LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

[john61ct]

Originally Posted by JmanC

I think I can live with less cycle life.

Accepting that certainly allows for simpler design.

[Cpt Pat]

Originally Posted by JmanC

thanks
I would just use a relay or dc breaker between the mppt & panels. One reason I thought the controller needs to be first connected to a battery before any solar is to get an idea of the voltage/state of battery. But now I think about it, that cant be true. It should just start charging when the sun shines.

I've been doing the same for years: disconnecting the PV panels with a relay from the MPPT controller when on shore power and the AC charger. Otherwise, my BlueSky MPPT controller will charge my lead-acid batteries to 14.4 volts every day - which is abusive. My LFP batteries have a separate charge cut-off and so would be unaffected.

[JmanC]

Originally Posted by john61ct

That **is** true, hook up the battery first, and disconnect it last.

Even if it isn't "dangerous" for a given SC.

Good habit, like always*removing jewelry, or removing the battery's negative before positive, and reconnect negative last.

Thanks john

[JmanC]

I'm wondering how should a dropin be balanced in the real world using basic AC battery charger.

I first fully charged to my regular 14V until taper current 0 according to monitor. Then set absorb & float to 14.4V and charge rate low.

At 14.4 The current tapered down to about 1% of C within a few minutes, but terminal voltage was actually 14.5V according to DMM.
The cell voltages according to internal bms were 3.69, 3.67, 3.67, 3.52

Over 20 deep cycles this is my second attempt at top balance on this new battery & still the last cell is always lower. During flat curve underload they are all within 8-15mv, so is this low last cell anything to worry about?

I held for another 20mins until taper current was just under 0.5% of capacity but terminal voltage was now 14.7V, so I turned off charger and put a load on the battery.

Why the rise in voltage? Is it because they are already balanced?

[mikedefieslife]

Surely since it's a drop-in you don't have access to the cells. You shouldn't need to balance them on first use as they should be well matched and balanced from the factory. All you can do is rely on the internal BMS

[john61ct]

That is the fatal flaw with drop ins, you must rely on their internal BMS, and lose the ability to balance manually.

Fantastic you can at least see the individual cell voltages to become aware of imbalance problems.

You should find out the "start balance" voltage, and if possible the "bleeding "balancing current rate mA.

Are these published? If not call and ask.

Since you have a user-adjustable charger, set it to 0.1V above that start balance voltage point, but nowhere near that 14.4/3.6Vpc, going that high is likely **causing** the cells to go out of balance.

Drop battery's SoC first by say 10A to reduce the risk of overcharging.

If you have control over the current rate, drop that down to 500mA (half an amp), or just at the same rate as the balancing current.

That is now the closest you can get to a "balancing protocol", let it sit there a long time, you should see the cell voltages (very slowly) converge, as the weaker / faster / higher cells trigger a stop-charge, are then bled by resistors at the (very slow) balance rate, then charge resumes, etc.

Inherent in that (common but IMO very stupid) balancing method, is that once cells are greatly out of balance, getting back to proper balance can literally take days.

Hopefully once that has been done, it will happen during the last few minutes of normal cycle usage charging as it is supposed to in theory.

You can help **prevent** getting too far out of balance by, while normal cycle usage charging,

stay at a healthier lower voltage setpoint, as low as possible just over the BMS' start-balance voltage.

Anything over 13.8V will get you to 100% Full, but likely that is too low for the BMS.

Basically, the profile "top goal" should be to stop as soon as the cells are balanced, keeping on pushing to any higher SoC serves no constructive purpose, only reduces lifespan and causes balance problems.

If you are concerned about a so-called "memory effect" then do go up to the mfg-spec stop-charge spec (14.4V) say once or twice a month, but don't worry about precise balancing at that higher point, just watch amps taper to 0.01C then stop.

Also, be aware that the BMS' "stop-bleed-balance" method may be causing you to think the tapering amps has dropped low enough, when in fact it will jump back up to 0.05C or above, after the bleeding cycle has finished.

Originally Posted by JmanC

I'm wondering how should a dropin be balanced in the real world using basic AC battery charger.

[john61ct]

If CC load discharge capacity testing is easy and convenient for you, then wait until you see **evidence** of a memory effect

before going back to higher-voltage charging, treat that as an only-if-needed maintenance protocol.

[CatNewBee]

Originally Posted by JmanC

I'm wondering how should a dropin be balanced in the real world using basic AC battery charger.

I first fully charged to my regular 14V until taper current 0 according to monitor. Then set absorb & float to 14.4V and charge rate low.

At 14.4 The current tapered down to about 1% of C within a few minutes, but terminal voltage was actually 14.5V according to DMM.
The cell voltages according to internal bms were 3.69, 3.67, 3.67, 3.52

Over 20 deep cycles this is my second attempt at top balance on this new battery & still the last cell is always lower. During flat curve underload they are all within 8-15mv, so is this low last cell anything to worry about?

I held for another 20mins until taper current was just under 0.5% of capacity but terminal voltage was now 14.7V, so I turned off charger and put a load on the battery.

Why the rise in voltage? Is it because they are already balanced?

They are designed to balance themselves when using standard chargers usually in GEL SMF configuration (it is the closest FLA profile setting to what LFP are able to survive long term) , absorption at 14.4... 14.6V and float at 13.6V, no recondition!!! .

The long float phase usually gives enough time at low current to keep the cells balanced using the internal BMS.

They are designed for this, and the life expectancy in the data sheet reflect this regime. Anything else is gambling, probably causing more harm than good getting them out of balance.

14.6V translates into 4 x 3.65V, the recommended end of charge voltage of the cell manufacturer equalling 100% SOC
LiFeYPO4 cells can stand up to 4.0V before getting damages, this is also the recommended voltage for initialization of fresh cells, so they are completely full and top balanced before building a battery.

They undergo this regime usually at the manufacturer or importer tquality check to validate capacity and inner resistance, customers usually get the cells already initialized, or the manufacturer puts a note to do the initialization prior first use along with the certificates and warranty. . .

12V packs are all pre-initialized and usually pre-charged when shipped, so normally ready to use.

[Q Xopa]

Originally Posted by john61ct

That is the fatal flaw with drop ins, you must rely on their internal BMS, and lose the ability to balance manually.

Fantastic you can at least see the individual cell voltages to become aware of imbalance problems.

You should find out the "start balance" voltage, and if possible the "bleeding "balancing current rate mA.

Are these published? If not call and ask.

Since you have a user-adjustable charger, set it to 0.1V above that start balance voltage point, but nowhere near that 14.4/3.6Vpc, going that high is likely **causing** the cells to go out of balance.

Drop battery's SoC first by say 10A to reduce the risk of overcharging.

If you have control over the current rate, drop that down to 500mA (half an amp), or just at the same rate as the balancing current.

That is now the closest you can get to a "balancing protocol", let it sit there a long time, you should see the cell voltages (very slowly) converge, as the weaker / faster / higher cells trigger a stop-charge, are then bled by resistors at the (very slow) balance rate, then charge resumes, etc.

Inherent in that (common but IMO very stupid) balancing method, is that once cells are greatly out of balance, getting back to proper balance can literally take days.

Hopefully once that has been done, it will happen during the last few minutes of normal cycle usage charging as it is supposed to in theory.

You can help **prevent** getting too far out of balance by, while normal cycle usage charging,

stay at a healthier lower voltage setpoint, as low as possible just over the BMS' start-balance voltage.

Anything over 13.8V will get you to 100% Full, but likely that is too low for the BMS.

Basically, the profile "top goal" should be to stop as soon as the cells are balanced, keeping on pushing to any higher SoC serves no constructive purpose, only reduces lifespan and causes balance problems.

If you are concerned about a so-called "memory effect" then do go up to the mfg-spec stop-charge spec (14.4V) say once or twice a month, but don't worry about precise balancing at that higher point, just watch amps taper to 0.01C then stop.

Also, be aware that the BMS' "stop-bleed-balance" method may be causing you to think the tapering amps has dropped low enough, when in fact it will jump back up to 0.05C or above, after the bleeding cycle has finished.

'Fatal flaw' sounds like you are suggesting they are going to die from this? Over dramatic perhaps?
Many of us agree that not being able to balance cells is not desirable.

[john61ct]

Originally Posted by CatNewBee

The long float phase usually gives enough time at low current to keep the cells balanced using the internal BMS.

I've yet to see a BMS with a start-balance voltage range that low.

Maybe expensive ones, but the internal ones in drop-ins are not that.

[newhaul]

Originally Posted by john61ct

I've yet to see a BMS with a start-balance voltage range that low.

Maybe expensive ones, but the internal ones in drop-ins are not that.

ok please post the technical of the internal bms in the drop ins that explicitly supports your statement .
Btw my bms by design balances constantly regardless of bank voltage . I only paid 10 bucks for it .

[newhaul]

Well I just did a 30 second search on
https://battlebornbatteries.com/shop...cycle-battery/

Downloaded the spec sheet and the manual . Here are a couple screenshots .

Due diligence should be done prior to posting on a new to me subject .

Here is what they say concerning the bms and cell balancing

[CatNewBee]

Originally Posted by newhaul

Well I just did a 30 second search on
https://battlebornbatteries.com/shop...cycle-battery/

Downloaded the spec sheet and the manual . Here are a couple screenshots .

Due diligence should be done prior to posting on a new to me subject .

Here is what they say concerning the bms and cell balancing

That is true. Cheap passive balancer usually start balancing around 3.55V, this is to prevent self discharge when resting, balancing works only near the shoulders because below 80%SOC the voltage differences on cells with different SOC are marginal. Cheap passive balancer simply kick in at the starting voltage and burn energy with increasing voltage, the maximum nominal current e.g. 1A is reached at 3.8V
It is like a Zener diode and a resistor in series, the resistor needs to burn 0.3V at 1A, making it 0.3Ohm 0.5W or 1W, small enough for a cell module and not heating up too much.
They burn the energy independently of each other, no logic necessary. A cell having a higher voltage simply burns more power over the resistor than a cell with lower voltage, causing less current to be stored. Over time the cells are balanced and stay balanced, all 4 balancers burn the same energy at absorption and no energy at float. Dead simple.

OVP /LVP is simple too, the signals are created at the cell and daisy chained, if the cells are in operating range, the signals are passed through, if one cell is outside, the chain is open. This allows to built up large blocks in series for any desired pack voltage, the signal voltage is not related to the pack voltage, usually this are open collector or open drain transistors, opto couplers or the like, the chain is powered by the external logic, one side of the chain usually is connected to ground.

To combine the busses for drop in batteries you can daisy chain ovp and lvp at the cell level or the pack level, you loose the an indicator to the cause of an exception.

[Simi 60]

Anyone heard anything about these?
Seems about half the price of other brands in Australia

240ah 12v lifeP04 deep cycle lithium battery
$1295



https://www.ecocommercial.com.au/240...thium-battery/

[swampbush]

Originally Posted by Simi 60

Anyone heard anything about these?
Seems about half the price of other brands in Australia

240ah 12v lifeP04 deep cycle lithium battery
$1295



https://www.ecocommercial.com.au/240...thium-battery/

I had a look at them but with a 50A bms I would need a lot to run a decent load on the inverter.
Some alternative drop ins for a few dollars more at least have a better current rating.
New solarking 200ah is prismatic cells, but pretty light with a 100amp bms for $1400 https://www.ebay.com.au/itm/NEW-12V-...QAAOSwNe9dSQMw

https://www.ebay.com.au/itm/LiFePO4-...-/253556426388

or
https://www.amptron.com.au/12v-200ah...4-battery.html

I think I wilil go with EV Power Australia with GBS cells and bms with 500A relay. Cost is slightly higher but they have a good reputation.