4 hours ago, Wick said:

@ebrsa Please don't hijack threads; rather start a new one to ask about your specific situation.

@ebrsa is one of the old guys around here. He participates far too infrequently these days. And believe me, we've had some disagreements (always respectfully of course) many times over the past 7 years or so 🙂

Let me be a bit more specific just so that there are no misunderstandings. I always say that you get different levels of BMS functionality.

On level one you have basic protection. If a cell is low or if another cell is high, then the BMS disconnects. On this level there isn't even cell balancing, and though you may not believe it, there are some very very low end battery packs (usually for toys, not serious stuff) that have no more than this most basic of protections.

On level 2, you get cell balancing. At this level there is still no comms with anything.

Level 3, basic protection features in the shape of a relay that opens/closes to indicate that you should stop charging or discharging. This is very very basic comms, and is useful because you can avoid that absolute shutdown that leaves the entire house in the dark. Victron Smart Lithium batteries are on this level.

Level 4, SOC tracking.

Level 5 adds full communications where the battery can mandate a charge and discharge rate.

Now my point in this whole long thread was simply that you don't need level-5 capability to run an LFP battery. But you need at the very least level 2 for this game.

In a properly designed system (where your PV is sized correctly to the battery capacity), a BMS never has to intervene. This is how you want it.

Now with all of that said, you must also look at the fine print of your battery warranty. Some of them have shorter warranties if you don't have that level 5 charge and discharge control, so again, don't just take my word for the gospel just because I talk a lot 🙂

Also, chemistry play a role. For the longest time (maybe still, I haven't checked lately) LG Resu batteries could not be used off-grid. Why? Cause they are not LiFePO4, they are a different chemistry, and in an off-grid system (or a non-hybrid one) there is no way to control charge and discharge current.

Edit: The above "levels" is just my own understanding of the matter. They are not text-book 🙂

Edited August 9, 20206 yr by plonkster

On 2020/08/08 at 10:06 AM, Wick said:

From a cost vs lifetime perspective, active cell-level balancing is absolutely essential - and this is not something your inverter charger is going to do for you - not even a fancy Victron. They will see only the overall battery,  not the individual cells. Caveat emptor, unless you want to risk severely unbalanced cells and the knock-on effects of that over time (cells with permanently different profiles, at best resulting in capacities reduced to the lowest common denominator).

Care to share some actual statistics from your vast experience and/or research. How many years..months...weeks...days...hours...minutes... seconds will a pleb like me lose from a LiFePO4 battery if not utilising active cell balancing? Perhaps you prefer to rather state this in total kWh loss? It will be especially illuminating to know the real world effect of active vs passive (differentiating top and bottom balancing) vs no balancing.

On 2020/08/08 at 10:06 AM, Wick said:

For a few days' test though? Fine without. Manually rebalance your cells and carry on

How many days? 5 okay but 6 you lose your entire investment? 

On 2020/08/08 at 10:06 AM, Wick said:

Bottom line for newcomers - be wise - get a BMS that can talk your inverter. Always. In 2020 (onward) there is very little reason not to.

 So, clearly you should ALWAYS use a BMS that can talk to the inverter except you ( @Wick ) know of some reason/s not to... care to elaborate what it might be?

On 2020/08/08 at 10:06 AM, Wick said:

(And no, I don't buy that older lithium systems that were set up without BMS & only inverter settings, are "just fine", unless that means only functional... functional does not imply optimal.

What is the criteria for an optimal lithium system?

On 2020/08/08 at 10:06 AM, Wick said:

If it were optimal, then BMS technology and sales wouldn't be advancing at a rapid pace... BMS would be no more than a curious side feature of the lithium market.)

Strange how no one bought Valentine's days cards...until someone started selling them. Not sure something selling is proof that it is somehow important.

3 hours ago, Wick said:

@ebrsa Please don't hijack threads; rather start a new one to ask about your specific situation.

I saw some kids smoking behind the bike shed... do I report them to you?

3 hours ago, Wick said:

"BMS / inverter comms or not" is a whole separate discussion from what I broached here yesterday.

But will you allow it in this thread, or must it be a totally new thread? The OP specifically referred to "the BMS (Battery Management System) that is built into your expensive new Lithium battery should ALWAYS be connected to your inverter via a comms cable".... "unless its physically not possible".

2 hours ago, Wick said:

I read your post and understood it very clearly.

Then why did you answer the fictitious question of "does my existing setup meet Wick's list of criteria for a LiFePO4 system?" as opposed to @ebrsa's actual question of "when utilizing a LiFePO4 system in the future with an ANT BMS and an inverter with ICC on RPi, is there any extra benefit to having the BMS communicate directly with the inverter?" The latter question is actually totally in keeping with the topic of this thread and even some of your posts?

2 hours ago, Wick said:

 self-serving and / or doesn't have to do with the original topic.

Please share how the question of what additional, if any, benefit is gained by BMS-inverter comms from a particular BMS is either self-serving or clearly totally irrelevant to the thread. 

1 hour ago, Wick said:

*user ignored for gaaning aan and derailing thread further*

User posting something in total contradiction of his/her stated aim of allowing only posts deemed 100% relevant to the topic of the thread.

This young grashopper eagerly awaits further teaching by the master

26 minutes ago, introverter said:

active cell-level balancing is absolutely essential

I just noticed you quoted this and realised I have to disagree with that...

Active balancing means you have small isolated DC/DC converters and switching gear so that charge can be sucked off one cell and put into another.

Passive balancing means you have resistors across each cell, again with some switching gear, usually MOSFETs, that bleeds off/bypasses some energy from the high cells so that the lower ones can catch up.

Active balancing is more expensive but more efficient.

Now here is some news for those who don't know.... the bulk of the batteries out there, big names in the industry... have only passive balancing, and they only balance at the top. This means you have to fully charge the battery every now and then, usually once a week or once a fortnight (that's a British term meaning two weeks). It really is good enough.

What is more, an active balancer is also limited in what it can do. While it can in theory balance all the time, this doesn't actually work that well. When the battery is being charged or discharged heavily, phantom imbalances show up all over (well not really phantom, but due to the fact that no two cells are alike across their whole range) and if the BMS tried to move charge around it would just be wasting its time. An active balancer can only really balance when the cells are at rest or close to it, and of course right at the top and at the bottom.

So again, it really is a good question whether the premium you pay for that active balancer is worth it. Sure it is really nice, and I often rave about batteries where this is done right (such as the Discover AES), but it really isn't essential.

Edited August 9, 20206 yr by plonkster

47 minutes ago, introverter said:

The OP specifically referred to "the BMS (Battery Management System) that is built into your expensive new Lithium battery should ALWAYS be connected to your inverter via a comms cable".... "unless its physically not possible".

Given that I'm the OP and my previous statements are being quoted with meaning in these... Exchanges... I should probably clarify a few things. 

That quote above was, in retrospect, probably a bit too specific, and hyperbolic, and the "always" in capitals was a bit over the top without clear context

I should have been clear that I meant that in the specific context of only the battery and an inverter involved in the whole stack, and in the context of it being a choice between the inverter itself using the BMS data to manage the battery, vs it ignoring the BMS and going old school. 

I was not making allowance for scenarios where the battery and or inverter are connected to some other thing, like a Pi, which is doing additional monitoring and management, in which case, as fas as I can tell, it looks like you don't ALWAYS need the inverter talking to the BMS directly because the BMS will be looking after the cells regardless, and the Pi (or whatever other thing you have talking to your inverter and running management software) will be getting involved in other decisions, and potentially even monitoring the batteries directly too, without the inverter involved. 

So technically, my inflammatory ALWAYS assertion is not quite true, depending on specific context. 

Sorry if that OP comment caused confusion and disagreement.

 

Edited August 9, 20206 yr by SiliconKid

32 minutes ago, SiliconKid said:

That quote above was, in retrospect, probably a bit too specific, and hyperbolic, and the "always" in capitals was a bit over the top without clear context

So technically, my inflammatory ALWAYS assertion is not quite true, depending on specific context. 

Sorry if that OP comment caused confusion and disagreement.

For what it is worth, I referred to your original post only in relation to whether a question about BMS and inverter communication could be considered off-topic to the thread and I for one do not think your post/s contributed to disagreement.... EDIT: and even if it did, disagreement does not have to be inherently negative - so no apology called for 🙂

Edited August 9, 20206 yr by introverter
EDIT

Sjoe, some Keyboard warrior going wild on this post. 

 

11 hours ago, Wick said:

@ebrsa Please don't hijack threads; rather start a new one to ask about your specific situation.

His questions seems fair, no need to start a new thread... 

 

11 hours ago, Wick said:

It is for newbies like you that I gave that warning -

Wow, be careful @Wick, this kind of attitude will not be tolerated on Power Forum. 

@ebrsa has been a member of this forum for a few years already and his by no means a "newbie". Lithium's might be new to him, but thats why his asking...

 

8 hours ago, ebrsa said:

That has never been the spirit in which commmunications on this forum has been conducted and I sincerely hope it is not an indication of what is to come.

Rest assure,  not at all..

16 hours ago, ebrsa said:

 I have re-read the thread and noticed that you have essentially answered my question. Your reply confirms my perception that communication between a BMS and a properly controlled inverter is not a requirement. It would seem that if a supported BMS is connected to a RPi running ICC-Pi  a BMV7xx connected to the RPi is not required as the BMS would communicate the required accurate information. So if one already has a RPi with connected BMV7xx and replaces lead-acid batteries with LifePO4 cells and a suitable BMS, there would be no benefit or indeed purpose in also connecting the BMS to a RPi running ICC-Pi.

Just like the near impossibility of standardising the off-grid vs hybrid vs grid-tie inverter terminology, the battery and BMS terminology can also be somewhat problematic - me thinks.

One probably has to distinguish between off-the-shelf batteries like the pylontechs etc. and the DIY buy-your-cells-add-what-you-need/want batteries. "BMS" also does not mean just one thing (as very succinctly pointed out by @plonkster). When adding ICC into the mix it becomes more complicated still. It seems like ICC can use the communication ability of some of the "off-the-shelf" battery BMS (like pylontech) to control the inverter.

With a DIY battery setup, you most likely have a slim chance of (direct) comms between inverter and BMS at all. Does ICC allow for any direct comms from any non (Pylontech, Revov, Narada, Hubble) BMS?

One specific benefit from having comms and associated inverter control from a BMS will likely be that the ability of the BMS to move/stop current to individual cells is limited. So, to help out the BMS asks/tells the inverter/charger to cut back on the charging current. So unless the DIY (ANT) BMS can do this via ICC, the BMV7XX will likely not add that ability either - the BMV7XX will only see total current in/out of the battery and not be influenced by the battery BMS wanting/needing reduced current? The risk then would be potential development/worsening of cell imbalance/s. 

So, the question is whether DIY cells + ANT BMS + ICC +( ? BMV7xx) = properly controlled inverter. ?

@introverter maybe if someone can ask ICC them if they can maybe get hold of a ANT+ Smart bms and design a cable and to get it working with there software, then that will be nice. The screen actually got CAN-H and CAN-L output but it needs the VP230 chip on it. The screen is RX en TX to communicate to the BMS.  Maybe a SN65HVD2300 can work for this. Revov is using the Smart ANT bms on there 24v units. 

Edited August 10, 20206 yr by Gerlach

@plonkster While we did vigorously though politely discussed the legality of the Axpert inverters based on CofCT's regulations in the past, I was just trying to find a legal way to connect my Axperts to the grid. I recall that you proposed that replacing them with Victron would be a solution but, with some justification, questionable as the Victron equipment would probably outlast me. All that was to be expected as you are after all a commited member of the Blue Warriors whereas I am one of the Axpert Barbarians. This is meant to be a joke before someone gets sensitive and for those who do, go buy Douglas Murray's book "The Madness of Crowds" and read it.

Jokes aside, thanks a great deal for your detailed answers to my question. I also appreciate your post on active equalisers and it corresponds with those of one Will Prowse who tested  them and posted a video on Youtube. His test of the Smart ANT BMS was also quite interesting and he seems quite enthusiastic about it. It is therefore good to see that a local importer now also has the 100A version available.

@introverter  Your detailed and logical analysis and answers is likewise appreciated.

Regarding your post of this morning, it would seem to me that the ICC-Pi/RPi combination with a BMV7xx provides the intelligence that the Axpert lacks. It seems to alter the Axpert settings as required to manage the inverter. As @plonkster said, if you have a well designed system, the BMS should not have to interfere. In his post of 24 February he said "the best BMSes out there are the ones that don't apply charge current limits". Since the BMV provides accurate information to ICC-Pi regarding battery voltage, current and SOC, ICC-Pi can process the information and appropriately control the inverter. It my understanding that a BMS  manages these parameters as well as cell balancing. The video by Will Prowse on Youtube was quite interesting and the information of the control app on a mobile phone very impressive.

What I don't know is whether there are inverters that are smart enough to process all the information that a BMS can supply and control the inverter accordingly. This kind of intelligence and control seems to be provided by ICC-Pi to control an essentially dumb inverter. These are my perceptions but of course I stand corrected if I have erred and any information that will improve my understanding of the issue will be much appreciated. Also when the day comes that my T105's start failing, it would be good to have a plan in place and since I enjoy tinkering with stuff, I am always looking for a DIY solution, even if it is not the Rolls Royce of what is possible.

@Gerlach  It is good to hear that the ANT BMS with some modification may well be able to communicate with ICC-Pi. Perhaps Manie, the developer of the program, will at some time be able to investigate the possibility. That will at the very least save one the cost of the BMV7xx which in my case was more than that of the ANT.

Thanks very much to all other members for their posts on the discussion, all of which has enhanced my knowledge and I do appreciate those who have understood my question and defended its relevance on this thread.

 

23 hours ago, plonkster said:

On level one you have basic protection. If a cell is low or if another cell is high, then the BMS disconnects. On this level there isn't even cell balancing, and though you may not believe it, there are some very very low end battery packs (usually for toys, not serious stuff) that have no more than this most basic of protections.

On level 2, you get cell balancing. At this level there is still no comms with anything.

Level 3, basic protection features in the shape of a relay that opens/closes to indicate that you should stop charging or discharging. This is very very basic comms, and is useful because you can avoid that absolute shutdown that leaves the entire house in the dark. Victron Smart Lithium batteries are on this level.

Level 4, SOC tracking.

Level 5 adds full communications where the battery can mandate a charge and discharge rate.

Now my point in this whole long thread was simply that you don't need level-5 capability to run an LFP battery. But you need at the very least level 2 for this game.

OK, I have  a victron system, and I eventually want to go big with a DIY LiFePO4 bank with the full super duper BMS at that time.

In the meantime, I intend to build a 16S 280Ah bank to play with and get a handle on this.

To that end:

Victron inverters have a low voltage load cut-off setting and is capable of dealing with charging the lithiums from the grid.

My BMV is capable of SOC tracking and of a "high voltage" relay output, I can use that to cut-off charging like a two wire BMS and drive.

 I have Outback MPPT's, they can be set, but ultimately solenoid protection so I have to dream up something for that, but that doesn't seem too complex a job.

Because I had 48 (4S16P) 12v lead acids, I have a 16 HA02's, 3.6V is one of there stated capabilities. (Probably vastly overkill balancers).

I also have 48 tiny little digital voltmeters that I have across each of cell's already. No fancy bluetooth, but a glance tells you what you need to know.

Temperature shut off is not an issue I'll have to deal with.

I think @plonkster, I probably have the making of a rudimentary BMS re-purposing what I've already got.

Thanks for breaking it down into bite-size chunks.

 

Edited August 10, 20206 yr by phil.g00

@Gerlach If Revov uses the Smart-ANT BMS for their batteries and ICC supports Revov, one would with some justification, expect that ICC already may support the Smart-ANT when used in a DIY configuration. Perhaps you are able to find out what modifications have been done to the ANT used by Revov to make it compatible with ICC.

@phil.g00 what i did with my MLT inverter setup, I adjusted the bulk charge toe 10% and the float to 6% charge. So when the MPPT's is running , then the solar will charge the batteries at full rate it can supply the batteries and supply the house and the grid will fall away "standby", when the load gets bigger and the solar can't supply the bigger load, then it will start add from the grid but the batteries will keep charge 6% charging. I only connect to the grid if the weather is crappy and i see that my lifepo's SOC is getting low and i need to start charging my batteries. What i pick up, if i keep it to the grid connected and leave it charging till the lifepo's is fully charge, it will start dropping the charge till 0% while supplying  the house grid power via die inverter part, this on the 6% float charge. What i like about the 6% charge to, the bms start active  balancing because there is 10amp charge going in 2 sets of Lifepo's.  

14 minutes ago, ebrsa said:

@Gerlach If Revov uses the Smart-ANT BMS for their batteries and ICC supports Revov, one would with some justification, expect that ICC already may support the Smart-ANT when used in a DIY configuration. Perhaps you are able to find out what modifications have been done to the ANT used by Revov to make it compatible with ICC.

@ebrsa Jip, they use it on there 24v batterye units. A place up in JHB is building it custom for them for there 24v units. We must just find out from Revov and ICC if there is a way to do this. 

On 2020/02/25 at 10:05 PM, SiliconKid said:

I need to ask @Coulomb to check the firmware code and confirm or deny for us.

I saw that post from February today and had a go at reading some more of the Growatt BMS firmware. It's a bit easier having made some progress with the Axpert King removable display firmware. Nothing dramatic, just slow plodding progress.

In case anyone is interested, the Growatt BMS firmware is quite different to that of the Axpert King or Axpert VM III (in the removable display). My guess is that it didn't originate with King firmware; Growatts are not clones. The task processing is different; there is no yielding to other tasks as there is in Axpert code. All tasks are run from an endless loop in main(). Also, the ARM chip used is different; the addresses of the UARTs and the register maps are completely different.

Growatt if you are listening: you can save a lot of RAM and flash space by declaring your data arrays as char instead of int. With just the two CRC tables alone, you'd save 256 x 3 x 2 = 1.5 KiB of flash space. Three of every 4 bytes in those tables are zero. You'd save even more RAM.

A bit of a random inquiry here from my end, as I searched without any real results for hours for an answer and this forum post was the closest resource I could find that was remotely relatable, hopefully someone can help.

I'm trying to setup the communication protocol between a Growatt inverter and a Must solar lithium battery. Currently, I have it setup as user defined because I couldn't figure out which one is the right RS485 communication protocol when choosing Lithium as the battery type on program 5. Closest I got is when I put protocol 5 in, the inverter stopped beeping  but it would not charge the battery, there are 50 other protocols which got daunting while trying them all one by one before I quit trying and found this post.

 

I already contacted Growatt for assistance like a week ago, I'm not sure they can help. The battery company are still drafting the user manual and it's not yet available on their website, which I found it to be weird tbh.

 

So, to be clear, does someone actually have an idea how to figure out the right protocol? Maybe there is something to be done with the dip switches also? 

 

I don't know what I'm expecting here, this is a shot in the dark I guess. The original post gave me a little hope that encouraged me to ask. Thank you!

 

EDIT ** SOLUTION**

I found and followed another post from OP  here:

The only different thing I did is that I used protocol L05 not L01, turned on the battery and inverter, waited a little and coms were online. Thank you.

Edited April 7, 20224 yr by Jhin
Found an answer for my question

On 2020/02/24 at 3:53 PM, SiliconKid said:

I've new to this game and I've been doing a lot of research lately and I'm concerned about one specific topic that keeps on coming up and seems to be causing a lot of confusion:

Why the BMS (Battery Management System) that is built into your expensive new Lithium battery should ALWAYS be connected to your inverter via a comms cable, properly, unless its physically not possible.

I'm seeing a lot of information about how BMS's are being bypassed completely and effectively ignored and inverters are being put into non Lithium specific modes (User mode) and configured manually so that they monitor the Lithium batteries using voltage monitoring only, as if they are the old Lead Acid or Gel type batteries.

And there seems to be a lot of acceptance that it's perfectly ok to do that and that the BMS really makes no real difference and it doesn't matter if your inverter is communicating with the BMS over a comms cable.

I have a real problem with that philosophy for a few reasons, and if you understand what actually happens when you connect your inverter to the BMS properly and proper comms is established, it becomes very clear why that is always a far better option.

Things to know and understand:

1. The reason you paid so much money for your new Lithium battery with a built in BMS is because that battery is not like the old Lead Acid or Gel batteries which are literally just a group of cells joined together with a positive and negative terminal.

The BMS built into Lithium batteries is a computer and is monitoring the internal state of your battery down to cell level micro voltages. It is aware of everything going on inside that battery and it knows when the battery needs to be charged, how much current it needs to draw, exactly what the current SOC (state of charge) is (as an extremely accurate % value).

2. When inverters are only connected to a Lithium battery via the voltage leads, and ignore the BMS, they can only use the voltage level they are monitoring across those voltage leads to make any decisions related to discharging the battery or trying to show you the current SOC of your battery (which they have to attempt to calculate based on voltage floor and ceiling values that you've manually configured and the voltage they are currently seeing across the battery terminals).

That does work, but it's not nearly as accurate as the BMS is.

The problem is that:

       a. Most inverters, particularly cheaper ones (under 20K ZAR as a generalisation) don't seem to be able to detect very fine grained changes in the voltage across the battery leads. And consequently they aren't able to give you a SOC value that is dead on accurate to what is actually going on with your battery. Depending on how coarse grained the voltage monitoring of your specific inverter is, the changes in charge level that you will see displayed will vary all over the place and it will not change by 1% at a time, it will jump values (random example: It might drop from 95% straight down to 90%).

       b. Lithium batteries have a narrower voltage range between fully discharged and fully charged, than the other types of batteries, and that makes the situation even worse for inverters that can't pickup small voltage changes because smaller changes in voltage now mean bigger changes in SOC.

3. If you get your inverter to talk to the BMS correctly, as intended by the battery manufacturer, the following happens:

     a. You have what we refer to in the software industry as an "inversion of control".  This is very important to understand. When the BMS establishes proper comms with your inverter the BMS TAKES OVER responsibility for what happens to the battery. In that scenario the BMS is now in control and NOT the inverter. That is why an inverter that is properly connected to an Li BMS, and is put into a proper Li mode, LOCKS multiple settings related to voltage floor and ceiling, charging current limits, and some other things. The reason is because the inverter is no longer responsible for deciding those values, and neither is the user (which is why you can't set them), the BMS is. 

The BMS now constantly reports it's SOC and other relevant information to the inverter AND it will tell the inverter when it needs to be charged etc. The inverter just does what it's told, how it's told, when it's told.

The inverter will also now display real time, extremely accurate SOC values and real time charge current values etc., because those values are constantly being sent to it by the BMS.

    b. If you have multiple batteries stacked, then one of those batteries is the master and the BMS will act on behalf of all of the batteries in that stack and make sure that charge is evenly distributed to all batteries and that things are always in balance across the stack.

 

The bottom line is that if you have Li batteries with a BMS, you should always want your inverter connected to that BMS properly, and using the old voltage monitoring approach is NOT the same thing.

I fully understand that if you have an older inverter you may be in a position where there is no new firmware available and it doesn't have an Li profile and can't communicate with a BMS, in which case you have no choice but to rely on voltage monitoring, and you still get multiple benefits from using Li batteries.

My problem is with brand new inverters being setup to willfully bypass the BMS on expensive new Li batteries and being configure to run in USE (User mode) and use voltage monitoring and that being considered perfectly acceptable and ok.

I've personally just spent 80K ZAR on a new battery backup system with a 5Kva Growatt inverter and 2 x Pylontech US3000 batteries and it took me a week of communicating with Growatt in China and doing my own research to figure out why my new inverter would not communicate with the BMS correctly (during which time I had USE mode and voltage monitoring active as temporary workaround). But I refused to accept that the inverter would not connect to the BMS properly and eventually I resolved the issue, upgraded the firmware, and got it right.

And now my system is far more accurate and I know that those very expensive Li batteries I bought are being managed properly and not abused, and I know that the information I'm seeing in the monitoring app and on the inverter display is dead on real time accurate.

If your new inverter is not connecting to your BMS properly then in my opinion that's a problem and needs to be addressed. New firmware must be provided if necessary to upgrade the inverter to be properly compatible with your batteries, and proper documentation must provided explaining exactly what type of cable needs to be used for BMS comms in your specific case, what dip switches need to be set on the battery (if applicable) and what mode the inverter must be put into to trigger proper BMS comms and run in a proper Li profile.

There is a reason we are paying 20K per battery for Li batteries with fancy BMS's built in.

Please use them.

Old Post , but Good Post , fully agree .

On 2020/02/24 at 5:47 PM, Fuenkli said:

There is inverters (like Goodwe) who have current measuring capability on the battery input and do not rely on the voltage to determine the SOC of the batteries. 

Yes, but it's not as good as coms between BMS and inverter. I have often found myself with two versions of the truth - what the BMS sees and what the inverter sees.