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Optimal float setting nmc cells

glamsland

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Jan 13, 2022
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Hi.

I got this offgrid cabin, 800w pv, 220v/3kw hybrid mppt inverter/cc , generator, 24v/6.3kw nmc battery pack from a KIA Soul.., qucc 200a smart bms. Bms low/high set to 3v/4.2v

Cell min/max is 2.5/4.3v .

Ihave set the bulk at 28.7v/4.1v and float at 28.5v/4.07v . Bulk reconnect at 28v/4v.

At "rest" in float, the battery stays around 28.35-28.4v..


This seems do work just fine.. battery cells balance nicely every time..

I'v been working with different solar setup for the cabin in many years now, always planning a upgrade of some kind.. and this one works eealy great.

But i'd like to learn more about how to optimice the settings. If i change the float settings, what is it i'm looking for? Is it better to have it closer to bulk voltage or closer to the bulk reconnect? Or all 3 of them close together? If i do some adjustments , what's the signs of doing the right ting? Bad?
Thanks,

Runar
Norway
 

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What do you mean by optimize? What's your goal? Your only real choice is:

"How much do I want to increase/decrease cycle life by decreasing/increasing cycle depth, respectively."

Float is pretty irrelevant beyond it should be just barely under absorption.

IMHO, limit to 3.5-3.92V/cell with float 0.1V below absorption. That will give you about 50% of rated capacity and will age out before it cycles out.
 
Thanks for ansver.

My goal is just to get the most out of the battery and the sun.. now, its summer, and no problem other than its "full" all the time. So now in summertime i guess it is not a good thing to fully charge the cells up to like 4.2v.. so.. if the float is a bit low, the battery stay in a lower resting voltage, that is a healthy thing.. i believe.

but in the wintertime, maybe its better to increase the bulk and float to get more amp out of the battery. There is also less sun-hours in winter so its important to get the use of the sun as long the sun is up.

I guess its important to have the correct float setting then to let the sun get as many amp into the cells , and therefore a higher resting voltage.

I'm just thinking out loud here, i might be wrong. Please share your thoughts..

Runar
 
Thanks for ansver.

My goal is just to get the most out of the battery and the sun..

What does this mean? You need quantifiable goals to establish what you need.

Do you mean you want more capacity?

Do you mean you want more cycle life?

Something else?

now, its summer, and no problem other than its "full" all the time. So now in summertime i guess it is not a good thing to fully charge the cells up to like 4.2v..

This is correct in any temperature, but more important when warm.

It also is independent of temperature in that higher chargE voltages = reduced cycle life. Charging is the most stressful things to cells. Lower voltage and lower current reduce that stress.

but in the wintertime, maybe its better to increase the bulk and float to get more amp out of the battery. There is also less sun-hours in winter so its important to get the use of the sun as long the sun is up.

I assume you mean amp-hour, not amp. This has nothing to do with time of year. It depends on what your battery storage needs are.

I guess its important to have the correct float setting then to let the sun get as many amp into the cells , and therefore a higher resting voltage.

Again, I assume you mean Ah.

How much capacity do you need. Assuming that module has 75Ah available, how many Ah do you need daily?

I'm just thinking out loud here, i might be wrong. Please share your thoughts..

Here's the most important question...

WHAT BMS ARE YOU USING WITH THIS MODULE?
 
As said earlier, it's a Qucc 200a smart bms. Same as jbd and overkill.
Tested and works just fine. All my settings are set . As low voltage shutdown, i use the chargecontroller settings, if this fails, it's the bms that take over.
 
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