Power Supply issues

Are you just measuring a "too low" voltage, or are you experiencing problems?

Every fuse will incur a voltage drop across it. The larger the current rating the lower the voltage drop. 120 mV does not sound unreasonable to me. I'll measure mine later today for you.

Although people state that the 5V should be within 4.75-5.25, that is not completely true in practise. In fact the 'pi itself should be able to run perfectly down to about 4.4V. The voltage at the outgoing USB ports will be "out of spec" though. Still nothing that is likely to immediately cause malfunctions with simple things like a keyboard.

As long as your powersupply is rated at 1000mA or more, it is most likely the USB cable that is causing the voltage to sag a little.

Thanks Rodger.

 

Are you just measuring a "too low" voltage, or are you experiencing problems?

 

I'm using an HDMI to DVI adaptor, and when the voltage dips below 4.8v, the display drops out.

The USB devices are fine.

 

As long as your powersupply is rated at 1000mA or more, it is most likely the USB cable that is causing the voltage to sag a little.

While the cable and micro adaptor is adding a little (120mV), I think the power supply dropping is the major problem.

I will rectify it with a 7805 regulator and 9v power pack in the meantime.

Unfortunately here in NZ, the micro usb phone chargers are an arm and a leg, unless it came free with the phone.

Thanks

mark

Ok. FYI,  my RPI uses about 350mA average. No dynamic measurements have been made yet.

For your convenience, you could connect the 5V to the GPIO 5V pin. This is AFTER the fuse, so you'll eliminate the voltage drop across the fuse as well. The 7805 is "dynamically fused" as well, so there shouldn't be much of a drawback.

Good luck!

Rodger

Thanks for the check.

I have a cheap hub, and intend to add the 7805 there, to form a powered hub, which then provides the 5v for the USB devices, and a feed to the micro usb.

Having spent the last 30+ years as an electronics technician, fixing it wasn't the problem, but providing some information to others that may be experiencing the same issue would be beneficial.

I thought the tracks to the GPIO weren't rated for the full current... (I had considered soldering to either side of C6)

I like fuses...however it became the last straw in my case.

I do prefer the ones where you hold it up to the light and then get the magnifying glasess out ..!

Mark

Mark,

  You could try adding

     config_hdmi_boost=4

to your config.txt file.  That boosts the hdmi signal strength,

which is needed for longer cables.  The signal strengh was

reduced by default for RF compliance.

coder27 wrote:

 

  You could try adding config_hdmi_boost=4

 

Thanks Coder

I did add that, but it tends to make it worse. I suspect it drops the voltage a little more.

Its also possible the HDMI to DVI is partly the issue, but with no HDMI input device, I'm using what I have.

I have just picked up a 230v to micro USB charger, so I'll try that before adding power to the hub.

Mark

coder27 wrote:

 

  You could try adding config_hdmi_boost=4

 

Thanks Coder

I did add that, but it tends to make it worse. I suspect it drops the voltage a little more.

Its also possible the HDMI to DVI is partly the issue, but with no HDMI input device, I'm using what I have.

I have just picked up a 230v to micro USB charger, so I'll try that before adding power to the hub.

Mark

Update

The $30 Warehouse micro USB Wallwart (powerpack here down under) worked a treat.

Board now has 5.1v when running (too hard to measure unplugged), and the display has no missing pixels.

Thanks for the feedback and suggestions.

Mark