Do I keep my BMV? When is the BMS good enough?

Batteries Battery Management Systems (BMS)
61

I agree 100% with @Louisvdw
I agree 100% with @plonkster

Where we differ is because I’m an end-user that knows little enough about software to make me very VERY dangerous, that in my learning curve on a DIY bank (read, I don’t have warranty concerns), I am seeing things that make me believe that we do not know it all yet.

We can explain to each other WHY it happens … justify it … and less support (I agree btw) … but like we learned about lead acid banks over decades, lithium SOFTWARE and HARDWARE is still NEW.

In my view, as time progresses, the lithium-battery SOFTWARE and HARDWARE will become more accurate, just like Victron figured out over time how to get a BMV as accurate as damn for lead acids.

Andy’s channel, Neey listened to his and his follower’s feedback … they upgraded the hardware and software.

My posts above, the screenshots, were to show those who want to ponder more on it, see for themselves what I see, that maybe like say developers :wink:, can ponder on how to make the SOFTWARE better … the shunt in BMSs lacking somewhat. So yeah, there is that.

Customer feedback some may call it.

Further:
Used to say to people with lead acids, people who pay 10s of thousands for a lead acid battery, who then refuses to buy an “expensive” battery monitor, one that will last them for YEARS, longer than their lead-acid banks will ever last, that if that device can save them one early bank replacement, that the BMV would have been “free”.

Now we have lithiums, even more expensive, and we have BMSs in them (some with shunts), but the SOFTWARE is “new”. Then we have new models and upgrades of that same brand where there are massive improvements on the previous model’s HARDWARE/SOFTWARE, sometimes we have older model BMSs that were “cutting edge” at one time which is crap today. I have one. My first one.

Then we have LS in SA … the batts cycle more than once a day …

I won’t trust my massive investment in batteries to just a BMS. They have bugs.

My take:

  • BMS does what BMS does, cuts out the bank with too low volts, too high volts. Lithium has to have that.
  • Keep the cells in line as far as possible, the balancing, but we tell each other it takes weeks.
  • Balancers should be a separate big mother of a balancer for WHEN it is needed like when the bank gets old.
  • I will NOT trust the BMS in the same way, on Ah calcs, as I will trust a BMV … till the hardware is similar. And I have a big shunt in the BMS, it cannot read as low as the BMV, EXACTLY why I got drama in the past … and it is passive … but it is a BIG amp BMS … so there is that. Tough to make big amp BMS to split the charge/discharge. I get that too.

This chat about BMV or not reminds me of Will Prowst. On another big forum there was this one video used about why a BMV is not a good buy and why not to get one. He “dissed it something fierce”. So expensive!

So I had to reply … see, ±1 year after that first video, Will did another video on the same BMV and he could not stop extolling its virtues cause he finally dug deeper into what that “expensive” device can add to his life … (hy was amper liries.) … and that was on a lithium bank in his electric quadbike. :wink:

There you have it … I’m using a BMV (and I am NOT saying go and buy new) cause I had it. I will use the BMV until the day I can find a BMS that has the SOFTWARE and HARDWARE to match what a BMV has shown me what is possible … with firmware upgrades thrown in. Software is upgraded all the time.

Ps. BMV only needs calibration every few months. Perfectly normal.

Pss. Some darker view … I’m gonna say this here … 10-year warranties, fine. So, the cheapest part of that entire battery is a BMS. Fine. So that BMS is an old model, it has shortcomings and bugs … new models have that fixed. So how does that impact on the older BMS, the 10-year warranty?

We won’t know … till we get there.

BMV, in my case, will give me recorded data …

62

Why don’t you click the little “controls” icon and play with it? :slight_smile:

The most interesting one is usually the min/max cell voltage chart. That is shown for the BMS, but not for the (lesser) monitors such as the BMV. Conversely, a BMV will show a midpoint voltage (if so configured, on a lead acid bank) that you can plot, but the BMS won’t have that one. It all depends on what data is available.

63

I cant find this? is it somewhere on that same screen I posted? The controls icon.

64

I’ve synced today. But I don’t believe you.

65

Here is the steps in a 1000 words :slight_smile:

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66

Thank you!

How does this look? Anything to be concerned about?

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67

There at the big spike. It says max cell voltage 3,63 and min 3,44

68

Your lowest cell is at 3.45V when the step-out happens. That’s perfectly okay and normal.

Here is mine… it needs work.

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69

Let the BMS do the BMS thing … that is why you have a balancer in it.

But, at the risk of getting “slapped” … rather see it as “customer feedback”, what I’ve learned the last few years, the only thing I need to watch out for, is the Delta … 3.63v - 3.44v = 0.19v Detla.

My Delta on a DIY bank is at less than 0.09v when charging at big amps. When the bank is done, end result is 0.008v Delta.

A clever way I figure to help the BMS at times, switch on a big load, and let the inverter draw from the battery a couple of % points … it sorts it out chop chop, the spikes.

Or let the BMS be …

Customer feedback:
Maybe one day the Delta would be the defacto standard to throttle down the charge current to the batts, and not the SOC. Or an individual cell volt.

If I had the development skills, would have made that a standard on my system, exceed a Delta of 0.1v, drop the charge amps.

To demonstrate exactly what I’m talking about… see the Delta, it is 0.048v, and it can go to 0.085v

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Then I switch on like i.e. a geyser, oven:

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Also,a good method, if you have the time, is to use “raw power” to help the BMS top balance faster.

My 2 cents.
(Maybe this helps someone one day, to tie them over with an issue.)

70

I’m guessing you want the battery to ask for a reduced charge current when it sees a delta, so as to give the battery more time to balance? From a support person, I can already tell you I do NOT want that. All those customers wanting to know why their battery is at 80%, with only light loads, and the MPPTs are throttling and wasting all that good sunlight.

Nope. This is a problem for the first month of a 15 year bank lifetime. You slow down to prevent a voltage overshoot, and you reduce the charge voltage to accommodate your highest cell. In a perfect world anyway.

71

And mine
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72

After just over a day, the BMV was 3% lower than the BMS and this morning still shows 37% vs 40%. Will see how this holds during the week.

73

It’s worth checking the settings on the BMV are Lithium specific. (@TheTerribleTriplet can also post his here please)

They need to be modified to suit the battery specifically!

eg:

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From: https://community.victronenergy.com/questions/61784/initial-smart-shunt-mppt-settings.html

74

You might be on to something here.

Here is my current settings:

Peukert: 1.25
Charged voltage: 55.8V (55.2V for your example above?)
Tail current: 2.8%
Charged detection time: 30 min
Charge efficiency factor: 95%

Which should I alter? Or all of them?

The charged voltage was made slightly higher if memory served because of some sort of issue I had when the lithiums was installed involving the inverter going to Eskom instead of the batteries/PV at certain times it should’ve.

75

Lets wait for TTT to wake up :wink:

Def start with
Charged Eff Factor and that should be 99% - Lithium charges way better than LA.
Peukert: 1.05

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76

Yeah, one must adjust the BMV for lithium. Rather important little detail. There are vids too … just Google “Victron BMV lifepo4 settings”

Here is mine … for the last while I’m using Andy’s setting from the Offgid Garage.

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At that time I took the snip the BMS was saying 12% SOC too … minutes later Victron went into ESS #1 and started channeling all solar to the batts and the SOC “jumped” to 14%. Perfectly normal for the BMS
… and BS ito coulomb counting, its own shunt.

If the average is “close as damn”, then I’m happy. BMV also drives my SOC for the system.

There is this other small detail … What the BMS is set to ito cell voltages correlating to SOC … but that is only for DIY BMS systems. One must be able to trust the brand names and what they determine the SOC must be at what volts.

EDIT: Why do I use Zero for the Discharge floor … cause I have already built-in the upper and lower parameters … what is left, can be used to zero. The inverter cuts off at 2.9v per cell. Does not go over 3.5v … key here … as long as the cells are in BALANCE.

77

Another thing I’m looking at is the BMV Consumed AH … as it is a 280ah bank. BMS Consumed AH … bleh.
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Inverter, now that the weather is better, is set at 2.5kw at 6 pm till the sun takes over.

Titbit: When people sleep, better if they switch stuff off … then there is a happy medium in this house.

78

So, in a nutshell, the reason why I agree 100% with @plonkster (support issues should never be dealt with by developers btw) and @Louisvdw, is that that is the best we have today with NEW hardware and software.

BMV for me is there to make sure I can pick up fast when cells are out of whack … as the BMS will give a silly result ito SOC, the BMV is close as damn ito coulomb counting and SOC. Like, BMS says 100% SOC, BMV says 30% SOC. Jip, have the T-Shirt.

Lithium banks, their Achilles heal, are when a cell shoots out “chasing” 3.65v, whilst the bulk is still in balance.

Hence why I kept my BMV, as I have spent months dabbling with it all. Unscientific yes, but what is in stark contrast to the nuances of why BMS does things, when a bank is getting unbalanced, you have to deal with it and fast.

Handle the issue BEFORE it becomes THE issue … hence the Delta charging “client feedback”. Rather have support field the calls than have the battery taken in “too late”, out of commission due to severely unbalanced cells.

EDIT: Let me put it like this … if the cells are top quality, they have the same resistance, then the BMS SOC is pretty fine to use. No argument about that. Takes all factors into account.

But I don’t care for when things go “right” … never have … what do I need to have in place to see in advance that there is a problem brewing?

I cannot trust the BMS SOC as it is based on volts AND linked to volts per cell … so in effect, it is reliant on 15/16 (in my case 18) different cells to behave in sync for years to come. With each cell, I am increasing my “risk” of the SOC being wrong.

Looking at the Delta … now that is a sure way of determining a brewing problem …

My 2 cents are based on more than ±2 years of dabbling with lithium bank issues of my own doing. :smile:

79

Thanks guys, I have made adjustments as advised by mmaritz, and also lowered my charge detection times to TTT’s - 10min. It was set at 30min.

What about the tail current? Currently at 2.8%. Should I lower this as well?

80

I cannot answer … more clever people than me can guide you.

My default go-to … use the Victron official settings, start there, and watch it over a few weeks … that is where I started.

Over time, if needed, you can tune the settings to your bank’s particular behaviors… but ONLY once the imbalance is resolved. Till then, stick to Victron’s settings.