Solar BMS a solar charge controller for LiFePO4

[mtdoc]

If that is 26V at 65C you still get current at 27V a bit less and not optimum but you do.

Those voltages are not adequate to fully charge a nominal 24V  lead acid or LiFePO4 (8s) battery bank.

What does slow spontaneous discharge means ?

The discharge that occurs in any battery when it just sits, unconnected to any load or charging source.

The two months for my system seems more than reasonable since I will never be away from the system for more than two months. And the chance of PV array to fail is extremely low.

No argument there.

I was only pointing out that your prior statement that for LiFePO4 it "is not possible to damage by keeping it discharged because you have no sun or not doing proper maintenance"  is incorrect - which it is.

[electrodacus]

Those voltages are not adequate to fully charge a nominal 24V  lead acid or LiFePO4 (8s) battery bank.

They are more than adequate at 3.4V under 0.3C charge rate a battery is around 90% SOC
And looking at that IV graph again you can see about 32V open circuit voltage with cell temperature at 65C
So even at 28V battery voltage you still get a decent charge current with cell temperature at 65 even 75C
As I also mentioned few times before if you have any load connected voltage will drop quite a bit more and current from the panel will go to load thus PV panel even in those high temperature work close to max power point.
If you do not have any load and temp of the panels are so high and your battery is at 27V or above it means is in the middle of the day sunny and your battery is above 90% SOC and for LiFePO4 it will be a good thing to slow down charging at this point they hate to be fully charged.
But you are probably a half hour from full charged if your panels is 65 or 75C and battery voltage is 27V.
 

The discharge that occurs in any battery when it just sits, unconnected to any load or charging source.

That self discharge on any good LifePO4 is below 2% capacity per month so as long as you stop at about 10% SOC (3V very low discharge rate OffGrid or 2.8V high discharge rate eBike) you have enough time to recharge as I mentioned before.

[mtdoc]

They are more than adequate at 3.4V under 0.3C charge rate a battery is around 90% SOC
And looking at that IV graph again you can see about 32V open circuit voltage with cell temperature at 65C
So even at 28V battery voltage you still get a decent charge current with cell temperature at 65 even 75C

You will not fully charge a LiFePO4 cell with 3.4V or below.
There's a reason LiFePO4 chargers use a voltage of 3.6-3.65 per cell for the constant voltage portion of the charge cycle.
What voltage does your charger use?

That self discharge on any good LifePO4 is below 2% capacity per month so as long as you stop at about 10% SOC (3V very low discharge rate OffGrid or 2.8V high discharge rate eBike) you have enough time to recharge as I mentioned before.

Sure, but that has nothing with the point I was making about your incorrect statement that you can't damage LiFePO4 batteries by failing to charge them or maintain them.

Look - I'm a big fan of LiFePO4. If I was designing an off grid solar system today I would seriously consider using them instead of LA batteries.  But this is an EE forum and  hyperbolic, incorrect statements such as "MPPT is uneccessary due to cheap PV prices" and " you can't damage LiFePO4  like you can LA by not charging or properly maintaining them" are not going to go unchallenged

[HackedFridgeMagnet]

That self discharge on any good LifePO4 is below 2% capacity per month so as long as you stop at about 10% SOC (3V very low discharge rate OffGrid or 2.8V high discharge rate eBike) you have enough time to recharge as I mentioned before.

Any specs on this?
So if you left some LiFePO4 at 10% SOC. would it be 8% next month, 6% after 2 months, 0% after 5 months?

Roughly at what point do they start getting damaged? Or what SOC should they never go below?

[electrodacus]

You will not fully charge a LiFePO4 cell with 3.4V or below.
There's a reason LiFePO4 chargers use a voltage of 3.6-3.65 per cell for the constant voltage portion of the charge cycle.
What voltage does your charger use?

A LiFePO4 can be charged full 100% SOC with just 3.4V you just need to wait more and charge at lower charge rate.
This not what I wanted to say. I wanted to say that at 3.4V normal 0.2C or 0.25C charge rate the SOC is around 90% so is just a half hour from a full charge when it gets to 3.55V
My charger uses constant current charging only and will stop the charging as soon as the highest cell gets to 3.55V
constant voltage portion of the charge only adds at most 5% more capacity while reducing the life of the battery substantially. This is valid for LiCoO2 also.
A LiCoO2 is you mobile phone or laptop is usually charged in two stages first bulk or constant current up to 4.2V then the constant voltage part until the current drops to 10 or 5% or the initial charge current.
If you only do the fist part of the charge on a LiCoO2 you only get about 85% SOC but the life of the battery will be almost double same thing if you reduce the charge voltage for every 100mV you double the battery life wile reducing a bit the max available capacity.
In military applications 3.95V was used with LiCoO2 so that battery life cycle was about 8x higher. Lithium degradation is related to the amount of time the battery spends at the higher end voltage.
In Phones or other mobile devices the energy density is way more important than cycle life since those are usually upgraded by customers before the battery will die but that 15% extra capacity is more valuable.

Sure, but that has nothing with the point I was making about your incorrect statement that you can't damage LiFePO4 batteries by failing to charge them or maintain them.

Look - I'm a big fan of LiFePO4. If I was designing an off grid solar system today I would seriously consider using them instead of LA batteries.  But this is an EE forum and  hyperbolic, incorrect statements such as "MPPT is uneccessary due to cheap PV prices" and " you can't damage LiFePO4  like you can LA by not charging or properly maintaining them" are not going to go unchallenged

I was referring to a battery protected by a BMS where the discharge is terminated by the BMS at proper voltage level based on battery and application requirement. If that low cut of voltage is properly set for that particular application so that at least 10% capacity is still available then that 10% is enough for that battery and protection circuit to survive a few weeks or months without a charge.
In an OffGrid application you will notice immediately if the load is disconnected and that should never happen in a properly dimensioned installation.

So yes all you need to do to protect a LifePO4 is to keep it between 2.8V and 3.6V and not charge when battery temp below 0C seems way simpler than all the conditions that affect Lead Acid life and can be done by BMS.   

[electrodacus]

That self discharge on any good LifePO4 is below 2% capacity per month so as long as you stop at about 10% SOC (3V very low discharge rate OffGrid or 2.8V high discharge rate eBike) you have enough time to recharge as I mentioned before.

Any specs on this?
So if you left some LiFePO4 at 10% SOC. would it be 8% next month, 6% after 2 months, 0% after 5 months?

Roughly at what point do they start getting damaged? Or what SOC should they never go below?

The open circuit voltage should not go below 2.8V you get all this in any proper LiFePO4 battery spec 2% self discharge is an average some are better some are worst.
here for example is quoted as less than 3% per month for Winston 100Ah cells http://en.winston-battery.com/index.php/products/power-battery/item/wb-lyp100aha?category_id=176
This self discharge rate is also quite dependent on storage temperature the higher the temperature the higher the self discharge rate.
The GBS that I have is also stated as less than 3% per months sorry this is the 200Ah version but I'm sure the 100Ah has the same spec http://liionbms.com/pdf/gbs/LFP-GBS200AH.pdf
Not all manufacturers put this in the spec not sure why.

[HackedFridgeMagnet]

Just noticed, you got funded. Congrats.

[electrodacus]

Just noticed, you got funded. Congrats.

Yes a few hours ago. Thanks.

[mtdoc]

Yes, congrats on getting your funding!.

Roughly at what point do they start getting damaged? Or what SOC should they never go below?

A LiFePO4 cell at 2.0V or below is generally considered permanently dead.

constant voltage portion of the charge only adds at most 5% more capacity while reducing the life of the battery substantially.

Any references on that?  I have seen that stated for other Lithium battery chemistries but not for LiFePO4.

It seems you're claiming something different than all the other LiFePO4 charger manufacturers I've seen.  All the ones I've researched have a constant current stage followed by a constant voltage stage at 3.6-3.65V. This is true for the charges used by home build EVs with LiFePO4 banks and Ebike users. Also, the people who I know of using large LiFePO4 banks for off grid homes are using one of the currently available programmable MPPT controllers with CC and CV stages.

I was referring to a battery protected by a BMS where the discharge is terminated by the BMS at proper voltage level based on battery and application requirement. If that low cut of voltage is properly set for that particular application so that at least 10% capacity is still available then that 10% is enough for that battery and protection circuit to survive a few weeks or months without a charge.
In an OffGrid application you will notice immediately if the load is disconnected and that should never happen in a properly dimensioned installation.

So yes all you need to do to protect a LifePO4 is to keep it between 2.8V and 3.6V and not charge when battery temp below 0C seems way simpler than all the conditions that affect Lead Acid life and can be done by BMS.

Ok thanks for clarifying but that's entirely different than your previous statement and in fact no different than Lead Acid batteries in that as long as you properly maintain them they do no suffer premature damage.

[electrodacus]

Yes, congrats on getting your funding!.

Thanks.

Any references on that?  I have seen that stated for other Lithium battery chemistries but not for LiFePO4.
It seems you're claiming something different than all the other LiFePO4 charger manufacturers I've seen.  All the ones I've researched have a constant current stage followed by a constant voltage stage at 3.6-3.65V. This is true for the charges used by home build EVs with LiFePO4 banks and Ebike users. Also, the people who I know of using large LiFePO4 banks for off grid homes are using one of the currently available programmable MPPT controllers with CC and CV stages.

LiFePO4 is no different in this regard from any other Lithium-ion battery. The less time it spends above 3.4V the better.
There is actually even less advantage for LiFePO4 to be fully charged (using CV) since you only get about 5% extra vs LiCoO2 where is more significant at 15% extra.
If you charge LiCoO2 with about 0.3C up to 4.2V CC and then terminate charging immediately the capacity is at 85% SOC
If you charge LiFePO4 with about 0.3C up to 3.6V CC and then terminate charging the capacity is 95% SOC
The degradation on both is based on the time spend charging at that higher voltage and temperature.
In portable applications those 15% extra make sense as I mentioned.
The manufacturers of LiFePO4 of course want to specify a larger capacity so by using CC and CV charging in their spec they can quote a 5% larger capacity.
They usually do cycle life test at high charge discharge rates around 1C so time spent at 3.6V is extremely small not enough to make a significant impact in cycle life.
In a solar setup using normal MPPT Lead Acid charger with CC and CV charging you will keep the battery for many hour every day forced at that higher than 3.4V level.
LiFePO4 at rest is below that 3.4V so keeping it above that creates stress and encourages dendrite growth.
The dendrite formation on LiFePO4 is less problematic than LiCo variants but will still exist and affect the life of the battery even if is harder to see in real life do to superior cycle life of the LiFePO4.

Ok thanks for clarifying but that's entirely different than your previous statement and in fact no different than Lead Acid batteries in that as long as you properly maintain them they do no suffer premature damage.

Is different from Lead Acid in the sense that if lead acid is kept at a partial state of charge for long periods the life of the battery is affected and in OffGrid solar that is where the battery spends most of is life and not fully charged. As soon as the sun is set the battery will be at a partial state of charge and there can be many days in a row in this partial state of charge.
In this conditions LiFePO4 feel the most comfortable is where they love to be, where Lead Acid will sulfate and battery capacity will be affected.
Lead Acid has also a much higher self discharge rate but normally not a problem in OffGrid applications same as lower energy density is also normally not a problem in stationary off grid applications.

[mtdoc]

In a solar setup using normal MPPT Lead Acid charger with CC and CV charging you will keep the battery for many hour every day forced at that higher than 3.4V level.

No - not many hours. Usually just until you meet your specified end amps.

LiFePO4 at rest is below that 3.4V so keeping it above that creates stress and encourages dendrite growth.
The dendrite formation on LiFePO4 is less problematic than LiCo variants but will still exist and affect the life of the battery even if is harder to see in real life do to superior cycle life of the LiFePO4.

Ok - sounds reasonable enough but it seems that you're making a pretty remarkable claim - that is that you know something the other LiFePO4 charger manufacturers don't - some actual references to support your theory would be nice. I mean there are many battery chemists, physicists, and engineers who have spent a lot of time developing LiFePO4 technology.  How is it that you know something they don't - or if they do - where have they published it?

[electrodacus]

Ok - sounds reasonable enough but it seems that you're making a pretty remarkable claim - that is that you know something the other LiFePO4 charger manufacturers don't - some actual references to support your theory would be nice. I mean there are many battery chemists, physicists, and engineers who have spent a lot of time developing LiFePO4 technology.  How is it that you know something they don't - or if they do - where have they published it?

What other LiFePO4 chargers ?
I do not know how Sony and Bosch implemented their chargers for their complete solution but I can guess they only use CC as I do to get the most out of their battery.
Also all car manufacturers have implemented 80% fast charging so that the battery can last much longer with the option of full charge in case you realy need that extra range to the detriment of battery life. This is with LiCo variants.
With LiFePO4 and stationary storage is just 5% that you gain by doing CV charging and no advantage (like the extra range on cars).
There are very few experts in Lithium battery charging and most chargers you probably refer to as those Lead Acid chargers where they added support for LiFePO by just adding a new limit are far from experts and do not care if your battery life is affected it will still be long enough that no one will notice or realise.
And most of those BMS designed for DIY EV cars are as or even worse designed.
With those usually cell voltage is allowed to even exceed 3.6V accelerating even more battery degradation. Inefficient cell balancing done on individual cell not taking in to account the other cell voltages so no being able to do an effective cell balancing.
All this and more are the reason I decided to invest the time and do my own version.
Most laptops for example will charge the battery with CC and CV to 4.2V with no option to set that lower to prolong the battery life except for some expensive IBM / Lenovo models that have that functionality in BIOS. I mostly used laptops plugged in and kept the battery there as an UPS sort of protection but that damaged the battery quite fast I will have liked to have such a function so that battery will only be charged to 80% and last a lot longer.
It dose not mean that other laptop manufacturers did not know about this benefit is just that they did not care the battery lasted enough anyway and they preferred that they clients where happy with the run time did not care they will need to buy another laptop or battery soon after the warranty was gone
Same with my current phone with non removable battery that is almost dead because the phone is always connected to charger since the phone is used for internet acnes all day.

You probably know this graph from battery university about the cycle life versus just small cell over voltage on LiCoO2 the LiFePO4 has better tolerance to over voltage but the life cycle will still be affected in a similar way.

[mtdoc]

Ok - sounds reasonable enough but it seems that you're making a pretty remarkable claim - that is that you know something the other LiFePO4 charger manufacturers don't - some actual references to support your theory would be nice. I mean there are many battery chemists, physicists, and engineers who have spent a lot of time developing LiFePO4 technology.  How is it that you know something they don't - or if they do - where have they published it?

What other LiFePO4 chargers ?

Many. Here's two companies to start:

Manzanita Micro
Powerstream

From Powerstream (the second link):

During the conventional lithium ion charging process, a conventional Li-ion Battery containing lithium iron phosphate (LiFePO4) needs two steps to be fully charged: step 1 uses constant current (CC) to reach about 60% State of Charge (SOC); step 2 takes place when charge voltage reaches 3.65V per cell, which is the upper limit of effective charging voltage.

You probably know this graph from battery university about the cycle life versus just small cell over voltage on LiCoO2 the LiFePO4 has better tolerance to over voltage but the life cycle will still be affected in a similar way.

Nice graph but not relevant to the question.

BTW - I'm not disputing that you can charge LiFePO4 cells at 3.4V - it's just that I've never seen any data supporting what you say about a CC stage followed by a CV stage at 3.6V shortens battery life.

LiFePO4 do have the advantage over LA in that the don't sulphate or otherwise degrade by chronic mild undercharging.  But with LiFePO4 batteries relatively expensive - I don't think anyone will want to pay for more capacity than necessary/

[electrodacus]

Many. Here's two companies to start:

Manzanita Micro
Powerstream

From Powerstream (the second link):

During the conventional lithium ion charging process, a conventional Li-ion Battery containing lithium iron phosphate (LiFePO4) needs two steps to be fully charged: step 1 uses constant current (CC) to reach about 60% State of Charge (SOC); step 2 takes place when charge voltage reaches 3.65V per cell, which is the upper limit of effective charging voltage.

They have absolutely no idea of what they talking about.
How will a LiFePO4 with CC charging to 3.65V be just 60% SOC it will be around 95% and even their own graph shows that. I do not what to insert that graph here since it shows LiFePO4 charging to 4.2V that no LiFePO4 battery manufacturer will approve.
If you look at their graph it shows around 90% (not 60%) charge level after CC up to 3.6V and that is at 0.5C rate a bit high most battery manufacturers recommend 0.2 to 0.3C for long life not fast charging.
Then they talk about LiFePO4 self balance (again absolute garbage) I hate to see that website as reference to anything. There is no loss reaction like hydrogen production in Lead Acid to allow for self balancing by wasting energy on the overcharged cell.
The say all this garbage so they can sell 12V LiFePO battery without any real protection. All and I mean all 12V LiFePO4 sold as replacement for Lead Acid are useless at best for many reasons. Cells will become unbalanced since proper balancing and charging can not be stopped on cell over-voltage unless it gets critical and second they do no make a good starter battery replacement since they will get damaged if charged below freezing (by an effect called lithium plating that is irreversible and leads to capacity loss).
Sorry about language I got a bit annoyed by that Powerstream page

Nice graph but not relevant to the question.

BTW - I'm not disputing that you can charge LiFePO4 cells at 3.4V - it's just that I've never seen any data supporting what you say about a CC stage followed by a CV stage at 3.6V shortens battery life.

LiFePO4 do have the advantage over LA in that the don't sulphate or otherwise degrade by chronic mild undercharging.  But with LiFePO4 batteries relatively expensive - I don't think anyone will want to pay for more capacity than necessary/

Like I mentioned before Battery manufacturers give spec based on dual stage CC and CV up to 3.6V most mention that 3.65V is acceptable in a sting of series connected cells for the highest cell.
The Solar BMS does not charge the battery at 3.4V but at 3.55V (highest cell not average pack voltage) then as soon as it gets there it stops charging so that battery is as much as possible above 3.4V and charging. With this do to the nature of the solar PV panels I can achieve 100% SOC wile only using constant current charging and not exceeding 3.55V on any cell.
Cells are also balanced within 10mV because the balancing is done at any voltage level by comparing each individual cell voltage and not using fixed voltage threshold where balancing is performed independent of the other cell voltages as other less complex balancers do.
 

I say price of LiFePO4 can be the same as quality Lead Acid because you can do the same thing with half capacity do to higher charge-discharge efficiency and higher DOD accepted.
I use a 2.5kWh battery with an average monthly power consumption of 80kWh. For that you will need probably around 3x capacity with Lead Acid even if is just about the 0.1C charging recommendation on Lead Acid. My panels put up to 30A in cold whether that is acceptable for 100Ah LiFePO4 but will require a 300Ah Lead Acid.
I actuals have even better ideas for the future with the integration of the Solar BMS and Digital MPPT and large PV array where with this same battery I can increase power consumption to 150 even 200kWh/month with infinite autonomy in any sort of whether conditions.

[mtdoc]

Many. Here's two companies to start:

Manzanita Micro
Powerstream

From Powerstream (the second link):

During the conventional lithium ion charging process, a conventional Li-ion Battery containing lithium iron phosphate (LiFePO4) needs two steps to be fully charged: step 1 uses constant current (CC) to reach about 60% State of Charge (SOC); step 2 takes place when charge voltage reaches 3.65V per cell, which is the upper limit of effective charging voltage.

They have absolutely no idea of what they talking about.
How will a LiFePO4 with CC charging to 3.65V be just 60% SOC it will be around 95% and even their own graph shows that.

I think you're misreading what they wrote. I read it to mean it is the second, CV stage with a charging voltage of 3.65 that completes the charging.  The 60% is what they cite for the 1st, CC stage.

But regardless, I don't hold them to be "the experts". You asked for links to charger manufacturers that use CC - CV staged charging and I just linked them as one. I am not familiar with them or their products beyond what their web site says.

I am familiar with Manzita Micro who make very high quality chargers used for EVs and who also do CC - CV staged charging.

Like I mentioned before Battery manufacturers give spec based on dual stage CC and CV up to 3.6V most mention that 3.65V is acceptable in a sting of series connected cells for the highest cell.
The Solar BMS does not charge the battery at 3.4V but at 3.55V (highest cell not average pack voltage) then as soon as it gets there it stops charging so that battery is as much as possible above 3.4V and charging. With this do to the nature of the solar PV panels I can achieve 100% SOC wile only using constant current charging and not exceeding 3.55V on any cell.

You realize that a charge voltage of 3.65 during the CV stage does not mean you actually charge the cell to that voltage, right? As soon as it is disconnected from the charger the voltage will drop - just as it at the end of the absorption stage in traditional LA 3 stage charging algorithms.

So, I'd still like to see some references to support your idea that using lower charge voltages and only a CC stage improves the lifespan of LiFePO4.   This is not an academic question. If it's true I'd really like to see the evidence so that I can consider it in the care of my eBike LiFePO4s and probable future LiFePO4 battery bank for off grid use.

Any actual references to support your idea?
 

[electrodacus]

I think you're misreading what they wrote. I read it to mean it is the second, CV stage with a charging voltage of 3.65 that completes the charging.  The 60% is what they cite for the 1st, CC stage.

Yes I read correctly no misunderstanding with the first CC charge to 3.65V you get well over 90% even at 0.5C charge rate and not 60%.

You realize that a charge voltage of 3.65 during the CV stage does not mean you actually charge the cell to that voltage, right? As soon as it is disconnected from the charger the voltage will drop - just as it at the end of the absorption stage in traditional LA 3 stage charging algorithms.

You can only say you do CV charging when the voltage is at that level you specify as CV charging voltage before that is CC charging.
If you apply a CC-CV charger (can even be a lab power supply)
You set the Voltage at 3.65V and constant current limiting say at 5A for a 10Ah cell
Say cell is fully discharged when you connect.
Cell will be in CC mode for about 110 minutes probably and then get to 3.65V and constant voltage will start and current will slowly drop at this point cell is well over 90% charged probably 95% and during constant voltage part of the charge where battery voltage will stay for around 20 minutes or so at 3.65V and current will drop you will gain the rest of that 5% or so SOC to 100% but this part of the charge is the one having the most stress on battery for almost no gain (that extra 5% is useless but the battery degradation is relatively high)
Not sure anyone has done long therm testing on this but I expect about 20% lower life for batteries charged with the second stage CV so you gain 5% additional capacity that you have no use for anyway and lose 20% of your battery life.
Anyway this is fine but charging LiFePO4 to 4.2V fast charging as they suggest on the page will drop the battery life by at least a factor of 5 and instead of 10 to 20 years you get at most 2 to 4 years out of your battery.
Yes LiFePO4 will not catch on fire at 4.2V but will suffer the same way as if you charge a LiCoO2 at 4.35V instead of 4.2V as you seen in that graph a few post earlier.
There are quite a few variation of LiFePO4 my GBS for example is LiFeMnPO4 the Winston is LiFeYPO4 some do not specify any additional elements and are more plain LiFePO4 but still have some unlisted additives that make they battery spacial. Each of this will react a bit different to overcharging but they will all get affected.
Is quite easy to see what the optimum working voltage is for any Lithium battery by just looking at a charge discharge curve.

In a car people want a charger that gets 100% SOC so CC-CV    because they want as much capacity as they can get even if arguably this is useless for LiFePO4 where you only gain 5% by that CV stage.
Most EV car manufacturers use LiCo because it has 2x the energy density of LiFePO4 and can get 2x the range. There they gain 15% extra by using CV so is more significant and they implement that but they also have a recommended 80% charge if you do not need the extra so that you can have a longer battery life.
You can go and check the spec and recommendation of any care manufacturer.
So they care about battery life but at the same time are interested in higher range in the detriment of battery life.
Stationary energy storage normally dose not care about using the entire battery capacity especially since this comes to the detriment to battery life.
All DIY solar installations use a car BMS in combination with a Lead Acid charger in combination with LiFePO4 and that is because there is no real alternative and because there is not enough eduction about Lithium in stationary energy storage.
If you did not see this you should watch is a relatively good video about Lithium-ion batteries in general

[mtdoc]

I think you're misreading what they wrote. I read it to mean it is the second, CV stage with a charging voltage of 3.65 that completes the charging.  The 60% is what they cite for the 1st, CC stage.

Yes I read correctly no misunderstanding with the first CC charge to 3.65V you get well over 90% even at 0.5C charge rate and not 60%.

That depends entirely on how long the CC stage is. Also the goal of a CC stage is not to "charge to 3.65V".  Surely you understand how multistage charging works ?

I do agree that CC-CV charge algorithms generally do not bring the battery to only 60% SOC by the end of the CC stage - I suspect it was a typo and meant to be 90%

But what you said is:

They have absolutely no idea of what they talking about.
How will a LiFePO4 with CC charging to 3.65V be just 60% SOC it will be around 95% and even their own graph shows that.

Which I don't understand how that came from what they wrote (right or wrong) - but that's besides the point.

All DIY solar installations use a car BMS in combination with a Lead Acid charger in combination with LiFePO4 and that is because there is no real alternative and because there is not enough eduction about Lithium in stationary energy storage.

No. There are BMS designed specifically for RE installations. Though I agree there needs to be more.

In any case, based on your (non) answers - I guess your charging algorithm is based on your own ideas. Nothing wrong with that.  It will be interesting to see the evolution of LiFePO4 charging as they become more widely used in home RE systems.

Good luck with your Kickstarter product.

[electrodacus]

In any case, based on your (non) answers - I guess your charging algorithm is based on your own ideas. Nothing wrong with that.  It will be interesting to see the evolution of LiFePO4 charging as they become more widely used in home RE systems.

Good luck with your Kickstarter product.

The advantage of my Solar BMS is that is fully programmable by user over 30 parameters can be programmed that affect how the charging is done.
There are present parameters that I recommend but if you think something else is better you can do that very easy.
99% of Off-Grid people still use Lead Acid so there is a long way to go for Lithium batteries.
Education about lithium batteries is extremely important for their adoption.
I see Lead Acid vs LiFePO4 as Incandescent vs LED was a few years ago.

[mtdoc]

I agree. It's early in the LiFePO4 adoption phase. Lots of room for experimentation. 

LiFePO4 prices still need to come down a bit and BMS systems to be more robust.

One thing LA still has on LiFePO4.  One bad mistake will generally not kill a LA battery as it will a LiFePO4 cell.

[electrodacus]

I agree. It's early in the LiFePO4 adoption phase. Lots of room for experimentation. 

LiFePO4 prices still need to come down a bit and BMS systems to be more robust.

One thing LA still has on LiFePO4.  One bad mistake will generally not kill a LA battery as it will a LiFePO4 cell.

I will say LiFePO4 is already cheap enough especially when considering the alternative.  My choice of LiFePO4 was based on price mostly.
As I mentioned using a good BMS should not allow for any mistakes.

Price calculation should be done something like this. Here is the best Lead Acid (the new so called smart carbon) vs the best China based LiFePO4 (Sonny or A123 will be way better but they are harder to get)
This are idealized prices based on spec real life cost of energy storage will be higher so prices are for comparison and no one should take this as the real life price and go OffGrid (grid is still better than OffGrid)

 

 

[mtdoc]

Sorry, but you lose some credibility with a table like that which is very skewed in its numbers and assumptions.

The Trojan L16RE-2V batteries are a top of the line LA battery with a 7 year warranty and can be expected to routinely last 10 yrs or more from a company with a  long history of real world experience and your comparing them to a no name Chinese brand with no warranty and no proven track record with an optimistic guess of 20-25 yr lifespan.

The L16RE-2V have a (20hr) Ah rating of 1110 not 1021.
Charging efficiency of these is typically going to be much better than 75%  - more like 85%,

Again - I'm a big fan of LiFePO4 based on their real merits. No reason to overhype them. It just makes knowledgable consumers skeptical of what you're selling.


Also, where are you finding that price for the WB- LYP400AHA? the best price i can find online is about $1000 more than your number.

[electrodacus]

Sorry, but you lose some credibility with a table like that which is very skewed in its numbers and assumptions.

The Trojan L16RE-2V batteries are a top of the line LA battery with a 7 year warranty and can be expected to routinely last 10 yrs or more from a company with a  long history of real world experience and your comparing them to a no name Chinese brand with no warranty and no proven track record with an optimistic guess of 20-25 yr lifespan.

The L16RE-2V have a (20hr) Ah rating of 1110 not 1021.
Charging efficiency of these is typically going to be much better than 75%  - more like 85%,

Again - I'm a big fan of LiFePO4 based on their real merits. No reason to overhype them. It just makes knowledgable consumers skeptical of what you're selling.

This comparison is purely based on manufacturer data-sheet.
Is not reasonable to use capacity at 20h since most of the energy consumption will be at much higher discharge rate.
Charge efficiency of a Lead Acid in the top 20% of SOC where most Lead Acid are use are way worse close to 50% so my 75% average efficiency was relatively optimistic.
85% is close to the best case if you do not include the top SOC charge.
But even if you want to ad this more optimistic values price will improve just slightly to $0.233/kWh so still as bad compared to LiFePO4
And LiFePO4 will have more chances to met the spec since it will probably not be discharged daily at 70% and the number of charge cycles rise almost exponentially and not in a direct linear way as on the new Lead Acid battery where there is zero advantage to cycle the battery at 20% vs 50% DOD at least based on spec it was not the case with older Lead Acid where using the battery closer to the top SOC provided a somehow better cycle life so more energy over life.
I'm a bit sceptical on their claim but I take the spec as it is.   
Winston is a large battery manufacturer and independent tests done by universities and private laboratories show their spec is correct or extremely close.

I will know more in a month when I have two years of full offgrid on my LiFeMnPO4 battery from GBS I expect 4% capacity loss if my expectations are met then this battery will be the one I recommend (based on spec is one of the worse compared to other LiFePO4)
And again if that 4% loss is right my cost per kWh including all equipment (SBMS + inverter + PV panels) + battery amortisation cost per kWh is 16 cent
So that will make even grid look bad in many countries. But that is just equipment dose not include installation cost so the price will be valid just for DIY that enjoy installing this and do not count their time as money .
I have a youtube video with the way I made capacity measurement on my GBS battery 3 years ago (one year battery was mostly in storage) and I have all the equipment so I can replicate exactly and precision will be good enough to be able to see a few % difference.

[mtdoc]

The 20AH rate is the standard number used in the RE industry since it most closely approximates a 24 hr day. It's impotant to use that number when discussing AH ratings with RE system designers.

I can find nothing on where the 400 AH rating comes fom on the WB-LY400AHA datasheet. Is it 10h, 20h, 100h?

You really need to compare apples to apples.

Charging efficiency does drop off at higher SOC but it's not as simple as you state.

When discussing charge efficiency, you need to be sure you understand the difference between energy efficiency and AH efficiency.  As you know when batteries (LA or LiFePO4) are close to full they do not accept charge as easily. But PV panels as current sources simply decrease current.  Potential electricity production from the PV is wasted but that does not mean that the AH in/AH out - which is what most people mean when they discuss charge efficiency - is dropping off that quickly as well.

Real world experience from off grid users who cycle their batteries daily and closely track SOC, AH in and out via shunt based battery monitors and SG readings shows average efficiencies > 80% IME - and depending on the type of LA battery can be >90% (e.g. with AGMs).

When people quote 95% charge efficiency for LiFePO4 they are talking about AH efficiency not energy efficiency.

Again - you need to compare apples to apples for a fair comparison.

Anyways, my point is really that you shouldn't pick best case numbers for LiFePO4 and worse case for LA when doing a comparison. LiFePO4 stands up on its own merits and skewed comparisons damage credibility.

[Mike_del_Caribe]

Have you retested the capacity of your system now that it has passed the two year mark?

Is there any need to balance or equalize LiFePO4 cells?  If so, how is this done?  Would periodic CV charging do this?

[electrodacus]

Have you retested the capacity of your system now that it has passed the two year mark?

Is there any need to balance or equalize LiFePO4 cells?  If so, how is this done?  Would periodic CV charging do this?

I was extremely busy and did not had time to test the capacity I will do that probably in the spring when there are 3 years of full offgrid use 4 years since I purchased the battery.
Is a bit hard to test since this is my main source of energy.
I'm also curious is for sure less than 10% since if it will have been more I will have noticed.
Yes a small cell balancing current is required to maintain the cells in balance. The charge discharge rate is very small in offgrid energy storage around 0.3C for charging and 0.5 to 0.6C for discharging.
In this conditions my cells (100Ah GBS) without any cell balancing will get about 1 to 2% imbalance after 3 to 4 months of use.
But now there is no imbalance since I use the SBMS4080 for the last year and that keeps the cells in balance with small cell balancing current.
I'm working now on the next version SBMS100 so I'm really busy with this but in spring I will take one day to test the capacity loss on this GBS cells.