LYFEYPO4 working temperatures

[karrak]

What cell are you referring too?

From your post http://www.solarpaneltalk.com/showth...l=1#post154383 you give the following figures.

LFP resting SOC Voltages.

100% = 3.450
90% = 3.338
80% = 3.331

Only once a day. Most of th ehigher end CC's lock out when the get to Float and will not cycle until next day.

Yes, but they keep the voltage at the float voltage which will require then to start charging again if a load drops the voltage below the float voltage. If the load is greater than power the solar panels can supply the load will start drawing power from the battery. When the load is removed the charge controller will then recarge the battery back up to the float voltage.

Simon

[Sunking]

If you are off grid, how can you run your batteries down to 20% and have reserve capacity for cloudy days?

Huh? What are you talking about? Your battery is sized for 3 days reserve to operate between 80/20. It would take 3 days of use with no sun to go down to 20%

A float voltage of 3.4 volts is > than 90% SOC.

What cell are you referring too?

Anyway if you float at 3.4 volts you will be doing micro discharges/charges every time your panels cannot supply your loads.

Only once a day. Most of th ehigher end CC's lock out when the get to Float and will not cycle until next day. This is not correct, see this post http://www.solarpaneltalk.com/showth...l=1#post166399 from someone who should know, also see this post http://www.solarpaneltalk.com/showth...l=1#post166231 which back up wb9k's assertion that capacity loss is roughly proportional to SOC.

What if the ambient temperature goes above 31C?

Have a glass of ice tea and relax.

[karrak]

This is exactly what I did the first time but then I read on the forum that floating is a killing so I changed strategy with a capacity meter cutting the panels from the mppt recharger when I reach the 100% which for me was 3,45 and current below 0,25C.

Hi Barba,

I have an off-grid power system with a Winston LFP battery that I installed in April 2013. I used to think that floating was a bad thing but am not so sure now. My current regime is to charge to 3.4 volts/cell at an end current of 0.02C and then terminate the charge until the next day. The reason I use such a low cut-off current is to give a reasonably consistent SOC regardless of the power coming from my solar panels. I go to 3.45 once a week to reset my Ah counter. There are a number of people on the Australian Energy Matters forum who charge to around 3.45 volts, lets call this 100% SOC and then float at 3.34 volts which they have found give then a relative SOC of around 100% at the end of the day. From the evidence I have seen to date I would think this is not such a bad regime. I am still looking for more data on how SOC effects longevity of the battery.

Simon

[karrak]

You would be much better off if you use a different strategy of running between 20 and 80% SOC.

If you are off grid, how can you run your batteries down to 20% and have reserve capacity for cloudy days?

Start off by setting your Charge Controller Bulk = Absorb = Float = 3.4 volts per cell, and allow the batteries to Float.

A float voltage of 3.4 volts is > than 90% SOC.

Those micro charges are significantly cutting into your battery cycle and calendar life.

Please give data to back up this statement. Anyway if you float at 3.4 volts you will be doing micro discharges/charges every time your panels cannot supply your loads.

Barb floating at 100% will stress the batteries, but not Floating at say 80%. You are really stressing your batteries going to 100% especially several times a day. By only going to 80 to 90% SOC is going extend your battery cycles life of about 100%.

This is not correct, see this post http://www.solarpaneltalk.com/showth...l=1#post166399 from someone who should know, also see this post http://www.solarpaneltalk.com/showth...l=1#post166231 which back up wb9k's assertion that capacity loss is roughly proportional to SOC.

Sunkink, if you bothered to read Barba's original statement you would note that he/she only charge their battery to 3.45 volts at a termination charge rate of 0.25C which will not charge up to 100% as you well know.

As for battery temps is not much of a problem below 40 C or 104 F. 88 is 31 C so you are not really pushing any limits. And by lowering the voltage to 80% SOC all that heat goes away.

What if the ambient temperature goes above 31C?

Simon

[Sunking]

Bard just try lowering the voltage for a couple of days and monitor things. Report back cell voltages and temps when charged up. I think you will be pleasantly surprised. Lithium batteries are not made to be kept at 100% SOC like lead batteries. They do best operated in PSOC (partial state of charge) which is perfect for solar and many other applications. They do best at 20/80 and 10/90 SOC. There is no reason to go to 100%.

[Sunking]

Hello sunking This is exactly what I did the first time but then I read on the forum that floating is a killing so I changed strategy with a capacity meter cutting the panels from the mppt recharger when I reach the 100% which for me was 3,45 and current below 0,25C.What about the temperature? What is the best range?

Barb floating at 100% will stress the batteries, but not Floating at say 80%. You are really stressing your batteries going to 100% especially several times a day. By only going to 80 to 90% SOC is going extend your battery cycles life of about 100%. As for battery temps is not much of a problem below 40 C or 104 F. 88 is 31 C so you are not really pushing any limits. And by lowering the voltage to 80% SOC all that heat goes away. __________________________________________________ __________________________________________________ __________________________________ Then once every 6 months or so, you can turn the controller voltage up high enough to turn on the Balance Boards so you can re-balance the cells. But you are going to find they just do not stray much. I am at 8 months and no need to re-balance. Not sure what voltage you operate at but set Bulk = Absorb = Float to:_______________________________________________ ______________________ 13.5 volts_____________________________________________ _____27.0 volts_____________________________________________ ___54.0 volts _______________________________________________ All your cells should top off around 3.375 volts per cell

[Barba]

Hello sunking
This is exactly what I did the first time but then I read on the forum that floating is a killing so I changed strategy with a capacity meter cutting the panels from the mppt recharger when I reach the 100% which for me was 3,45 and current below 0,25C.

What about the temperature? What is the best range?

[Sunking]

Hi there,I have a battery bank made by 16 winston 300 ah.I recharge to 3,45 and I stop when I reach it @ 0.25C.For me 3,45 is 100% SOCI do not float.

You would be much better off if you use a different strategy of running between 20 and 80% SOC. Start off by setting your Charge Controller Bulk = Absorb = Float = 3.4 volts per cell, and allow the batteries to Float. Those micro charges are significantly cutting into your battery cycle and calendar life. So say your batteries reach 3.4 volts per cell by noon and your charger is Floating the batteries. Any power demand will come from the panels and NOT the batteries. Only time you will use battery power is when demand exceeds panels, cloudy days, or at night. No more multiple charges in a day. Just once a day.

[Barba]

The Yttrium oxide itself can resist a high temperature. And the battery is suitable for fast charging with a long cycle life, and its charge and discharge are quite consistent. So a storage cabinet or power station has a use life of more than 25 years.

This is what I read in their web page, it is a generic info so I don't know what in means in practice.

I now cycle my battery between 90% and 10% SOC and I will cool down the battery cabinet to 75F with the extra power I don't use.

Do u think is good now since the temperature is not an issue? Or the biggest issue is to microcycle in the high 85-90% SOC?

[PNjunction]

Since you reaching full charge (relatively) multiple times per day, AND you are reaching 88F regularly when charging, I'd drop the daily cycling to no more than 80% SOC max for a lower psoc or just increase your discharge.

I see the catch-22 that prompted the question. We know that holding a cell high in voltage (or taking ages to get through absorb) is not a good thing, but on the other hand, if you do mini-cycles multiple times per day fast enough, does this average out to an ok value in regards to elevated voltage degradation?

I still think that a lower overall PSOC range is beneficial if long-term life is the goal because of the slightly elevated temps.

However, this is solar, so the other question is what is your solar-insolation like in winter? In that case, perhaps you won't be reaching 5-6 cycles per day, and with your current load, you'll end up in a lower psoc naturally without having to do anything - ie, only being able to reach 1 relatively-full-charge and fortunately at a lower temperature to boot.

This is what makes it hard to pin down anything exactly specific in solar without knowing ALL the figures and operational criteria, and of course accounting for the worst in solar-insolation.

In the end, *as it stands right now*, I'd be tempted to just lower the range of psoc operations. Come December, I might have a different answer.

[Barba]

My 100% SOC is the the 90% of the battery more or less
Does it make any difference or I should stay in the region of 80% SOC of the battery?
Thx

[PNjunction]

Yes - it is not a good idea to keep lifepo4 "topped up" as you are doing with the micro-cycles, unless you are forced to by needing a lot of instantaneous reserve capacity or very lengthy autonomy.

I sure hope you are not doing active balancing each and every cycle either - another contributor to lengthening the clock at high levels of charge with weeny bleeder boards.

Long time spent at high levels of charge are statistically not in our favor, and the more time you spend up there, even if it is not an absolute full charge is not advisable if you can avoid it. This will vary among manufacturers - ie, an A123 cell may handle this behavior better than a GBS/Winston/Calb. Consider that cells are delivered around 40-50% capacity to help ensure longevity during retail storage, rather than being shipped full charge. There is a reason for this.

While this may not be an immediate problem, going there 5 or 6 times a day just lengthens the period of time daily that you do.

I note that you are only charging until your absorb is only 0.25C. Just so you know, this is different from the norm of reaching full charge when current drops to C/20! I'm assuming you are doing this on purpose so you don't really get fully charged, but hang somewhere lower.

Thing is, as far as I know, nobody can put an exact figure on the Winston cells treated like this. I see you are also active on another forum, so you know where to go to get the authorized documents - but I don't think any percentages or figures are available for your micro-cycle use.

What I would do (I use GBS not Winston, but they are all still in the large prismatic family), is extend your depth of discharge, or purposely run in a lower state of PSOC, *IF* you can afford the loss of autonomy for solar requirements.

[Barba]

Thx for the quick reply!
To measure the capacity left I use a shunt and my system has a precision of 0,01 A which is in my experience the only way to go as the other coulumb counter go always wrong.

Does anyone know anything about going 6-7 times a day up and down from my relative 100% soc to 95% soc if it does anything bad to my cells?

Thx so so much again

[PNjunction]

From your description at this distance, it does not sound like you are fully charging - which is ok.

The fact that you are pulling very little out of your bank before it recharges again, suggests to me that you either desire a lot of reserve autonomy for a solar setup. However, it does appear that you may have room to take advantage of lifepo4's ability to do PSOC, or partial states of charge at a lower level. Perhaps you might want to shoot for say a spread of about 50-80% DOD, whereas in reality you may be just doing 80-90% DOD cycles.

As we know voltage alone is not a good indicator of SOC, especially when it comes to lithium when you are in the flat part of the curve. You may want to do some coulomb countings.

I see no problem with going to 88F, and I even exceed that here for many hours in the summer. But of course, a cooler temp is always preferable. Sometimes you just have to live with it.

For those Winstons, you may want to take a look at the users-manual:

http://en.winston-battery.com/index.php/products/download-center

Lots of good info!

[Barba]

Hi there,
I have a battery bank made by 16 winston 300 ah.
I recharge to 3,45 and I stop when I reach it @ 0.25C.
For me 3,45 is 100% SOC
I do not float.
The bms I use actively balance when I discharge and balance when I charge with 40 Amps.
At 3,45 the cells have 0,002 volts difference so I am very satisfied with it.
The only thing that worries me is that cells temperature is 88F and now in the summer the SOC goes from 100-95% soc (3,45-3,39 volts) lots of times per day, let say 5-6 times.
What do you think?
Is there any limitations for LIFEYPO4 in doing micro cycles at 88F in the upper SOC?
Thx