# RPI sometimes reporting low supply voltage

**URL:** <https://discourse.nodered.org/t/rpi-sometimes-reporting-low-supply-voltage/54392>\
**Category:** General\
**Created:** [28 November 2021 08:17 UTC](https://discourse.nodered.org/t/rpi-sometimes-reporting-low-supply-voltage/54392 "2021-11-28T08:17:05Z")\
**Posts on this page:** 6\
**Page:** 1

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**Author:** ![henkkas](https://sea2.discourse-cdn.com/flex026/user_avatar/discourse.nodered.org/henkkas/32/39844_2.png) [@henkkas](https://discourse.nodered.org/u/henkkas)\
**Post date:** [28 November 2021 08:17 UTC](https://discourse.nodered.org/t/rpi-sometimes-reporting-low-supply-voltage/54392/1 "2021-11-28T08:17:05Z")

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Sometimes when I open VNC viewer on my RPI I get low voltage report. I have measured supply voltage several times, but always measure bit more then 5 volts. I don't know what to think. My question is:  
Is there a way to read the supply voltage, so I can put it in a trend chart?

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**Author:** ![jbudd](https://avatars.discourse-cdn.com/v4/letter/j/5f8ce5/32.png) [@jbudd](https://discourse.nodered.org/u/jbudd)\
**Post date:** [28 November 2021 09:48 UTC](https://discourse.nodered.org/t/rpi-sometimes-reporting-low-supply-voltage/54392/2 "2021-11-28T09:48:20Z")

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There is no way to measure supply voltage to a Raspberry Pi without extra components, all you have is the vcgencmd get\_throttled command which can tell you if the Pi has had an undervoltage incident since booting. There is a script to help interpret vcgencmd get\_throttled at [https://gist.github.com/aallan/0b03f5dcc65756dde6045c6e96c26459](https://gist.github.com/aallan/0b03f5dcc65756dde6045c6e96c26459)

I suppose you could use Node-Red to call vcgencmd and display the time undervoltage occurred.

An undervoltage can be a very transitory voltage dip; you might need an oscilloscope to detect it.

Use a good power supply, and if the USB cable is removable, make sure it's a good quality one.

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**Author:** ![Paul-Reed](https://sea2.discourse-cdn.com/flex026/user_avatar/discourse.nodered.org/paul-reed/32/66906_2.png) [@Paul-Reed](https://discourse.nodered.org/u/Paul-Reed)\
**Post date:** [28 November 2021 09:53 UTC](https://discourse.nodered.org/t/rpi-sometimes-reporting-low-supply-voltage/54392/3 "2021-11-28T09:53:52Z")

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Have a look at [node-red-contrib-vcgencmd (node) - Node-RED](https://flows.nodered.org/node/node-red-contrib-vcgencmd)  
That's a very easy to use solution to monitor for low voltage throttling, plus lots of other useful information.

Another tip is don't use a USB power cable longer than what you need! The longer the lead - the greater the voltage drop.  
If the power lead resistance measures just 0.5 Ohm, that would give a voltage drop of up to 1 Volt, before it even gets to the pi.

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**Author:** ![henkkas](https://sea2.discourse-cdn.com/flex026/user_avatar/discourse.nodered.org/henkkas/32/39844_2.png) [@henkkas](https://discourse.nodered.org/u/henkkas)\
**Post date:** [28 November 2021 12:51 UTC](https://discourse.nodered.org/t/rpi-sometimes-reporting-low-supply-voltage/54392/4 "2021-11-28T12:51:13Z")

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@jbudd @Paul-Reed , thanks very much for your advise guys, I will make use of this node. I think it might be helpfull in monitoring what;s going on.

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**Author:** ![TotallyInformation](https://sea2.discourse-cdn.com/flex026/user_avatar/discourse.nodered.org/totallyinformation/32/31_2.png) [@TotallyInformation](https://discourse.nodered.org/u/TotallyInformation)\
**Post date:** [28 November 2021 14:26 UTC](https://discourse.nodered.org/t/rpi-sometimes-reporting-low-supply-voltage/54392/5 "2021-11-28T14:26:44Z")

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My Pi3 ran for years with periodic warnings. Never seemed to actually be an issue. Even so, Paul's advice is spot-on.

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**Author:** ![system](https://us1.discourse-cdn.com/flex026/uploads/nodered/original/1X/d073cd938eafa2e558d7c2cd59003b3ef4963033.png) [@system](https://discourse.nodered.org/u/system)\
**Post date:** [12 December 2021 14:27 UTC](https://discourse.nodered.org/t/rpi-sometimes-reporting-low-supply-voltage/54392/6 "2021-12-12T14:27:24Z")

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