Krafter
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Current draw

Tue Aug 09, 2016 1:47 am

I'm working on a project where current draw must be as low as possible. I have an external power source for the pi V2 and other components (12V reduced down to 5V). Right now with the components I have installed, I'm using 8.2 ma of power (12V side). But..... without the monitor hooked up via HDMI I'm using 15 ma. Why is that and is there a way around it? Makes no sense to me.... Using a monitor is not an option in the end.

klricks
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Re: Current draw

Tue Aug 09, 2016 2:53 am

Krafter wrote:I'm working on a project where current draw must be as low as possible. I have an external power source for the pi V2 and other components (12V reduced down to 5V). Right now with the components I have installed, I'm using 8.2 ma of power (12V side). But..... without the monitor hooked up via HDMI I'm using 15 ma. Why is that and is there a way around it? Makes no sense to me.... Using a monitor is not an option in the end.
Which model RPi? (I don't know what pi V2 means)?
8.2mA at 12V is only 0.1W. That is too low for the RPi to even boot.
You need a very good quality meter to make accurate readings that low.
Maybe show a diagram or photo of how your system is wired and how you are making measurements.
Unless specified otherwise my response is based on the latest and fully updated Raspbian Buster w/ Desktop OS.

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alexeames
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Re: Current draw

Tue Aug 09, 2016 4:14 pm

Your numbers look a bit low to me. Here are mine, which agree quite closely with those of other people and the official figures...
Screen Shot 2016-08-09 at 18.08.29.png
Screen Shot 2016-08-09 at 18.08.29.png (653.33 KiB) Viewed 807 times
People have managed to get Pi Zero down to about 60 mA credibly with USB and HDMI services switched off. But that is still 0.3 Watts which is 3 times what you claim.

There is really only one conclusion I can draw from this, which is that your measurements canot be accurate. What are you using to measure the current?
Alex Eames RasPi.TV, RasP.iO

Krafter
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Joined: Wed Jan 27, 2016 11:36 pm

Re: Current draw

Thu Aug 18, 2016 2:20 am

Sorry for the late reply. You are correct. My measurements are low. For some odd reason, I'm getting different measurements when measuring in series on the 0 volts side than what I am measuring in series on the +12 Volts side (higher). I have no idea why. I'm using a Fluke 787 Process meter. Unfortunately, it's only good for up to 30 mA before it overloads. But the buck I'm using has a current readout. So on the 5 Volts side, the buck is reading ~0.45 mA at idle. That should be ~0.1875 mA @ 12 Volts if I'm calculating it correctly.

I will turn of the HDMI and go from there. I may however end up using the USB so I probably wont turn that off. I will be using a lawnmower battery to power my project with a 10 watt solar panel to recharge it. I believe I should have enough power either way. I just want to be sure.

klricks
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Re: Current draw

Thu Aug 18, 2016 4:57 am

Krafter wrote:Sorry for the late reply. You are correct. My measurements are low. For some odd reason, I'm getting different measurements when measuring in series on the 0 volts side than what I am measuring in series on the +12 Volts side (higher). I have no idea why. I'm using a Fluke 787 Process meter. Unfortunately, it's only good for up to 30 mA before it overloads. But the buck I'm using has a current readout. So on the 5 Volts side, the buck is reading ~0.45 mA at idle. That should be ~0.1875 mA @ 12 Volts if I'm calculating it correctly.

I will turn of the HDMI and go from there. I may however end up using the USB so I probably wont turn that off. I will be using a lawnmower battery to power my project with a 10 watt solar panel to recharge it. I believe I should have enough power either way. I just want to be sure.
Depending on where the measurement is taken there may be multiple paths to ground. Mains power supplies, HDMI etc.
Assuming a 90% efficiency of the buck converter you need to add 10% to the 12V side.
Note it's 0.1875 A or 187.5 mA + 10%
Unless specified otherwise my response is based on the latest and fully updated Raspbian Buster w/ Desktop OS.

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