LiFePo4 - UPS gets a small but important upgrade!

Hi. A while ago, I have showed you how to rebuild a Lead Acid 12V UPS into a LiFePo4 cell version. The UPS is working as expected, but there is a small problem if the battery gets drained to minimum. Let me show you what I added to improve the system...
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#LiFePo4 #UPS Battery Replacement #32650 LFP Cells

[@TYGAMatt]

I recently swapped the 7Ah lead acid for LiFePo4 cells and encountered this very same problem. So I will try this fix over the weekend. Hopefully it solves the issue. Makes total sense! 😊

[@user-tj5nk7lb8l]

Great stuff, an obvious solution when pointed out. Maybe add a low voltage cutoff relaY before reaching the bms low low safety cutoff as well. Now nee to address the difference between LAb charge curve and LFP charge (doesnt need or invite equalisation period charge - that should be minimised somehow?

[@RolandW_DIYEnergyandMore]

LFP cells don't care about any of the equalisation, absorption, etc Its just important to stay within the voltage limits. Of you want to avoid BMS cutout, then a voltage relay might be a good idea indeed

[@bkpayakorn8214]

Thank you, khun Roland. Congratulations on your 1k plus subscriber. I'm your room no.2 guest at resort. (My old account have trouble to be premium status so I use this new one)

[@RolandW_DIYEnergyandMore]

Khap khun krap khun Punyachon. Hope all is well and I see you soon again :)

[@John-xu5rr]

I have a similar problem on an old APC Smart UPS 1400. I was able to use the COM port to connect to the UPS and enter PROG mode. From there you can set the voltage calibration. What you can do is to start with a 12V lead acid battery and measure the voltage both fully charged, and then run the battery down till the UPS shuts off. Using a voltmeter at the battery posts you can directly see what the UPS fully depleted voltage is. You can then adjust the calibration constant in the UPS firmware up so that the calibrated depleted voltage in the UPS creates an actual voltage at the LFP battery posts that is above the BMS disconnect voltage. The only downside is that the UPS never registers fully charged and is likely continuously try to overcharge the LFP battery, but the BMS is cutting off the top. The other way I've tried it is to set the calibration such that the top of the voltage window is the top of the UPS pre-programmed charge window. When I do this, I need to be careful to set the maximum % allowable discharge such that the LFP battery voltage on the posts never gets below the BMS cutoff (ie: set the UPS to start shutown at 35% instead of 10%). This happened to me when I was first setting up the LFP module. Couldn't get the UPS to take a charge to turn back on. Had to rig up 24V to get the battery over the minimum UPS turn on voltage. If i was to do it again, I'd use 8 bare LFP cells for 24V and only use a balancer not a full BMS, and make sure that the top of charge window calibration was set correctly to not exceed the max charge voltage.

[@user-tj5nk7lb8l]

that second option is dangerous - not advisable and not for noobs

[@sanjalon]

thank you so much for the tip, i needed it!

[@RolandW_DIYEnergyandMore]

Glad it was helpful!

[@offgridwanabe]

Nice fix I just boost with another battery.

[@RolandW_DIYEnergyandMore]

i was tired of opening up the case periodically so i thought this was the easiest way 😀

[@sachinfilinto]

ouch !! I just ordered 3 kits with LiFepo4 batteries from AliExpress. The UPS are installed at a remote location with no human presence for a couple of weeks / months. Hopefully my UPS has a higher low-voltage cutoff. alternatives i can think of are: 1) the management software (APC powerchute) can be configured for a higher low-voltage cutoff 2) replace the BMS with a "Smart BMS" which can be configured with a higher cutoff. (expensive alternative).

[@vaughanza]

Hi Thanks for a great video. I can get a 12v Lifepo4 battery that looks like the lead acide battery and the BMS is sealed inside. How can I do the modification without cutting open the Lifepo4 battery to do this ? Thanks

[@RolandW_DIYEnergyandMore]

Hi. What you could do is use a simple 12V DC power supply in parallel to the battery over a momentary switch. So, if the UPS goes down because the battery is isolated from the BMS, you just press the switch and the UPS gets shown 12V from the external power supply and can revive its charger. Once it starts charging you can just release the switch again.

[@patelvimal3591]

Hi i had purchased 12v 12ah lipo4 battery for ups, but my ups is not able to charge it more than 14 v so it never fully charged the battery so, i can only switch on the ups using grid power, and it gives backup if grid power cut after switching 9n the ups, but problem is that is i have already power cut from grid, then i can not switch on my ups directly 9n this battery. The ups is ok as it was designed for 12v 7 ah lead acid battery and if i put old lead acids battery then it work normally. Help me to overcome this problem

[@gideonlapidus8996]

Thank you, can you still use the existing lead acid charger inside the ups to charge the lithium ion phosphate cells, how does it work?

[@RolandW_DIYEnergyandMore]

Yes, the UPS stays unchanged. The existing lead acid charger matches the main parameters of LiFePo4 as long you do not have extensive grid outages.

[@gideonlapidus8996]

@@RolandW_DIYEnergyandMore Thank you so much for the info.

[@BorgyManotoyOnline]

I tried changing my stock battery with lifepo4 but I have similar issue.. when I connected the positive and negative wires.. my ups beeps like normal (yellow light) indicating it is running on battery. When I try to plug it in.. it lights to green which is normal too. Problem is power switch seems not working. It is always on and I cannot turn if off. Also, when I try to insert a load (charger to charge my phone)... my ups lights to red and continuously beeps (monotone and irritating beep). Since switch not does not turn off. I open the ups again.. and remove the ground (black wire) so the ups turn off as well as the irritating beep. Not sure why my ups turns red with irriting monotone beep. Btw, I bought a LiFePO4 battery which looks like my original lead battery. I am not sure if there is BMS included on my bought battery.

[@RolandW_DIYEnergyandMore]

Hi. The new finished battery will have BMS built in. Maybe the voltage on the new battery was a bit to low at your test. Led it charge up on green light for a while. How much voltage do you measure on the lifepo battery when it is full?

[@1996_Dude]

i belive the best batteries to use for UPS are headway's 38120 HP. they are plenty powerfull and rated for 100% DOD compined with a simple active balancer would do the job i belive

[@user-tj5nk7lb8l]

I want to convert my 750VA APS ups into an LFP powerwall (24V x 280 Ah). So I run my day day pc load (ca 250W) off UPS and run mains/recharge ups on 8 hrs night time rate (which is 1/3rd of day time). I wonder if the UPS could handle continuose usage given that its only intended for a 15min operation on its 24V 5Ah LABs. Would be very good if it could do duty like that as a Victron equivalent is ca £750

[@RolandW_DIYEnergyandMore]

a 750w Ups can surely run a 250w load continuesly. i saw some people use ups as inverters

[@sailork3506]

Thanks for the video. Can you not just parallel a small lead-acid battery with the LIFEPO4/BMS? Since they have similar charging profiles, the LA battery should have enough juice available to trigger the UPS?!?

[@RolandW_DIYEnergyandMore]

You mean a permanently inter-connected LFP/LA combo pack? Technically it could do it. The question is only how does LFP and LA behave in parallel. The charging and discharging profiles are Not similar. LFP only has similar limiting voltages in a 4S configuration when compared to a 12V LA battery. We can use those similar voltages in our case in the UPS.

[@cdoublejj]

@@RolandW_DIYEnergyandMore according to videos on KZbin of people trying it, quite well, apparently it balances out

[@jimmybrad156]

A 4S lifepo4 battery and a 6s lead acid battery compliment each other quite nicely in parallel. The lifepo4 will do ~80% of the work before the lead acid starts 'taking up the slack'.

[@seymourpro6097]

If using a larger capacity LiFePO4 battery that the original fitment use an additional charger direct to the battery to charge in a reasonable time and charge regardless of the BMS.

[@RolandW_DIYEnergyandMore]

Yes, by increasing the complexity there would surely be some ways to go around the BMS issue and your suggestion is valid. But all this is adding up in money as well. It's everyone's decision how much it is worth to him to upgrade what was a rather cheap product in the first place. And the question will then still be how many times will the UPS fully discharge...

[@dv42300]

Thanks! I've been looking for this exact fix. I'm just getting into electronics and am very cautious. I was thinking of buying a DC to DC charger. Good one from Renogy to put between the ups and lithium battery with built in BMS...... anyone rolling their eyes yet?😅

[@RolandW_DIYEnergyandMore]

Don't know if that works as the DC-DC converter will make the battery invisible for the UPS controller. It will not know how long to charge, how to discharge, low voltage state, etc. DC to DC converters are cheap. Just try it ;)

[@dv42300]

Yes you are correct! I was going to complicate it further with relays somehow with some sort of delay so it won't loop. Hope I'm explaining this well

[@dv42300]

I think I've watched too many battery fires LoL but I do understand how safe these are or I wouldn't even try this

[@dv42300]

Thanks for the reply

[@dv42300]

I should mention I'm concerned about the charging amps. If the DC to DC converter can output 20a does that mean any battery attached to it will take 20a and cook itself? This is the reason I was thinking of a battery with built in BMS. A little bit of knowledge is a dangerous thing.....

[@raycunning4906]

Hi i have a SyberPower ups that usess two lead acid batterys in series, can i use LFP batterys and will it charge? I am buying two LFP batterys with built in BMS. And how do i get to hook the switch up on thoese batterys?

[@RolandW_DIYEnergyandMore]

Hi. I would buy either 8x LFP cells or a 24V LFP battery if available. Using one BMS is easier then having 2 sets of packs inside. If you have 2 LFP batteries in series, each of the 2 BMSs might disconnect when a cell is low. So you would need to open up each battery and solder a bypass switch to the mosfet bank. You would then have 2 switches and in case of a reset, press both simultaneously.

[@raycunning4906]

@@RolandW_DIYEnergyandMore Hi thank you for your video's and your time and for reaching out to me so quick. Have a grate day.

[@AliceTaylor98]

Eaton UPS available for stock，Happy cooperation.

[@coz0015]

how to charge the lifepo4 4s? how many voltage ups did to charge the battery

[@RolandW_DIYEnergyandMore]

there is nothing to change. the built in ups charger will do it similar as if there is a lead acid battery inside.

[@coz0015]

@@RolandW_DIYEnergyandMore I believe lifepo4 4s need 14.5 to full charge so if using ups charging is only 12v? so lifepo4 will keep charging or can be full with only 12v

[@RolandW_DIYEnergyandMore]

@@coz0015 lead acid battery is charged to around 14V as well

[@Da_enex]

Which bms did you use , is it 4s or 3s

[@RolandW_DIYEnergyandMore]

This is a 4s LFP BMS

[@nsingh1393]

@@RolandW_DIYEnergyandMore What is the A rating (im assuming A is for Amperage)? I am planning on getting 4s 100A BMS, will that work?

[@RolandW_DIYEnergyandMore]

@@nsingh1393 yes BMS's are rated for maximum amperage. Sometimes there is a different rating for charge and discharge. What are you using a 100A BMS for? Must be a battery bank for a big UPS then...

[@nsingh1393]

@@RolandW_DIYEnergyandMore No, Just a small UPS, similar to yours. It has small 12v 4.5Ah SLA battery that has been replaced 3 times. Approximately once every year. Should I use 30A BMS like the one you are using? and drawbacks to using 100A?

[@RolandW_DIYEnergyandMore]

@@nsingh1393 right. But a 100A BMS will probably be much bigger then the 30A board that I have used. It might not fit into your UPS.

[@b1on1cdog48]

Seems like a hassle, cant you use a relay instead of a manual switch?

[@RolandW_DIYEnergyandMore]

A relay? Don't forget the UPS is dead at that moment as the battery is disconnected and must stay like that as long as there is no AC present to not further drain the cells. That relay would have to be activated once AC is back on and just make contact for a few seconds. Then the override must be released to allow proper BMS function. You would have to build a control circuit around that feature powered by a separate AC power supply, etc. Sure, that would be doable if required for your application. The manual switch isn't a solution for a system in a remote location but for the typical case of home UPS it will suffice.

[@BruceMallett]

I had the same thought. A bridge rectifier, a DC relay, a capacitor, and a resistor (and maybe a diode to shunt the relay?) should work to make a circuit that does the same as the switch and is on only until the cap. charges up. In this way one does not have to be home to hit the switch when the power comes back on, no?

[@RolandW_DIYEnergyandMore]

@@BruceMallett I don't think it's going to be so easy as the UPS control needs to power up first, then you have to give it enough time to "see" the battery at the relay reset, etc. A small microprocessor like an arduino mini pro with a relay board, programed to make a onetime contact (3-5 sec) after maybe 10 sec of AC available.

[@sachinfilinto]

also.... i don't agree on your cost comparison ( at least for the long term) cause LiFePo4 batteries have many more times the cycle capability hence you dont have to replace the batteries often like lead acid. also... less of trouble for many years. hence in the long terms cheaper then Lead Acid.

[@gee620]

its been a year since you created this project, so how was it now after a year??? still working/? did it blow up? update us.thanks

[@RolandW_DIYEnergyandMore]

Yes, the UPS is still working fine. It just turned out thet the cell which i got where used so the capacity isn't that great, but else all OK. Nothing blew up yet ;)

[@patelvimal3591]

Hi i had purchased 12v 12ah lipo4 battery for ups, but my ups is not able to charge it more than 14 v so it never fully charged the battery so, i can only switch on the ups using grid power, and it gives backup if grid power cut after switching 9n the ups, but problem is that is i have already power cut from grid, then i can not switch on my ups directly 9n this battery. The ups is ok as it was designed for 12v 7 ah lead acid battery and if i put old lead acids battery then it work normally. Help me to overcome this problem

[@coastdownhills]

Same issue here.

[@patelvimal3591]

Hi i had purchased 12v 12ah lipo4 battery for ups, but my ups is not able to charge it more than 14 v so it never fully charged the battery so, i can only switch on the ups using grid power, and it gives backup if grid power cut after switching 9n the ups, but problem is that is i have already power cut from grid, then i can not switch on my ups directly 9n this battery. The ups is ok as it was designed for 12v 7 ah lead acid battery and if i put old lead acids battery then it work normally. Help me to overcome this problem

[@RolandW_DIYEnergyandMore]

Hi. 14v is 3,5v per Lifepo cell. That is considered full as there is only maybe 5% extra capacity left. And as your pack is 5Ah bigger than the original lead acid one, I don't understand the problem. Do you have extensive power cuts which cannot be managed by that battery size?

[@patelvimal3591]

@@RolandW_DIYEnergyandMore these batteries give enough power backup but i have only one problem that is if there is already power cut and i want some urgent work to do on my pc i can not wake the ups directly on battery. Thats the problem which i want to overcome, thanks for the quick reply...

[@RolandW_DIYEnergyandMore]

@@patelvimal3591 OK, i guess that the UPS control board is not satisfied with a parameter for a restart without AC available. How about if you connect the external lead acid battery in parallel with the LFP pack via a momentary switch just for a restart attempt. And when the UPS restarts, just release the switch.

[@patelvimal3591]

@@RolandW_DIYEnergyandMore don't understand what u want to say, do you have any link for that?

[@RolandW_DIYEnergyandMore]

I just mean that you wire up the lead acid battery in parallel with the lifepo battery. Plus to plus, minus to minus. But not permanently, only when you want to restart the ups without grid. And only for short, for the purpose of the restart, like a jumpstart of a car... maybe the ups would then see the battery differently