problem with charger i bought?

[hbcheng]

Hi!

I bought three 5V 1A USB chargers (ID: 501)

http://www.adafruit.com/products/501

they seemingly work fine on my rasperry pi -- but one won't charge my ipod touch (4th gen): with that one, the ipod won't even acknowledge that it is connected to power at all.

As for the other chargers I got: one of the two other chargers I bought is acknowledged and charges fine with the itouch; the third charger I gave away and don't have immediate access to test.

is this a returnable problem? And if not, should I be worried about using the charger with my RPi?

thanks!

[adafruit_support_bill]

It is hard to measure the voltage on an iPhone cable, but when you are powering the Pi, do you get a solid 5v from it?

[hbcheng]

I seemed to have misplaced my multimeter... I'll get my hands on one and report back..

(what concerns me is that the other identical chargers I bought are able to charge the
Ipod)

thanks!

[adafruit_support_bill]

Just trying to understand the problem. Sometimes it is sagging regulator voltage (charger problem). But we have also seen cases where the voltage drop over the cable (cable problem) causes a phone not to charge.

[hbcheng]

hi...

I've done some measurements...

all the chargers I bought (3 of them) measure around the same voltage:

about 5.16V - 5.18V at the end of the USB cable that connects to the pi.

when the pi is powered on with a load of: ethernet, wireless USB, USB external hard drive (connected to its own power supply) .. I'm running it headless so no mouse, keyboard, monitor.. I get around 4.62V.

at minimal load of only ethernet, I'm at 4.70V.
and when powered off, I'm at 5.02V.

everything seems to be working ok.. but aren't these voltages a bit low (except for powered off)?

thanks!

[adafruit_support_bill]

That sounds like a cable resistance problem. Voltage drop across a resistance is proportional to the current (V=IR). With no load, there will be no drop at all. With a big load, the drop can be substantial. A typical headless Pi with minimal peripherals will be drawing 350-400mA. Most phones these days charge at 500mA (or more if they can get it).

Try a few different cables. You will find that some work better than others.