Power Adventures

[thczv]

I ordered my first RPi from RS Components in late June. I haven't heard anything since. I ordered numbers 2 and 3 on July 3, and have received them both already. I figure the one from RS will come eventually.

I had a difficult challenge getting either RPi to run properly. I tried many different things until I finally measured the voltage across tp1/tp2. I found it alarmingly low (somewhere in the 3.8v range). So I have been testing various power sources that I have in my electronics graveyard. I am surprised that very few of them are adequate. I tested with a 4GB SD card plugged in, and nothing else. The best my genuine ipad charger could do is 4.4v. The motorola lapdock could muster only 4.5v with HDMI plugged in. The best was a little Lenmar battery (ipod charger) that got up to 4.8v. The lesson I learned (which most people here have already discovered), is that the average charger will not do. I will look for something better.

But here is the intriguing thing: I tested both of my RPis. One of them consistently shows about 0.4v lower than the other, regardless of which power supply I use. Everything else is the same between them. Could this other RPi with the lower voltage be defective? Could it still be okay as long as I supply enough power to it?

I welcome your thoughts.

Thanks,
Dave

[gritz]

There is a polyfuse (a kind of current controlled thermal trip) between the Pi's power inlet and the rest of the gubbins. It's possible that one has a bit of a high resistance. It's also possible that one Pi is for some reason drawing more power than the other. Anything getting hotter on the Pi that's showing the low voltage? At any rate 4.8V is pushing it for the USB ports (which themseves suffer further voltage drop due to the polyfuses on their +5V output). It might be an idea to set about getting it returned if you can't track down the drop to anything external.

[thczv]

I will check out the temperature of these units when I get back home. Maybe this is the excuse to buy that IR thermometer I have always wanted. Anything for a new tool!

One of the projects I am considering is a RPi based asterisk or freeswitch server. Neither of those would require any USB devices, or even a display. So if I can get the RPi with the lower voltage to run reliably, it might be better to just use it rather than try to do a return. I haven't done any research yet on returns, but for a $35 device I can see that the cost of shipping back and forth could become wasteful before tool long.

Dave