Voltage Question

[killerrats]

I toubleshooted the pi to check for power.

power adapter is 5v 1.0a
I have connected
USB: wifi adapter, wireless keyboard / mouse
Web Cam
HDMI video

I volt metered the tp1 to tp2 and got 4.5v
i volt metered the tp2 to fuse 1 on the back and got 4.83

I am running a script to send out video using gstreamer and after awhile the wifi turns off. I can't figure if the pi is the issue or there might be too much power being drawn.

can anyone help me?

[SonOfAMotherlessGoat]

Are you running all those USB devices straight off of the Pi, or off of a powered USB hub connected to the Pi?

[joan]

power adapter is 5v 1.0a
...
I volt metered the tp1 to tp2 and got 4.5v

Use a 5V 2A power supply.

[RaTTuS]

or change the micro USB lead to a fatter / shorter one

[rurwin]

You are losing about 0.17 volts in the cable and 0.33 volts in the polyfuse. Even if you used a beter USB cable, you would still only have 4.67 volts on the Pi, which is barely enough for it to work, (It tends to fail at 4.6 volts,) and is significantly under the specification (4.75 volts.)

You should test it using a powered USB hub; it may be that the current they are drawing is too high. But if your power supply can only provide 1 amp, and it appears to be operating well within its capabilities, I would doubt that was the problem.

Which model of Pi is it, and do you have a USB cable with two full-sized plugs on?

[killerrats]

model b is my pi

I use both usb slots that don't use extensions and no usb hub.

what do you mean by two full sized usb plugs?

[rurwin]

If you had a Pi without polyfuses on the USB, then you could power it through the USB ports instead. You could try a powered hub, but I doubt that would reduce the current enough to make a difference.

Your other option is a power supply that gives 5.2V, such as the Adafruit one.

[RaTTuS]

or change the micro USB lead to a fatter / shorter one

to reiterate
a better quality Power lead may do the trick

[rurwin]

To re-iterate, no it won't. The power lead is only dropping 0.17V
The problem is a combination of the current drawn and the polyfuse, leading to a voltage drop of 0.33V in the polyfuse (and 0.17V in the power cable).

A powered hub will remove the current drawn by the USB devices which will reduce both voltage drops.

I have a feeling that the polyfuse has been over-worked in the past or has always been rather high resistance. I think they changed the parts for a higher current limit at some point because the early Pi's tended to drop a lot of voltage in the polyfuse. It might have a maximum inactive resistance of 0.45 ohms, nearly half a volt of voltage drop per amp -- or 0.32V of drop for 700mA. (See viewtopic.php?f=28&t=58359)

Using a powered hub will drop the current down to about half of that: 0.08V in the lead and 0.16V in the polyfuse; a total of 0.24V. So the Pi will be getting 4.76V -- still low but it should work.

[RaTTuS]

To re-iterate, no it won't. The power lead is only dropping 0.17V
The problem is a combination of the current drawn and the polyfuse, leading to a voltage drop of 0.33v.

DOH you are right
I blame the train
stupid Monday morning eye's not working

[killerrats]

when I got the pi I ended up taking out the usb and plugging it back in again and restarts automatically. could that have ruined it?

[rurwin]

It would have risked corrupting your SD card, but it won't have damaged anything in the power supply circuitry or anywhere else.

[killerrats]

so what is interesting is that I found a ipod power supply with 5.1v and 2.1a so I used that and it didn't go out at all. I left it for an hour.