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Mini DC UPS packs
#1
I want to build some small packs to run some of my DC items if the power goes off. The main things I want to run are the wireless wifi mesh nodes for my network and a wireless hub for my weatherflow tempest wx station. Ideally I could keep the internet and wx online in a power outage. The weather hub runs on a simple 5v 1amp micro usb plug and only uses a few wh per day. The mesh nodes run on 12v and I haven't measured their power consumption yet.

The pack would have to tolerate being plugged in 24/7. I was thinking a 4s and maybe 2 or 3 in parallel. I would use dc-dc converters for each device that I need to power. I'd like to keep these small and simple. I can 3d print the cases if I need to do that. It might even make sense to use a jehu style pcb mount for this.

My only real concern is having a charger plugged in all the time and not pulling power off the cells.
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#2
How about a small UPS on ebay and build a 18650 battery to match - probably 7s. 

Maybe something like this - https://www.ebay.com/itm/APC-UPS-450VA-U...1195.m1851

It will automatically have charging, grid->ups failover etc.  You can easily convert 120v output to suit what you need.   

I use 18650 DIY battery packs on several APC UPSs and they just sit there...  oldest one is 2 years and going strong Smile
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#3
I just figured skip the AC -> DC -> AC -> DC (wall wart) conversion since one runs on usb and the other a 12v barrel plug.
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#4
Interesting idea/plan.
To get around the always plugged in problem, you could add a little extra circuitry. Have a couple diodes on the input side of main power feed. This keeps backfeeding to the sensor. Then on the power side of the diodes use an SSR to turn on/off the battery pack in case the grid goes down. On the load side of the diodes a capacitor to help keep any dips from happening.
For charging, i suppose any of the cheaper chargers would work. Though, matching 12V is hard on standard Li-Ions.

Basically this would become a cheap/simple DC ups Wink

Of course the idea and general plan is crude. That would need to be worked out through R&D Tongue
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#5
(06-11-2020, 05:22 AM)gpn Wrote: I just figured skip the AC -> DC -> AC -> DC (wall wart) conversion since one runs on usb and the other a 12v barrel plug.
You could tap the battery (of the UPS) directly - no AC involved except UPS keeping the battery charged.   Maybe the key is you want to build something from scratch - and I get that Smile
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#6
If any group understands doing it yourself I would hope it is this one! Big Grin

The SSR is an interesting idea. They have super fast switching times and the load is minimal so I don't need to worry about heat sinking or super large SSRs.
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#7
keep your vpc near 4.0v and let it float.
holding at 4.2 greatly increases degradation.
limiting to 4.0 drops an insignificant amount of capacity in exchange for extended life.
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#8
Here is a slightly different question. Lets say I used something like a tp4056 to charge a 1s2p cell pack to power the weather station only. Can I have it plugged into a 5v source as well as running the load at the same time? Or is there a simple charging circuit for something like that?
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#9
Can someone point me to discussions about a multi-TP4056 board please? I know I read it but can't find it. I also recollect a mention of an upgraded version. A nudge would be helpful here to please.
-----------------------------------------------------------------------------------------------------------------------------------------------------------
As at Mid May 2020 -Total cells 1,135/Shucked 1,045/To be shucked 90/Processed 194/To be processed 608/Zero volt 183/Bad/rusted 19/Sanyos 1/21700s 24
All tool batteries comprising of Milwaukee, Makita, AEG, Hilti, with Samsung, LG, Sony and Sanyo cells from 1.3AH to 3.0AH (OEM)
Chargers... 1 x Nitecore D4/1 x LiitoKala 500/1 x iMAax B6AC
On order... 5 x LiitoKala 500/1 x LiitoKala 500/1 x iCharger 4010 Duo
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#10
(06-22-2020, 11:53 AM)Wayne\s World Wrote: Can someone point me to discussions about a multi-TP4056 board please? I know I read it but can't find it. I also recollect a mention of an upgraded version. A nudge would be helpful here to please.
Well you can always read about the one I built.

https://secondlifestorage.com/showthread...6#pid38976

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