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Interesting Idea for relatively Low Cost 120v UPS using LiFePO4

mightybara

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Jul 11, 2020
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I've been using Pure Sine Wave APC UPSes (1000VA) for a long time to keep the basic things running like Modem, Router, Networking, Office, etc so that I can work from home and not worry about electricity going causing an issue. I've orderd a 50AH 24v (25.6V) LiFePO4 battery with then intention of swapping my two AGM 12V batteries for just one 24V LiFePO4 battery, but I know that floating the lithium battery under the max voltage isnt going to be all good for it in the long run, so I had an interesting idea.

Why not use a Portable Power Station, like the Bluetti EB3A to act as the UPS for when power goes out? So to extend the battery runtime, I can easily plug in my 24V LiFePO4 battery to its DC Input port and that can act as 'solar' or 'car' power to extend the runtime of the 268Wh by another 1,000Wh so that my office can stay without mains power for a long long time (usually about 150w max, 100w average).

To keep the battery charged up, I can use a Lithium charger externally always plugged in the wall or even a small solar panel with a basic mppt charge controller.

The total cost of this is comparable with a 1000VA Pure Sine Wave UPS, but with now, a battery that will last 10 years.

What am I missing or is my assumption that this will work fine is purely off?
 
Following. It feels like the float charge LFP thing is still poorly defined.
An interesteing question is how do regular hybrid inverters charge and keep 24v batteries charged to 100% until they are ready to be used in an emergency? I believe this is safe to do and should not affect the LiFePO4 battery lifespan, but I would leave it up to the experts in this forum to advise if keeping the battery at 100% with a lithium charger 99% of the time is a good idea.

An alternative arrangement would be to deplete the battery to around 30% and charge it back up to 100% a few times a week. You can do this easily with a smart plug with a timer if the load is constant and the Wh usage is predictable. Can get even more fancier with a smart shunt talking to homeassistant, to control a plug to turn on the charginig then the battery is clost to 30%, but that is getting way over complicated.
 
I've been using Pure Sine Wave APC UPSes (1000VA) for a long time to keep the basic things running like Modem, Router, Networking, Office, etc so that I can work from home and not worry about electricity going causing an issue. I've orderd a 50AH 24v (25.6V) LiFePO4 battery with then intention of swapping my two AGM 12V batteries for just one 24V LiFePO4 battery, but I know that floating the lithium battery under the max voltage isnt going to be all good for it in the long run, so I had an interesting idea.

Why not use a Portable Power Station, like the Bluetti EB3A to act as the UPS for when power goes out? So to extend the battery runtime, I can easily plug in my 24V LiFePO4 battery to its DC Input port and that can act as 'solar' or 'car' power to extend the runtime of the 268Wh by another 1,000Wh so that my office can stay without mains power for a long long time (usually about 150w max, 100w average).

To keep the battery charged up, I can use a Lithium charger externally always plugged in the wall or even a small solar panel with a basic mppt charge controller.

The total cost of this is comparable with a 1000VA Pure Sine Wave UPS, but with now, a battery that will last 10 years.

What am I missing or is my assumption that this will work fine is purely off?
From your solution it sounds like you still float the 24v Lifepo4 via the charger.So not much difference.
 
Is there a paradigm where you charge the battery to 100% and completely disconnect the charger (and load) until the power fails? Sounds like folks here have brought batteries out of storage after a year to find they only lost a few percent.
 
I've been using Pure Sine Wave APC UPSes (1000VA) for a long time to keep the basic things running like Modem, Router, Networking, Office, etc so that I can work from home and not worry about electricity going causing an issue. I've orderd a 50AH 24v (25.6V) LiFePO4 battery with then intention of swapping my two AGM 12V batteries for just one 24V LiFePO4 battery, but I know that floating the lithium battery under the max voltage isnt going to be all good for it in the long run, so I had an interesting idea.

Why not use a Portable Power Station, like the Bluetti EB3A to act as the UPS for when power goes out? So to extend the battery runtime, I can easily plug in my 24V LiFePO4 battery to its DC Input port and that can act as 'solar' or 'car' power to extend the runtime of the 268Wh by another 1,000Wh so that my office can stay without mains power for a long long time (usually about 150w max, 100w average).

To keep the battery charged up, I can use a Lithium charger externally always plugged in the wall or even a small solar panel with a basic mppt charge controller.

The total cost of this is comparable with a 1000VA Pure Sine Wave UPS, but with now, a battery that will last 10 years.

What am I missing or is my assumption that this will work fine is purely off?
This will work but a couple of things.

Will 300W output be enough?

Also the eb3a is known to be quite a defective piece of crap based on many online stories. perhaps consider a river 2

I can tell you that with my Delta 2 max, when using just its mppt trackers connected to a 48V battery,and no AC input it will discharge down to 98% then charge up to 100%. There is no solar pass thru like it would use if AC input was connected.

So what I did was get a Victron Phoenix 48/1200 inverter, connected to same 48V bank, and use that as the pass thru source for the d2m. This way there's no unneeded microcycling of the internal battery.

In your case, I would suggest a 24/1200 inverter plus the ve direct BT smart dongle. That in conjunction with 24V battery and charger (Victron IP22 24/16?) will give you a far more reliable system that will be likely be working 10 years down the road when the eb3a is long in the garbage.
 
This will work but a couple of things.

Will 300W output be enough?

Also the eb3a is known to be quite a defective piece of crap based on many online stories. perhaps consider a river 2

I can tell you that with my Delta 2 max, when using just its mppt trackers connected to a 48V battery,and no AC input it will discharge down to 98% then charge up to 100%. There is no solar pass thru like it would use if AC input was connected.

So what I did was get a Victron Phoenix 48/1200 inverter, connected to same 48V bank, and use that as the pass thru source for the d2m. This way there's no unneeded microcycling of the internal battery.

In your case, I would suggest a 24/1200 inverter plus the ve direct BT smart dongle. That in conjunction with 24V battery and charger (Victron IP22 24/16?) will give you a far more reliable system that will be likely be working 10 years down the road when the eb3a is long in the garbage.
Hey Thanks for the suggestion. Was more looking at a cost effective solution that is under $600 USD total for a somewhat reliable UPS System with over 1000Wh. $300 for the SoGen and <$300 for a 24V LiFePO4 battery @50AH. Can go bigger if budget permits. If money wasn't an issue, for sure I'd go a full Victron setup.

EB3A is just an example, there are lots of other Power Stations that has UPS Relay function that can switch quickly between Line and Battery enough to keep PCs running. Jackery, Ecoflow, etc etc.

The idea here is to keep the AC connected at all times, which essentially bypasses the internal battery from being drawn down from, but also have an external battery to act as a DC 'charger' when the power actually goes out.

The external 24V doesn't need to be floating, but charged to 100% and left there for when the power goest out. A simple circuit that closes when AC power isnt there can act as a switch to the input of the Power Station/SolarGen to auto connect the battery to the power station when electrity is out. Using something like this -> https://www.amazon.com/TWTADE-Electromagnetic-YJTF08A-Quality-assurance/dp/B07C78PHS2/

So the real quesiton is, does anyone have a PowerStation/Solar Gen lying around with UPS functionality lying around to help test this scenario?

IF it does work, the masses can surely have a budget but long runtime UPS Backup solution, not just for small office use, but even for things like refrigerators, etc.
 
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Hey Thanks for the suggestion. Was more looking at a cost effective solution that is under $600 USD total for a somewhat reliable UPS System with over 1000Wh. $300 for the SoGen and <$300 for a 24V LiFePO4 battery @50AH. Can go bigger if budget permits. If money wasn't an issue, for sure I'd go a full Victron setup.

EB3A is just an example, there are lots of other Power Stations that has UPS Relay function that can switch quickly between Line and Battery enough to keep PCs running. Jackery, Ecoflow, etc etc.

The idea here is to keep the AC connected at all times, which essentially bypasses the internal battery from being drawn down from, but also have an external battery to act as a DC 'charger' when the power actually goes out.

The external 24V doesn't need to be floating, but charged to 100% and left there for when the power goest out. A simple circuit that closes when AC power isnt there can act as a switch to the input of the Power Station/SolarGen to auto connect the battery to the power station when electrity is out.

So the real quesiton is, does anyone have a PowerStation/Solar Gen lying around with UPS functionality lying around to help test this scenario?

IF it does work, the masses can surely have a budget but long runtime UPS Backup solution, not just for small office use, but even for things like refrigerators, etc.
So if it's strictly a UPS, for example I have a couple river 2s. You connect your fully charged 24V LFP battery to its mppt port. you connect AC input. in the ecoflow app settings under Labs/advanced you enable the "AC always on" setting.

River 2 will power the load via pass thru. Upon failure of AC input it will switch to its internal battery, and keep itself topped off with the external 24v battery. eventually 24V battery will drop below 11V limit of DC input and river 2 will then drain its own 256Wh battery.

Be aware these units are called "EPS" because their transfer time is longer than a true ups unit, so for sensitive loads you may find it's not fast enough.

A double conversion online system with zero transfer time is not far outside your budget:

24/1200: $328

24V 50Ah: $239

ip22 24/16: $180

So you'd be at around $750+tax, provided your steady pass thru inverter load is less than 16A, assuming 26V around 400W.

edit, forgot the smart vedirect dongle so a smidge over $800.
 
So if it's strictly a UPS, for example I have a couple river 2s. You connect your fully charged 24V LFP battery to its mppt port. you connect AC input. in the ecoflow app settings under Labs/advanced you enable the "AC always on" setting.

River 2 will power the load via pass thru. Upon failure of AC input it will switch to its internal battery, and keep itself topped off with the external 24v battery. eventually 24V battery will drop below 11V limit of DC input and river 2 will then drain its own 256Wh battery.

Be aware these units are called "EPS" because their transfer time is longer than a true ups unit, so for sensitive loads you may find it's not fast enough.

A double conversion online system with zero transfer time is not far outside your budget:

24/1200: $328

24V 50Ah: $239

ip22 24/16: $180

So you'd be at around $750+tax, provided your steady pass thru inverter load is less than 16A, assuming 26V around 400W.

edit, forgot the smart vedirect dongle so a smidge over $800.
Wouldn't that be consuming power to just
1. Keep inverting 24v to AC all the time (in this case, it isnt a UPS but an always on inverter connected to an always charging battery)?
2. The issue of the micro charging of the battery will still be present, because the IP22 or IP65 chargers are always trying to keep the batteries topped up because of the inverter always pulling from the battery?

Or would the Victron IP22 be powering the Inverter directly and not charging the battery unless the inverter draws more current than the charger can give?

In any event, it defeats the purpose of trying to figure out which SoGen can work as a UPS with an extended runtime, whilst also not drawing any extra power for double conversion losses 24/7. AC Pass through is just that, it passes through.

The victron always on inverter setup is good for another area of the house, but I'm concerned about the wasted watts 24/7.
 
It's a double conversion online UPS. Yes there will be efficiency losses versus a standby/offline pass thru UPS.

In that case the ip22 would deliver enough power to feed the load and keep the battery in float. Basically battery always fully charged and charger power going to inverter.

The river 2 plus even a 12V LFP battery works fine as a psuedo UPS, understanding that the transfer time may be too slow to avoid having your electronics reset.
 
I have both an EB3A and an APC SmartUPS 1000VA converted to LiFePO4.

The EB3A can function as a UPS and I've done that for a month testing on my home computer. I have also used a battery to give it extra runtime. As mentioned, the success of the switchover time is dependent on your loads. Specifically for the EB3A, while it worked for me, the firmware for charging and fan mgmt seems broken and is massively annoying (you can find lots of info about this). So I don't personally recommend it. However, I am quite sure your idea can work with the right equipment, maybe better with some power stations than others.

On the other hand, I bought this second-hand APC UPS for $125 and put a used $45 24v LiFePO4 battery in it. The battery has 9Ah with a 20A discharge limit which supports only 400+W continuous. I originally planned to squeeze 2 batteries into it but my equipment only draws ~150W so I just installed one battery and put it into service. It works well, plus notifies my NAS when to shutdown.

My conclusion: the real UPS was cheaper and works better than the power station at being a UPS.

With that said, there are certainly advantages to the power station, e.g. portability and solar input. So it might be good enough as a UPS for some people.
 
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