fasten the bare wires, which I presume
are very very thin, and therefore fragile?
Also, we'd need a way to insert the ammeter inline to measure
Any test jig ideas I can benefit from?
NOTE: This is an offshoot of the USB charger thread, where we
determined that a 3.1 Amp dual-USB charger that is 10 Watts
is very different than the same spec at 15 Watts.
: If I cut the cable in half, and isolate the wires, how would you
: recommend I set it up so that it could become a test jig
: (to see how much charging current a device actually draws)?
: Have you done this before and have advice for how to make that jig?
: Specifically, how would you fasten the bare wires, which I presume
: are very very thin, and therefore fragile?
: Also, we'd need a way to insert the ammeter inline to measure
: Any test jig ideas I can benefit from?
: NOTE: This is an offshoot of the USB charger thread, where we
: determined that a 3.1 Amp dual-USB charger that is 10 Watts
: is very different than the same spec at 15 Watts.
Look on eBay "NEW Universal portable USB power mobile mini Current voltage tester
Cool...I was ready to order one until I saw that the data doesn't pass thru.
WTF? The connectors are almost touching, why no data?
Kinda hard to measure the drain of a disk drive in action when it won't
come out of sleep.
Why would you not connect the data unless there were problems?
Anybody bridged the data? Results?
Here's an interesting thing, I've been thinking of getting
Especially recently as my main phone seems to take a fairly long time to
charge sometimes. Doesn't seem to be a specific charger that has
Basically this USB Tester is just a conveniently shaped PCB with USB
connectors and some holes where you can very conveniently attach a
multimeter to measure current (or voltage). Data lines pass through and
they can also be probed easily.
There's a bundle with a little microcontroller based multimeter too.
On Sat, 04 Jan 2014 09:09:54 +1100, Colin Horsley wrote:
That works, but I was just going to slice a cable in half, and then attach
the inner wires to a series of screws.
What I'm thinking is to screw two row of (five?) brass screws into a
piece of wood, and then attaching the cable wires to each row.
Then I can either jump the distance with a copper wire, or with the
But before I build the test jig, someone might suggest a better platform
out of parts commonly found in the garage or shop.
That works if you never want any data thru it.
Better would be to cut the power wire and run that thru a meter.
Get out your ohms law calculator and verify that your meter resistance
won't defeat you.
Leave all the high speed data wires and ground alone.
On Sat, 4 Jan 2014 00:24:58 +0000 (UTC), Danny D'Amico
Oh lordy. For more than nominal charge currents (or standard supported
currents) the thing is "negotiated" with the source device. Get yourself
a copy of the Standard, 3.1 is current, older versions can be found.
With a sharp knife, remove 2 inches (50 mm) or so of the outer
insulation of the cable, in the middle of the cable. Try hard not
to nick the insulation on the four individual wires inside the cable,
but if you do, it's not a total disaster.
Next, try to identify the two data wires and the two power wires. Often
the data wires will be twisted; the power wires may or may not be. The
power wires will also often be one or two wire gauges thicker than the
data wires, but not always, and this is kind of hard to tell. The power
wires *might* be red and black, but don't count on this.
Pick what you think is one of the power wires and cut it, right in the
middle of the stripped part. Strip the cut wire ends 1/4" (6 mm) or so.
Get your multimeter and test between all four contacts on the big (PC)
end of the cable, and the stripped wire that comes from that connector.
It may help to use a paper clip or other small piece of solid wire to
touch the contacts in the USB connector if the multimeter probe won't
If the stripped wire is continuous with only one of the two outside
contacts in the USB plug, you did indeed cut one of the power wires.
If the stripped wire is continuous with only one of the two inside
contacts (it doesn't matter which one), you picked a data wire; solder
the stripped ends back together, insulate with a small amount of tape
(electrical tape is ideal, Scotch tape will work fine for this), and
pick another wire.
If the stripped wire is continuous with more than one contact, then
you probably nicked the insulation on more than one wire when you were
initially stripping the cable - find the places that are touching and
separate them, and maybe insulate the bare spots individually with
Once you have figured out that you did indeed cut the power wire, you
can figure out how to hook the power wire up to your multimeter. Your
meter may have come with alligator clips that go on the probe ends; if
you have those, use them. What I use for things like this, because I
already own some, are clip leads - short stranded wires with alligator
clips on each end. Rat Shock 278-1157 or 278-1156 are typical; Fry's
probably has a better price on similar products.
If you have alligator clips that fit your meter probes, put them on the
probes. If you have a digital meter, clip one probe to one stripped
wire and the other probe to the other one - it does not matter which
way around the red and black wires are. If you get the probes
"backwards", you will get exactly the same current reading, just with
a minus sign in front of it. If you have an analog meter, you have to
get the probes the right way around, but IIRC you have a digital one.
If you have clip leads, clip a red clip lead to the red probe of your
meter and to one of the stripped wire ends. Clip a black clip lead
to the black probe of your meter and to the other stripped wire again.
As above, if you have a digital meter, it does not matter which way
around the red and black wires are.
Next, figure out how to make your multimeter measure current. With the
meters most people have, you need to rotate a dial to an "A DC" range,
and move the red meter lead over to a different jack on the meter. Do
whatever you need to for your particular meter.
Plug the mini-USB end into your peripheral (external hard drive or
whatever). Put the peripheral somewhere close to the meter, so you can
watch it and the meter at the same time. While watching both the
peripheral and the meter, plug the PC end of the USB cable into the PC.
If all is well, the peripheral should come on (hard drive spins up /
LED comes on / whatever), and the meter should show some amount of
current. If nothing is happening, or if you smell smoke, unplug the
USB cable from the PC immediately and investigate. If the peripheral
draws "too much" current, the PC may shut down that particular USB port;
this isn't permanent, but sometimes it takes a reboot to re-enable the
Don't be surprised if the current jumps around some as the device
operates. Even "simple" stuff like keyboards will draw slightly
different amounts of current when you are typing vs not, or when (say)
the Caps Lock LED is on, or whatever. If your meter has a "max hold"
or "peak hold" function, that can be useful to capture the highest
current reading the meter sees. Some peripherals will have a current
rating printed on them, but this is usually the maximum current it
will ever draw - it won't usually draw that much continuously.
When you are done measuring current with your multimeter, disconnect
the leads from the circuit, and *IMMEDIATELY* move the red lead back
over to its regular socket - don't wait until later to move it back.
The reason is that in the amps range, the meter is nearly a dead short.
It's *easy* to measure current and then try to measure voltage without
moving the lead back, and blow the fuse in the meter. I've watched it
being done and I've even done it myself.
Standard disclaimers apply: I don't get money or other consideration
from any companies mentioned.
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