# Question about using LiFePO4 in a UPS



## theforce (Jan 1, 2010)

I've done some searching on UPS battery backups that use pretty much anything other than lead and I cant find much out there. Just about everything I search for on LiFePO4 batteries points to this forum. So I hope I can get some help here and point me in the right direction.

I was wondering about converting a UPS to use LiFePO4 batteries.

I found this battery for sale.
http://www.batteryspace.com/lifepo4...with10timeslongerlifeand597lighterweight.aspx

It says its a direct replacement for SLA. This is perfect since its the same size as the one I want to replace.

The problem I see with using LiFePO4 in the UPS is the charging of the battery.

My question is can I just let my UPS charge the 12.8v LiFePO4 battery since its about the same voltage or do I need to use a LiFePO4 charger?

If I must use a LiFePO4 charger can anyone suggest the best way to get my UPS running on LiFePO4?

I know a little about electronics and can either do adjustments to the main board of the UPS or disable the charging if that is even possible.

So my two ideas are...

1. let the UPS charge the LiFePO4
or
2. disable the charging circuit of the UPS and find a LiFePO4 charger that will charge and do a float charge. 

If I do option 2 would there be a charger that could just sit in line with the battery? something like UPS>charger>LiFePO4

If I can disable the the UPS charger and still have it use the batteries charge is there a charger that would allow me to do a float charge 24/7? I could have the charger hooked up to a standard wall outlet so when the electric goes out the charger would turn off. That way the UPS does not try to suck the juice from the charger when the electric goes out.

I hope you understand what I'm trying to do.


I'm wanting to convert my UPS for two reasons.

1. I have to keep replacing the lead batteries every other year and I hope that LiFePO4 will just last longer. I don't really care about extended run time of the UPS just the longevity of the battery.

2. I want to understand how to use LiFePO4 on a smaller scale because in the near future I hope to convert larger objects like an electric cordless push mower and an electric riding mower when the lead batteries die.



Just to let you know I have a 2006 Toyota Prius that has been converted to a plug in using the Hymotion battery. So I hope I'm not too out of place here.  I can go to the grocery store and back on all electric. My best tanks on my normal commute to work are 299mpg ( about 117mpge when you include the electric) and 2750 miles without stopping for gas.


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## Amberwolf (May 29, 2009)

That unit says it has a built-in PCB, Which is probably a BMS that handles charge and discharge voltages and currents to literally make it a drop-in replacement for an SLA. If so, then there is nothing you need to do besides doing just that. SInce they list UPS among it's applications, I see no reason it shouldn't be a drop-in-and-forget-it replacement. 

That said, a hundred bucks is awfully expensive for your usage of it, since you don't need the lighter weight it provides, and you'll hardly ever be cycling it (assuming not a lot of power failures where you are), so it's higher number of cycles compared to SLA isn't all that relevant. 

It only has a 30-day warranty, so anything that goes wrong with it (and it's fairly complex, so there are a lot of possible things to go wrong) had better do so right away, meaning you'll need to test it thoroughly and repeatedly within that time.

Since an SLA 12V 7Ah bought locally should cost only about 1/3 or even 1/4 to 1/5 of that, if each one lasted you two years, it'd probably be more cost-effective to keep replacing with SLA, assuming 6 to 10 years of life with the SLA. I don't know what the expected life is of this unit; it could be anything from 3 to 10 years. 

Also, take note that BatterySpace has a habit of posting "sale prices" that aren't much of a sale (if any), because they raise the "regular" price to show you how much you'd be "saving" with the "sale" price. (just google for a specific URL of a product on their site, and compare the cached version with the current one; usually there's a huge difference in "regular" price if the cached version is from before the "sale").

EDIT (ADDED): As far as it being educational in how to use LiFePO4 elsewhere, it doesn't seem like the way it is designed (drop-in SLA replacement) will make it any different for your experience than using SLA, except that it is lighter and would last longer than a single SLA battery (most likely). 

That said, the little BMS board they use is interesting, as it would allow creation of 12V units of lithium, but the board itself costs more than a 7Ah SLA....  And it is only for LiFePO4, not for Li-Ion (which would make it useless for my own projects.  ).
________
Vaporizers.


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## BMI/LiFeTech (Aug 12, 2009)

The Batteryspace option you have suggested would be a waste of money.
This is why.
They claim 10 times the life of lead acid but are only willing to provide 30 days warranty! 
So your money is down the drain when the battery fails in 6 or 12 months.
I have seen this happen so often with cheap Chinese LiFePO4 batteries.
There is good reason why they are not prepared to provide a decent warranty of a couple of years or more.
So you basically have two options.
Either just stick with cheap SLA batteries as amberwolf has suggested or if you definitely want to go LiFePO4 then pay the money to buy a quality battery with long warranty which will provide reliable performance.

You will need to use a LiFePO4 charger since the end of charge voltage of the onboard chargers fitted to UPS's are designed for SLA batteries and if you fit a LiFePO4 battery the battery won't be able to become fully charged due to the lower end of charge voltage. 
There are a few different options available for charging which I would be happy to explain in more detail if you wanted more specific information.


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## theforce (Jan 1, 2010)

Well $100 is a bit much for a UPS battery but if it works like I want it to I may try to use it in other devices that use 12v. Plus if the batteries did go bad it would not be the first time I burned $100. 

For me spending $100 on this is really nothing. Even if it is a direct drop in replacement I wont mind because that it really what I'm really looking for in replacing every day 12v lead batteries. But if I need to actually do some modifications and have a separate charger and BMS thats fine too as I don't mind learning along the way.

As far as getting a full charge with the LiFePO4 in a UPS I don't really care about a full charge because one of two things happen.

1. If I'm at home and the electric goes out the first thing I do is shutdown all computers that are hooked into a UPS. I can do that with in minutes.

2. If I'm not at home when the electric goes out I don't have any UPS monitors hooked into the computers so they just keep going until the battery dies. For my lead batteries this means they go to a pretty low voltage. I'm pretty sure this is why my lead batteries die pretty quick.

Now if the battery I pointed to cuts off at 10v because of the BMS then that should save the battery from dieing. And if the BMS limits the charge to 15.2v and the UPS only charges to 14.5 that should keep the battery in the SOC range of maximum life.

BMI/LiFeTech I am open to any info you can give. Is there a place that offers LiFePO4 with long warranties?

From my understanding of the Thunder Sky batteries and ones like it the reason why they fail is mostly because of a bad BMS. Since the TS cells vary in capacity so much when discharging them from a full balanced state one cell will reach say 2v before the rest. Then as you keep discharging that one cell keeps going down and by the time the other cells reach 2.6v or whatever that one low capacity cell is now at 0v and dead.

Now if you keep that one low capacity cell with in its limits and keep the other cells in their limits there should not be any problems.

Please correct me if I'm wrong as I'm still learning about LeFePO4 and BMS.


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## BMI/LiFeTech (Aug 12, 2009)

theforce said:


> Well $100 is a bit much for a UPS battery but if it works like I want it to I may try to use it in other devices that use 12v. Plus if the batteries did go bad it would not be the first time I burned $100.
> 
> For me spending $100 on this is really nothing. Even if it is a direct drop in replacement I wont mind because that it really what I'm really looking for in replacing every day 12v lead batteries. But if I need to actually do some modifications and have a separate charger and BMS thats fine too as I don't mind learning along the way.
> 
> ...


It sounds like you have quite a good understanding already of LiFePO4.
Yes your example of varing capacity of Thundersky cells is pretty accurate. Of course there are several reasons for this including poor quality control during manufacture.

To my way of thinking is is far smarter to spend around $300 on a really top quality battery which will give reliable service for up to 10 years rather than spend $100 on a battery which has a very high liklihood of failing in 12 months. As you mention if you can use the same battery for multiple applications such as UPS, camping, fishing trips, etc. then it works out to be very economical.

You could say I am pretty familiar with batteries used for UPS applications since in my last job (before my current position representing one of the few makers of quality Phostech licenced LiFePO4 batteries) I was the senior electrical engineer for one of the world's largest UPS companies. I have commissioned new UPS systems used in critical power aplications, performed contract UPS maintenance and replaced literally thousands of lead acid UPS batteries over the years for companies such as IBM, Apple Computer, Exxon Oil, McDonalds, Coca-Cola, GE...etc..(to name a few of my former customers from my time in the UPS industry).

On our Lifetech XPS LiFePO4 packs we provide 5 years / 3000 cycles (100%DOD) warranty for our batteries when used for standby power applcations such as UPS, solar power etc.
We just shipped the first lot of batteries to China to power solar powered street lighting. The Chinese are smart. They won't use their own product like Thundersky because they know the poor quality of their product and how it is made. They would rather use a quality battery themselves and import it for their own use. They make poor quality batteries such as Thundersky which are cheap by lithium battery standards, not provide any warranty and sell them to "silly westerners" who think they are getting a bargain priced LiFePO4 battery. 

As I said before, if you have mulitiple applications for the same battery it makes far better sense to pay the extra for a quality battery.
I have a customer who has just ordered 12V batteries (12 packs) which will have mulitiple uses. They will be used to store power charged by the solar panels which the customer has recently had installed on the roof of his house. The same batteries will also be fitted with quick connect/disconnect plugs so they can be fitted in the customer's trailer of a recreational vehicle since the owner travels around the countryside a few months of the year. Two of these batteries will also be used to power an e-bike which travels in the recreational vehicle.
It is all about getting the most use and value from your battery investment!

Below is a photo showing some of the batteries in our factory which are about to be packed in readiness for shipping to China to power solar lighting in that country.


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## major (Apr 4, 2008)

theforce said:


> But if I need to actually do some modifications and have a separate charger and BMS thats fine too as I don't mind learning along the way.


Hi theforce,

I've seen your post here and am interested. I live out in the sticks and use some UPS units as back-up power. I was able to buy some nice ones for very cheap, from 1.3 to 4.3 KVA. Both 120 and 240 VAC output. Smaller ones are 12VDC and larger are 48 VDC. Also have a 500 VA small unit.

My theory is that UPS units have crummy battery chargers. This makes the Pb-Acid batteries go bad in a few years. Places don't want to replace batteries, so sell off the whole unit cheap. So what I do is remove the old batteries and use whatever I have on hand, usually AGMs left over from an EV project. They are down on energy density, but good enough to run my well pump or refrig for a few hours.

I don't even bother trying to use the battery charger in the UPS. I use a trusted stand alone charger. So, I guess I'm saying, beware of the UPS charger. And from what I see, there is little chance you can adjust it.

I have come across some surplus lithium batteries which I might try on my UPS stand-by system. So, I am interested in your story here. I also have some Nickel-Iron batteries which I might try to hook up to the system. 

I also have several "yard EVs" which run on 48V. So I may try to package the Lithium into a 48V modular pack which could run in the vehicles or the UPS. A lithium pack would be a lot easier to transport from the barn to the basement 

Good luck and keep us posted.

major


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## theforce (Jan 1, 2010)

BMI/LiFeTech Is there a place to buy the batteries you speak of? I looked at the link in your sig but did not see a place to buy them. I just skimmed over the website. Am I correct that those batteries are a drop in replacement for lead batteries or will those batteries still need a special charger? major I agree that UPS have crappy chargers and in most cases no battery management. All of my UPS are used and were found in the trash. The only thing wrong with them were the batteries. I will keep this topic updated.


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## BMI/LiFeTech (Aug 12, 2009)

theforce said:


> BMI/LiFeTech Is there a place to buy the batteries you speak of? I looked at the link in your sig but did not see a place to buy them. I just skimmed over the website. Am I correct that those batteries are a drop in replacement for lead batteries or will those batteries still need a special charger? major I agree that UPS have crappy chargers and in most cases no battery management. All of my UPS are used and were found in the trash. The only thing wrong with them were the batteries. I will keep this topic updated.


I have attached the battery product list below for all of the batteries which are the best solution for UPS application. All of the packs have inbuilt voltage management systems (VMS) for cell balancing and have DB9 data connectors fitted so you can plug a computer in to the battery for checking internal cell voltages and any errors for over charge, over discharge and over temperature. The number of full battery charge cycles is also stored in the VMS memory. All batteries are made to order and shipped by airfreight directly from the factory.
If you require more info, technical specifications or pricing on any particular battery model feel free to contact me directly on either of the email addresses on the contact us page on the website.

Yes, I agree it is best to use a dedicated LiFePO4 charger rather than use the "crappy" chargers which are used on all of the small UPS's. These cheap UPS's use a very basic trickle charger with no battery management. These UPS's are either classed as "off line" or "line interactive". The higher power units used to protect data centres and in industry are "online double conversion" UPS's and have much better chargers which are usually programmable to suit the type and capacity of battery used.

Either a trickle charger could be used or alternatively due to the very low self discharge rate of LiFePO4 batteries possibly a LiFePO4 charger on a timer could be used. This could be set to switch the battery charger on perhaps once a month just to top up any self discharge with manual switching when battery power has been used due to a power failure.

There are several possibilities when it comes to charging depending on how complex you want the system to be and whether you are happy to have a more simple manual system or a more complex automated system.


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## theforce (Jan 1, 2010)

Well I got the 6.8Ah lead acid replacement from batteryspace.com yesterday. Here is the link again. http://www.batteryspace.com/lifepo4...with10timeslongerlifeand597lighterweight.aspx

After handling the 7Ah Lead batteries for years when picking this thing up you just have to wonder if there is anything inside since its so light.

I installed it in my little APC 410 watt UPS to charge over night. So far its holding at about 13.38v. I tried a quick load test of about 10 seconds with my spare computer and it worked just fine. The PC was drawing about 115 watts or about 10A or so from the 12v battery if my calculations are correct. The battery has a 25A limit PCB so I will try to test that out later.

I'm going to let it keep charging again overnight and in the morning I will try to see how long the battery will keep my 115 watt load turned on and see if the over discharge circuit actually works.


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## COS (Dec 23, 2008)

theforce said:


> Well I got the 6.8Ah lead acid replacement from batteryspace.com yesterday. Here is the link again. http://www.batteryspace.com/lifepo4...with10timeslongerlifeand597lighterweight.aspx
> 
> After handling the 7Ah Lead batteries for years when picking this thing up you just have to wonder if there is anything inside since its so light.
> 
> ...


It sounds like you are concerned about how the charger will charge your battery. Consider getting one of their charge management boards for a 4S pack...
http://www.batteryspace.com/cmbchargemanagementboardforli-ionpacks.aspx

Just pick the right one for your battery chemistry. This board will allow you to use any DC source to charge your pack, ~16VDC - ~18VDC.
One thing though, you'll have to bypass the load, meaning keep the battery connected as you have it but move the positive and negative of the charge leads to this charge mgmt board and the output of the charge mgmt bord to the battery/BMS.
________
HERB SCALES


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## theforce (Jan 1, 2010)

Well my main concern with charging was if the stock UPS charger which was designed for lead would do the job.

Since this will be used in a UPS I dont care about having a 100% full LiFePO4 battery. In fact I would prefer to only use 70%-80% to make sure the battery lasts as long as possible. So as long as the UPS charger can charge the battery enough to give me that 70%-80% or somewhere near that I'll be happy.

Now for my portable 110v battery backup I may consider one of those boards since it does not have an on board charger.


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## yarross (Jan 7, 2009)

theforce said:


> I was wondering about converting a UPS to use LiFePO4 batteries.


Unless you have a really good reason, this serves no purpose. VRLAs are a cheap, proven, well established solution. Typically two-quadrant UPS inverter is designed to work with particular VRLA's voltages without any additional circuity. Why to make things more complicated?


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## crap (Dec 5, 2009)

If battery life is an issue the best solution would be a set of nickel-iron batteries. A bit hard to get, but NiCd batteries have very long life aswell and are easier to get.

Although when searching I actually found a site that seems to sell NiFe: 
http://www.ironcorebatteries.com.au/page8.php

Only problem is the price...


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## JRP3 (Mar 7, 2008)

yarross said:


> Unless you have a really good reason, this serves no purpose. VRLAs are a cheap, proven, well established solution. Typically two-quadrant UPS inverter is designed to work with particular VRLA's voltages without any additional circuity. Why to make things more complicated?


Well if you're going through LA's every 3 years or so Lithium might actually be cheaper in the long run. If your LA's are lasting more like 5 years or better then it probably doesn't make sense.


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## theforce (Jan 1, 2010)

My lead batteries are only lasting about two years at most. I'm thinking the main reason they fail is because the UPS will drain the battery dead. Plus they dont have great of a BMS or any at all.

The reason I want to use LiFePO4 is because they claim they last longer. The only way to find out is for people to start using them. I dont mind testing new technology.


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## yarross (Jan 7, 2009)

JRP3 said:


> Well if you're going through LA's every 3 years or so Lithium might actually be cheaper in the long run. If your LA's are lasting more like 5 years or better then it probably doesn't make sense.


Keep in mind that by UPS application I mean standby one, not deep-cycling. Maybe calendar lifetime would be the limiting factor for Li batts. Good VRLAs should serve 5 or more years, especially those with internal oxygen cycle partially replaced by recombination. And there's no need for a BMS.



theforce said:


> My lead batteries are only lasting about two years at most. I'm thinking the main reason they fail is because the UPS will drain the battery dead. Plus they dont have great of a BMS or any at all.


Main reason is high temperature. Batts are so close to power electronics and get warmed. Each 5 degrees above 20degC can decrease expected life span by half. Second common reason is too high voltage (for example, APC Smart 700 due to cost savings does not use op amp to shift useful batt voltage swing to ADC full range and volts readout is rather coarse - I've found 0.08-0.12V overvoltage in my unit - this may be enough for premature positive plate failure or dryout).



theforce said:


> The reason I want to use LiFePO4 is because they claim they last longer. The only way to find out is for people to start using them. I dont mind testing new technology.


Go ahead and try. We'll apprectiate your efforts


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## theforce (Jan 1, 2010)

Well after I got home I found out that the battery was still charging. The voltage increased to 13.96v. So I waited a while longer. Well tonight the voltage was still at 13.96v so I went a head and tried it out.

I used my 115 watt computer as a load.

The computer stayed on for a total of about 33 minutes.

If I done the math right I used around 5Ah or about 74% of the battery. 

As long as the 3000+ cycle claim holds true and the battery can physically last more than 10 years this looks like its going to be perfect. 

Here are some things I noticed while doing the test.

During the first few minutes the voltage dropped to around 12.1v then slowly raised to about 12.35v.

After 25 minutes the voltage started to drop at about 0.01v per second or slightly more.

When the voltage reached about 11.25v it started to drop very quick.

When voltage reached about 10.5v the battery went dead. Literally! It registered as 0v.

To get the battery to wake back up I just had to briefly apply the charge voltage. When the battery woke back up it registered as 11.72v

The battery reached a temperature of about 100F


When the battery charges back up I will try a larger load.


If this battery works well then I will scale it up to a 40Ah battery for my larger UPS.


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## COS (Dec 23, 2008)

theforce said:


> Well after I got home I found out that the battery was still charging. The voltage increased to 13.96v. So I waited a while longer. Well tonight the voltage was still at 13.96v so I went a head and tried it out.
> 
> I used my 115 watt computer as a load.
> 
> ...



Shit, if the battery has it's own PCB in it (and it does), and appears to protect the cells for OVP, OCP, LVP then I say your good to go!
Although I think your closer to 2000 cycles than you are 3000 cycles, but hell, demsalottacycles!
________
LIVE SEXY CAMS


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## theforce (Jan 1, 2010)

Well I ran my large load test today. Here are the results.

Over current protection is there and works. The battery just shuts down until the load is gone. This was just a short test.

For the long test I put about a 310 watt load on it this time.

First starting out the voltage dropped to about 9.9v in the first minute.

It then climbed to 10.64v in 5 minutes.

It then started to drop to about 10v at 7 minutes 52 seconds.

Max temperature at the terminals was about 180F and the casing about 120F.

If I did the math right I used about 3.2Ah? 

I think my UPS was the one that cut out first due to voltage sag. After the test the battery was sitting at 13.16v.


Now normally I don't run that many watts on a small battery and UPS like that. In fact I was just about the pull the plug on this test because the temperatures at the terminals was getting too hot. But right as I was about to pull the plug the UPS decided it better quit.


So I think I'm good to go with these drop in replacements. Although they are more expensive by about 5x I'm hoping that they will actually last 5x or more than the lead batteries. Only time will tell.

I will try update this topic once a year with a battery update and test. And if the battery does fail I will also let you know.


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## theforce (Jan 1, 2010)

I think this is long overdue.

My batteries are still running great.

I have not had the time to do a real test on them but I can tell you that they still hold about a 75%-90% charge. Since these UPSs are designed for lead they dont fully charge the lithiums. Thats OK with me.

Even though the lithium batteries are still expensive I will still be buying them when my lead batteries die.


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## Tecchie (Jun 15, 2014)

theforce said:


> I think this is long overdue.
> 
> My batteries are still running great.
> 
> ...




How about an update? I'm running three (3) APC Smart 1500VA (865watt iirc) UPS units. They are a two-cell SLA battery setup to 24v

Found here: http://www.apc.com/resource/include/techspec_index.cfm?base_sku=BX1500LCD
The link to the battery and specs can also be found on that page...


I was curious if those battery replacements would work for mine? I'm mainly looking for longevity. I've replaced the batteries twice in each unit over 5-6 years. Longer run time would be great too.

On average, they see a couple hundred watt loads during power issues.

I have them tuned pretty right. The voltage fluctuations where I live likes to kill electronics.

It switches to the battery if voltage dips below 110 or above. 130. I've seen as low as 90, and a spike & surge around 145 or higher.

These units cost me $200 each when I purchased them years ago. They have served me well.

Please advise if you can about a drop-in replacement with it's own management system. Thanks!


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## Ivansgarage (Sep 3, 2011)

Tecchie said:


> How about an update? I'm running three (3) APC Smart 1500VA (865watt iirc) UPS units. They are a two-cell SLA battery setup to 24v
> 
> Found here: http://www.apc.com/resource/include/techspec_index.cfm?base_sku=BX1500LCD
> The link to the battery and specs can also be found on that page...
> ...


Years ago I had that problem in Lake Havasu City, AZ monsoon season
and I was running a BBS that had a large data base file, when it screwed up it would take about 6 hours to rebuild the UPS would not run very long, I finally got two big 100ha sla batteries for 24v and run wires through a out side wall, the computer would run for days on UPS power.

As far as that goes you don't have to pay the price for a UPS just get an inverter and a couple of batts and small battery maintainer.. hell of a lot cheaper. 

I no every one will tell ya you need a full sign inverter, BUTTT most power supplies on computers will take care of the modified wave inverter power.

I have been running computer stuff for years on modified wave inverters.
Modofied wave inverters are a LOT cheaper....

Ivan


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## Roy Von Rogers (Mar 21, 2009)

Just to chime in here, I also have an APC XS1300 under my table. Originally I wanted to change to Lithium when my batteries went bad, but I had 6 AGM's from a brand new ZAP PK, that I upgraded to lithium, and decided to use two of them on my UPS, I just checked the voltage, this post reminded me I hadn't checked it for a while lol, the total voltage was 26.7, one at 13.4 and the other at 13.2.

I have to agree, using high amp sealed is a better idea, even though my voltages would be ok, but the idea of the charging system failing without a back up to shut it down in case of a overcharge, made me feel uncomfortable, and since I had them there was no reason to go lithium.

I was also going to put them in a box outside, especially since they are so damn big and heavy, but considering the temp variations outside, I decided against it.

The funny thing is, it has a automatic timed discharge cycle build in, it will still shut down when it thinks the original battery capacity is going empty.

And there is nothing I can do about it, its hard wired in.

Roy


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## stickman (Aug 25, 2015)

Hello,

Thanks for being the *guinea* pig for us.  Can you update your experience?

I am using LIFEPO batteries in my truck, forklift and car.

So far so good. The only issue is possible over charging. I had one die prematurely, but I'm not sure what the cause was. Most sit on a maint. charger 24/7, so the voltage is kept up. What I think killed the one was it was NOT on a maint. charger and not used for several months. During that time the voltage dropped and the trucks alt. may have overcharged it. It was very warm.

So I have really wanted to try them in a UPS. 3 of the UPS I have go up high on a shelf and are very hard to get to. So having them lighter and lasting longer would be great for me. 

Thanks for the info so far.


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## JRP3 (Mar 7, 2008)

stickman said:


> So far so good. *The only issue is possible over charging*. I had one die prematurely, but I'm not sure what the cause was. *Most sit on a maint. charger 24/7, so the voltage is kept up.*



Good way to overcharge lithium is keep them on a maintenance charger 24/7. Lithium is better sitting slightly undercharged.


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## stickman (Aug 25, 2015)

All the chargers are smart chargers. they turn off when it gets to the proper voltage.


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## Duncan (Dec 8, 2008)

stickman said:


> All the chargers are smart chargers. they turn off when it gets to the proper voltage.


And there is the rub - what is the "correct voltage"

http://www.diyelectriccar.com/forums/showthread.php/float-charging-lfp-batteries-161649.html


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## stickman (Aug 25, 2015)

Based on my non scientific method of sticking a voltmeter on several different batteries it would be 13.03-13.09Volt. If it drops below that, it comes on for a few seconds to bring it to 13.4 or so and then off again for quite awhile.


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## mira9_cz (Feb 27, 2013)

Hi guys. I'm also considering this LiFePO4 application and my concern is this:










full article

Maintaining LiFePO4 at full charge voltage (anything from let's say 3.5V up) is damaging. I have seen hundreds of 12V Winston block batteries destructed by regular overcharging - with no balancing of indivudual cells maintaining full voltage simply will overcharge one cell sooner or later no matter how matched they are from factory. And from that moment, cells will get out of balance more and more with every charging cycle up to the point when one of the cells dies by being overcharged every cycle. 
This maintaining at full voltage situation may be, and usually is caused by float mode of lead-acid battery chargers. And unfortunately UPS does this too because it integrates charger determined for lead-acid batteries.

There are however small LiFePO4 batteries with integrated balancing and protection module, like this one for example:
http://www.ev-power.eu/LiFeYPO4-batteries-12V-1-1/LiFePO4-Battery-Pack-12V-7Ah-PCM.html

Internal battery management can do some very limited balancing, usually from 50 mA to 100 mA. In my opinion this could save the day, IF the float current of UPS is very small - from 50 to 100 mA. Do you have some experience with how much float current really is? 

I do have few LiFePO4 12V7Ah batteries opened here next to me, but before I will try to connect Ammeter between strongest cell and balancing PCB and start testing, I decided to ask you guys if I'm seeing all this whole issue right. Feel free to correct me.


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## bigmotherwhale (Apr 15, 2011)

I have used LiFePO4 cells with a UPS, luckiliy the float voltage on the charging circuit was about right for 8S @ 27.5v 
I used a Cell-Log 8M with the alarm output connected to shut it off if the voltage went above or below specs, i suggest you use something similar as a safety feature. 
It worked fine.


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## mira9_cz (Feb 27, 2013)

bigmotherwhale said:


> I have used LiFePO4 cells with a UPS, luckiliy the float voltage on the charging circuit was about right for 8S @ 27.5v
> I used a Cell-Log 8M with the alarm output connected to shut it off if the voltage went above or below specs, i suggest you use something similar as a safety feature.
> It worked fine.


Thanks for reply. Voltage is not problem for LiFePO4 here. Luckily LiFePO4 nominal voltage is suitable for most of hardware designed for lead-acid. Lead-Acid chargers usually Float at maximum 14.4V, which means 3.6V per cell in LiFePO4 and less. This is good. But I wondered about float current. LiFePO4 can not relieve surplus energy as lead-acid battery can do. As I explained in previous post, 14.4V x 0.00X A = 0.0X Watts, which must be wasted somehow, or LiFePO4 will be overcharged and destructed in long time view considering no discharge cycle in many months, which is how most of UPS works. 

As I see it, the only chance is that balancing PCB would do this wasting of surplus energy caused by Float mode, or any LiFePO4 can not be trusted to survive tens of years lifetime as it can do if you cycle it within recommended voltage range. 

Adding secondary protection as you did with CellLog makes sense, but I'm worried about the situation that grid will go offline exactly in the moment when CellLog will keep the battery disconnected from UPS because of high voltage.


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## mira9_cz (Feb 27, 2013)

OK, so I went for it.










I will let you know as soon as I will have some output. I will open the battery in few days and measure cells voltage. If everything will be o.k., I will start monitoring cells separately.


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## bigmotherwhale (Apr 15, 2011)

mira9_cz said:


> Thanks for reply. Voltage is not problem for LiFePO4 here. Luckily LiFePO4 nominal voltage is suitable for most of hardware designed for lead-acid. Lead-Acid chargers usually Float at maximum 14.4V, which means 3.6V per cell in LiFePO4 and less. This is good. But I wondered about float current. LiFePO4 can not relieve surplus energy as lead-acid battery can do. As I explained in previous post, 14.4V x 0.00X A = 0.0X Watts, which must be wasted somehow, or LiFePO4 will be overcharged and destructed in long time view considering no discharge cycle in many months, which is how most of UPS works.
> 
> As I see it, the only chance is that balancing PCB would do this wasting of surplus energy caused by Float mode, or any LiFePO4 can not be trusted to survive tens of years lifetime as it can do if you cycle it within recommended voltage range.
> 
> Adding secondary protection as you did with CellLog makes sense, but I'm worried about the situation that grid will go offline exactly in the moment when CellLog will keep the battery disconnected from UPS because of high voltage.


The float voltage you are using is too high, the maximum float voltage for LiFePO4 is 3.45v and no higher. if you are float charging at a higher voltage than this the you need to drop some voltage at the regulator, or as a quick trick i use a back to back diode pair to drop the charge voltage 0.2v for carbide devices or 0.5v roughly for Si you can of course add as many as you need on the reverse (charging current), make sure you put them on a good heat sink as they will be dissipating a lot under load. Use a SIC diode for the forward current as it wont heat up as much and you don't need to drop V in this direction. 

you can periodically charge them to 100% soc using a separate charger with the correct cut off.


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## Roy Von Rogers (Mar 21, 2009)

I ended up using two 100ah AGM's I had from converting a led sled. The problem is the smart UPS's doesn't know you have larger ah battery, and it still will shut down at a pre determent time cause they go by what batteries came with the unit. 

Haven't tried to see what happens running on the battery.

But at least I wont have to buy their sorry gel cell batteries that they seem to overcharge, so they can sell you more APS batteries.

But if I wanted to use Lithium Ion I would use a JLD 404, or something similar, to control the high and low side.

Roy


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## mira9_cz (Feb 27, 2013)

bigmotherwhale said:


> The float voltage you are using is too high, the maximum float voltage for LiFePO4 is 3.45v and no higher. if you are float charging at a higher voltage than this the you need to drop some voltage at the regulator, or as a quick trick i use a back to back diode pair to drop the charge voltage 0.2v for carbide devices or 0.5v roughly for Si you can of course add as many as you need on the reverse (charging current), make sure you put them on a good heat sink as they will be dissipating a lot under load. Use a SIC diode for the forward current as it wont heat up as much and you don't need to drop V in this direction.
> 
> you can periodically charge them to 100% soc using a separate charger with the correct cut off.


You are right, the float 3.45V per cell I have overstated, in reality it is lower.


Anyway first graph is here:










Now I have set logging interval once per hour and I'm going for long time test, let's say 2 months. It should be enough to determine if very small floating current will rise the voltage of battery somehow or not.


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## mira9_cz (Feb 27, 2013)

31 days graph of total voltage below. No change in voltage - good. Now I'm logging cells individually, graph will follow in about a month.


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## bgeery (Oct 17, 2011)

Roy Von Rogers said:


> The problem is the smart UPS's doesn't know you have larger ah battery, and it still will shut down at a pre determent time cause they go by what batteries came with the unit.


This does not happen with my Cyberpower CP850PFCLCD. Will run untill it reaches low voltage cutout. Cyberpower also seems to use lower float voltages (don't know if low enough for LiFePO4 as stock).


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