Lithium Battery for UPS

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TheStealth

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Oct 29, 2020
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Hi,

I've been lurking around for awhile, but decided to sign up to get some advice. My UPS is in need of a battery replacement and currently uses two 12v SLA 9aH batteries in series to give 24V. I'm trying to decide what is the best approach to replace these with a DIY lithium solution (wetting my feat before jumping into a powerwall).

I will determine how many cells can be put in parallel based on what will fit inside my UPS . Each solution will include an appropriate BMS (suggestions welcome on this, was thinking of a Daly BMS).

So far these are the ideas I have come up with:

  • LiFePo4 in a 8s#p setup using 36700 cells
  • Lithium in a 7s#p setup using 18650 cells
  • Lithium in a 6s#p setup using 18650 cells
What I would like to know is which of the above solutions is the best drop in fit to replace a 24V lead acid setup in my UPS. If none, is there a better config that you can suggest? Is there anything else I should think about for this projet?

Thanks!

Mike
 

daromer

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LiFePo4 8s is the best since they have characteristics that are closest to la

7s liion works but they are a tas more sensitivd.
6s wont work. To low voltage.


All require bms and that you have knowledge of the difference between la and lithium. And know that Ups systems are made for la not lithium ;)
 

Korishan

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Go with LiFePO4's if you have them. Best conversion with lithium cells, almost a 95+% perfect match.

With LiFePO4's, you "can" let the UPS charge them up and it won't really degrade them. However we still recommend using a proper charger for those cells. With Lithium Ion, DEFINITELY use a Li-Ion charger and do NOT use the UPS to charge them. It will kill them in short order.
If you have to use the UPS to charge, make sure you are using one that can be programmed, ie, not the cheap units for computer backup.

What UPS unit are you planning on using?
 

OffGridInTheCity

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Agree with above. For me, I have an excess of 18650 - so I have several 7s7p battery packs that I use in APC 1500/3000(s)and a 14s13p that I use in one of myAPC 3000s.

7s7p is a perfect footprint size to replace lead-acid(leaves plenty of room for BMS)and is perfectly compatible for 24v nominal. You can double deck them if you want to go to the (kind of) extreme extra build to 7s14p double-deckerto get a larger battery - but then you need a flat/smaller BMS.

APC UPSs top out at27.0v-27.5v for 7s or 3.9v/cell - great for long life. The APC bottoms out at 21v or3.0v/cell which is fine for18650. I use my APCs asUPSs to smooth the ATS switchovers each day between Grid and Off-Grid -so the cells mostly sit at3.9v all the time with small power drains during the daily switchovers.

Here's a pic with a Chargery 8T BMS (has a box + shunt - kind of bulky).

image_mlkeau.jpg

This is my workbench power supply for the iCharger 8x so it has some extra wires coming out - but others just have the regular APCcover with Chargery view panel sitting on top for monitoring.

Here's a pic of a APC 3000 with 2 separate 7s7p(s)....

image_webrkf.jpg


Have been running a couple of these for nearly 3 years - with no noticeable degradation.
 

TheStealth

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Oct 29, 2020
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Hi All,

Thanks for the quick replies. Looks like LiFePo4 in a 8s#p will be my best choice. However, a 7s#p setup is intriguing. I could go either way as I do not have any cells yet. I'll try and answer some of your questions and have more of my own.

Korishan said:
What UPS unit are you planning on using?

I have a Geek Squad GS-1500U (a rebranded 1500VA CyberPower) I have not opened it up yet, but found this photo on the internet.
upsbattery.jpg


OffGridInTheCity said:
APC UPSs top out at27.0v-27.5v for 7s or 3.9v/cell - great for long life.

Here's a pic of a APC 3000 with 2 separate 7s7p(s)....

Have been running a couple of these for nearly 3 years - with no noticeable degradation.

Your experience nudges me towards using 18650 cells in a 2x 7s3p config so it would fit in my UPS(wired in parallel to make a 7s6p pack that will be ~12aH, also easier to scavenge ;) ). With this setupI could use only one BMS, correct?

I see that you are using BG-8S on your dual 7s7p setup. How are you using the BG-8S in that setup? Only to balance and you are trusting the UPS to charge and cutout at the correct voltage? Is there an advantage to doing this over using a Daly BMS that has a built in cutout? Did you add any circuit protections (CB or fuse)?

Thanks
 

OffGridInTheCity

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TheStealth said:
Your experience nudges me towards using 18650 cells in a 2x 7s3p config so it would fit in my UPS(wired in parallel to make a 7s6p pack that will be ~12aH, also easier to scavenge ;) ). With this setupI could use only one BMS, correct?

I see that you are using BG-8S on your dual 7s7p setup. How are you using the BG-8S in that setup? Only to balance and you are trusting the UPS to charge and cutout at the correct voltage? Is there an advantage to doing this over using a Daly BMS that has a built in cutout? Did you add any circuit protections (CB or fuse)?
Good questions. The 2 xBG-8S is not good - especially since these are 2 separate 7s7p(s) batteries that the APC sees as 2 batteriesin series to make 48v (14s) internally.They let me monitorso its not immediately dangerous as long as I check often (like every day)but its not good. Its aplaceholder till I get a regular 14s BMS*and*rewire the APC 3000 Anderson plugsto see/plug into a single14s7pinstead of 2 separate 7s7p(s).

>...using 18650 cells in a 2x 7s3p config ...[size=small]I could use only one BMS, correct?
[/size]
You can have 2 separate 7s3p batteries with parallel power leads *and* parallel the balance leads to a single BMS... but then you're pretty close to a 7s6p physically and might be easier to just do a single 7s6p OR 2 BMSs on 2 x7s3p. IF the 7s3p(s) are in series for 48v nominal - then its like my case above and you need 2 separate BMSs.
 

Korishan

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Using that UPS "DEFINITELY" use LiFePO4's if you must use that unit. Those small units are basically dumb, even if they say "Smart" on them. They are programmed from factory and almost impossible to reprogram. It may have a com port on the back, but good luck finding software to change anything.
 

TheStealth

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Oct 29, 2020
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If I can get 7s6pnto fit I would definitely go that route. If it doesn't, well 2x 7s3p in parallel to get 24v, one good BMS with parallel balance leads. If there are half decent cheap BMS out there I would do two for simplicity. Recommendations welcome here.

As for my dumb UPS, how is it that different from an APC 3000? From what I know most of these work in much the same way. Please enlighten me on how it would be any different from the one I have.
 

Korishan

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The APC3000 is software controlled and you can use PowerChute software to change it's settings. The one you have there has a firmware, maybe some dip switches to change basic settings.

PowerChute software, or similar for other brands, allows you to change Float charge, top/bottom voltage, some can change max current, etc. Plus give you live data of usage over time. Server grade UPS units have lots of stats that are available too.

I could be wrong on the one you have there, but most of those cheaper units are not very configurable. Usually the "smart" portion of the UPS means they are closer to a pure sine wave, and they are able to trigger a little better/faster on low/high line voltage than the other non-smart units
 

TheStealth

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Thanks for the clarification, much appreciated. I assume for powerchute you need the pro version and not the personal one? I also have an APC SmartUPS 500va, though this only uses a 12v battery, so 18650s are somewhat less interesting for this one. That is unless I can tweak the charge, float, and discharge voltages appropriately. I did find this site that has some useful tips:
http://www.jjoseph.org/notes/apc_smartups_battery_float_voltage

As for the cyperpower I will investigate what tweaks can be done. If nothing then I'll settle for LiFePo4, but will likely need an external enclosure to hold the batteries to get the equivalent or better capacity.

Perhaps I need to find myself an old Smart UPS 1500 or 3000 VA.
 

winny

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OffGridInTheCity said:
Agree with above. For me, I have an excess of 18650 - so I have several 7s7p battery packs that I use in APC 1500/3000(s)and a 14s13p that I use in one of myAPC 3000s.

7s7p is a perfect footprint size to replace lead-acid(leaves plenty of room for BMS)and is perfectly compatible for 24v nominal. You can double deck them if you want to go to the (kind of) extreme extra build to 7s14p double-deckerto get a larger battery - but then you need a flat/smaller BMS.

APC UPSs top out at27.0v-27.5v for 7s or 3.9v/cell - great for long life. The APC bottoms out at 21v or3.0v/cell which is fine for18650. I use my APCs asUPSs to smooth the ATS switchovers each day between Grid and Off-Grid -so the cells mostly sit at3.9v all the time with small power drains during the daily switchovers.

Here's a pic with a Chargery 8T BMS (has a box + shunt - kind of bulky).

image_mlkeau.jpg

This is my workbench power supply for the iCharger 8x so it has some extra wires coming out - but others just have the regular APCcover with Chargery view panel sitting on top for monitoring.

Here's a pic of a APC 3000 with 2 separate 7s7p(s)....

image_webrkf.jpg


Have been running a couple of these for nearly 3 years - with no noticeable degradation.

Beautiful! You "stole" my idea. :)
Where did you get that DC connector and how did to attach it to your batteries? Can you PM me any details, BOM or photos?
 

TheStealth

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Where did you get that DC connector and how did to attach it to your batteries? Can you PM me any details, BOM or photos?


Actually I would be interested as well. Maybe post it in this thread for all to see?
 

OffGridInTheCity

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TheStealth said:
Where did you get that DC connector and how did to attach it to your batteries? Can you PM me any details, BOM or photos?

Actually I would be interested as well. Maybe post it in this thread for all to see?
The grey connectors? These are standard Anderson 50a connectors - https://www.ebay.com/itm/ANDERSON-C...067068?hash=item20dfc33a3c:g:MJgAAOSw-jhT~REF APC UPSs use these.

Search "Anderson Connector" and you'll find various sizes / amps / install :)
 

Overmind

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12 V : Li-ion - not good / LiFePo4 - fine. 3 Li-ions in series for 12 V UPS will be overcharged a lot by the 13V+ the UPS will give. So at best you make continuous power drain for nothing.

For 24 and 48V both Li-ion and LifePo4 are fine.
 

winny

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OffGridInTheCity said:
TheStealth said:
Where did you get that DC connector and how did to attach it to your batteries? Can you PM me any details, BOM or photos?

Actually I would be interested as well. Maybe post it in this thread for all to see?


How did you go about soldering the cables from said connector to your battery pack?
The grey connectors? These are standard Anderson 50a connectors - https://www.ebay.com/itm/ANDERSON-C...067068?hash=item20dfc33a3c:g:MJgAAOSw-jhT~REF APC UPSs use these.

Search "Anderson Connector" and you'll find various sizes / amps / install :)

Thanks! What did you use to crimp them?
How did you terminate your cables to your battery pack?
 

Korishan

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@winny Please put your replies to comments outside of the quote block. It's hard to see where the quote ends and your comment begins.
 

winny

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Korishan said:
@winny Please put your replies to comments outside of the quote block. It's hard to see where the quote ends and your comment begins.

Dang it! I'm not used to this WYSIWYG style editor. Is it possible to get plain BBcode?
 

daromer

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ctrl + shift + k or press the view source button and you can write in full code format. In the full-text-editor that is
 

OffGridInTheCity

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winny said:
OffGridInTheCity said:
TheStealth said:
Where did you get that DC connector and how did to attach it to your batteries? Can you PM me any details, BOM or photos?

Actually I would be interested as well. Maybe post it in this thread for all to see?


How did you go about soldering the cables from said connector to your battery pack?
The grey connectors? These are standard Anderson 50a connectors - https://www.ebay.com/itm/ANDERSON-C...067068?hash=item20dfc33a3c:g:MJgAAOSw-jhT~REF APC UPSs use these.

Search "Anderson Connector" and you'll find various sizes / amps / install :)

Thanks! What did you use to crimp them?
How did you terminate your cables to your battery pack?

>What did you use to crimp them?
I soldered mine - but they are hollow tubes closed on one end so any kind of tube crimper should work.

[size=small]>How did you terminate your cables to your battery pack?[/size]
[size=small]Soldered them to the buss bar.[/size]
 

winny

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OffGridInTheCity said:
>What did you use to crimp them?
I soldered mine - but they are hollow tubes closed on one end so any kind of tube crimper should work.


[size=small]>How did you terminate your cables to your battery pack?[/size]
[size=small]Soldered them to the buss bar.[/size]

No ifs or buts what so ever? Just straight high powered soldering iron?
 
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