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What voltage to charge min max ?
#1
Hello
Im starting to learn about charging voltages and how to lengthen the life of the battery somim wondering what is the best voltage to charger at, be interested, in what people charge thares at, i know the lower you charge the less capacity you get just wond3ring if there is a sweet spot?
Thank you
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#2
The longest is at 3.6-3.6V and not touching it.

Your question is hard to answer and everyone here will give their answer based on things they read.

For instance you never said what type of chemistry you talk about?
The Ultimate DIY Solar and build place
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Current: 10kW Mpp Hybrid | 4kW PIP4048 | 2x PCM60x | 83kWh LiFePo4 | 10kWh 14s 18650 |  66*260W Poly
Upcoming: 14S 18650~30kWh | Automatic trip breakers, and alot more
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#3
Sorry 18650s
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#4
18650 is just a size of a cell.

What Chemistry? I guess LiIon but thats not said.. For instance I have LiFe in form factor 18650
The Ultimate DIY Solar and build place
YouTube / Forum system setup / My webpage  Diy Tech & Repairs

Current: 10kW Mpp Hybrid | 4kW PIP4048 | 2x PCM60x | 83kWh LiFePo4 | 10kWh 14s 18650 |  66*260W Poly
Upcoming: 14S 18650~30kWh | Automatic trip breakers, and alot more
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#5
Top balanced, 4.05V ~ 3.3V(+/-50mV*) for my powerwall.
I think it's a good balance between capacity and lifespan. Also plenty of safety space if a pack should come out of balance due to faulty cells.

*packs with lower capacity end up at lower voltage
emerca likes this post
Modular PowerShelf using 3D printed packs.  40kWh and growing.
https://secondlifestorage.com/t-AJW22-s-...PowerShelf
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#6
I have top voltage of 4.0 on my LiIon packs. Lower end is 2.8V for protection and normal reconnect is around 3.4V. Its a bit hard to say since its under load and the load differs.
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The Ultimate DIY Solar and build place
YouTube / Forum system setup / My webpage  Diy Tech & Repairs

Current: 10kW Mpp Hybrid | 4kW PIP4048 | 2x PCM60x | 83kWh LiFePo4 | 10kWh 14s 18650 |  66*260W Poly
Upcoming: 14S 18650~30kWh | Automatic trip breakers, and alot more
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#7
Like Daromer said.
3.4 to 4.0v
Still learning English. Learning Li ion and solar technology.

4200 cells in packs Exclamation above 2500mah and 90%soh.
1500 waiting for testing.

Saving for 3 times phoenix inverter 48/3000 230v to gain also 380v
3 chargers?

Time is our enemy, must work to, the sun is our friend, must relax to.
With best regards
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#8
Short Version:
I'm running 54.6v (3.90v/cell) float high and 48.5v (3.46v/cell) low.

Long Version of how I got there:
The goal for my system is to
1) Consume (power my house) with 100% of PV array input. Don't want to loose PV power to battery full / float.
2) Extend the battery life as much as possible as long as the grid is available (normal operation). If grid is down (disaster), then battery life is not a top priority.

The battery is 14s260p 18650 Lithium-ion with 780ah@48v - e.g. 40kwh. The PV array is 7kw.

My PV array summer max is 45kwh / day and my average consumption is running 2071kw/hour during inverter on time. My monitoring shows that 30kwh is being consumed 'directly' (during day) and my battery is supplying an average of 15kwh (excess from the day burned off at night). In other words, Inverter on is around 10am and Inverter off is between 1am and 3am.

I started the year with 48v (3.43/cell) inverter off and a 56.4v (4.02v/cell) float but went up to 48.5v (3.46v/cell) inverter off because this is just ahead of the knee of the discharge curve for my battery. I have not yet gotten to 56.4v (4.02v/cell) max - the summer max so far is 54.6 (3.90v/cell). The average for the year is close to 53v (3.80v/cell).

This has resulted in an average of DOD of 34.6% for 178 days so far this year AND the DOD is more at the 3.90v high than 4.0v high - but I allow the system to go up to 4.0v/cell high. I plan to start a thread to document what happens... but I hope that this strategy will lead to my battery running 1000(s) of cycles. I understand the consensus is this hope is not realistic!

Where this has lead me in my thinking....
1) The battery is sized to my overall system so that I have the option to run a low daily DOD. This cost more but will increase the life span... I'm must not sure if extra $ up front will result in less $ down the road - that's partly what this experiment will help me determine.
2) By starting with a lower % battery demand - e.g. 15kwh of 40kwh battery - as the battery degrades I can expand the voltage range and keep delivering 15kwh/day from the battery... even when the battery has degraded to 70% of original capacity.
3) I am adjusting my home consumption options with idea in mind of consuming all the direct PV power (e.g. day time power) that I can. I have increased the options around the house to turn on/off different circuits to adjust the the consumption. I don't want to burn up 45kwh in 4hrs (larger battery strain) but adjust it so that 45kwh is spread thru PV array active (daylight) hours and minimize battery strain and night-time supply. For example, I can flip 2 circuit breakers to enable AC during summer and disable electric water heater to adjust the power consumption - but then reverse that during the winter.
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#9
(07-20-2019, 12:50 AM)OffGridInTheCity Wrote: I started the year with 48v (3.43/cell) inverter off and a 56.4v (4.02v/cell) float but went up to 48.5v (3.46v/cell) inverter off because this is just ahead of the knee of the discharge curve for my battery.

This is how everyone should be determining their low cell voltage - based on observation of the behaviour of their cells in operation. Trying to use the negligible capacity found after the knee curve is tempting fate and not conducive to pack longevity.
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#10
(07-20-2019, 08:53 AM)Sean Wrote:
(07-20-2019, 12:50 AM)OffGridInTheCity Wrote: I started the year with 48v (3.43/cell) inverter off and a 56.4v (4.02v/cell) float but went up to 48.5v (3.46v/cell) inverter off because this is just ahead of the knee of the discharge curve for my battery.  

This is how everyone should be determining their low cell voltage - based on observation of the behaviour of their cells in operation. Trying to use the negligible capacity found after the knee curve is tempting fate and not conducive to pack longevity.

To illustrate @Sean's point on my own system (and thanks to Sean for emphasizing the 'knee') here's what my packs looked like when I was going down to 47.5v (3.40v/cell)

This was a 3.31v to 3.44v spread (130mv)

Same battery but with 48.5v (3.45v/cell) bottom

This is a 3.43v to 3.51v spread (80mv)
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