Among my mini & micro USB devices, I have a Motorola RAZR that I want to
charge in my 2.1 Amp USB car cigarette adapter.
Everything charges with this setup EXCEPT the Motorola RAZR V3.
Digging into why, apparently Motorola uses a 5-wire cable instead of
a 4 wire cable.
How do I find a 5-wire USB2.0-to-mini-USB cable?
Googling, I find tons of cables, but none SAY how many wires they have.
What you need is one of these
<http://dx.com/p/mini-usb-power-connector-for-moto-v3-32583 which they
no longer sell. It modifies the Mini USB connector so the phone will
charge from a standard Mini USB charger or USB-A to Mini-USB cable. I've
used these successfully.
If you could find a Mini USB cable with five wires you could modify it
as described at
you're unlikely to find such a cable unless you cut one off of a
Motorola compatible car charger (not sure if the resistor is inside the
Mini USB plug or inside the charger).
I was worried about that RESISTOR!
Nobody mentioned it, but you - but I did see the resistor in the original
So, can you confirm that simply getting a 5-pin cable won't help. Right?
It has to be a 5-pin cable with the Motorola-sized RESISTOR in it, right?
That's correct. But it's the wrong question. The USB-A side is only four
pins so a cable with a five pin Mini-USB plug will have only four wires,
there's just no place for the fifth wire to connect. Unless it's a cable
specifically designed to solve the Motorola problem.
On the Motorola chargers, it's a five wire cable into the charger where
the resistor is located.
Try this cable: <http://www.thecellguru.com/Products/5974 .
I'm sorry - but I'm still confused, especially after reading one of the
reviews at that web site which said "This cable works to charge my
Motorola Razr v3 from a USB port without needing the Motorola charging
To my knowledge, I don't have any "motorola charging software" on my
Linux laptop - but I just plugged in a standard mini-USB cable (USB 2.0
on one end, mini-USB on the other) and it charged the Motorola RAZR V3.
Then I took the exact same setup, and plugged it into a wall-wart USB
charger, and it failed. Likewise with the cigarette lighter USB charger
in my car.
Clearly this cable does NOT have the resistor (it's a generic USB cable),
and I don't know that motorola phone tools was ever installed. Looking
on my system (using updatedb) I see there are "some" files with the
word "motorola" in them, e.g.,
But, no specific motorola software seems to be installed - yet - the
4-pin cable is charging the phone. How is that?
I suspect that Linux includes the Motorola USB drivers that enable
charging from a USB port. Windows doesn't.
That looks like the Motorola USB driver.
You could sacrifice an old Motorola car charger or home charger to get
half of the proper 5 pin Mini USB cable and solder it to a USB A cable
and put in the resistor. Or buy the appropriate cable.
BTW, on my Google Nexus tablet, it won't charge from a standard USB
cable connected to a USB charger. I have to short the USB data pins to
get it to charge.
The reason Motorola and Asus and other manufacturers do this sort of
thing is not just to be annoying and to sell more of their own chargers.
The device needs to know how much current the charger can provide. A USB
port needs to provide 500mA but the reality is that many USB chargers
can provide much more the minimum, and even many computer USB ports can
provide much more than the minimum. The device can charge at a higher
rate if it knows the charger can provide higher current.
"According to the spec sheet for the Enhanced Mini USB interface
circuit, shorting pin 2 to pin 3 (the data lines) and putting a resistor
of 200kOhm on the ID pin x to pin GND will put the phone into Dumb
Mid-Rate Charger (500mA) mode with 1.225 volts on pin x. Putting a
440kOhm resistor on pin x to pin GND will put the phone into Dumb Fast
Charger (1.25A) mode with 1.68 volts on pin x."
Have you contacted Motorola to find out /exactly/ what cable is needed?
I believe the resistor is needed to "clue" the power supply that something
that "wants" to be charged is connected.
Cables are cheap. I'd buy one and see what happens.
By the way, the USB-cabled charger for my Samsung cell phone will also charge
my Garmin GPS. Very handy.
I'm confused because I just tested a "normal" cable and this was
Motorola RAZR V3 connected to wall-wart USB charger --> fail
Motorola RAZR V3 connected to automotive USB charger --> fail
Motorola RAZR V3 connected directly to Linux PC --> charged!
The weird thing is that I used the same cable for all 3 tests!
USB has power control from the host. The Linux system is going to
interrogate the phone and set up the internal hub/controller to whatever
power level the phone wants.
A brainless charger can't do that negotiation. So there has to be a
setup where the phone will sense the resistor and see that it's hooked
up to a brainless charger and just go ahead and charge.
Mark Zenier email@example.com
Googleproofaddress(account:mzenier provider:eskimo domain:com)
On a Windows box, the Motorola phone driver isn't built in. It looks
like Linux includes it so you don't need to install Motorola Phone Tools
in order to charge.
But I think you've got it backwards. The USB power controller on the
computer does not allow setting different current levels as requested by
What really is happening is that the USB driver is telling the phone
that it's plugged into a USB port and that the phone can charge at
500mA. If you trick the phone into charging at 1.25 amp by using a
resistor in the cable then the over-current protection on the USB port
will probably trip (it doesn't trip at 501mA, more likely to trip at
800-1000mA, but 1250mA is probably going to trip it). If you trick the
phone into charging at 500mA with a resistor then it would work fine.
On my Asus/Google Nexus tablet, if you short the USB data pins then it
thinks it's plugged into a 2.1A charger no matter what it's plugged
into. You need to do this to use a dumb 2.1A to 12V to USB adapter, and
it's part of the USB spec. But it will charge from a Motorola Micro USB
car charger too, just slower.
USB ports were not designed to be used as chargers, but the USB 3.0 spec
has addressed the charging issue pretty well.
Yes, no, maybe so.
There's no short answer. A USB 3.0 port _could_ provide a higher maximum
current if the computer manufacturer decides to provide the higher
current, but it's not required.
A USB 2.0 port should supply a mininum of 500mA and is technically
required to shut down if the current exceeds 1.25A. A USB 3.0 port
should supply a minimum of 900mA and is supposed to shut down at 1.5A.
But there are also higher power options if communications is not
The reality is that both the USB 2.0 and 3.0 ports probably are able to
provide 900mA, but this depends on the laptop. For example, I have a
Dell netbook that shuts the USB ports down at about 700mA, but on other
machines I have they'll go well over 1000mA.
I doubt if the USB driver and the phone are smart enough to negotiate to
provide 900mA if the cable is plugged into the higher power port.
Remember, it's the phone that decides how much current to try to draw
from the USB port. The phone manufacturer has to err on the side of
caution and draw only 500mA from the USB 2.0 port even though most USB
2.0 ports could supply more than 500mA.
Overloads at startup will produce error messages, followed by prompts to reset
Ports /not/ wired directly to the mainboard can fail to supply even the
nominal spec'd maximum current. I have a USB 3.0 external drive that won't
work with the ports on the front of the machine, but does work with those on
If a USB port shuts down because of too much current draw, would it
turn itself back on after a delay? If so, what is the delay in
seconds? If the port does not reset, what does the user have to do
to reset the port?
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