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HermannSW
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Powering Pi from 3S lipo with LM2596 step-down converter

Wed Sep 12, 2018 7:56 pm

Until recently I did run several Pi Zero[W]s from 1S lipo (nominal 3.7V, fully loaded 4.2V) by directly connecting to Pi GND/5V pins.

This stopped to work (steady reboots, directly when LCD gets initialized) for my first mobile Pi ZeroW. It seems that Pi CPU, Pi Wifi, 320x240 SPI LCD and wireless keyboard USB dongle were just too much for a 1S 600mAh 25C lipo. I don't understand that because the lipo should be able to deliver 3.7V at 25*0.6=15A?!?!?

I replaced the 1S lipo with a 3S 1000mAh 25C lipo and now have 12.6V fully loaded.
And use LM2596 step-down converter with voltage LCD to step down to 5V:
https://www.aliexpress.com/wholesale?Se ... wn+display

There is a switch on the step-down module that decides whether input or output voltage gets displayed.
Output voltage is interesting for calibrating the module to deliver 5V, input voltage to see when lipo needs to be recharged:
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Brandon92
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Re: Powering Pi from 3S lipo with LM2596 step-down converter

Wed Sep 12, 2018 8:57 pm

I'm not 100% what you are asking.
HermannSW wrote:
Wed Sep 12, 2018 7:56 pm
Output voltage is interesting for calibrating the module to deliver 5V, input voltage to see when lipo needs to be recharged:
But if you are using a LM2596, the output voltage should not change much if the voltage at the input is changing.

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HermannSW
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Re: Powering Pi from 3S lipo with LM2596 step-down converter

Thu Sep 13, 2018 12:07 am

Hi,

as I said output voltage is only needed to adjust to 5V once, LM2596 output voltage range is 1.25V ~ 37V.

My question is why the potential 15A for 1S lipo directly connected to GND/5V Pi pins do not sufffice driving ZeroW+Wifi+LCD+wireless dongle.
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Imperf3kt
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Re: Powering Pi from 3S lipo with LM2596 step-down converter

Thu Sep 13, 2018 1:10 am

How thick are the wires coming off the lipo cell?
Most lipo cells only come with wiring rated to 1A
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HermannSW
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Re: Powering Pi from 3S lipo with LM2596 step-down converter

Thu Sep 13, 2018 8:04 am

Thanks, that is a good point.

I don't want to look inside the 2mm(?) cables.
But I assume the 25C lipo rating would not make sense if the lipo cables could not do 25*0.6=15A.
But you pointed to the problem, I used small breadboard cables to connect the lipo connector to Pi ZeroW GND/5V pins.
I will have to retest with attaching lipo connector directly on Pi pins 4+6 (5V+GND).

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HermannSW
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Re: Powering Pi from 3S lipo with LM2596 step-down converter

Thu Sep 13, 2018 8:17 am

Thanks again, I did the test, disconnected the cables coming from LM2596 and directly plugged the 600mAh 25C 1S lipo onto pins 4+6 -- works perfectly, and reliably. Did some tests, graphics on screen, accessing internet, ... no problems. Now I need to find cables that can deliver >1A which the breadboard cables obviously were not able to -- because I don't want to loose the power switch functionality of my mobile Pi by having to open the box and connect/disconnect the lipo to pins 4+6.
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Imperf3kt
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Re: Powering Pi from 3S lipo with LM2596 step-down converter

Thu Sep 13, 2018 8:37 am

It is how those Lipo are made. Many wholesale manufacturers where I live stress this point.

For example, I recently purchased a 10,000mAh cell directly from the Chinese manufacturer. It came with a datasheet which claims the cell is capable of 1C (10A) but the wiring is rated for [email protected]
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