18 cell "48v" Bank

I may have another analogy. Back in the 90s, there was this oil additive called Prolong (perhaps it is still around). This thing was rumoured to keep old engines running for longer, and to make new engines last twice as long, etc etc. My father had just dropped a brand New Cummins engine into a lorry at the time, and he told me that the cost of the oil additive over the lifetime of the engine exceeds the cost of an overhaul. Whether the additive is as good as they say it is didn’t even matter (hint: It isn’t!), the “protection budget” wasn’t warranted.

Edit: That is also why 1) I don’t have cell phone insurance, based on my personal profile, the cost of insurance would exceed the replacement of the device, and 2) I do have excess waiver on my short term insurance, because based on my ability to suffer a prang every 2 years or so, it is worth it… :slight_smile:

Boils 100% down to risk profile and discipline to keep some funds around … self-insurance if you want to label it.

One thing we recently became acutely aware of, is medical aid top-up cover. Someone we know was T-boned in a car accident, not their fault, broken neck and back, he is fine, but he has R200k and counting medical bills arriving over and above what the medical aid already paid. Maybe RAF covers it in a few years, maybe not, but that level of unforeseen expenses has shaken my “foundation” a teeny bit recently. Can wipe you out overnight.

Back to on-topic … my Frankenstein bank is still balanced with no intervention from my side.

The new cells, now only arriving in Dec … 3rd ship they are booked on. :man_facepalming:
Imports are not for sissies.

Yeah sorry to stay off-topic a bit longer, but I do want to agree with you. Many years ago, I did some IT work for a broker, who among others did medical aid work. One thing he said to me back then, was to forget about the bells and whistles. You look at two things, 1) Hospitalisation cover, 2) Emergency services. You want those to have unlimited cover. You want no annual limits or overall limits on those. And because these are part of the risk component, an area very well understood by the actuaries behind all this, it’s actually not that expensive to get this covered. As long as you are happy to kiss the third part goodbye, which is known as “day to day” cover. That’s the part you need to pay from your own pocket, because that is where it comes from anyway.

I’ve never had a shortfall on the hospitalisation part. That bill has always been fully settled for me, even when it was a R80 000 bill for two weeks in the NICU. I do however have the top-up cover, as you mentioned, because the doctors themselves usually charge more than the fund pays. And this is also very cheap, because it’s an insurance product.

Many people don’t realise this subtle difference. A medical aid is a mutual fund. It is a giant stokvel, deeply regulated by law, where the rules dictate that the people who got hurt are the beneficiaries this month. All premiums paid (minus admin costs) remain in the fund for the benefit of the members. Gap-cover on the other hand is an insurance product. Less regulated by law, there are shareholders, some of the funds go towards them… the fine print may bite you harder … etc etc. But gap cover remains a hugely beneficial product to have.

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This is how it should be but there’s nothing to rectify it if it gets unbalanced…
Now this is fine if you are nursing your battery pack on a daily basis and can charge/discharge offending cells.
My LiPo battery pack goes out into ‘the market’ and there everything’s got to be plug and play!

BMS is balancing quite nicely at ±260mA once it goes over 3.4v per cell … does a good job on low wattages like <1000w and lower, as what happens >90% SOC, system calling halt on 3.45v per cell.

Methinks the brand names did some serious testing to get their bank ideally “positioned”, whilst using top of the pops cells, lower settings, calling lower AH than the cells are rated at.

At THIS moment I cannot see banks cycling day in and day out with the cells staying perfectly in line year after year, even a decade. Cells manufacturing is not that good yet … is my gut feel.

I do see more “effort” going in when there is bad weather though … when the SOC stays below like say 90% for a day or more.

Learning more and more I tell you.

Yeah, so I did not think this through all the way to the “end”.

I want to add cell 18 into the bank … problem is, 17 cells are keeping “in line”, no 18 will have a difference, and I’m so NOT interested in getting “involved” again till the new cell is “settled”.

And to take it all apart again, top balancing all 18 … no.

Bugger.

Shall wait for the 280ah cells to arrive in Dec.

The plan:
Connect 18 x 280ah cells charging at max 3.45v per cell = 62.1v, set on MPPT, Inverter and in the BMS driver.

Because I can now, for the first time ever, see the system stop at 17 x 3.45v = 58.65v … ok, mostly slightly over but I “control” that with stopping charge on the driver at 96% SOC and by keeping Grid Setpoint at Zero, above zero a bit “leaks” back to the cells all the time, pushing the volts ever so slowly higher.

Unless @Phil.g00 (he made me do it :laughing:) has 2nd thoughts/reservations?
Or @plonkster tells me why I should not go down this path?

For if it works, can work, being lightly cycled i.e. min of 20% SOC and max of 96% SOC (3.45v):
18 x 3.2v x 280ah = 16.128kWh

Or where I call it “fully charged”:
18 x 3.45v x 280ah = 17.388kWh

Or what I see mostly the cells settle too + or -:
18 x 3.35v x 280ah = 16.884kWh

The standard seems to be 3.2v that everyone uses …

Want to have a lot of spare, “lightly” used for the size by keeping the cells on the flat curve, and see if Will Prost can be right, such a bank can last 20+ years?

@TheTerribleTriplet I still think 18S is the way to go with Victron equipment.

3.45v per cel?

Somewhere around there, seems about right.

I’m not going to get in the way of your experiments, you seem to have a lot of fun doing them…

I like 17, because it’s a prime number. That’s where it ends.

Bar that piece of wisdom, anything else that comes to mind that could be an issue? :slight_smile:

Nothing I haven’t said before.

We all have those “distractions”, as @Gman had with his system.

Lately, this is mine … Oupa moet babysit …

So I fitted her in with my schedule, to keep her mother and my wife, Ouma, calm.

I play her some music … and when she wakes up, I teach her how to play Grand Theft Auto … ok, Solitaire … ag ok, maybe later I will show her how to top balance cells, ok! :raised_hand:

O, less I forget, I have NEVER seen a baby getting spitting mad, ever!

Happens when:

  1. you dare change her nappy,
  2. or not change her nappy fast enough …
  3. and do NOT let her wait for her milk …

… otherwise we have quality hours together.

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When I got here in the past, the drama started … cells “full”, low AC load, cells run away = DC Ripple eventually, when the BMS disconnects.

image

Today, with better cells, top balanced - even though so vastly different ito AH’s - with a BMS that can balance, a driver that stops the charge (I made it so on >96% SOC), I can safely go to 58.65v with no drama’s.

YES!!!

By late afternoon, Delta will be < 0.010v, like maybe 0.008v … ready to cycle down to 20% tonight again.

Is this sustainable … Nope, not at all. It is a temp situation in conjunction with “learning” how to control the system “better” … so do not try this at home. :wink: … the mixing of 100ah and 280ah cells that is.

At least I now know it can be done … in case of emergency, the mixing of different ah cells.

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Just to show the flip side, the system is using the panels, the geyser came on … and NO drama with the cells …

image

The ONLY thing I am still figuring out, is why the system sometimes stops dead the production from the panels at times … there was more than enough sun:
image
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I THINK it has to do with the MPPT reaching 58.65v … will adjust the volts up a bit on the MPPT next time I see it.

Re. “more than enough sun” … I can see what the local Solar Radiation is, close to us here: WeatherCloud

I can’t seem to drill that into customers’ heads. The MPPTs work on voltage. The “External control” part really just means we give it a voltage to aim for… and then the MPPT does its own thing from there on.

If the MPPT is not spooling up… it is almost always because the voltage hasn’t suitably dropped out.

I’m walking the drilling … as I recall you mentioning it over and over … the difference being I can now see it for myself for the first time with no “other interferences” clogging the matter.

Ideally, what must the MPPT be set at to avert it “stopping” using the panels when the cells are full, yet the house can use what the panels can still provide, if my system is set to 3.45v per cel, 58.65V

MPPT be at like 3.5v x 17 = 59.5v

Or am I, again, missing what you mean when you say:

Teach me using actual numbers, I will colour it in later.

There is no need to endlessly tinker. You decide what voltage you consider full. If you decide on 3.45V per cell, then you charge to 58.7V or thereabouts… and then you forget about it.

Then it works like a full dam with a ball valve. Water flows out (aka energy is used), the level drops (the voltage), and the ball valve opens and the dam is filled back up (aka mppt wakes up and charges it back up). Of course this tends to level out, so the MPPT tends to run roughly at the level required to power the loads.

And that’s that. Yes, you’re losing production… but that’s because the battery is full and there is no load to sink it into. Pffft. Sugar, honey and ice tea happens…

Will set the MPPT to 58.7v … and see what happens.

Then the inverter … but that makes no sense to me, if both are on the same volts setting, then I’m back to the current situation. no?

I’m misunderstanding something here I think?

Yes, the battery is full BUT there are loads to sink panel production into … the house!

Sometimes when I see it, I simply drop the Min SOC to like 50% or some such, MPPT ramps up, mostly near-instant, I put the Min SOC back to 95% … and MPPT happily continues sinking production into the house circuits on a full batt.

If it refuses to budge, which happens sometimes, I set the system to feedback to Eskom … for a second … MPPT ramps up, I disable feedback, MPPT continues happily sinking loads into the house again.

I simply cannot fathom, in my inexperience, why it happens.

AHA, it happened again!!!

Here, let me show you …
image

MPPT stops, only charges the batts a bit … ESS #1, but how, the SOC is not low?

I drop the SOC to like 50% … It ramps up again …
image

It will now work again … OR, sometimes I must set the Min SOC to like 90% if it is in this “loop”.

Will set the MPPT now to 58.7v and see what happens.