How to charge a small server DIY UPS?

[Archerite]

I have a small server, intel NUC, that uses less than 5 watts at 12-19 volt input. So it fit perfectly in the range of charging voltages for a lifepo4 battery. I have a 12V 8Ah lifepo4 cell I want to use for this UPS. Combined with a victron smartshunt/bmv to monitor the SoC. It will not be connected directly to solar, but I do have a larger battery bank this will be charged from. For all intents and purposes...this one is "unlimited" in it's capacity. Charged from either solar or grid automatically to keep it in the range 20%-50%.

On that "automated battery bank" I have two victron orion 12/24-10 that are in parallel for a 24.5V 20A line. This is where this UPS needs to be charged from. The 8Ah battery can take 10A of charge current but anything between 2-5A will be fine I think. Another victron orion is an option...but one that is actually meant for charging requires the smart version. Meaning at least 200+ euro's! I have a few MPPT's as reserves on the shelf...and I know it works by taking the 24V line into the MPPT's PV input.

My question is if there is a better solution to charge this battery. With the configurable charge profile like the MPPT has.

 

[sunshine_eggo]

but I do have a larger battery bank this will be charged from. For all intents and purposes...this one is "unlimited" in it's capacity. Charged from either solar or grid automatically to keep it in the range 20%-50%.

You have a battery monitor on it?

Are you aware that extended periods without fully charging will cause the cells' states of charge to diverge and capacity will be reduced?

Better to cycle to nearly fully charged at 13.8V (3.45V/cell) rather than target repeated short cycling and capacity loss due to imbalance.

On that "automated battery bank" I have two victron orion 12/24-10 that are in parallel for a 24.5V 20A line.

What kind of battery is being charged at 24.5V. 6S Tesla module?

This is where this UPS needs to be charged from. The 8Ah battery can take 10A of charge current but anything between 2-5A will be fine I think. Another victron orion is an option...but one that is actually meant for charging requires the smart version. Meaning at least 200+ euro's! I have a few MPPT's as reserves on the shelf...and I know it works by taking the 24V line into the MPPT's PV input.

My question is if there is a better solution to charge this battery. With the configurable charge profile like the MPPT has.

You can feed the MPPT with higher voltage DC from battery.

 

[Archerite]

You have a battery monitor on it?

Are you aware that extended periods without fully charging will cause the cells' states of charge to diverge and capacity will be reduced?

Better to cycle to nearly fully charged at 13.8V (3.45V/cell) rather than target repeated short cycling and capacity loss due to imbalance.

offcourse there is a monitor on it.


This is my custom dashboard in HomeAssistant. Pulls in data through node-red from MQTT on a raspberry pi with VenusOS. I have a thread about it on here. I think you replied there too about my 11 x 8Ah battery bank (88Ah). Or on one of my previous threads.

The idea with the low SoC settings is that most charge would come from solar. And yes, I am aware of the drift after a couple days on the smartshunt. Or actually BMV712 on this battery bank. They are lifepo4 12V battery packs with internal BMS, in each one. And as you can see on my dashboard the values are adjustable too on the fly. So you say I should make them higher? I already did that a bit yesterday.

What kind of battery is being charged at 24.5V. 6S Tesla module?

Hahaha, I would guess no normal battery right? Maybe I worded that sentence wrong. What I meant is that my 12V battery bank is used to power two victron orions set to a voltage of 24.5V. The reason is that I need to span a length of 20 meter 4mm2 wire and wanted to minimize voltage loss...so the orion was my solution to that. If it's a good one or the best I leave up to you. All I can tell is it works great. And since there are (or wil be) two in parallel I have 24.5V at 20A max.

I also use car chargers on this 24.5V line to charge anything with USB ranging from 5W-100W with the right adapter. USB A and USB C. And I have a 24V victron inverter running of it.

The main reason I chose this exact voltage is that I also wanted to directly charge an EcoFlow River from it...and that has a 25V input limit. Which is why I chose this "safe" value. Also...I tried higher voltages but that made the losses higher in the conversion from 12V.

You can feed the MPPT with higher voltage DC from battery.

I know that I can. I have already tested that a while back as I described hooking the 24.5V into the MPPT's PV input. So I know it works. I am just asking if there are alternative chargers or a better way to do it in my specific situation.

Maybe this already is the best option given the circumstances.

 

[sunshine_eggo]

The idea with the low SoC settings is that most charge would come from solar. And yes, I am aware of the drift after a couple days on the smartshunt. Or actually BMV712 on this battery bank. They are lifepo4 12V battery packs with internal BMS, in each one. And as you can see on my dashboard the values are adjustable too on the fly. So you say I should make them higher? I already did that a bit yesterday.

If you're using the charger as a "backstop" to prevent the battery from depleting and allowing headroom to be topped off by solar, that's fine. If the battery will regularly attain 3.45V/cell for a couple hours, then it it should retain cell balance.

Hahaha, I would guess no normal battery right? Maybe I worded that sentence wrong. What I meant is that my 12V battery bank is used to power two victron orions set to a voltage of 24.5V. The reason is that I need to span a length of 20 meter 4mm2 wire and wanted to minimize voltage loss...so the orion was my solution to that. If it's a good one or the best I leave up to you. All I can tell is it works great. And since there are (or wil be) two in parallel I have 24.5V at 20A max.

I just can't imagine anything being charged to a meaningful level at 24.5V except a 6S Tesla module.

I know that I can. I have already tested that a while back as I described hooking the 24.5V into the MPPT's PV input. So I know it works. I am just asking if there are alternative chargers or a better way to do it in my specific situation.

Maybe this already is the best option given the circumstances.

You have already discovered a dedicated charger is going to be spendy.

Use whatcha got!

 

[Archerite]

If you're using the charger as a "backstop" to prevent the battery from depleting and allowing headroom to be topped off by solar, that's fine. If the battery will regularly attain 3.45V/cell for a couple hours, then it it should retain cell balance.

Exactly. I use HomeAssistant to keep an eye on the SoC and that activates the grid charger when the set low value is reached. To prevent the battery goes to low. I just upgraded this a few days ago to a new more powerful Victron BluePower 12V 30A actually. I am planning on also replacing the battery bank with two 100ah batteries and did not want to wait a whole day for it to recharge at 10A from the grid. I don't have access to the individual cell voltage since the BMS'es are internal and have no bluetooth or something. but the battery bank voltage is usually between 12.9-13.4. I have a constant 20-30W load on it. I have 14.25V absorbtion and float 13.5V.

In summer I had 100% before 11AM on some days. Now...it rarely get's full at the end of the day. Lot's of rain at the moment here.

I just can't imagine anything being charged to a meaningful level at 24.5V except a 6S Tesla module.

I know your joking now but what I charge is: mobile phones, tablets, laptop, powerbanks etc...via USB chargers. At the various USB PD voltages. And also the inverter for my TV, just because I can not because I have too. And...my ecoflow river. Works great!

And for this project...it's a high enough voltage to let the MPPT turn on for 12V battery charging.

You have already discovered a dedicated charger is going to be spendy.

Use whatcha got!

Yes, they are very expensive....especially for my intended purpose. Maybe it's justified when used on an alternator charger in an RV or something.

Thanks for the advise. I will just use those few components and see if it all works. When it's "presentable" I'll post some pictures. ?