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ab1jx
Posts: 901
Joined: Thu Sep 26, 2013 1:54 pm
Location: Heath, MA USA

Just got a DrOK power meter

Fri Jun 23, 2017 3:57 pm

Maybe these numbers have been reported before, I haven't happened to see them. I just got https://www.amazon.com/gp/product/B00S2 ... UTF8&psc=1

I measured my Pi with a Logitech mouse and keyboard plugged into it. Plug facing directions didn't work out such that I could run from the official power supply so I was running from a D-Link powered USB hub, which only gave me 4.79 volts so the lightning bolt icon was on. I used Pooler's cpuminer as a CPU test load, mining scrypt/Litecoin. These numbers were much lower than I expected. Oh, it was a model 3B.

Idling but with X running 0.18 amps
cpuminer on 1 thread 0.22 amps 1.062 watts load average 0.6
cpuminer on 2 threads 0.26 amps 1.207 watts load average 1.54
cpuminer on 3 threads 0.30 amps 1.394 watts load average 2.53
cpuminer on 4 threads 0.33 amps 1.577 watts load average 3.75

With all 4 threads running it was only hashing at 1.84 khash/s, but oh well. Not bad at 1.577 watts.

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ab1jx
Posts: 901
Joined: Thu Sep 26, 2013 1:54 pm
Location: Heath, MA USA

Re: Just got a DrOK power meter

Sun Aug 20, 2017 10:16 pm

And I used it on my Zero and saw 0.18 amps or 0.912 watts idling, 0.23 amps or 1.159 watts loaded.

I was wondering about running the Zero on a couple of 18650 lithium-ion rechargeable cells and an LM2596 regulator. I also have an Adafruit 3.5 inch touch screen display. You mostly need a powered USB hub to do much with a Zero but with a touch screen sort of replacing the mouse and keyboard maybe. I think there's a back light in the display to worry about, but also that I have an extra OTG cable and USB WiFi adapter.

skspurling
Posts: 198
Joined: Fri Jul 27, 2012 1:44 pm
Location: US. Right in the middle...

Re: Just got a DrOK power meter

Mon Aug 21, 2017 3:36 am

There's got to be something funny on these power meters. I have a couple of different branded ones, and did similar measurements, and got similar results. When I use them to measure charge current to a phone, I get large numbers that look about right. When I did the Pi's, the power numbers didn't look right.

I think you are pulling way more amps that that. I would be surprised if you weren't. Try using a proper multi meter by cutting into a USB cable. I bet the numbers are going to be different.Voltage is probably accurate, but I am not sure if the current is. There is also a lot of voltage drop across those tiny gauge wires they use in USB cables. I found that if I can find something with a larger diameter power wire in a USB cable, it helps pull good power from those 2 and 3 amp USB fast charge bricks and multiport chargers.

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