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Replacing UPS lead acid batt w LiFePO4

JWLV

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May 27, 2020
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There has been some discussion in the past about putting in a LiFePO4 battery in a consumer grade UPS. There were no real conclusions except everyone sort of agreed that it would work, but no one has actually done it.

Well, I'm going to do it tomorrow. I have a small APC UPS that has a dying lead acid battery. I've ordered a Chins 12v 8Ah LiFePO4 battery that will be delivered tomorrow. The current battery is kind of an odd size at 6" x 3.75" x 2". It's that 2" which is kind of odd. It rather thin at 2". But when I opened up the APC UPS, there was a spacer inside that is about 1/2" thick. So I just used some tools and cut off the plastic spacer so that it should fit the Chins battery. Chins specs says 5.96 x 3.72 x 2.55 inches. Everything else should be plug and play. See attached pictures. I'll update this thread after I install it tomorrow.

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The specs say the continuous discharge rate is 8A and the max is 24A.
I'm not too concerned about that because the only devices I connect to the UPS side is a cable modem, router, and ethernet hub. They are all low power devices. I have a few other devices connected to the surge-only side/non-UPS.

Later today when I hook it all up I will run some tests. I'll pull the AC plug and see how well it holds up.
 
UPS rating is 450 VA / 257 watts. Max battery draw is about 35 amps., but your loads are likely in 100 watt range so about 8 amp range.

Check to see if UPS does absorb cycle. It should go to about 14.4v volts then drop back to about 13.8 vdc. This is needed to keep cells balanced.
My guess is it will do an absorb cycle whenever there is some backup event and when you first plug it in. Best if you can get it to do an absorb cycle at least every 3 to 6 months to keep cells balanced.
 
Just got the new battery. It's a perfect fit! Even the connector clips fit perfectly. It's now connected to the mains power so that the battery will charge. The UPS isn't complaining, no beeps or warning lights.
 

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LOL Yep. I have a label maker just for that!
I was reading up the specs for this UPS. It says that it charges the battery at 2 watts. It also says that when installing the UPS for the first time to let it charge the battery for 16 hours. So I assume the original lead acid battery is somewhere around 32 Whr. I should be getting at least 2x the backup time with the LiFePO4 battery in case of a black out. I'm pretty happy about that. The new battery is happily settling in the UPS at 13.3V right now. The manual does not say anything about an absorb cycle. I have no idea if it will do it or not. If I had to guess, probably not. This is a cheapo UPS and I don't expect it has anything that would help prolong its life.
 
Thanks for this post. I have several UPSs with bad batteries and have been thinking of doing this same thing. Please keep us updated on how this works long term.
 
Dish Doc, please keep us posted when you do decide to swap out your SLA batteries for LiFePO4 in your UPS. I'd like to see how it's working out for others.

So far, my upgraded APC UPS is operating normally. It's working so well that I've forgotten about it. :)
 
I have been using an APC Smart UPS 1500 for about 15 years to provide backup power to multiple devices. I removed the internal batteries and brought out the wires to two 12v car batteries. This worked well but lead acid batteries are a pain, require maintenance, should not be discharged too much, and did not last that long (~3 years). A couple of years ago, I replaced them with eight 120AH LiFePo4 batteries for use on my current SMT1500. These are wonderful and I have had virtually no issues. The only minor issue is that the time remaining display is meaningless since I guess it assumes you only have the original batteries installed. So after a few minutes of a reasonably load, it sounds the warning beeper (which I have to manually silence) but it keeps running just fine for many hours or even days. I live in Northern CA where we have had power shutoffs for 2-3 days, but the UPS kept running the entire time under a fairly light load.

The UPS charges the batteries to 3.42v each, which is just about perfect (>99% charge.) It also automatically cuts the power at around 2.75v; also about perfect. I did use a BMS, although I am not sure I really needed it. Of course, the charging rate is low at about 3A, but since power outages are rare, this is not an issue. I do not care if it takes a week to recharge it, although I do have a 24v LiFePo4 charger just in case.

This works so well, I am actually in the process of upgrading them to 304AH batteries that I just received and will use my old batteries for a similar backup system at another house that still uses car batteries.
 
I have been using an APC Smart UPS 1500 for about 15 years to provide backup power to multiple devices. I removed the internal batteries and brought out the wires to two 12v car batteries. This worked well but lead acid batteries are a pain, require maintenance, should not be discharged too much, and did not last that long (~3 years). A couple of years ago, I replaced them with eight 120AH LiFePo4 batteries for use on my current SMT1500. These are wonderful and I have had virtually no issues. The only minor issue is that the time remaining display is meaningless since I guess it assumes you only have the original batteries installed. So after a few minutes of a reasonably load, it sounds the warning beeper (which I have to manually silence) but it keeps running just fine for many hours or even days. I live in Northern CA where we have had power shutoffs for 2-3 days, but the UPS kept running the entire time under a fairly light load.

The UPS charges the batteries to 3.42v each, which is just about perfect (>99% charge.) It also automatically cuts the power at around 2.75v; also about perfect. I did use a BMS, although I am not sure I really needed it. Of course, the charging rate is low at about 3A, but since power outages are rare, this is not an issue. I do not care if it takes a week to recharge it, although I do have a 24v LiFePo4 charger just in case.

This works so well, I am actually in the process of upgrading them to 304AH batteries that I just received and will use my old batteries for a similar backup system at another house that still uses car batteries.

Nice.

To be clear, you do need a BMS. Cells will drift even when being held at a constant voltage as they all self-discharge at different rates. You need the BMS to compensate unless your cells are truly perfectly matched.
 
@JWLV those cheap units have a garbage waveform. Read the printing on the underside. I would purchase a good pure sine unit before throwing any more money at it.

Some UPSs ignore the battery voltage and will shutdown on time. They are designed to run out of battery just before they overheat. Additional info: Testing an APC 600W UPS by powering my fridge

I recommend the APC “XL” models that are bulletproof, pure sine and rated for continuous operation. Watch eBay for used units with a bad battery. Downside is the fans are a bit noisy when acting as an inverter.
 

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While I agree that some UPS models have crappy waveforms, the APC SMT1500 is a nice sine wave. I compared the normal line waveform to the UPS on battery and actually had to repeat it because the UPS output on battery was much cleaner than my line voltage, although that could be related to the much different loads. It does not shut down as long as the battery has power, although the battery life indicator seems to be time/load dependent and is useless.
 

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Good video illustrating the cheap UPS garbage sine. @caesarv What is the full model number of your SMT1500? Does the fan constantly run on UPS power regardless of load?

 
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I have done three CyberPower UPS conversions using Zooms 6ah batteries. They have been working fine, but they have definitely sacrificed their output ability. These use two batteries in series for 24v, so you only get about 130W max output, which is enough for my Orbi's and Wyze cameras around the house.
 
Wow. I just looked closely at the second photo posted by the OP. Model BN4001, and harmonic distortion is listed at 45 percent. Yikes!

I've always wondered if the UPS that looks like a slightly fatter outlet strip compromised quality. I guess I have my answer!
 
I have been using an APC Smart UPS 1500 for about 15 years to provide backup power to multiple devices. I removed the internal batteries and brought out the wires to two 12v car batteries. This worked well but lead acid batteries are a pain, require maintenance, should not be discharged too much, and did not last that long (~3 years). A couple of years ago, I replaced them with eight 120AH LiFePo4 batteries for use on my current SMT1500. These are wonderful and I have had virtually no issues. The only minor issue is that the time remaining display is meaningless since I guess it assumes you only have the original batteries installed. So after a few minutes of a reasonably load, it sounds the warning beeper (which I have to manually silence) but it keeps running just fine for many hours or even days. I live in Northern CA where we have had power shutoffs for 2-3 days, but the UPS kept running the entire time under a fairly light load.

The UPS charges the batteries to 3.42v each, which is just about perfect (>99% charge.) It also automatically cuts the power at around 2.75v; also about perfect. I did use a BMS, although I am not sure I really needed it. Of course, the charging rate is low at about 3A, but since power outages are rare, this is not an issue. I do not care if it takes a week to recharge it, although I do have a 24v LiFePo4 charger just in case.

This works so well, I am actually in the process of upgrading them to 304AH batteries that I just received and will use my old batteries for a similar backup system at another house that still uses car batteries.
Sounds Great.
I make my UPS Batteries with BMS. Since the UPS acts as a BMS, controls the charging max and min voltages. >10 working without a glich..
 
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I just completed my upgrade to 304 AH batteries. I used a 100A BMS just in case, although the max load is about 50A. Under normal conditions, a BMS may never be needed...but you never know...and it can't hurt (except my checkbook.)
 
Sounds Great.
I make my UPS Batteries without BMS. Since the UPS acts as a BMS, controls the charging max and min voltages. >10 working without a glich..
No it does not, it acts as a charger and a load, working only on overall battery values, the UPS may read 12.8v at the battery terminals but inside cell one is 3.6v cell two is 3.6v cell three is 3.6v and cell 4 is 2.0v
 
No it does not, it acts as a charger and a load, working only on overall battery values, the UPS may read 12.8v at the battery terminals but inside cell one is 3.6v cell two is 3.6v cell three is 3.6v and cell 4 is 2.0v
Exactly what I meant.
To prevent the 2V you mentioned: Use High Quality, Reputable Cells. Top Balance in parallel. Then Connect in Series.
Process is everything
 
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