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.

[ben999]

Guys

I am planning to use a 4S li-ion 18650 battery.

Please have a look at my Fritzing sketch

Battery pack will be monitored by this item :
http://www.ebay.com/itm/4S-6A-Li-ion-Lithium-Batterie-3-7v-18650-Charger-Battery-Protection-Board/382109076738?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2057872.m2749.l2649

When off-grid ISDN box and RPi will be powered with that battery via this board :
http://www.ebay.com/itm/Automatic-Buck-Boost-Step-Up-Down-DC-DC-Power-Supply-Converter-Replace-XL6009/142371180585?ssPageName=STRK%3AMEBIDX%3AIT&var=441392018812&_trksid=p2057872.m2749.l2649

When on-grid, this charger will charge the battery pack and power ISDN box/Rpi :
http://www.ebay.com/itm/EU-Plug-4S-16-8V-2A-AC-DC-Charger-Adapter-for-18650-Lithium-Li-ion-Battery-Cell-/262728544983?epid=507598255&hash=item3d2bd772d7:g:m6oAAOSwcLxYJaSF

Is this the correct way of building my UPS ?
Can i draw current from the charger to power box and RPi while it is charging ?

Thanks again for your input/advice.

[rozpruwacz]

isn't it better to buy ready made solution ? e.g. http://www.powerwalker.com/index.php?page=select&lang=en&cat=dc

[ben999]

@rozpruwacz

No DIY, no fun !

[rozpruwacz]

haha yeah, totally agree

[gohan]

@ben999 said in UPS:

@rozpruwacz

No DIY, no fun !

No DIY, no problems, no fun

[dbemowsk]

I didn't read all the comments, so forgive me if this was mentioned. What if you just used an SLA or AGM battery and connected a battery tender to it. The battery tender should keep the battery topped off without over charging it, and I would think have enough power to power the PI also. Then you are converting 220 down to 12, and if the power goes down, the battery tender will just shut off and the battery would take over. No extra loss in converting 12 to 220 and back to12 again.

[gohan]

I think nobody wants to convert 12 to 220v

[ben999]

@dbemowsk
Thank you for your message

@gohan said in UPS:

I think nobody wants to convert 12 to 220v

I think @gohan got me right here. I have a spare "standard" ups at home... but i dont find that tech very sexy (on top of it it's huge)

It's fun to scratch head !!!

[ben999]

Guys,

One last question :

Can i draw current from the charger to power box and RPi while it is charging the home-made UPS ?

I might be ordering this in case it is possible:

link text

[gohan]

if the charger is not drawing too much current I'd say yes, but you need a buck converter

[dbemowsk]

@ben999 The highest current draw from the list of Pi models is 2.5A on the model 3B (https://www.raspberrypi.org/help/faqs/#powerReqs). If you have a power supply slightly larger than whatever model you are running, you should be good. you just need to be able to supply enough so that the PI has enough to run whatever it is doing and some for charging.

[dbemowsk]

As I mentioned in my previous post a few days ago, you will want a battery tender, and not just a charger. A battery tender will shut off if the battery is fully charged, whereas just using a battery charger could overcharge the battery.