APC Smart UPS + EG4-LL

[Runaway Tractor]

Lets say I have an APC Smart UPS SMX750 which is $310 with shipping and tax. It is designed for 48 volt battery packs (can you guess where I'm going with this). The APC battery packs are lead acid batteries, (2) parallel strings of (4) 12v 9a SLA batteries in series (48v 9a x2) per pack totaling ~90 amps or ~900wh per pack. I believe it can take maximum of 5 external packs, so a maximum of 4.5kwh of battery storage. Each external pack has a 1kohm resistor on a sense circuit to tell it how many packs are connected (pleasantly simple...). Each external pack refurbished costs $500 x 5 plug shipping and tax for $2,750 for the maximum APC packs.

What if instead I used a single EG4-LL 48v battery? At 100amps or 5.1kwh of battery storage, it is slightly more storage than the maximum quantity of APC packs and the same nominal voltage as the SLA (I think). The EG4 battery with shipping and tax is $1,623. The cost of 3 APC packs. So 5 for the price of 3 basically.

A grand total of $2,000 would give me 14-16hrs of UPS run time on my rack. What I do not know is if there is any reason to believe the APC SMX750 UPS couldn't recharge the EG4 battery?

Why do this instead of something like an EG4 3000? Communication. All of my computers, servers, home assistant, and other gadgets can communicate using APCUPSD for runtime and safe shutdown.

 

[Brucey]

I would suggest an ecoworthy 5kWh rack mount for $840 shipped. Or two for a little more than one eg4 ll shipped.

48v (51.2v) 100ah Server Rack Batteries

The Eco-worthy Server Rack Battery 48V(51.2V) 100AH provides reliable energy storage for server racks.Versatile connectivity(RS485/CAN/RS232, Bluetooth/WiFi), robust safety features, 6000+ cycles (80% DOD), and a 10-year warranty make it ideal for various applications. Supports up to 15 parallel...

www.eco-worthy.com

One of the thing to watch out for is usually a smaller ups has a limited charge circuit and duty cycle. But sounds like yours is designed to potentially charge a decent amount of capacity when daisy chained. Just be aware the charge rate may be rather slow from the apc.

 

[Brucey]

LFPs don't like to be held at full charge at higher voltages continously. Do you have control over charge voltages in the apc?

 

[MakeMePower]

LFPs don't like to be held at full charge at higher voltages continously. Do you have control over charge voltages in thread apc?

Ups's typically charge to float voltages on cheap units. they use standby charge profiles. which means his unit would generally not get charged over 60%, I don't know if the larger units has stages, the cheap ones don't

 

[robbob2112]

Not a good idea

Best idea is to get an inverter that does pass-through and set it for prefer AC or prefer DC....

Something like either of these, they are what I am using

Amazon.com

Amazon.com

They are basically the same gut with a size difference torrid coils/transformers.

They make a good UPS with 5 to 10ms switch-over. I have them plugged into a heavy duty wall timer so it runs from battery until the SOC is around 50%. Just takes a little calculation to guess at the time.

 

[Runaway Tractor]

LFPs don't like to be held at full charge at higher voltages continously. Do you have control over charge voltages in the apc?

Honestly I don't know. But I assume nearly full since it's designed for SLA batteries.

Not a good idea

Best idea is to get an inverter that does pass-through and set it for prefer AC or prefer DC....

Something like either of these, they are what I am using

Amazon.com

Amazon.com

They are basically the same gut with a size difference torrid coils/transformers.

They make a good UPS with 5 to 10ms switch-over. I have them plugged into a heavy duty wall timer so it runs from battery until the SOC is around 50%. Just takes a little calculation to guess at the time.

Not a good idea how?

 

[wpns]

What I do not know is if there is any reason to believe the APC SMX750 UPS couldn't recharge the EG4 battery?

The builtin charger expects lead-acid and Lithium has different charging requirements. Plus, lithium is made for cycling, and does not react well to standby operation, as even a slight bit of overcharge during “float“ operation can lead to lithium plating and permanent capacity loss.

 

[Runaway Tractor]

I would suggest an ecoworthy 5kWh rack mount for $840 shipped. Or two for a little more than one eg4 ll shipped.

48v (51.2v) 100ah Server Rack Batteries

The Eco-worthy Server Rack Battery 48V(51.2V) 100AH provides reliable energy storage for server racks.Versatile connectivity(RS485/CAN/RS232, Bluetooth/WiFi), robust safety features, 6000+ cycles (80% DOD), and a 10-year warranty make it ideal for various applications. Supports up to 15 parallel...

www.eco-worthy.com

One of the thing to watch out for is usually a smaller ups has a limited charge circuit and duty cycle. But sounds like yours is designed to potentially charge a decent amount of capacity when daisy chained. Just be aware the charge rate may be rather slow from the apc.

I like. Since I'm not powering the house, I don't mind value engineering to a budget friendly battery, as long as it is safe and respected for what it is. Which looks to be the case.

 

[robbob2112]

Honestly I don't know. But I assume nearly full since it's designed for SLA batteries.



Not a good idea how?

The builtin charger expects lead-acid and Lithium has different charging requirements. Plus, lithium is made for cycling, and does not react well to standby operation, as even a slight bit of overcharge during “float“ operation can lead to lithium plating and permanent capacity loss.

@wpns has it perfect - the voltage is low for LFP, the cycles are wrong, and it will lead to premature battery failure - how premature - I don't know.

I have a APC smartUPS 2200 that I used for many years and I even repaired it once from a bad design choice, 2 resistors in the charge circuit had changed value and chared the outer coating. They were originally 1/4W resistors and needed to be 1W from calculation - I put in 2W resistors and up away from the board to allow for airflow.

Anyways,
That unit charges at 54.5v -- just simple constant voltage with a max current limit- it leaves the the battery to limit the current as it fills up... so you would be constantly applying that voltage to your battery 24x7x365 ... And you would never reach a correct voltage for LFP. There is a potentiometer to adjust the charge voltage with a range of 52v -55.5v if those same two resistors haven't changed values.

Now, if you have the same revision of board as I did - it was common on UPS from 2200~3000 for a while - I could dig it out notes and take a pic before I toss the thing in the trash... and you could adjust their value to move the range up or down but it would probably mean failure of some other part of the circuit.

So, do yourself a favor and stick to an inverter/charger that is designed around LFP batteries.

 

[Runaway Tractor]

So, do yourself a favor and stick to an inverter/charger that is designed around LFP batteries.

Understood now, that makes sense.

I want to stick with APC for the UPS. Maybe what I need is a big ass 48v SLA battery?

 

[robbob2112]

Understood now, that makes sense.

I want to stick with APC for the UPS. Maybe what I need is a big ass 48v SLA battery?

IF you are determined to stick to APC then a large SLA bank is really the only way to do it.

Just a note - the charge circuit is designed around a certain size SLA battery - and if you increase the size beyond that it will run longer and generate more heat.

If you are worried about noise in the sine wave or surges then the bettery solution is to have an inverter connected to a LFP battery and it runs from that all the time. Good clean power. Now get a charger that is larger than your load and connect it to the battery and put a timer on the AC line to cycle it periodically - like 8hrs a day - So you always run from battery and you cycle the LFP to keep it happy. You can adjust the timer so it allows around 30% discharge before recharging... or connect a RPi and program it to just loop the cycle - 70% SOC to 100% SOC and repeat. And the RPi could trigger a clean shutdown of the server connected to it. There are a variety of utilities that you can install for this.

The expertpower I linked above in prefer DC does this sort of thing, but a non-adjustable 60% cycle. So at the low point it is at 40% SOC (based on voltage only) and if I had an outage at that time it would not run long.

The downside of double conversion UPS is there is always waste energy from efficiency losses.

 

[Runaway Tractor]

The reason I want to stick with APC is due to the network communication. My desktops, servers, Home Assistant, Raspberry Pis, and PFsense firewall can all communicate with APC using the apcupsd. I have everything configured to stage safe shutdowns in inverse order of priority. And I get push notifications. This is all just not possible with any of the AIOs, inverters, etc.

Seems that (4) 12v 100ah SLA batteries are pretty economical. I'll have to build and enclosure and wire it up more than a single packaged server rack battery. But I like that stuff.

 

[robbob2112]

I thought code red could do notifications like you describe for the RPI

 

[Runaway Tractor]

I use Home Assistant to send me push notifications with data from the UPS (outage, run time, etc). All the various inverters and AIOs have with no way to connect to convoluted complex schemes. Then I'd need to make various automations to shutdown some of my stuff. It is not practical.

 

[robbob2112]

I use Home Assistant to send me push notifications with data from the UPS (outage, run time, etc). All the various inverters and AIOs have with no way to connect to convoluted complex schemes. Then I'd need to make various automations to shutdown some of my stuff. It is not practical.

then I am out of ideas

 

[robbob2112]

Actually I have one more... many of the AIO inverters have a dry contact relay to start generator when the batteries are low.

If you were to use the box running apcupsd to detect that relay closing you could then send the shutdown signal... I know the program called NUT used to be able to do that based on the serial connector designed for it. There are any number of devices that will do it on adafruit's website...

They aren't trouble free, but they aren't a mountain of work either... you could even skip the dry contact and use a voltage hat on a pi to send a signal for shutdown..


Now I am out of ideas, I hope you figure it out and post back your solution

 

[Runaway Tractor]

I need more than just a single indicator from contact closure. APCUPSD tells me line voltage, status, SOC, estimated run time, etc. I can set my devices to shutdown based on different runtimes. Non critical devices go first. Then servers at the last few minutes. If this was battery backup for the house on a solar system, the use case would be different and the EG4 data through its various steps of integration would be fine. But controlling a rack of equipment needs a purpose built solution.

 

[RobertDari]

APC Smart SURT UPS works well in setups where pure sine wave output is needed, but keep in mind that these units can be picky with battery compatibility. If you're thinking about swapping out lead-acid for lithium, check the low voltage cutoff and charging parameters. Some models may throw errors or not charge properly if the BMS disconnects under load. Matching specs carefully saves a lot of headaches.

 

[robbob2112]

Have you looked at node red?

 

[speculant]

I have looked into this before. You don't want to recharge Lifepo4 with an SLA charger because the charging profiles between the two battery chemistries are different. If you want to use your APC Smart-UPS with your Lifepo4 battery pack, maybe you could bypass the UPS's charging circuit altogether by using some of these when connecting the Lifepo4 battery to the UPS battery connector: https://www.amazon.com/LCLCTC-Solar-Anti-Reverse-100Amp-Voltage/dp/B0C8N7LQGN then, just use an external Lifepo4 charger. I would say if you do that setup, cycle your Lifepo4 batteries on a regular basis so they aren't just sitting at 100% full for extended amounts of time. If it was me, I would cycle the Lifepo4 batteries once per week. Maybe you could set up a high amp smart plug on both the APC AC input and the Lifepo4 charger and set a schedule to turn both of for a set amount of time, enough for the Lifepo4 battery to get down to about 30% or so, and then turn both back on. I haven't ever set up a system like that, so it's just an idea, I'm not sure if it would work for you.