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diy solar

Which is worse, discharging to empty or charging to full?

Our application is identical, but we made opposite choices.
Not exactly. I can sell any excess to PG&E and I have 3 or 4 days worth of energy in my 42kWhr pack if the sun doesn't shine. Since back up is also a priority I prefer to keep my pack near full. When I say full, it is actually 90-95% because I only charge to 3.4 volts. Yes, we did reach different conclusions.
I am not sure anybody but a physicist would be able to answer the qoriginal question. Even then assumptions would have to be made about how ful or empty one is actually taking the pack. The only information I recall is that dendrite growth occurs more frequently at the top but that might just be skewed because the preponderance of the examples happened at the top.
 
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Not exactly. I can sell any excess to PG&E and I have 3 or 4 days worth of energy in my 42kWhr pack if the sun doesn't shine. Since back up is also a priority I prefer to keep my pack near full. When I say full, it is actually 90-95% because I only charge to 3.4 volts. Yes, we did reach different conclusions.
Yes, I agree. Backup was never a priority for me, so my array is sized to cover peak-period utilization and my battery a bit over that. During an extended PSPS event, I should be able to keep the main fridge running often enough to avoid spoiling food again, but that’s a once or twice a year event with plenty of advance warning.

Wanting to have 3-4 days of energy always available for an unexpected outage dictates keeping your battery full (and top-balance along with it).

I started with that same configuration but realized it was not the best fit for my self-consumption-driven requirements.

I am not sure anybody but a physicist would be able to answer the qoriginal question. Even then assumptions would have to be made about how ful or empty one is actually taking the pack. The only information I recall is that dendrite growth occurs more frequently at the top but that might just be skewed because the preponderance of the examples happened at the top.
Yes, members with a bottom-balanced battery seem much rarer on the Forum than those with the classic top-balance.

I think I’ve at least comforted myself that what I’ve decided to do is not nuts ;). Beyond that, I guess I’ll be the guinea-pig…
 
Fortress Powers guidelines to me were 100% to 20% SOC. An occasional Dip down to 10% SOC is ok if there is a power outage. I was warned that going down to 10% daily would significantly shorten the Battery life.
So I guess there answer to the OP from Fortress would be to never Discharge to empty.
 
They are large format prismatic (pouch).

They look like very early black Sinopoly cells - but they are Australian (made in Taiwan) LiFeTech cells. I believe the earliest of these cells was 2008.

This is after about 5 years of neglect - fitted with Batrium. I blew the dust off and fitted a REC after that once REC started making 16cell BMS’s.

I’m not saying there won’t be better cells available in a decade, fact is these are a decade old and the same thing was said back then.
Do you have any performance data on these when they were new versus now?
 
Fortress Powers guidelines to me were 100% to 20% SOC. An occasional Dip down to 10% SOC is ok if there is a power outage. I was warned that going down to 10% daily would significantly shorten the Battery life.
So I guess there answer to the OP from Fortress would be to never Discharge to empty.
Interesting, thanks.

I just slogged my way through this presentation which makes it sound as though charging up high is far more damaging than discharging down low:
 
Do you have any performance data on these when they were new versus now?

The pack is 400ah@48V. It is limited to the voltage range of 50 - 55.5V. Max charge current is 100a, max discharge current is 200a. Max temp is 30°C. Maximum drawdown from 55.5V is 300ah.

I regularly use between 250-300ah overnight, i have never performed a capacity check on the pack, i will just wait until i can’t get my 300ah, then investigate.

These cells have proven to be very stable, there have been 3 year + periods where the balancing function has been unused.
 
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