Power supply problem caused by charge cable

[Bosse_B]

A few days ago I started to create a media player for my TV using the Pi (version B release 1).
I used the NOOBS_v1_3_4 download on a 16 GB SanDisk class 10 SD-card.
After reading directions in several places I had gotten myself a 2.1A USB charger to power the Pi.
The installation had many problems and I have spent a lot of time in the Raspbms forum to try and sort it all.

The problem was actually the power feed to the Pi!
I measured an output voltage from the charger with the Pi running of about 5.2V but on the Pi board between TP1 and TP2 there was only 4.62V!!!!

So the conclusion is that the power supply is good but the USB-MicroUsb cable is not!
The leads inside this cable are way too thin to carry the current the Pi requires!
Since I have not seen any mention of this killer fact anywhere (I tried to search this forum for "power supply" but it would not let me do that claiming that these words were too common....), I decided to put up a post here so that whatever moderator there is here could put this information into a HOWTO somewhere.

I had to do the following:
1) Cut off the connectors from both ends of the cable with about 5 cm of retained wire length.
2) Splice in a much thicker wire in both the black and red connections

With this in place the voltage on the Pi Tp1-TP2 raised from 4.62V to 5.09V!

BOTTOM LINE
The most important item to get is a heavy duty charging cable to connect the USB charger with the Pi.
However, this might not be so simple because the cables carried in normal computer stores are unspecified regarding wire sizes and hence one can suspect that they are very thin, indeed.

Alternatively the Pi designers could change the power connector from the MicroUSB to a regular low power connector used in most 5V driven equipment so a proper charger/supply can be used.

I think that there are many Pi users falling into this trap out there!

[FTrevorGowen]

You are by no means the first to suffer poor micro-USB cable issues - but the volume of posts here sometimes leads to topics getting 'buried". You might find my measurements of various cables' resistance of interest: http://www.cpmspectrepi.webspace.virgin ... esChk.html
Glad you got things working in the end.
Trev.

[RaTTuS]

Cheep ass micro usb power cables are the bane of many people - not just for RPI's
the Micro USB adapter is now standard for mobile phones chargers in most places in the world [this is a very good thing]
4.75V to 5.25V is the acceptable tolerance range but try for 5V.
replacing the Micro USB adapter is not a good idea as there is no other standard that would work

[redhawk]

Alternatively the Pi designers could change the power connector from the Micro USB to a regular low power connector used in most 5V driven equipment

If you're referring to the barrel connector this is a bad idea because it doesn't dictate a specific voltage or polarity unlike the Micro USB which is always 5v and a known polarity.
It's bad enough when people accidentally shove 12v onto the GPIO we don't want clueless Pi owners using those evil unregulated black box of death universal power supplies on the Pi with the wrong polarity either.

If the Pi had it's on built-in regulator circuit then perhaps the power supply situation would had been different.

Richard S.

[Bosse_B]

Right,
I realize that the USB connector is a good selection for the reasons you state, however the cable issue is still rather a mess.

Before I started cutting up the Micro-USB end I first made a small connector that fit on the P1 pin connector on the Pi board. I used pins 2 and 6 to feed the power from the USB charger. And this worked just fine, problem was that the commercial plastic cover I bought did not have a cut-out for this connector.
And a person on the forum rightly pointed out that doing so would bypass the F3 fuse on the board so that I might damage the board if I did something bad on these pins.
That is why I bit the bullet and started soldering on the Micro-USB end of the cable too...

Now XBMC works fine on my Raspberry Pi and I am in the process of "neatifying" it such that it may stay in the living room...