ESP8266 Community Forum

- Tue Jun 26, 2018 2:24 pm #76646 The recommended power supply for a Pi 3 is indeed 2.5A but they allow extra for powering significant USB peripherals. The typical current draw of the base Raspberry Pi 3 is more like 900mA when doing fairly active work.

I have Pi3b and Pi 3b+ which draws even more running totally reliably on 2A power supplies.

BUT I do use my own home made heavy guage USB cables between the power supply and the Pi. It cannot be stressed how important the USB cable is. It is the volts at the Pi that matters not the volts coming out of the power supply.

Assume a 1A draw.

A typical reasonably quality USB cable might have a round trip resistance of 300 mOhm. That is 300mV drop taking a 5V supply down to 4.7V below the spec limit.

A poor USB quality can have a round trip resistance of 1 Ohm leading to a 1V drop and no chance of operation.

My home made cables have a round trip resistance of < 75 mOhm and minimal voltage drop.

Note that some power supplies e.g the official raspberry one deliberately source a slightly higher voltage (5.2V) to try to compensate for the cable loss. These often have the cable hard wired in at the PS end and use heavier guage wires.

- Tue Jun 26, 2018 5:11 pm #76647 Some interesting comments and I thought I was buying a reasonable PSU but it does not look that good when I opened it.
It is marked up as a 5V 2.5A PSU and the cables do look a little bit larger than the 2A PSU.

I looked online and found some nice chunky PSU's in America but nothing here in the UK.

Currently I have nothing else attached but was going to fit a BME280 sensor to it and a official touch screen later when I work out how to display my data nicely. I have just realised I have a keyboard and mouse attached; peripherals start adding up fast! I do not need the keyboard and mouse now as I was using them when I was setting up the pi .

Anyway I have set everything running and see what happens over the next week.

- Wed Jun 27, 2018 2:53 am #76662 If you have a multimeter then one way to check your power arrangements is to measure the voltage on the Raspberry Pi board itself. OK it won't see any spikes but it will give an indication of the health of the PSU + cable.

It should be > 4.75V and preferably close to 5.0V

- Wed Jun 27, 2018 1:45 pm #76680 Oh well the new PSU didn’t work although I had 10hrs 10 min after turning it on without a problem and apart from a couple of missed readings in between I had some more down time:
8:40 > 11:10 = 2hrs 30
12:40 > 14:30 = 1hr 50
15:40 > 17:20 = 1hr 40
18:40 > 19:20 = 50min

I will have to get a battery for my multimeter and check the pi voltage as suggested and keep an eye out for a pattern. Perhaps I need to learn how to write some python code to analyse it for me.

There is a bit of a pattern to the outages and this is what made me think the pi was going to sleep rather than failing:
They all start at something 40
Around 2 hours long
Start around every 4 hours