Iphone 4 Power Adapter Problem

[iwant5please]

Hey guys! Well today I received my Raspberry Pi and the only power adapter I have is the Iphone 4 power adapter rated for 5V @ 1A. When I use this adapter to power my Pi everything appears to work fine, but when I use a multimeter to measure the voltage at TP1 the voltage is only 4.70 V. I have three main questions... would this voltage damage my Pi? Also what may be failing, the power adapter or the micro usb cable? Last but not least what power adapter do you guys recommend that can deliver exactly 5V @ 1A? Thank you very much for your help!

[iwant5please]

UPDATE: I have just measured the output voltage of both of my iphone 4 power adapters and the first adapter is outputting 5.08V and the second one is outputting 5.06V. If this is the case why when I connect my Raspberry Pi the voltage drops to 4.70V? I have also tried a different micro usb cable and the same thing happens. Also I tried an ipad charger rated for 5.1V @ 2.1A and the same voltage appears at TP1 (4.70V). What might be wrong? Thanks!

[iwant5please]

UPDATE2: I just managed to measure the output voltage from the micro USB cable connected to the iphone 4 power adapter and the voltage is 5.06V. Might there be something wrong with the Raspberry Pi hardware or might just be a problem with the power adapter? Thanks!

[nick.mccloud]

It sounds like it the micro USB lead you are using that you want to investigate next.

[iwant5please]

What do you mean by the micro USB lead?? The cable?? Anyone has other ideas of what might be wrong?

[Burngate]

You've measured the adapters' outputs at 5.06v, but that's off-load - it may drop when the Pi is connected.
4.70v on the Pi is not far below the minimum of 4.75v - the Pi should be happy with that, but anything hanging on the USB will get less, and may complain.
It's not going to hurt anything, nothing should die, but if you get keyboard stutters, or WiFi dongles do strange things, try a better cable.
This is assuming your meter is accurate.

[nick.mccloud]

What do you mean by the micro USB lead?? The cable?? Anyone has other ideas of what might be wrong?

Sorry you don't want to check out my suggestion - I had the same issue with my 2.3A Apple genuine iPad power supply - as soon as I used a different micro USB lead (or cable if you prefer) it all worked.

[mahjongg]

Do you measure before or after the input fuse, as some voltage (not much) can drop over it if it has been hot recently. If you measure the direct output of the power adapter, and its tenths of a volt lower than 5.0 V I would expect it to be a poor cable, but it is also possible for a charger (instead of a power supply) to not be regulated, and in that case its output will always drop when loaded. For an official Apple product I would not expect that though, as they are not under dimensioned for their task.

The R-PI needs at least something like 4.9 volt, as otherwise USB devices might not get the 4.75 Volt they need, due to the relatively high resistance of the USB fuses used in this first batch.
USB devices must be able to do USB communication with only 4.4 Volt, (to avoid that a single device cripples the whole USB system) but an USB device (mouse, keyboard etc) needs 4.75 volt minimum.

[taylor]

I had exactly the same issue - usb and ethernet did not work at all. I tried several usb power supplies with ample power suspecting it was the supply but it was actually the cable. I had a micro usb to usb cable (from a Western Digital SE 500gb external usb drive) which I was using and as soon as I swapped it out for a HTC charger cable (micro usb to usb) everything worked.

I'm currently using an Apple iPad charger and works fine.

[iwant5please]

Thank you so much for your answers guys! I have one big question... I measured with a voltmeter the output voltage of the micro usb cable (or lead) with nothing connected to it and it was 5.06V... is it possible that when the Raspberry Pi is connected that voltage would drop because of the cable/lead? Thanks!

[simonbr]

Looking at the schematics: http://www.raspberrypi.org/wp-content/u ... s-R1.0.pdf you can see that TP1 is placed after fuse F3. That fuse can have a resistance of around 0.4 ohms. The current consumption of a Pi will be around 0.4A, and some more with USB devices connected. This can account for around 0.2V. F3 is the green square component near the voltage supply input, you can measure the voltage across it.

Also, the resistance of the lead from the adapter will add some voltage drop when it has to supply current.

Best regards
Simon

[iwant5please]

Thank you simonbr and everyone for answering! So I bought on friday a power adapter from http://www.adafruit.com and also a brand new micro usb cable. Power adapter: https://www.adafruit.com/products/501 Micro USB cable: https://www.adafruit.com/products/592. According to their website the power adapter is supposed to supply 5.25V instead of 5V so when a voltage drop occurs, it will stay exactly at 5V. I will be receiving these two products tomorrow so as soon as I test them I would let you guys know if they work. Thanks!


BTW: I forgot to mention that on Saturday I tested a Samsung Galaxy S II power supply a friend lent me and the voltage was perfect at around 4.94V instead of the 4.70V all the apple adapters gave me.

[iwant5please]

Guys thank you very much for your help!

I made a video explaining my results: http://www.youtube.com/watch?v=XX3kiRUf7mg

Thanks!

[ers]

I've western digital micro usb cable (which is from an external western digital hd)
I don't get hdmi output or boot or any signal showing that raspberry pi is working.
I thought the device was faulty but found this post.
Looks like there is an issue with western digital usb cables..

[ers]

update: turns out that the problem was with the sd card , western digital cables works just fine.

sandisk extreme hd video 30mb/s class 10 card doesn't work with raspberry pi

-ersin

[rleyden]

I intended to make my own power adapter from an unused 5V (1.0A) phone adapter by changing the coaxial plug to a micro USB plug. Unfortunately, the plug I planned to use was a micro USB-b not the required micro USB-a (I learned this after a quick trip to Wikipedia).

I live in a rural area without nearby electronic supply stores so I decided to solder the power leads to "tp1" and "tp2" (+5v red wire, -5V black wire. Does anyone else find the terms "power" and "ground" ambiguous in an operational sense?). Yes, I realize that I've by-passed the fuse.

It works well enough until I get the correct power connector.

[Vindicator]

I have a Motorola charger and cable that I acquired from my son who uses droid phones the charger is rated 5v @ 850ma, when attached to my brothers Raspi it works fine until you try to shutdown then it hangs.
with the Motorola charger and a 1 foot cable he bought it works good and shuts down cleanly.

With his I phone charger and the the Motorola cable the Raspi again shuts down as it should.
So I would say as an example the cable was the solution and the only real difference in the cables is that the Motorola cable is 1m cable.
I also tried with a 2m cable cheapy that I bought from WalMart the Motorola charger and the same result it worked good until shut down on his Raspi but hung at the shutdown, and again with his I phone charger it worked fine.
He has a small powered hub(Vantech I think) and a Logitech wireless keyboard and mouse combo, and a 1 foot cable he found at the local UPS store for 5$ hooked to a 19" dell monitor with a Phillips HDMI to DVI adapter cable with Sandisk ultra 8Gb class 6 cards and the keyboard mouse combo are plugged straight into the Raspi.
So any way that has been the brunt of my Raspi experiments on his RASPI when I could pry it from his grasp.
(cables seemed to make more difference than supplies we had hooked to them)Especially length!

[Lob0426]

Before you judge me an unfit brother, you need to hear the rest. While I am playing with the RasPi, I let him play with the Panda Board.

@iwant5please: @nick.mccloud has the most likely culprit, The Cable. Is it a 6 foot (2M) cable? we ran into problems with a 3ft (1M) cable.