UPS

ben999

Hi guys
I am using MySensors together with OpenHAB to protect my home and also for access control
To make more sense I decided that all security related sensors shall be powered via battery
To make even more sense I run my gateway and the box from an UPS. But...

That UPS uses 220V AC to keep its 12V DC battery in shape. That's fine.
But when it goes off the grid it converts 12V DC to 220V AC back to 12V DC for box (which powers Raspberry via USB)

Would it make sense to have a pack of LiIon batteries that supply directly the box via some DC-DC regulator? And have the LiIon cells charged/balanced via these boards found on eBay?

I imagine there would be a cut-off voltage unit that would protect the cells.

Your comments on this matter would be welcome.

As i am not able to design any electronics, best would be to use board found on eBay or similar...

Thanks a lot for reading and even more thanks for your input

See ya

tbowmo

@ben999

Something like this: https://hackaday.io/project/9461-lifepo4weredpi ??

ben999

@tbowmo

Thanks a lot ! Very neat !

But it seems that this unit can only power the Pi itself...

I am more looking at keeping the box AND the Pi alive for a few minutes (or more) :

at least enough time to let me know that there's a power cut
and (even better) plenty enough time to keep the alarm system going in case the power-cut is due to burglars...

Thanks a lot anyway... that device could be useful for some other projects :) Ta

mfalkvidd

@ben999 what type of box are you looking to power?

ben999

@mfalkvidd
Hi
Thank you for your message
The box I am talking about is the internet/phone ISDN box (sorry I didn't make that clear)
Power supply is rated 12v 2A
The box powers the Pi via USB

mfalkvidd

@ben999 thanks for clarifying.

Are you able to get details for the isdn box? If it can handle something like 11-13.8V in, you could probably use something as simple as a (small) car battery and a car battery charger.

Examples:
http://www.conrad.com/ce/en/product/200081/H-Tronic-AL800-2-12V-Lead-Acid-Battery-Charger-08A-12-40Ah?ref=searchDetail
http://www.conrad.com/ce/en/product/250165/VRLA-12-V-12-Ah-Conrad-energy-CE12V12Ah-250165-AGM-W-x-H-x-D-97-x-52-x-48-mm-48-mm-blade-terminal-Maintenance-free?ref=searchDetail

gohan

You can always make a small mod to ups and bring out the 12V from the internal battery and leave ups off, the internal circuit will keep the battery charged while not consuming power for dc-ac converter (if of course you can use the voltage a little higher than 12v).
I have a spare ups ready to be modified for this purpose

Nca78

For those looking at a backup for pi only, I found this on AliExpress with (claimed) 2500mAh battery so it should get 4-5 hours on a pi 3. I buy one and will give a feedback, I have regular and long power cuts here and this should ensure continuity for at least logging all MySensors events.

https://www.aliexpress.com/item/Geekworm-RPi-UPS-HAT-Board-for-Raspberry-Pi-3-Model-B-Pi-2B-B/32766227090.html

If someone knows about a safe DIY circuit for li-ion or even better li-FePO4 (much safer) that I could use for smaller things like a GSM node or wifi gateway, please share !

gohan

There is also this cheap solution https://www.aliexpress.com/item/6W-5V-UPS-mobile-power-Diy-Board-Charger-Step-up-DC-DC-Converter-Module-for-3/32790658678.html

Nca78

@gohan said in UPS:

There is also this cheap solution https://www.aliexpress.com/item/6W-5V-UPS-mobile-power-Diy-Board-Charger-Step-up-DC-DC-Converter-Module-for-3/32790658678.html

Thank you that can be useful for small nodes, I will buy one to test.
Not for Pi unfortunately as it's not powerful enough.

gohan

my rpi3 usually uses 0.3A @5v with peaks of 0.6, I think it will be within 6W without problems

Nca78

@gohan said in UPS:

my rpi3 usually uses 0.3A @5v with peaks of 0.6, I think it will be within 6W without problems

Wow that's surprisingly low, I guess it's not loaded too much, not using peripherals and video/hdmi output ?

gohan

actually it is just sitting there headless with a NRF24 connected to it. I checked consumption with relays and with 5 relays on the consumption goes from 0.3 to 0.6A. I have 8 relays but I guess there will not be many of them on at the same time for a prolonged time.

alexsh1

@ben999

I'm using on of these

http://www.pimodulescart.com/shop/

I have LiFePO4 4000mAh battery pack - this is enough to weather the longest power outage

Nca78

@alexsh1 thank you for the link.
I'll give a try to the AliExpress version first for financial reasons, but I'll check yours if the cheap one fails.

gohan

@Nca78 keep in mind that the one I posted is missing battery protection, so you need to have put one (unless your batteries have internal protection)

alexsh1

@Nca78 you are not too rich to spend you money on cheap stuff, are you? :-)

If you want a real UPS with many feathers programmable buttons and LEDs, it cannot be super cheap. Anyway, it's your call

Nca78

@gohan said in UPS:

@Nca78 keep in mind that the one I posted is missing battery protection, so you need to have put one (unless your batteries have internal protection)

Yes on the circuit you linked I'll put a 18650 with protection, I will test it on a wifi gateway.
For RPI I'll use the "hat" with battery that I linked in message above, only 17€ with battery.