rclark92
Posts: 1
Joined: Mon Jul 15, 2019 11:10 pm

'Uninteruptible' Power Supply

Mon Jul 15, 2019 11:27 pm

I've set up my pi to be able to directly plug to 120vac by using a step down converter to get a constant 5v supply. I have a 3.5V rechargeable battery hooked up in parallel and my question is:

-If the pi happens to lose the 120vac supply and therefore the 5vdc, would 3.5V rechargeable battery be enough to let the pi safely save its working memory and shut down?

I'm pretty new to raspberry pi; would a sudden power supply drop from 5v to 3.5v affect it? Or is there some kind of built in safety?

Thanks!

User avatar
Imperf3kt
Posts: 2652
Joined: Tue Jun 20, 2017 12:16 am
Location: Australia

Re: 'Uninteruptible' Power Supply

Mon Jul 15, 2019 11:51 pm

From your description, you have constructed an explosive / fire.
This is how I interpret your description
Image

Please post images of your circuit and any additional info about it, nobody here can help without it.
55:55:44:44:4C
52:4C:52:42:41

pfletch101
Posts: 500
Joined: Sat Feb 24, 2018 4:09 am
Location: Illinois, USA

Re: 'Uninteruptible' Power Supply

Tue Jul 16, 2019 12:23 am

rclark92 wrote:
Mon Jul 15, 2019 11:27 pm
I've set up my pi to be able to directly plug to 120vac by using a step down converter to get a constant 5v supply. I have a 3.5V rechargeable battery hooked up in parallel and my question is:

-If the pi happens to lose the 120vac supply and therefore the 5vdc, would 3.5V rechargeable battery be enough to let the pi safely save its working memory and shut down?

I'm pretty new to raspberry pi; would a sudden power supply drop from 5v to 3.5v affect it? Or is there some kind of built in safety?

Thanks!
I don't entirely agree with Imperf3kt's interpretation of your rather limited description of your setup, but I share his concern that what you have described is potentially dangerous. It sounds to me as if you have put a 3.5V battery in parallel with your 5V supply. If you don't have some sort of power conditioning circuitry round the battery, it is likely to burn up! In any event, a Pi requires a 5V supply. While much of its internal logic runs on 3.3V, the circuitry that derives this from the normal 5V supply will not function properly if the supply voltage drops below (from memory) something like 4.7V, and the Pi will crash, whether or not your battery has survived and is supplying its rated voltage.

amcdonley
Posts: 175
Joined: Mon Jan 26, 2015 5:56 pm
Location: Florida, USA

Re: 'Uninteruptible' Power Supply

Sun Jul 28, 2019 4:07 am

strongly suggest this UPS, I use it with my desktop RPi for over a year with no off time, even through hurricanes.

https://lifepo4wered.com/lifepo4wered-pi+.html

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