When Not To Let Your AIO Communicate With The Batteries

[timselectric]

I haven't touched my settings in several months.
I definitely wouldn't want to have to babysit it all of the time. I personally have nothing against coms. It's the best option for some people. I just prefer to set my system up to work the way I want it to.

 

[Darren67-72]

Yes!!! And awsome, I would have preferred it too. My issue came to, several days of bad weather caused a battery bms to turn the battery off. Then when scc charging reconvened, the battery that turned off, didn't charge. Of course. You see where this is going. To mitigate this problem, I would need to raise my cut out voltage. That gives me less battery usage. And lowering the high side voltage also reduces amp hour usage. Although it may seem like its not much, it adds up on both ends and everyday.
I looked at the value of more batteries versus DOD and decided to work, what I have harder and replace as needed. This decision can't, honestly, be calculated based on the hundreds of "professional" opinions and studies. At least, as of, my last research.

 

[Lt.Dan]

That's 27 years. Calendar degradation is FAR FAR going to kill the batteries before the high knee thinking.

I dont know much about the calendar aging thing, but my first thought is that we haven't had LiFePo4 around for long enough to have calendar aging take effect? Especially with the chemistry being tweaked over the last few years to get more cycles and more energy density etc.

To be honest, I don't think we actually know how calendar aging will affect the battery because it hasn't happened

I'm not a smart feller though, more like a fart smeller. Do we have hard evidence of this?

 

[timselectric]

I'm not sure how having com's solved this. But if you are happy with it that's all that matters.

 

[Darren67-72]

No, but the manufacture certainly does not boast of a 25 year battery and they would!! And they only warranty them for much less. That's a good indication.
BUT, I agree with you, we don't know, nor do we know that using the knee does the damage stated either.
It's the same argument. We are back to people must make their best decisions based off of the info you have and use your best judgment.

 

[Darren67-72]

Coms allows the inverter to communicate with all the batteries and their soc a battery will tell the inverter to stop drawing power, before any battery reaches a cut off voltage. They will not allow the inverter to discharge to the shut off voltage or soc.

 

[timselectric]

I have my inverter set up the same way manually.
BMS cutoff should be a last resort. Only used if everything else goes wrong.

 

[Darren67-72]

With Manually set, does it use voltage?
I'm really glad to hear this working for you. I have a Generty Solar 12k I will be using in this manner, for a shop and have not been looking forward to it. Now, I have a better feeling about it.

 

[timselectric]

Yes, mine uses a voltage setting.

 

[Kornbread]

Coms allows the inverter to communicate with all the batteries and their soc a battery will tell the inverter to stop drawing power, before any battery reaches a cut off voltage. They will not allow the inverter to discharge to the shut off voltage or soc.

Can't cutoff be set in the inverter? IIRC, most bms start to balance somewhere North of 54v, so if you do not use scc/battery communication, wouldn't the battery/battery packs still balance without taking the voltage quiet so high into the knees?

 

[Zwy]

No, but the manufacture certainly does not boast of a 25 year battery and they would!! And they only warranty them for much less. That's a good indication.
BUT, I agree with you, we don't know, nor do we know that using the knee does the damage stated either.

Actually, https://www.nrel.gov/docs/fy22osti/82801.pdf

and https://www.sciencedirect.com/science/article/pii/S2773153722000081

and https://mdpi-res.com/d_attachment/e...ploy/energies-14-01732.pdf?version=1616229789

It's the same argument. We are back to people must make their best decisions based off of the info you have and use your best judgment.

 

[Darren67-72]

Yes, to first part, but.... voltage is not, the best, gauge of soc, and this can get confusing, even if you set the inverter cut off voltage above the bms shutdown voltage, if a battery soc goes below the bms shutdown charge, it will turn off.
The second part, yes you can top balance at a lower voltage, but it's exponential the lower you go. (Takes longer or even longer)

 

[Darren67-72]

Actually, https://www.nrel.gov/docs/fy22osti/82801.pdf

and https://www.sciencedirect.com/science/article/pii/S2773153722000081

and https://mdpi-res.com/d_attachment/e...ploy/energies-14-01732.pdf?version=1616229789

Well, there you go.

 

[Darren67-72]

It's right in the title people. Just read for yourself. They just don't know!!!
Have a good night

 

[Kornbread]

Yes, to first part, but.... voltage is not, the best, gauge of soc, and this can get confusing, even if you set the inverter cut off voltage above the bms shutdown voltage, if a battery soc goes below the bms shutdown charge, it will turn off.
The second part, yes you can top balance at a lower voltage, but it's exponential the lower you go. (Takes longer or even longer)

Since it appears most bms passively balance the cells, I can see it taking longer to balance at a lower voltage. After several days of partly cloudy weather and shade due to Mr. Sun moving South for the winter, one of my batteries went into LV warning even though the aio was set 10% above the battery's LV alarm. SOC for the battery bank was something like 38% when the one battery alarmed out, which should't happen till 25%. Pretty sure if I hooked the laptop to the battery bank and looked at individual cells, there would be some rather large imbalances. Don't think the battery bank has been over 54v long enough to get a good cell balance.

 

[Ellcon123]

Voltage is a good gauge of SOC. You know when the battery is full or empty. Everything in between is a bit of guesswork and requires coulomb counting. BMS settings high and low should be last resort fail-safe settings. If the battery didn't charge after LVD then I'd say it's a dodgy BMS. BMS should reconnect if charge current is present.

As for potential ageing issues with full charge, I'll worry about that when someone reports they've reached 5000+ cycles. My system is there to be used so future problems are just that.

 

[Kornbread]

Since it appears most bms passively balance the cells, I can see it taking longer to balance at a lower voltage. After several days of partly cloudy weather and shade due to Mr. Sun moving South for the winter, one of my batteries went into LV warning even though the aio was set 10% above the battery's LV alarm. SOC for the battery bank was something like 38% when the one battery alarmed out, which should't happen till 25%. Pretty sure if I hooked the laptop to the battery bank and looked at individual cells, there would be some rather large imbalances. Don't think the battery bank has been over 54v long enough to get a good cell balance.

To further extrapolate this train of thought. As far as the eg4 LiFePo4 is concerned, it is said they do not use grade A cells, although, they are advertised as using grade A cells. It has also been discussed on many threads here, very few of the advertised grade A cells are actually, grade A as most are seized by the EV market.

1 + 1 = 3 right?

It is my opinion that due to the 1) eg4 not using grade A cells, 2) combined with poor matching between cells in a battery pack, 3) and the advertising lure of more is always better, the high voltage settings in the bms are there to help compensate (balance) for poorly matched cells ... and of course, advertising copy.

YMMV