Re: [RE-wrenches] Lithium battery in non cycling use

2022-02-28 Thread Kienan Maxfield 
Jay,

I believe that the secret to long LiFePO4 life is low charging voltage. (Of 
course, the temperature, and depth of discharge do make a big difference as 
well, but you probably can't control the temperature, and you already said it's 
not cycling, so DOD isn't an issue either.) There are two problems with just 
going and reducing charging voltages...

  1.  As has been mentioned, cell balancing might not work (depending on BMS)
  2.  BMS calibration errors and/or battery monitor calibration errors may occur

I have had this issue once, I tried to reduce the absorb & float voltage to 
somewhere around 53.2 volts for a non-cycling LiFePO4 battery. I don't remember 
the exact setting I used. This should keep the battery well over 90% full 
(probably around 95%) and the client figured that even storing the battery as 
low as 90% full was a good trade-off in order to extend the shelf life. The 
only issue is that this specific internal BMS calibrates when the batteries 
reach a voltage of at least 56 volts, so the BMS slowly kept reporting a lower 
and lower battery percentage. I was unaware of this, and the client didn't 
notice, but then the BMS shut the system shut down due to "low SOC".

So to sum it up, as far as the chemistry, if you could keep it around 90% SOC 
for non-cycling use, that would be awesome for shelf life, but because of 
BMS-related problems, that's probably not going to work well. So here's my own 
unconventional answer that I've never heard anywhere else, that I have decided 
is probably best for non-cycling use...


  1.  Set your float and absorb fairly low.
  2.  Set an automatic EQ cycle (perhaps once a month) to charge at a voltage 
that's high enough to calibrate the BMS and balance the cells (depending on the 
brand, probably around 56V?)
  3.  Don't let anyone else look at your settings, because nobody will 
understand why you're "equalizing" a lithium battery, and they'll think you're 
ignorant and you don't understand the lithium chemistry.

Disclaimer: consult battery manufacturer because I don't want any liability 😉. 
But honestly, it would be good to know what the BMS calibration voltage is, as 
well as what voltage it starts balancing the cells.

Caveat: the only issue with this that I can see is if the BMS needs a 
significant time to balance the cells. In this scenario, it would be better to 
get the battery up to the calibration voltage for just a couple of minutes to 
calibrate the SOC, and then go down to the balancing voltage for a while, then 
go back to the storage voltage. Unfortunately, I don't know any way to have 
this kind of cycle happen once a month...

Thanks,
Kienan

Maxfield Solar
maxfieldso...@hotmail.com<mailto:maxfieldso...@hotmail.com>
(801) 631-5584 (Cell)

From: RE-wrenches  on behalf of 
Darryl Thayer 
Sent: Wednesday, February 23, 2022 10:10 PM
To: RE-wrenches 
Subject: Re: [RE-wrenches] Lithium battery in non cycling use

Hi Jay I am not sure what non-cycling use is, I have mentioned before in my 
experience where a cell in the string can become lower in charge and the string 
loses capacity in discharge because the BMS shuts off the complete battery when 
the troubled cell reaches low voltage cut out. To prevent this, a string should 
go tho top balance.  This is of course true for both cycling and little cycling.

On Wed, Feb 23, 2022 at 9:36 AM Jay 
mailto:jay.pe...@gmail.com>> wrote:
Hi all the lithium experts.

Are there any issues with using LFP lithium in non cycling battery backup mode.
Or specific settings, brands etc that should be considered when designing for 
GTBB, non cycling.

Thanks

Jay
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Re: [RE-wrenches] Lithium battery in non cycling use

2022-02-23 Thread Darryl Thayer 
Hi Jay I am not sure what non-cycling use is, I have mentioned before in my
experience where a cell in the string can become lower in charge and the
string loses capacity in discharge because the BMS shuts off the complete
battery when the troubled cell reaches low voltage cut out. To prevent
this, a string should go tho top balance.  This is of course true for both
cycling and little cycling.

On Wed, Feb 23, 2022 at 9:36 AM Jay  wrote:

> Hi all the lithium experts.
>
> Are there any issues with using LFP lithium in non cycling battery backup
> mode.
> Or specific settings, brands etc that should be considered when designing
> for GTBB, non cycling.
>
> Thanks
>
> Jay
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Re: [RE-wrenches] Lithium battery in non cycling use

2022-02-23 Thread Jerry Shafer 
Look at Blue planet, they have a BMS and l do not know what draw it has.
Can you lock out the battery with a contactor to reactivate the system
Jerry
Jerry

On Wed, Feb 23, 2022, 10:56 AM Jay  wrote:

> Hi Jerry
>
> This is for a generic GTBB with no battery sell back. So basically for as
> many years as possible.
>
> Jay
>
>
>
> On Feb 23, 2022, at 9:21 AM, Jerry Shafer 
> wrote:
>
> 
> Well before l say anything, how long? I have locked out LFP for 180 plus
> days and they held the charge, now if the BMS is connected the battery will
> draw down. Now l can say that once a LFP that l use is full its fu and 99%
> bypass the battery. Now also different brands tend to act somewhat
> different so it may depend on BMS, duration and brand.
> Jerry
>
> On Wed, Feb 23, 2022, 7:36 AM Jay  wrote:
>
>> Hi all the lithium experts.
>>
>> Are there any issues with using LFP lithium in non cycling battery backup
>> mode.
>> Or specific settings, brands etc that should be considered when designing
>> for GTBB, non cycling.
>>
>> Thanks
>>
>> Jay
>> ___
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Re: [RE-wrenches] Lithium battery in non cycling use

2022-02-23 Thread Jay 
Hi Jerry

This is for a generic GTBB with no battery sell back. So basically for as many 
years as possible. 

Jay



> On Feb 23, 2022, at 9:21 AM, Jerry Shafer  wrote:
> 
> 
> Well before l say anything, how long? I have locked out LFP for 180 plus days 
> and they held the charge, now if the BMS is connected the battery will draw 
> down. Now l can say that once a LFP that l use is full its fu and 99% bypass 
> the battery. Now also different brands tend to act somewhat different so it 
> may depend on BMS, duration and brand.
> Jerry
> 
>> On Wed, Feb 23, 2022, 7:36 AM Jay  wrote:
>> Hi all the lithium experts. 
>> 
>> Are there any issues with using LFP lithium in non cycling battery backup 
>> mode. 
>> Or specific settings, brands etc that should be considered when designing 
>> for GTBB, non cycling. 
>> 
>> Thanks
>> 
>> Jay
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Re: [RE-wrenches] Lithium battery in non cycling use

2022-02-23 Thread Jerry Shafer 
Well before l say anything, how long? I have locked out LFP for 180 plus
days and they held the charge, now if the BMS is connected the battery will
draw down. Now l can say that once a LFP that l use is full its fu and 99%
bypass the battery. Now also different brands tend to act somewhat
different so it may depend on BMS, duration and brand.
Jerry

On Wed, Feb 23, 2022, 7:36 AM Jay  wrote:

> Hi all the lithium experts.
>
> Are there any issues with using LFP lithium in non cycling battery backup
> mode.
> Or specific settings, brands etc that should be considered when designing
> for GTBB, non cycling.
>
> Thanks
>
> Jay
> ___
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Re: [RE-wrenches] Lithium battery in non cycling use

2022-02-23 Thread Daniel Young 
The main thing you can do when non-cycling is to set the charge voltage a 
little lower than you normally would. 

Check the manufacturer for the recommended full charge voltage (usually 
3.6V/cell) that's 57.6V for a 48V pack. I set my absorb voltage to 57V even to 
begin with. And float is closer to 3.5V/cell or 56V. That constitutes roughly 
90% capacity (check your battery manufacturer spec, it can vary by brand).

Ageing of LFP tends to accelerate at both higher temperatures and higher charge 
voltages. There are some research papers out there testing this in various ways 
for various applications, but the conclusions are usually the same. Keep the 
lithium from getting too hot (I say stay below 30-35C when possible) and do not 
charge them to 100% unless you really need the capacity.

So my common sense tells me to set my absorb and float voltages such that the 
LFP batteries are not regularly going above 90% SOC in backup applications.

Another factor to account for is the BMS's cell balancing feature, you do want 
the float voltage set high enough that the BMS does get triggered to balance 
cells (many BMS's do not balance until the cells are near full, as this is 
where imbalances really start to show up, and it saves energy by not bleeding 
current off the cells constantly). For example, if the battery BMS starts 
balancing when cells are above 3.52V (56.32V for 48V packs), then the float 
voltage needs to be just above this (56.4-56.5) that way the BMS has the 
ability to balance cells regularly. The manufacturer would be the source for 
the cell balancing voltage threshold. If float was set to 55V for example, the 
cells could get relatively out of balance and the BMS would do little to stop 
it, only bleeding off current when a cell gets particularly out of balance with 
a higher voltage than its peers.

Always ask the manufacturer for advice on this first of course.

--

Danny Young
Engineering Team Lead
Solar Energy Solutions
Lexington | Louisville | Bloomington | Cincinnati | Evansville | Indianapolis
513-448-5176 (mobile)
877-312-7456 (Main Office)
da...@sesre.com

-Original Message-
From: RE-wrenches  On Behalf Of Jay
Sent: Wednesday, February 23, 2022 10:02 AM
To: RE-wrenches 
Subject: [RE-wrenches] Lithium battery in non cycling use

Hi all the lithium experts. 

Are there any issues with using LFP lithium in non cycling battery backup mode. 
Or specific settings, brands etc that should be considered when designing for 
GTBB, non cycling. 

Thanks

Jay
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Re: [RE-wrenches] Lithium battery in non cycling use

2022-02-23 Thread larrycrutcher 
Jay

We have some government customers using LiFeBlue Battery as a UPS for radio 
systems. Battery and radios are connected to a constant 14.2 Volt power supply. 
The battery only discharges if the utility power goes off and recharges after 
restoration. Operating for 3+ years.


Larry Crutcher
Starlight Solar Power Systems



On Feb 23, 2022, at 8:02 AM, Jay  wrote:

Hi all the lithium experts. 

Are there any issues with using LFP lithium in non cycling battery backup mode. 
Or specific settings, brands etc that should be considered when designing for 
GTBB, non cycling. 

Thanks

Jay
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Re: [RE-wrenches] Lithium battery in non cycling use

2022-02-23 Thread Kirk Herander 
anecdotal, but Blue Planet told me their LFP battery can sit uninstalled in
the box for several years with minimal self-discharge and no problems when
put into service.

On Wed, Feb 23, 2022 at 10:36 AM Jay  wrote:

> Hi all the lithium experts.
>
> Are there any issues with using LFP lithium in non cycling battery backup
> mode.
> Or specific settings, brands etc that should be considered when designing
> for GTBB, non cycling.
>
> Thanks
>
> Jay
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-- 

*Kirk Herander / **kirkh@vermont.solar *

*Owner|Principal, VT Solar, LLC*

*Celebrating our 31st Anniversary 1991-2022!!*

*www.vermont.solar*


dba Vermont Solar Engineering

802.863.1202
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[RE-wrenches] Lithium battery in non cycling use

2022-02-23 Thread Jay 
Hi all the lithium experts. 

Are there any issues with using LFP lithium in non cycling battery backup mode. 
Or specific settings, brands etc that should be considered when designing for 
GTBB, non cycling. 

Thanks

Jay
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